Patent Publication Number: US-11389146-B2

Title: Surgical visualization system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/589,058, filed May 8, 2017, which is a continuation of U.S. patent application Ser. No. 14/215,826, filed Mar. 17, 2014, which claims the benefit of priority of U.S. Provisional Application No. 61/803,371, filed Mar. 19, 2013. This application is also related to U.S. Provisional Application No. 61/665,243, filed Jun. 27, 2012, U.S. Provisional Application No. 61/670,550, filed Jul. 11, 2012, U.S. Provisional Application No. 61/703,727, filed Sep. 20, 2012, and U.S. Provisional Application No. 61/753,398, filed Jan. 16, 2013. Each of the above applications is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments of the present disclosure relate to surgical devices and visualization systems for use during surgery. 
     Description of Related Art 
     Some surgical operations involve the use of large incisions. These open surgical procedures provide ready access for surgical instruments and the hand or hands of the surgeon, allowing the user to visually observe and work in the surgical site, either directly or through an operating microscope or with the aide of loupes. Open surgery is associated with significant drawbacks, however, as the relatively large incisions result in pain, scarring, and the risk of infection as well as extended recovery time. To reduce these deleterious effects, techniques have been developed to provide for minimally invasive surgery. Minimally invasive surgical techniques, such as endoscopy, laparoscopy, arthroscopy, pharyngo-laryngoscopy, as well as small incision procedures utilizing an operating microscope for visualization, utilize a significantly smaller incision than typical open surgical procedures. Specialized tools may then be used to access the surgical site through the small incision. However, because of the small access opening, the surgeon&#39;s view and workspace of the surgical site is limited. In some cases, visualization devices such as endoscopes, laparoscopes, and the like can be inserted percutaneously through the incision to allow the user to view the surgical site. Alternatively operating microscopes may be used to view the surgical site through a small incision held open by one or a number of surgical retractors. 
     The visual information available to a user through laparoscopic, endoscopic, or operating microscope contain trade-offs in approach. Accordingly, there is a need for improved visualization systems, for use in minimally invasive surgery. 
     SUMMARY OF THE INVENTION 
     The systems, methods and devices of the disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein. 
     In accordance with one aspect, a medical apparatus comprises a surgical retractor configured to hold open an incision and thereby provide a pathway for access of surgical tools to a surgical site; and a plurality of cameras disposed on the surgical retractor, the cameras inwardly facing toward the pathway. In some embodiments, the surgical retractor can comprise a plurality of retractor blades and the cameras are disposed on the retractor blades. In some embodiments, the surgical retractor comprises a tube and the cameras can be disposed on an inside surface of the tube. In some embodiments, the surgical retractor can comprise: a proximal camera at a proximal location; and a distal camera at a distal location; wherein the distal location is configured to be disposed closer to the surgical site than the proximal location. In some embodiments, the medical apparatus can further comprise a plurality of proximal cameras at the proximal location and a plurality of distal cameras at the distal location. In some embodiments, the plurality of proximal cameras can comprise at least 3 cameras. In some embodiments, the plurality of distal cameras can comprise at least 3 cameras. In some embodiments, the surgical retractor can be configured for use in spine surgery. In some embodiments, the surgical retractor can be configured for use in head or neck surgery. In some embodiments, the surgical retractor can be configured for use in neurosurgery. In some embodiments, the plurality of cameras can comprise at least 8 cameras. 
     In accordance with another aspect, a method comprises: inserting a retractor into an opening in a body; holding open edges of the opening with the retractor, thereby providing a pathway for access of surgical tools to a surgical site; and inserting a surgical tool at least partially through pathway and to the surgical site, wherein the retractor comprises a plurality of cameras disposed on the surgical retractor, the cameras inwardly facing toward the pathway. In some embodiments, the surgical tool can comprise a scalpel, a rongeur, a kerrison, a laser, or a drill. In some embodiments, the surgical site is a portion of a spine of the body. In some embodiments, the surgical site is in a head or in a neck of the body. In some embodiments, the surgical site is in a brain of the body. In some embodiments, the opening is a mouth of the body. In some embodiments, the retractor comprises a plurality of retractor blades and the cameras are disposed on the retractor blades. In some embodiments, the retractor comprises a tube and the cameras are disposed on an inside surface of the tube. In some embodiments, the method further comprises removing bone at the surgical site with the surgical tool. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor; a plurality of cameras disposed on the retractor, said cameras producing respective images; and an image processing module configured to display said respective images, wherein said surgical visualization system is configured to track the location of said cameras. In some embodiments, said cameras are associated with tracking devices to track the relative location of the different cameras. In some embodiments, said tracking devices comprise electromagnetic (EM) tracking devices. In some embodiments, the cameras are disposed on movable blades of the retractor. In some embodiments, the surgical visualization system tracks the location of the plurality of cameras by tracking the position of the retractor blades. In some embodiments, the retractor blades comprise a plurality of segments connected by at least one hinge. In some embodiments, the retractor blades are malleable. In some embodiments, the cameras are removably coupled to the retractor. In some embodiments, the cameras are associated with tracking devices to track the relative locations of the different cameras, and the tracking devices are removably coupled to the retractor. 
     In accordance with another aspect, a method comprises: inserting a retractor into an opening in a body, the retractor comprising a plurality of cameras disposed thereon; and electronically tracking the locations of said cameras. In some embodiments, the method further comprises obtaining respective images from each of the plurality of cameras, and processing said respective images for simultaneous viewing. In some embodiments, said processing comprises using the tracked locations of said cameras. In some embodiments, said electronically tracking comprises electromagnetic (EM) tracking. In some embodiments, said electronically tracking comprises tracking the position of a first camera relative to the position of a second camera. In some embodiments, said cameras are disposed on blades of the retractor, and said electronically tracking comprises tracking position of the blades. In some embodiments, said blades are movable with respect to one another. In some embodiments, said blades are malleable or articulated. In some embodiments, said electronically tracking comprises tracking the degree to which said blades are bent or articulated. 
     In accordance with another aspect, a medical apparatus comprises: a surgical retractor configured to provide access to a surgical site; a plurality of cameras disposed on the retractor; a plurality of tracking devices configured to track the locations of at least some of the plurality of cameras. In some embodiments, the plurality of cameras comprises at least a first camera and a second camera each have tracking devices associated therewith to track the relative positions of the first and second camera with respect to each other. In some embodiments, the retractor comprises at least a first retractor blade and a second retractor blade each having at least one camera thereon, and each of said first and second retractor blades have tracking devices thereon to track the relative positions of the first and second retractor blades with respect to each other. In some embodiments, said tracking devices comprise electromagnetic (EM) tracking devices. 
     In accordance with another aspect, a medical apparatus comprises: a surgical retractor configured to hold open an incision and thereby provide a pathway for access of surgical tools to a surgical site; and a plurality of cameras disposed on the surgical retractor, said cameras inwardly facing toward said pathway. In some embodiments, said surgical retractor comprises a plurality of retractor blades and said cameras are disposed on said retractor blades. In some embodiments, said surgical retractor comprises a tube and said cameras are disposed on an inside surface of said tube. In some embodiments, said surgical retractor comprises at least one proximal camera and at least one distal camera. In some embodiments, the cameras are fastened to the surgical retractor using a clip-on fastener. In some embodiments, said clip-on fastener comprises a clip, a snap, a screw, a bolt, a nut, magnet. In some embodiments, the medical apparatus further comprises an electrical bus and electrical connector configured to connect said cameras to said electrical bus. In some embodiments, said electrical bus is fastened to said surgical retractor using a clip-on fastener. In some embodiments, the cameras are integrated into the surgical retractor. In some embodiments, said cameras produce respective images, and the apparatus further comprises an image processing module In some embodiments, the image processing module is configured to display at least a portion of said respective images as stitched together. In some embodiments, the image processing module is configured to display at least a portion of said respective images as tiled. In some embodiments, the image processing module is configured to display said respective tiled images as arranged with a first central image and a plurality of surrounding images, said first central image from a different camera than said plurality of surrounding images. In some embodiments, said first central image and a plurality of surrounding images correspond to a first central view and a plurality peripheral views. In some embodiments, said first central image has larger zoom magnification than said plurality peripheral views. In some embodiments, said first central image comprises at least a portion of said respective images stitched together. In some embodiments, said first central image comprises a stereo image. In some embodiments, said plurality of surrounding images comprises at least a portion of said respective images tiled together. In some embodiments, said plurality of surrounding images comprises at least a portion of said respective images stitched together. In some embodiments, the image processing module is configured to display said respective images as arranged with a main view and a plurality of images superimposed on said main view, said main view from a different camera than said plurality of superimposed images. In some embodiments, said first main view covers a larger field-of-view than any of said other superimposed images. In some embodiments, said first main view comprises a first background view. In some embodiments, the apparatus further comprises a picture-in-picture in said main view, said picture-in-picture having a larger zoom magnification than said main view. In some embodiments, said picture-in-picture comprises plurality of said images stitched together. In some embodiments, the image processing module is further configured to display a first central image disposed centrally with respect to said main view and said plurality of superimposed images. In some embodiments, said first central images has a larger zoom magnification than said main view. In some embodiments, said main view comprises at least a portion of at least a plurality of said respective images stitched together. In some embodiments, said main view comprises at least a portion of at least a plurality of said respective images tiled together. In some embodiments, said plurality of superimposed images comprises at least a portion of at least a plurality of said respective images tiled together. In some embodiments, said plurality of superimposed images comprises at least a portion of said respective images stitched together. In some embodiments, said respective images are arranged with a first main view and an image superimposed on said main view, said main view from a different camera than said superimposed image, said first main view comprising a larger field-of-view than said superimposed image. In some embodiments, said first main view comprises covers a larger field of view than any of said other superimposed images. In some embodiments, said first main view comprises a first background view. In some embodiments, said superimposed image comprises a picture-in-picture image. In some embodiments, said image processing module is configured to receive selection of views from a user via an interface. In some embodiments, said image processing module is configured such that a user can select a plurality of views and the image processor at least partially locates the views based on the location of said cameras with respect to each other. In some embodiments, said image processing module is configured such that a user can specify a mode and the image processor provides a collection of views associated with that mode without the user independently specifying the images or sensors. 
     In accordance with another aspect, a method comprises: inserting a retractor into an opening in a body; holding open edges of the opening with the retractor, thereby providing a pathway for access of surgical tools to a surgical site; and inserting a surgical tool at least partially through pathway and to the surgical site, wherein said retractor comprises a plurality of cameras disposed on the surgical retractor, said cameras inwardly facing toward said pathway. In some embodiments, the surgical tool comprises a scalpel, a rongeur, a kerrison, a laser, or a drill. In some embodiments, the plurality of cameras comprises at least 8 cameras. In some embodiments, the surgical site is an area of the spine of the body. In some embodiments, the surgical site is an area of a head or neck of the body. In some embodiments, the retractor comprises a plurality of retractor blades and said cameras are disposed on said retractor blades. In some embodiments, the retractor comprises a tube and said cameras are disposed on an inside surface of the tube. In some embodiments, the surgical retractor comprises at least one proximal camera and at least one distal camera. In some embodiments, the method further comprises obtaining respective images produced by the cameras. In some embodiments, the method further comprises displaying said respective images simultaneously. In some embodiments, the respective images are displayed as stitched together. In some embodiments, the respective images are displayed as tiled. 
     In accordance with another aspect, a medical apparatus comprises: a surgical retractor configured to hold open an incision formed in a body and thereby provide a pathway for access for surgical tools to a surgical site in said body, said retractor including proximal and distal locations, said distal location configured to be disposed further within said body than said proximal location; and a plurality of cameras disposed on the surgical retractor, including at least one proximal camera at said proximal location and at least one distal camera at said distal location. In some embodiments, said surgical retractor comprises a plurality of retractor blades and said cameras are disposed on at least one proximal and at least one distal location of said retractor blades. In some embodiments, said surgical retractor comprises a tube and said cameras are disposed on at least one proximal and at least one distal location on inside surface of said tube. In some embodiments, said cameras are fastened to the surgical retractor using a clip-on fastener In some embodiments, said clip-on fastener comprises a clip, a snap, a screw, a bolt, a nut, or a magnet. In some embodiments, the medical apparatus further comprises an electrical bus and electrical connector configured to connect said cameras to said electrical bus. In some embodiments, said cameras are integrated into the surgical retractor. In some embodiments, the proximal camera and the distal camera produce respective images, and the apparatus further comprises an image processing module configured to display respective images for simultaneous viewing. In some embodiments, the proximal camera is oriented along a first optical axis, and the distal camera is oriented along a second optical axis, and the first and second optical axes are substantially parallel. In some embodiments, the proximal camera is oriented along a first optical axis, and wherein the distal camera is oriented along a second optical axis, and wherein the first and second optical axes intersect at a first point. In some embodiments, the first point is within the pathway for access for surgical tools to the surgical site. In some embodiments, the proximal camera is oriented along a first optical axis, wherein the first optical axis is substantially orthogonal to a plane of a surface of the retractor at the proximal location. In some embodiments, the distal camera is oriented along a second optical axis, wherein the second optical axis is substantially orthogonal to a plane of a surface of the retractor at the distal location. In some embodiments, the proximal camera provides a first field-of-view and the distal camera provides a second field of view, the second field of view being smaller than the first field-of-view. In some embodiments, the first and second fields of view at least partially overlap. In some embodiments, the first field of view is between about 80 and 100 degrees. In some embodiments, the second field of view is between about 50 and 70 degrees. In some embodiments, the retractor is configured such that when holding open the incision formed in the body and thereby providing a pathway for access for surgical tools to the surgical site in said body, the first and second fields of view each encompass at least a portion of the surgical site. In some embodiments, said cameras produce respective images, and wherein the apparatus further comprises an image processing module configured to display respective images for simultaneous viewing. In some embodiments, the image processing module is configured to display at least a portion of said respective images as stitched together. In some embodiments, the image processing module is configured to display at least a portion of said respective images as tiled. 
     In accordance with another aspect, a surgical visualization system comprises: a surgical retractor having proximal and distal locations, said distal location configured to be disposed further within a body than said proximal location; a proximal camera disposed at said proximal location; and a distal camera disposed at said distal location. In some embodiments, said surgical retractor comprises a plurality of retractor blades and said cameras are disposed on at least one proximal and at least one distal location of said retractor blades. In some embodiments, said surgical retractor comprises a tube and said cameras are disposed on at least one proximal and at least one distal location on inside surface of said tube. 
     In accordance with another aspect, a method comprises: inserting a retractor into an opening in a body; holding open edges of the opening with the retractor, thereby providing a pathway for access of surgical tools to a surgical site; and inserting a surgical tool at least partially through pathway, wherein said retractor comprises a proximal camera and a distal camera, said cameras inwardly facing toward said pathway. In some embodiments, the surgical tool comprises a scalpel, a rongeur, a kerrison, a laser, or a drill. In some embodiments, the retractor comprises a plurality of proximal cameras and a plurality of distal cameras. In some embodiments, the surgical site is an area of the spine of the body. In some embodiments, the surgical site is an area of a head or neck of the body. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor having a plurality of cameras disposed thereon; a surgical tool having at least one camera disposed thereon; and an image processing module configured to display respective images from said plurality of cameras on said retractor and said camera on said surgical tool for simultaneous viewing. In some embodiments, the surgical tool is movable with respect to the retractor. In some embodiments, at least one of the plurality of cameras substantially faces another one of the plurality of cameras. In some embodiments, the image processing module is configured to display said respective images for simultaneous viewing as a composite first image. In some embodiments, the image processing module is configured to integrate a second image obtained from the at least one camera on the surgical tool with the composite first image. In some embodiments, the composite first image is produced by tiling or stitching the respective images from the plurality of cameras on the retractor. In some embodiments, the image processing module is configured to display the second image as a picture-in-picture over the composite first image. In some embodiments, the image processing module is configured to stitch the second image with the composite first image to produce a composite third image. In some embodiments, the plurality of cameras are attached to a surface of blades of the retractor. In some embodiments, the plurality of cameras are integrated within blades of the retractor. In some embodiments, the plurality of cameras comprises at least 8 cameras. In some embodiments, the surgical tool comprises a scalpel, a rongeur, a kerrison, a laser, or a drill. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor having a plurality of cameras disposed thereon; a camera configured to be associated with a surgical tool; and an image processing module configured to display respective images from said plurality of cameras on said retractor and images from said camera associated with said surgical tool for simultaneous viewing. In some embodiments, at least one of the plurality of cameras disposed on the retractor substantially faces another one of the plurality of cameras disposed on the retractor. In some embodiments, the image processing module is configured to display said respective images for simultaneous viewing as a composite first image. In some embodiments, the image processing module is configured to integrate a second image obtained from the camera configured to be associated with the surgical tool with the composite first image. 
     In accordance with another aspect, a method comprises: receiving from a plurality of cameras disposed on a retractor a first plurality of image data; receiving from a camera disposed on a surgical tool a second plurality of image data; processing the first plurality of image data to produce a first image; and processing the second plurality of image data to produce a second image. In some embodiments, producing the first image comprises stitching or tiling separate images obtained from the plurality of cameras. In some embodiments, the method further comprises integrating the second image with the first image. In some embodiments, integrating comprises disposing the second image as a picture-in-picture over the first image. In some embodiments, integrating comprises stitching the second image with the first image to produce a composite third image. 
     In accordance with another aspect, a surgical visualization kit comprises: a plurality of cameras configured to be disposed on a retractor, said cameras configured to produce respective images; an image processing module configured display said respective images; and a camera configured to be disposed on a surgical tool. In some embodiments, the image processing module is configured to display said respective images for simultaneous viewing as a composite first image. In some embodiments, displaying said composite first image is produced by stitching or tiling the respective images produced by the plurality of cameras. In some embodiments, the image processing module is further configured to display a second image obtained from the camera configured to be disposed on the surgical tool. In some embodiments, the image processing module is configured to display the second image as a picture-in-picture over the first image. In some embodiments, the image processing module is configured to stitch the second image with the first image to produce a composite third image. 
     In accordance with another aspect, a method comprises: inserting a retractor into an opening in a body, the retractor comprising a plurality of cameras disposed thereon; inserting a surgical tool at least partially into a working space of the retractor, the surgical tool comprising at least one camera disposed thereon. In some embodiments, at least some of the plurality of cameras are disposed on a blade of the retractor and substantially face the working space. In some embodiments, the plurality of cameras comprises at least 8 cameras. 
     In accordance with another aspect, a medical apparatus comprises: a surgical retractor configured to hold open an opening in a body and thereby provide a pathway for access of surgical tools to a surgical site, wherein the retractor comprises a rotatable platform; and a plurality of cameras disposed on the rotatable platform. In some embodiments, said retractor comprises retractor blades configured to hold open the opening. In some embodiments, said rotatable platform is movable with respect to the retractor blades. In some embodiments, said retractor blades move with rotation of said rotatable platform. In some embodiments, said retractor comprises a proximal end and a distal end, said distal end configured to be disposed further within said body, and wherein said rotatable platform is arranged proximal to the retractor blades. In some embodiments, the apparatus further comprises a second plurality of cameras disposed on the retractor blades. In some embodiments, said cameras are configured to produce respective images, the apparatus further comprising an image processing module configured to display respective images simultaneously. In some embodiments, rotation of said rotatable platform produces rotation of the simultaneous display of the respective images. In some embodiments, the image processing module is configured to display at least a portion of said respective images as stitched together. In some embodiments, the image processing module is configured to display at least a portion of said respective images as tiled. In some embodiments, the plurality of cameras comprises a first camera and a second camera, wherein the first camera has a first field of view, and the second camera has a second field of view. In some embodiments, the retractor is configured such the first field of view encompasses the surgical site. In some embodiments, the retractor is configured such the first and second fields of view each encompass the surgical site. In some embodiments, the retractor is configured such the first and second fields of view at least partially overlap. In some embodiments, at least one of the plurality of cameras substantially faces the pathway for access of surgical tools. 
     In accordance with another aspect, a surgical visualization system comprises: a surgical retractor having proximal and distal locations, said distal location configured to be disposed further within a body than said proximal location, said retractor comprising a rotatable platform; and a plurality of cameras disposed on the rotatable platform. In some embodiments, said retractor comprises retractor blades configured to hold open the opening, wherein the retractor blades are distal to the rotatable platform. In some embodiments, said rotatable platform is rotatable with respect to the retractor blades. In some embodiments, said retractor comprises a tube configured to hold open the opening, wherein the tube is distal to the rotatable platform. In some embodiments, said rotatable platform is rotatable with respect to the tube. In some embodiments, the retractor defines a pathway for access of surgical tools to a surgical site, and wherein at least one of the cameras substantially faces the surgical site. 
     In accordance with another aspect, a method comprises: inserting a retractor at least partially into an opening in a body, the retractor comprising a rotatable platform having a plurality of cameras thereon; holding open edges of the opening with the retractor, thereby providing a pathway for access of surgical tools to a surgical site; and rotating the rotatable platform, thereby altering the orientation of the plurality of cameras with respect to the opening. In some embodiments, the rotatable platform is disposed outside the opening of the body. In some embodiments, the surgical site is an area of the spine of the body. In some embodiments, the surgical site is an area of a head or neck of the body. In some embodiments, the opening is a mouth of the body. In some embodiments, the plurality of cameras comprises at least 8 cameras. In some embodiments, the retractor comprises a plurality of retractor blades, and wherein upon insertion of the retractor at least partially into the opening, said retractor blades are closer to said surgical site than said rotatable platform. In some embodiments, the retractor comprises a tube, and upon insertion of the retractor at least partially into the opening, said tube is closer to said surgical site than said rotatable platform. 
     In accordance with another aspect, a medical apparatus comprises: a surgical device; at least one camera disposed on the surgical device; and a hydraulic system configured to deliver fluid pulses to the at least one camera. In some embodiments, the surgical device is a retractor In some embodiments, the fluid comprises water. In some embodiments, the fluid comprises pharmaceuticals, fluorescent dyes, or saline. In some embodiments, the fluid pulses are configured to remove obstructions from the at least one camera. In some embodiments, the apparatus further comprises a plurality of cameras, wherein the hydraulic system is configured to deliver fluid pulses to each of the plurality of cameras. In some embodiments, the hydraulic system comprises a plurality of microfluidic channels coupled to a fluid source. In some embodiments, the microfluidic channels comprise a flex cable configured to be positioned over an electronic cable. In some embodiments, the microfluidic channels are disposable. In some embodiments, the distal end of the flex cable comprises an outer housing secured over the camera. In some embodiments, the shape of the outer housing is configured to direct fluid from the flex cable over a surface of the camera. In some embodiments, hydraulic system comprises a disposable diaphragm pump In some embodiments, the hydraulic system comprises at least one of: a rolling edge diaphragm, Bourdon tube, or a bellow. In some embodiments, the at least one camera comprises a lens including a stop behind a plano window, and wherein the hydraulic system is configured to deliver a fluid pulse over the plano window. In some embodiments, the hydraulic system is further configured to deliver pulses of pressurized air to the camera. In some embodiments, the pulses of pressurized air are configured to dry the camera following the fluid pulses. In some embodiments, the hydraulic system is controlled by a proportional foot pedal. In some embodiments, the hydraulic system is further configured to provide egress of gases and/or liquids. 
     In accordance with another aspect, a surgical visualization system comprises: a surgical retractor having a plurality of cameras disposed thereon; a surgical tool having at least one camera disposed thereon; and an image processing module configured to receive signals from said cameras on said retractor and said surgical tool for display of respective images from said cameras, wherein said image processing module is configured to track the locations of said plurality of cameras and of said surgical tool. In some embodiments, said surgical tool is movable with respect to said surgical retractor. In some embodiments, said surgical tool is associated with a tracking device to track the location of the surgical tool. In some embodiments, said tracking device comprises an EM tracking device. In some embodiments, said cameras disposed on the surgical retractor are associated with tracking devices to track the location of the cameras. In some embodiments, said tracking devices comprise EM tracking devices. In some embodiments, the image processing module is configured to track the location of said surgical tool with optical tracking. In some embodiments, the system further comprises an overhead camera, wherein the surgical tool includes identifying markers visible to the overhead camera, and wherein the image processing module is configured to track the location of the surgical tool by tracking the identifying markers on the surgical tool. In some embodiments, the image processing module is configured to display said respective images simultaneously. In some embodiments, the image processing module is configured to adjust the display of said respective images depending upon the tracked location of said surgical tool. In some embodiments, the image processing module is configured to display respective images obtained from the cameras disposed on said retractor for simultaneous viewing as a composite first image. In some embodiments, the image processing module is configured to display an image obtained from the camera disposed on said surgical tool simultaneously with the composite first image. In some embodiments, the image processing module is configured to display the image obtained from the camera disposed on said surgical tool as a picture-in-picture over the composite first image. In some embodiments, the image processing module is configured to stitch the image obtained from the camera disposed on said surgical tool with the first composite image to produce a second composite image. In some embodiments, the plurality of cameras are attached to a surface of blades of the retractor. In some embodiments, the plurality of cameras face inwardly towards a pathway defined by the blades of the retractor. In some embodiments, the blades of the retractor are malleable or articulated. In some embodiments, the blades of the retractor are movable with respect to one another. 
     In accordance with another aspect, a method comprises: inserting a retractor into an opening in a body, the retractor comprising a plurality of cameras disposed thereon, wherein the retractor defines a pathway for access of surgical tools to a surgical site within the body; inserting a surgical tool into the pathway, the surgical tool; electronically tracking the locations of said cameras and the location of said surgical tool. In some embodiments, the surgical tool comprises a camera disposed thereon. In some embodiments, the method further comprises obtaining respective images from each of the cameras, and processing said respective images for simultaneous viewing. In some embodiments, said processing comprises using the tracked locations of said cameras. In some embodiments, said electronically tracking comprises EM tracking. In some embodiments, said plurality of cameras are disposed on blades of the retractor, and wherein said electronically tracking comprises tracking position of the blades. In some embodiments, said blades are malleable or articulated. In some embodiments, said electronically tracking comprises tracking the degree to which said blades are bent or articulated. 
     In accordance with another aspect, a medical apparatus can comprise a surgical device, a hydraulic system providing hydraulic power to said surgical device, the hydraulic system comprising, a hydraulic fluid source, and a cassette assembly having a plurality of external fluid ports, one or more hydraulic pressure chambers, and a plurality of valves positioned on one or more fluid paths fluidly connecting the external fluid ports to the one or more hydraulic pressure chambers, the hydraulic fluid source being in fluid communication with the one or more hydraulic pressure chambers via one or more of the external fluid ports, and an electromagnetic tracking device. In some embodiments, the electromagnetic tracking device can be configured to track said surgical device. In some embodiments, electromagnetic tracking device can be configured to track camera modules on a retractor. In some embodiments, one or more of the plurality of valves can be a diaphragm valve. In some embodiments, wherein one or more of the plurality of valves can be a proportional valve. In some embodiments, one or more of the plurality of valves can be an elastomeric valve. In some embodiments, the cassette assembly can comprise disposable components. In some embodiments, the entire cassette assembly can be disposable. In some embodiments, the hydraulic system can further comprise a hydraulic turbine operably connected to the surgical device to actuate the surgical device. In some embodiments, the apparatus can further comprise one or more washing nozzles in fluid communication with one or more of the hydraulic pressure chambers or the hydraulic fluid source, the one or more washing nozzles configured to direct hydraulic fluid toward one or more light sources. 
     In accordance with another aspect, a medical apparatus can comprise a surgical device, a hydraulic system providing hydraulic power to said surgical device, the hydraulic system comprising, a hydraulic fluid source, and a cassette assembly having a plurality of external fluid ports, one or more hydraulic pressure chambers, and a plurality of valves positioned on one or more fluid paths fluidly connecting the external fluid ports to the one or more hydraulic pressure chambers, the hydraulic fluid source being in fluid communication with the one or more hydraulic pressure chambers via one or more of the external fluid ports, and one or more cameras for providing a view of an area in the body. In some embodiments, In some embodiments, the apparatus can further comprise an electromagnetic tracking device. In some embodiments, said electromagnetic tracking device can be configured to track camera modules on a retractor. In some embodiments, said camera can be on said surgical device. In some embodiments, said camera can be on a retractor in said area in the body. In some embodiments, one or more of the plurality of valves can be a diaphragm valve. In some embodiments, one or more of the plurality of valves can be a proportional valve. In some embodiments, one or more of the plurality of valves can be an elastomeric valve. In some embodiments, the cassette assembly can comprise disposable components. In some embodiments, the entire cassette assembly can be disposable. In some embodiments, the hydraulic system can further comprise a hydraulic turbine operably connected to the surgical device to actuate the surgical device. 
     In accordance with another aspect, a method of tracking a surgical device, the method can comprise providing a surgical device, operably connecting the surgical device to a hydraulic system, the hydraulic system can comprise: a hydraulic fluid source, and a cassette assembly having a plurality of external fluid ports, one or more hydraulic pressure chambers, and a plurality of valves positioned on one or more fluid paths fluidly connecting the external fluid ports to the one or more hydraulic pressure chambers, the hydraulic fluid source being in fluid communication with and providing hydraulic fluid to the one or more hydraulic pressure chambers via one or more of the external fluid ports; pressurizing the hydraulic fluid; tracking the surgical device using one or more of a camera and an electromagnetic tracking device. In some embodiments, the method of tracking a surgical device can further comprise operably connecting a hydraulic turbine of the surgical device to the hydraulic system. 
     In accordance with another aspect, a medical apparatus comprises: a retractor stage comprising a ring defining an aperture, the ring substantially aligned with a first plane substantially orthogonal to a first axis; a plurality of blades coupled to said stage and positioned within said aperture, each of the blades extending away from the first plane, wherein each of the blades is configured to be: rotationally moved with respect to said ring; radially moved inward and outward with respect to said ring; and tilted with respect to said first axis. In some embodiments, each of the blades is configured to be tilted by flexing. In some embodiments, each of the blades is be jointed, and each of the blades is configured to be titled by bending at a joint. In some embodiments, each of the blades is coupled to said stage by a stem extending between a proximal end of the blade and the stage. In some embodiments, the stem is coupled to the stage by a clamp. In some embodiments, the clamp is configured to be moved rotationally around the ring, thereby rotationally moving the stem and retractor. In some embodiments, the stem is configured to be slidably moved through the clamp, thereby moving the stem and the retractor radially inward or outward with respect to said ring. In some embodiments, the apparatus further comprises a plurality of cameras disposed on the retractor blades. 
     In accordance with another aspect, an articulated retractor blade comprises: a proximal segment; a middle segment coupled at a first joint to a distal end of the proximal segment; a distal segment coupled at a second joint to a distal end of the middle segment; a first actuator configured to cause rotation of the middle segment about the first joint; and a second actuator configured to cause rotation of the distal segment about the second joint. In some embodiments, the first actuator comprises a first internal cable extending through the proximal segment, across the first joint, and into the middle segment. In some embodiments, proximal movement of the first internal cable causes the middle segment to rotate about the first joint. In some embodiments, the articulated retractor blade further comprises a retention mechanism configured to releasably retain the position of the first internal cable. In some embodiments, the retention mechanism comprises a pinion key coupled to a ratchet. In some embodiments, the second actuator comprises a second internal cable extending through the proximal segment, across the first joint, and into the middle segment, across the second joint, and into the distal segment. In some embodiments, proximal movement of the first internal cable causes the distal segment to rotate about the second joint. In some embodiments, the articulated retractor blade comprises a retention mechanism configured to releasably retain the position of the first internal cable. In some embodiments, the retention mechanism comprises a pinion key coupled to a ratchet. In some embodiments, the articulated retractor blade comprises at least one camera disposed on a surface of the middle segment. 
     In accordance with another aspect, a method comprises: positioning a retractor stage over an opening in a body, wherein the retractor stage comprises a ring defining an aperture, the ring substantially aligned with a first plane substantially orthogonal to a first axis; arranging at least one blade coupled to said stage and positioned within said central aperture, the blade away from said plane and into the opening; positioning the at least one blade rotationally and radially with respect to said ring such that a surface of the blade abuts an edge of the opening; and tilting the at least one blade with respect to the first axis; and inserting a surgical tool at least partially through the aperture and into the opening in the body. In some embodiments, the method further comprises: arranging a plurality of blades coupled to said stage and positioned within said central aperture, each of the blades extending away from said plane and into the opening; positioning each of the blades rotationally and radially with respect to said ring such that a surface of each blade abuts an edge of the opening; and tilting each of the blades with respect to the first axis. In some embodiments, tilting the at least one blade comprises flexing the blade. In some embodiments, the at least one blade is jointed, and wherein tilting the at least one blade comprises bending the blade at a joint. In some embodiments, the at least one blade comprises: a proximal segment; a middle segment coupled at a first joint to a distal end of the proximal segment; a distal segment coupled at a second joint to a distal end of the middle segment; a first actuator configured to cause rotation of the middle segment about the first joint; and a second actuator configured to cause rotation of the distal segment about the second joint. In some embodiments, the at least one blade comprises at least one camera disposed therein. In some embodiments, the method further comprises obtaining an image from the camera and displaying said image. 
     In accordance with another aspect, a retractor comprises: a main body; a first blades comprising clip-on fastener for removable attaching said first blade to said main body, a second blades comprising clip-on fastener for removable attaching said second blade to said main body, at least one camera connected to at least said first blade. In some embodiments, at lease one of said first and second blades are flexible. In some embodiments, said first and second blades have different dimensions. In some embodiments, said first and second blades have different stiffness. 
     In accordance with another aspect, a retractor comprises: a main body; a first blades comprising clip-on fastener for removable attaching said first blade to said main body, a second blades comprising clip-on fastener for removable attaching said second blade to said main body, wherein at least one of said first and second blades have different dimensions, stiffness, or both. In some embodiments, at least one of said first and second blades are flexible. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor; and a plurality of cameras disposed on the retractor, said cameras producing respective images, wherein the cameras are fastened to the retractor using a clip-on fastener. In some embodiments, said clip-on fastener comprises a clip, a snap, a screw, a bolt, a nut, or magnet. 
     In accordance with another aspect, a clip-on camera system for clipping on a retractor comprises: a plurality of camera modules comprising a plurality of support platforms and at least one camera disposed on the support platforms; a fastened configured to clip-on the support platform onto the retractor; electrical signal lines from the camera; an electrical connector electrically connected to the electrical sensor; and a central bus box for receiving the plurality of electrical lines and connectors In some embodiments, said clip-on fastener comprises a clip, a snap, a screw, a bolt, a nut, or magnet. In some embodiments, said electrical signal lines are between about 1 to 4 inches long. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor configured to provide access to a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within an opening to which the retractor provides access; and an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive the video images acquired by the plurality of cameras; receive input from a user indicating a selection of at least two of the plurality of cameras, said selection being less than all of said cameras in said plurality of cameras; provide output video images based on the video images acquired by the selected cameras, the output video images being provided for simultaneous viewing; and resize or arrange the simultaneously viewable output video images from the selected cameras to present them on a display according to received input. In some embodiments, the image processing system is configured to increase a size of a first one of the simultaneously viewable output video images in relation to a second one of the simultaneously viewable output video images based at least partly on received input. In some embodiments the image processing system is configured to arrange a first one of the simultaneously viewable output video images in a more central location in relation to a second one of the simultaneously viewable output video based at least partly on received input. In some embodiments at least one of the simultaneously viewable output video images are represented by a reduced-size real-time video stream that is configured to be presented on a graphical user interface for selection by a user, wherein the graphical user interface includes a representation of a position of the retractor and the plurality of cameras. In some embodiments at least one of the simultaneously viewable output video images is represented by a reduced-size real-time video stream that is configured to be presented on a display for selection by a user, the reduced-size real-time video stream comprising video from the respective camera. In some embodiments the image processing system is (a) configured to display video images that are from a camera that is not selected and that are not displayed on the display after receiving input from the user indicating a selection thereof, (b) is configured to display video images that are from the camera that is not selected and that are displayed as a reduced-size real-time video stream more prominently after receiving input from the user indicating a selection thereof, or (c) configured as set forth in both (a) and (b). In some embodiments the image processing system is configured to the output video images in a tiled format. In some embodiments the tiled output images comprise at least three images. In some embodiments the tiled output images comprise at least four images. In some embodiments the image processor is configured to rotate the tiled output images around a single, common axis. In some embodiments the output video images from at least two of the plurality of cameras are discontinuous. In some embodiments, the system further comprises a second display, wherein the cameras that are not selected by the user can be displayed on the second display. In some embodiments the plurality of selected cameras comprise at least first and second cameras that are disposed on the retractor in positions opposite one another. In some embodiments the image processing system is further configured rotate video images from said first selected camera 180° with respect to video images from said second selected camera. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor configured to provide access to a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images of said surgical site; and an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive the video images acquired by the plurality of cameras; receive input indicating a selection of video images from a camera; and providing output video images based on video images acquired with the selected camera, wherein the image processing system is configured to present output video images from a first camera, and wherein the image processing system is further configured to swap the presentation of the output video images of the first camera with video images from a second camera in response to a request to resize the output video images from the second camera to be larger than a threshold size. In some embodiments, the image processing system is configured to recognize enlargement by the user of a reduced-size real-time video stream beyond the threshold value as the request to resize the output video images from the second camera. In some embodiments, the image processing system is configured to convert the first image to a reduced-size real-time video stream as part of swapping the presentation of the video images from the second camera with the video images of the first camera. In some embodiments, in response to selection by a user, the image processing system is configured to present output video images from a third camera positioned over output video images from the second camera, wherein the output images from the third camera are less than the threshold value. In some embodiments, in response to selection by a user after the presentation of the output video images of the first camera is swapped with video images from a second camera, the image processing system is configured to present output video images from the first camera positioned over output video images from the second camera, wherein the output images from the first camera are less than the threshold value. In some embodiments, the system further comprises a display in communication with said image processing system, said display configured to display said video images from said first and second cameras, wherein said threshold value is at least 70% and less than 85% of the size of the display. In some embodiments, said threshold value is at least 85% of the size of the display. In some embodiments, the system further comprises a second display, wherein the cameras that are not selected by the user can be displayed on the second display. In some embodiments, the second display presents a graphical user interface for configuration of the output video images on the display. 
     In accordance with another aspect, a surgical visualization system can comprise: a retractor configured to provide an opening in a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; and an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive the video images acquired by the plurality of cameras; provide representations of each of the plurality of cameras by a camera icon on a display, each camera icon presenting a real-time representation of the video images acquired by the camera associated with the camera icon; receive input indicating a selection of a camera based on a selection of the associated camera icon; and providing output video images based on video images acquired with the selected camera, the output video images initially arranged in a manner consistent with a physical arrangement of the selected camera. In some embodiments, the image processing system can be further configured to: receive input indicating a size with which to present output video images acquired with a designated camera, a relative position to present the output video images acquired with the designated camera, or both; and providing the output images of the designated camera according to the received input. In some embodiments, in response to selection by a user, the image processing system can be configured to present output video images from a first camera positioned over output video images from a second, wherein the output images from the second camera is larger than the output imagery from the first camera. In some embodiments, a the image processing system can be further configured to swap the presentation of the output video images of the first and second cameras in response to a request to resize the first output video images to be larger than a first threshold size or a request to resize the second output video images to be smaller than a second threshold size. In some embodiments, the image processor can be further configured to rotate the output video images of the first and second cameras around a single, common axis. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor; a plurality of cameras, at least one of said cameras being disposed on said retractor; and an image processing module in communication with said cameras, said image processing module configured to arranged a plurality of video images for simultaneous viewing on a display in a tiled format, said tiled video images being superimposed over a larger video image from one of said cameras. In some embodiments, said larger video image comprises a wider field-of-view image and said tiled video images comprise narrower field-of-view images. In some embodiments, said wide field-of-view image has a field at least 1.3 times larger than one of said tiled video images. In some embodiments, said wide field-of-view image has a field at least 1.5 times larger than one of said tiled video images. In some embodiments, said wide field-of-view image has a field at least 1.75 times larger than one of said tiled video images. In some embodiments, said wide field-of-view image has a field at least 2.0 times larger than one of said tiled video images. In some embodiments, at least two of said cameras are disposed on said retractor. In some embodiments, wherein said plurality of cameras are disposed on said retractor, at least one of said cameras being disposed on said retractor. In some embodiments, at least one of said cameras is disposed on a surgical tool. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor; t least one cameras disposed on said retractor; and an image processing module in communication with said camera, said image processing module configured to provide a main video image on a display, said image processing module further configured to receive a video image from a camera disposed on a surgical tool and superimpose said video image from said surgical tool camera on said main video image, wherein said main video image is larger than said video image from said surgical tool cameras. 
     In accordance with another aspect, a surgical visualization system comprises: a retractor; at least one cameras disposed on said retractor; and an image processing module in communication with said camera, said image processing module configured to provide a main video image on a display, said image processing module further configured to receive a video image from a camera disposed on a surgical tool and superimpose said video image from said surgical tool camera on said main video image, wherein said main video image is larger than said video image from said surgical tool cameras. In some embodiments, said main video image comprises a relatively wide field-of-view image in comparison to said video image from said camera on said surgical tool which comprise a relatively narrow field-of-view image. In some embodiments, said main field-of-view image has a field at least 1.5 times larger than said video images from said camera on said surgical tool. In some embodiments, said main field-of-view image has a field at least 1.75 times larger than said video images from said camera on said surgical tool. In some embodiments, said main field-of-view image has a field at least 2.0 times larger than said video images from said camera on said surgical tool. In some embodiments, said main field-of-view image has a field at least 2.3 times larger than said video images from said camera on said surgical tool. In some embodiments, at least two of said cameras are disposed on said retractor. In some embodiments, said plurality of cameras are disposed on said retractor, at least one of said cameras being disposed on said retractor. In some embodiments, at least one of said cameras is disposed on a surgical tool. 
     In accordance with another aspect, some embodiments provide for a surgical visualization system that includes a retractor configured to provide an opening in a surgical site. The surgical visualization system includes a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor. The surgical visualization system includes an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor. The image processing system is configured to receive the video images acquired by the plurality of cameras; receive input from a user indicating a selection of at least two of the plurality of cameras; provide output video images based on the video images acquired by the selected cameras, the output video images being provided for simultaneous viewing; and resize or arrange the simultaneously viewable output video images from the selected cameras to present them more prominently on a display in comparison to output video images based on the video images acquired by any of the plurality of cameras which is not selected. In some aspects, the image processing system is configured to increase a size of the simultaneously viewable output video images in relation to the output video images from the non-selected cameras. The image processing system can also be configured to arrange the simultaneously viewable output video images in a more central location in relation to the output video images from the non-selected cameras. In some implementations, the simultaneously viewable output video images include icons that are configured to be presented on a display for selection by a user. The icons can include images from the respective cameras. 
     In some embodiments, the image processing system is configured to arrange the output video images from the selected cameras in a manner consistent with a physical arrangement of the selected cameras. The physical arrangement of the selected cameras can include a location of the selected cameras, a field-of-view of the selected cameras, or both. In some aspects, the image processing system is configured to the output video images in a tiled format. The tiled output images can be arranged in a geometrical arrangement consistent with locations of the plurality of cameras with respect to each other, with orientations of the plurality of cameras with respect to each other, or both. The tiled output images can include in some aspects at least four images. In some implementations, the image processor is configured to rotate the tiled output images around a single, common axis. In some aspects, the output video images from at least two of the plurality of cameras are discontinuous. 
     In some embodiments, at least two of the plurality of cameras can be disposed on the retractor positioned opposite one another. The image processing system can be further configured to output video images from the at least two cameras disposed on the retractor that are rotated 180 degrees with respect to one another. The image processing system can be further configured to arrange the output video images from the selected cameras in a manner consistent with a location of the at least two cameras disposed on the retractor, a field-of-view of the at least two cameras disposed on the retractor, or both. 
     In accordance with another aspect, some embodiments provide for a surgical visualization system that includes a retractor configured to provide an opening in a surgical site. The surgical visualization system includes a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor. The surgical visualization system includes an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor. The image processing system is configured to receive the video images acquired by the plurality of cameras; to provide representations of each of the plurality of cameras by a camera icon on a display, each camera icon presenting a real-time representation of the video images acquired by the camera associated with the camera icon; to receive input indicating a selection of a camera based on a selection of the associated camera icon; and to provide output video images based on video images acquired with the selected camera, the output video images initially arranged in a manner consistent with a physical arrangement of the selected camera. In a further aspect, the image processing system is configured to receive input indicating a size with which to present output video images acquired with a designated camera, a relative position to present the output video images acquired with the designated camera, or both; and to providing the output images of the designated camera according to the received input. In some implementations, in response to selection by a user, the image processing system is configured to present output video images from a first camera positioned over output video images from a second, wherein the output images from the second camera is larger than the output imagery from the first camera. The image processing system can be further configured to swap the presentation of the output video images of the first and second cameras in response to a request to resize the first output video images to be larger than a first threshold size or a request to resize the second output video images to be smaller than a second threshold size. In some aspects, the image processor is configured to rotate the output video images of the first and second cameras around a single, common axis. 
     In accordance with another aspect, a surgical visualization system can comprise: a retractor configured to provide an opening in a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; and an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive the video images acquired by the plurality of cameras; receive input from a user indicating a selection of at least two of the plurality of cameras; provide output video images based on the video images acquired by the selected cameras, the output video images being provided for simultaneous viewing; and resize or arrange the simultaneously viewable output video images from the selected cameras to present them more prominently on a display in comparison to output video images based on the video images acquired by any of the plurality of cameras which is not selected. In some embodiments, the image processing system is configured to arrange the output video images from the selected cameras in a manner consistent with a physical arrangement of the selected cameras. According to some variants, the physical arrangement of the selected cameras comprises a location of the selected cameras, a field-of-view of the selected cameras, or both. The image processing system can configured to increase a size of the simultaneously viewable output video images in relation to the output video images from the non-selected cameras. In some embodiments, the image processing system is configured to arrange the simultaneously viewable output video images in a more central location in relation to the output video images from the non-selected cameras. The simultaneously viewable output video images can comprise icons that are configured to be presented on a display for selection by a user. In some embodiments, the icons comprise images from the respective cameras. 
     In accordance with another aspect, a surgical visualization system can comprise: a retractor configured to provide an opening in a surgical site; a plurality of cameras, each camera having a field of view and configured to acquire video images of a portion of the surgical site corresponding to the field of view, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; and an image processing system in communication with the plurality of cameras, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive the video images acquired by the plurality of cameras; for each of the plurality of cameras, provide output video images based on the acquired video images, the output video images being provided for simultaneous viewing; and arrange each of the output video images from the plurality of cameras in a manner consistent with their respective fields of view. The image processing system can be configured to the output video images in a tiled format. In some embodiments, the tiled output images are arranged in a geometrical arrangement consistent with locations of the plurality of cameras with respect to each other, with orientations of the plurality of cameras with respect to each other, or both. The tiled output images can comprise at least four images. In some embodiments, the image processor is configured to rotate the tiled output images around a single, common axis. The output video images from at least two of the plurality of cameras can be discontinuous. 
     According to some variants, the plurality of cameras are each represented by an icon that is configured to be presented on a display for selection by a user. The icons can be configured to present a real-time representation of the video images acquired by the respective camera. In some embodiments, the image processing system is configured to receive input from a user indicating a size with which to present output video images acquired with the selected camera, a relative position to present the output video images acquired with the selected camera, or both. Some embodiments can be configured such that, in response to selection by a user, the image processing system is configured to present output video imagery from a first camera positioned over output video imagery from a second, wherein the output imagery from the second camera is larger than the output imagery from the first camera. The image processing system can be configured to swap the presentation of the output video imagery of the first and second cameras in response to a request to resize the first video output to be larger than a first threshold size or a request to resize the second video output to be smaller than a second threshold size. In some embodiments, at least two of the plurality of cameras are disposed on the retractor positioned opposite one another. In some embodiments, the image processing system is configured to output video images from the at least two cameras disposed on the retractor that are rotated 180 degrees with respect to one another. 
     In accordance with another aspect, a medical apparatus comprises: a retractor configured to provide access to a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; a binocular viewing assembly comprising a housing and a plurality of oculars, the plurality of oculars configured to provide views of at least one display disposed in the housing; a viewing articulating arm, the binocular viewing assembly disposed on the viewing articulating arm, the viewing articulating arm configured to adjust a position of the binocular viewing assembly; a support, the viewing articulating arm attached to the support such that the viewing articulating arm can move relative to the support; and an image processing system in communication with the plurality of cameras and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the plurality of cameras, provide output video images based on the received video images, and present the output video images on the at least one display so that the output video images are viewable through the plurality of oculars, wherein the binocular viewing assembly does not provide a view of the surgical site through the oculars via an optical pathway that passes through the housing. In some embodiments, the image processing system is configured to provide 3-D viewing of camera images through the binoculars. In some embodiments, the apparatus further comprises an auxiliary camera disposed on the binocular viewing assembly, the camera having a field of view that can be configured to include the surgical site, wherein the camera is configured to provide a surgical microscope view of the surgical site. In some embodiments, the auxiliary camera disposed on the binocular viewing assembly comprises an optical assembly providing an adjustable working distance of between about 15 cm and about 45 cm. In some embodiments, the optical assembly has a variable magnification of between about −0.5× and about 10×. In some embodiments, the medical apparatus further comprises a second articulating arm; and an auxiliary camera disposed on the second articulated arm, the auxiliary camera having a field of view that can be configured to include the surgical site wherein the camera is configured to provide a surgical microscope view of the surgical site, wherein the image processing system is configured to display the surgical microscope view on the at least one display. In some embodiments, the auxiliary camera disposed on the camera platform comprises an optical assembly providing an adjustable working distance of between about 15 cm and about 45 cm. In some embodiments, the optical assembly has a variable magnification of between about −0.5× and about 10×. 
     In accordance with another aspect, a medical apparatus comprises: a retractor configured to provide access to a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; an auxiliary camera having a field of view that can be configured to include the surgical site, wherein the auxiliary camera is configured to provide a surgical microscope view of the surgical site; a binocular viewing assembly comprising a housing and a plurality of oculars, the plurality of oculars configured to provide views of at least one display disposed in the housing; a viewing articulating arm, the binocular viewing assembly disposed on the viewing articulating arm, the viewing articulating arm configured to adjust a position of the binocular viewing assembly; a support, the viewing articulating arm attached to the support such that the viewing articulating arm can move relative to the support; and an image processing system in communication with the plurality of cameras, the auxiliary camera, and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the plurality of cameras, receive video images acquired by the auxiliary camera, provide output video images based on the received video images, present the output video images on the at least one display so that the output video images are viewable through the plurality of oculars, and switch between displaying the output video images comprising at least one output video image from the auxiliary camera and at least one output video image from the at least one camera disposed on the retractor, wherein the binocular viewing assembly does not provide a view of the surgical site through the oculars via an optical pathway that passes through the housing. In some embodiments, the auxiliary camera comprises a 3-D camera and the displays are configured to provide 3-D viewing of images from the 3-D cameras. In some embodiments, the auxiliary camera comprises an optical assembly having an adjustable working distance of between about 15 cm and about 45 cm. In some embodiments, the optical assembly has a variable magnification of between about −0.5× and about 10×. In some embodiments, the auxiliary camera is configured to provide views of the surgical site from a distance further than the cameras disposed on the retractor. 
     In accordance with another aspect, a medical apparatus comprises a retractor configured to provide access to a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; a viewing assembly comprising a housing and at least one display within the housing, the at least one display being configured to provide images from the plurality of cameras; at least one virtual display input device configured to acquire input from a user of the medical apparatus; and an image processing system in communication with the plurality of cameras, the at least one virtual display camera, and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the plurality of cameras, provide output video images based on the received video images, detect the input from the user, interpret the input from the user, and provide a virtual touchscreen wherein interaction with the virtual touchscreen is provided through the detected and interpreted user input. In some embodiments, the user input is associated with features of a graphical user interface displayed on the at least one display. In some embodiments, the graphical user interface includes reduced-size video image feeds provided by the image processing module. In some embodiments, the viewing assembly comprises a pair of oculars, and optical paths from the oculars to the at least one display. In some embodiments, the at least one virtual display input device is disposed on the viewing assembly. In some embodiments, the apparatus further comprises virtual display sensors configured to provide information related to the user input to the image processing system, the information being provided in addition to the data acquired with the virtual display input device. In some embodiments, the apparatus further comprises at least one auxiliary camera configured such that images from the at least one auxiliary camera can be viewed on at least one of the displays, said auxiliary camera configured to provide a surgical microscope view. In some embodiments, the at least one virtual display input device comprises a camera. In some embodiments, the at least one virtual display input device comprises at least 3 cameras. 
     In accordance with another aspect, a medical apparatus comprises: a retractor configured to provide an opening in a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; a binocular viewing assembly comprising a housing and a plurality of oculars, the plurality of oculars configured to provide views of at least one display disposed in the housing; a viewing articulating arm, the binocular viewing assembly disposed on the viewing articulating arm, the viewing articulating arm configured to adjust a position of the binocular viewing assembly; a support stand, the viewing articulating arm attached to the support stand such that the viewing articulating arm can move relative to the support stand; and an image processing system in communication with the plurality of cameras and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the plurality of cameras, provide output video images based on the received video images, and present the output video images on the at least one display so that the output video images are viewable through the plurality of oculars, wherein the binocular viewing assembly does not provide a view of the surgical site through the oculars via an optical pathway that passes through the housing. In some embodiments, the image processing system is configured to provide 3-D viewing of camera images through the binoculars using at least two displays. In some embodiments, the apparatus further comprises a camera disposed on the binocular viewing assembly, the camera having a field of view that can be configured to include the surgical site, wherein the camera is configured to provide a surgical microscope view of the surgical site. In some embodiments, the camera disposed on the binocular viewing assembly comprises an optical assembly providing an adjustable working distance of between about 15 cm and about 45 cm. In some embodiments, the microscope objective microscope objective has a variable magnification of between about 1× and 6×. In some embodiments, the apparatus further comprises: a second articulating arm attached to the support stand; a camera platform attached to the second articulating arm such; and a camera disposed on the camera platform, the camera having a field of view that can be configured to include the surgical site wherein the camera is configured to provide a surgical microscope view of the surgical site, wherein the second articulating arm is adjustable independent of the viewing articulating arm, and wherein the image processing system is configured to display the surgical microscope view on the at least one display. In some embodiments, the camera disposed on the camera platform comprises an optical assembly providing an adjustable working distance of between about 15 cm and about 45 cm. In some embodiments, the microscope objective microscope objective has a variable magnification of between about 1× and 6×. 
     In accordance with another aspect, a medical apparatus comprises: a retractor configured to provide an opening in a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; a surgical microscope camera having a field of view that can be configured to include the surgical site, wherein the surgical microscope camera is configured to provide a surgical microscope view of the surgical site; a binocular viewing assembly comprising a housing and a plurality of oculars, the plurality of oculars configured to provide views of at least one display disposed in the housing; a viewing articulating arm, the binocular viewing assembly disposed on the viewing articulating arm, the viewing articulating arm configured to adjust a position of the binocular viewing assembly; a support stand, the viewing articulating arm attached to the support stand such that the viewing articulating arm can move relative to the support stand; and an image processing system in communication with the plurality of cameras, the surgical microscope camera, and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the plurality of cameras, receive video images acquired by the surgical microscope camera, provide output video images based on the received video images, and present the output video images on the at least one display so that the output video images are viewable through the plurality of oculars, the output video images comprising at least one output video image from the surgical microscope camera being presented with at least one output video image from the at least one camera disposed on the retractor, wherein the binocular viewing assembly does not provide a view of the surgical site through the oculars via an optical pathway that passes through the housing. In some embodiments, the surgical microscope camera comprises a pair of 3-D cameras and the displays are configured to provide 3-D viewing of images from the pair of 3-D cameras. In some embodiments, the surgical microscope camera comprises a microscope objective having an adjustable working distance of between about 15 cm and about 45 cm. In some embodiments, the microscope objective microscope objective has a variable magnification of between about 1× and 6×. In some embodiments, the surgical microscope camera is configured to provide views of the surgical site from a distance further than the at least one of the plurality of cameras disposed on the retractor. 
     In accordance with another aspect, a medical apparatus comprises: a retractor configured to provide an opening in a surgical site; a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor; a viewing assembly comprising a housing and at least one display attached to the housing, the at least one display being configured to provide images from the plurality of cameras; at least one virtual display camera configured such that images from the at least one virtual display camera can be viewed on at least one of the displays, the at least one virtual display camera providing views of gestures by a viewer of the display; and an image processing system in communication with the plurality of cameras, the at least one virtual display camera, and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the plurality of cameras, provide output video images based on the received video images, and provide a virtual touchscreen by detecting the gestures made by the viewer imaged by the virtual image camera. In some embodiments, the gestures are associated with imaged features displayed on the at least one display. In some embodiments, the image features comprise icons provided by the image processing module. In some embodiments, the viewing assembly comprises a housing, a pair of oculars, and optical paths from the oculars to the at least one display, the at least one display disposed in the housing. In some embodiments, the at least one virtual display camera is disposed on the viewing assembly. In some embodiments, the at least one viewing assembly is disposed on an articulating arm. In some embodiments, the apparatus further comprises at least one surgical microscope camera configured such that images from the at least one surgical microscope camera can be viewed on at least one of the displays. 
     In accordance with another aspect, a surgical system can comprise: one or more surgical tools that can be configured to be powered by hydraulic fluid; a hydraulic pressure system fluidly connected to the one or more surgical tools, the hydraulic pressure system can be configured to pressurize the hydraulic fluid, the hydraulic pressure system can comprise a first hydraulic pressure source having a first hydraulic fluid chamber in selective fluid communication with the one or more surgical tools, the first hydraulic pressure source having a compression stroke in which the first hydraulic pressure source increases the pressure of the hydraulic fluid within the first hydraulic fluid chamber and an expansion stroke in which the first hydraulic pressure source decreases the pressure of the hydraulic fluid within the first hydraulic fluid chamber; a second hydraulic pressure source having a second hydraulic fluid chamber in selective fluid communication with the one or more surgical tools, the second hydraulic pressure source having a compression stroke in which the second hydraulic pressure source increases the pressure of the hydraulic fluid within the second hydraulic fluid chamber and an expansion stroke in which the second hydraulic pressure source decreases the pressure of the hydraulic fluid within the second hydraulic fluid chamber, wherein the second hydraulic pressure source can be configured to operate its compression stroke when the first hydraulic pressure source operates its expansion stroke and wherein the second hydraulic pressure source can be configured to operates its expansion stroke when the first hydraulic pressure source operates its compression stroke; and one or more valves positioned in a fluid path between the one or more surgical tools and one or more of the first hydraulic pressure source and the second hydraulic pressure source, the one or more valves can be configured to selectively close and open fluid communication between the one or more surgical tools and one or more of the first hydraulic pressure source and the second hydraulic pressure source; and one or more hydraulic fluid sources in selective fluid communication with one or more of the first hydraulic pressure source and the second hydraulic pressure source. In some embodiments, a surgical system can further comprise a first pneumatic pressure source, the first pneumatic pressure source can comprise: a pneumatic fluid chamber; a piston positioned within the fluid chamber; and an actuator operably connected to the piston, the actuator can be configured to move the piston in a compression stroke and an expansion stroke; wherein the pneumatic fluid chamber can be in selective fluid communication with one or more of the first hydraulic fluid chamber and the second hydraulic fluid chamber. In some embodiments, the surgical system can include a pneumatic pump in selective fluid communication with the pneumatic fluid chamber. In some embodiments, the surgical system can further comprise a hydraulic turbine that can be configured to actuate one or more of the one or more surgical tools, the hydraulic turbine in selective fluid communication with the hydraulic pressure system. In some embodiments, the hydraulic turbine can be powered by pressurized hydraulic fluid from the hydraulic pressure system. In some embodiments, at least a portion of the pressurized hydraulic fluid used to power the hydraulic turbine can be returned to the hydraulic pressure system after powering the hydraulic turbine. In some embodiments, the surgical system can further comprise one or more surgical tools configured to be powered by pneumatic fluid. In some embodiments, the surgical system can further comprise a pneumatic assembly that can be configured to selectively power one or more of the one or more surgical tools that can be configured to be powered by pneumatic fluid, the pneumatic assembly in selective fluid communication with a pneumatic pump. In some embodiments, the surgical device can be a drill. 
     In accordance with another aspect, a surgical system can comprise: one or more surgical tools that can be configured to be powered by hydraulic fluid; a hydraulic pressure system fluidly connected to the one or more surgical tools, the hydraulic pressure system can be configured to pressurize the hydraulic fluid, the hydraulic pressure system comprising: a cassette assembly that can have: a cassette housing; a first hydraulic fluid chamber positioned at least partially within the cassette housing and in selective fluid communication with one or more of the one or more surgical tools; a plurality of fluid ports positioned on the cassette housing; and one or more valves located in or on the cassette housing; a first hydraulic pressure source fluidly coupled with the first hydraulic fluid chamber, the first hydraulic pressure source having a compression stroke in which the first hydraulic pressure source increases the pressure of the hydraulic fluid within the first hydraulic fluid chamber and an expansion stroke in which the first hydraulic pressure source decreases the pressure of the hydraulic fluid within the first hydraulic fluid chamber; one or more valves positioned in a fluid path between the one or more surgical tools and the first hydraulic fluid chamber, the one or more valves configured to selectively close and open fluid communication between the one or more surgical tools and the first hydraulic fluid chamber; and one or more hydraulic fluid sources in selective fluid communication with one or more of the first hydraulic pressure source and the second hydraulic pressure source. In some embodiments, the cassette assembly can further comprise: a second hydraulic fluid chamber positioned at least partially within the cassette housing and in selective fluid communication with one or more of the one or more surgical tools; and a second hydraulic pressure source fluidly coupled to the second hydraulic fluid chamber, the second hydraulic pressure source can have a compression stroke in which the second hydraulic pressure source increases the pressure of the hydraulic fluid within the second hydraulic fluid chamber and an expansion stroke in which the second hydraulic pressure source decreases the pressure of the hydraulic fluid within the second hydraulic fluid chamber, wherein the second hydraulic pressure source can be configured to operate its compression stroke when the first hydraulic pressure source operates its expansion stroke and wherein the second hydraulic pressure source can be configured to operates its expansion stroke when the first hydraulic pressure source operates its compression stroke. In some embodiments, the surgical system can further comprise one or more valves positioned in a fluid path between the one or more surgical tools and the second hydraulic fluid chamber, the one or more valves can be configured to selectively close and open fluid communication between the one or more surgical tools and the second hydraulic fluid chamber. In some embodiments, the cassette assembly can be disposable. In some embodiments, the surgical tool can be disposable. In some embodiments, the surgical system can further comprise one or more washing nozzles in fluid communication with one or more of the first hydraulic fluid chambers or the second hydraulic fluid chamber or the hydraulic fluid source, the one or more washing nozzles can be configured to direct hydraulic fluid toward one or more light sources. 
     In accordance with another aspect, a medical apparatus can comprise: a surgical drill; and a hydraulic motor providing hydraulic power to said drill. In some embodiments, the surgical drill can be configured mill. In some embodiments, said hydraulic motor can comprise a turbine connect to a saline supply. 
     In accordance with another aspect, a hydraulic actuation system can comprise: a user interface; a drive system in communication with the user interface; a chamber; an inflatable element at least partially in the chamber, the inflatable element inflatable upon the user interface sending a signal to the drive system causing fluid to flow into the inflatable element; and a piston configured to be linearly displaced by the inflatable element upon inflation of the inflatable element. In some embodiments, the inflatable element can comprise a balloon. 
     In accordance with another aspect, a medical apparatus can comprise: a surgical tool; and a hydraulic system providing hydraulic power to said surgical tool, wherein said hydraulic system can comprise (a) a pump with disposable components and (b) disposable lines. In some embodiments, the hydraulic system can comprise a disposable spindle valve body. In some embodiments, the hydraulic system can comprise disposable Kerrison balloons. In some embodiments, the surgical tool can comprise a disposable drill. In some embodiments, the surgical tool can be disposable and non-autoclavable. In some embodiments, the hydraulic system can comprise a disposable and non-autoclavable slave pump actuator. In some embodiments, the hydraulic system can comprise a disposable and non-autoclavable slave turbine. In some embodiments, the hydraulic system can comprise a disposable and non-autoclavable valve. 
     In accordance with another aspect, a method of cleaning a hydraulic system for coupling to a surgical tool, the method can comprise: flushing fluid through at least part of the hydraulic system; flushing air through said part of the hydraulic system; and sterilization of said part of said hydraulic system. In some embodiments, said flushing fluid can be followed by flushing air. In some embodiments, said flushing air can be followed by sterilization. In some embodiments, said flushing fluid can be followed by sterilization. In some embodiments, said flushing fluid can be followed by flushing air and said flushing air can be followed by sterilization. 
     In accordance with another aspect, a medical apparatus can comprise: a surgical device; a hydraulic system providing hydraulic power to said surgical device; and manifold configured to selectively direct hydraulic fluid to different applications. In some embodiments, said manifold can be disposable. In some embodiments, said manifold can comprise valves. In some embodiments, said manifold can comprise pumps. 
     In accordance with another aspect, a surgical tool can comprise: a drill; a hydraulic impeller assembly can comprise: a turbine housing defining a blade cavity, a flow director positioned at least partially within the turbine housing, an impeller having a plurality of impeller blades, the impeller positioned at least partially within the blade cavity, an output shaft rotatably connected to the impeller, the output shaft configured to transfer a torque from the impeller to the drill, and one or more ports in a wall of the blade cavity providing fluid communication between an interior of the blade cavity and an exterior of the blade cavity; a hydraulic pressure source; a return fluid line configured to connect to facilitate fluid communication between the one or more ports and the hydraulic pressure source; and a vacuum source configured to extract fluid through the one or more ports from the blade cavity. In some embodiments, the vacuum source can be a pump. In some embodiments, the vacuum source a bypass channel can be configured to direct high velocity fluid past the blade cavity, wherein a pressure differential between the high velocity fluid in the bypass channel and a low velocity fluid in the blade cavity draws low velocity fluid through the one or more ports from the blade cavity to the bypass channel. 
     In accordance with another aspect, a medical device system can comprise: a surgical tool; a hydraulic fluid source; a disposable cassette comprising: a housing; one or more hydraulic fluid chambers housed at least partially housed within an interior of the housing; a plurality of fluid ports positioned on the housing and configured to facilitate fluid communication between an exterior of the fluid housing and the interior of the housing; a plurality of proportional valves positioned on the housing; and a plurality of fluid channels configured to facilitate fluid communication between the plurality of ports, the one or more hydraulic fluid chambers, and the plurality of proportional valves; a tool fluid line fluidly connecting one of the plurality of fluid ports to the surgical tool; and a fluid source line fluidly connecting the hydraulic fluid source to one of the plurality of fluid ports. In some embodiments, one or more of the plurality of proportional valves can comprise a valve cavity in the housing and a flexible pad sealingly disposed over the valve cavity. In some embodiments, one or more of the plurality of proportional valves can be actuated by a linear electromagnetic actuators. In some embodiments, the surgical tool can be controlled by one or more of the plurality of proportional valves. In some embodiments, the hydraulic fluid source can be an IV bag. In some embodiments, the hydraulic fluid can be saline. In some embodiments, the hydraulic fluid can be a physiologically compatible fluid. In some embodiments, the hydraulic fluid can be a physiological saline. In some embodiments, the medical device system can further comprise one or more optical components. In some embodiments, the medical device system can further comprise one or more nozzles in fluid communication with one or more of the plurality of ports, the one or more nozzles configured to direct a high velocity, low volume flow of hydraulic fluid to the one or optical components. 
     In accordance with another aspect, a surgical visualization system comprises a binocular viewing assembly comprising a housing and a pair of eyepieces, said eyepieces configured to provide a view of at least one display disposed in the housing; an optical assembly disposed on the binocular viewing assembly, the optical assembly configured to provide a surgical microscope view of a surgical site, the optical assembly comprising at least one auxiliary camera; an articulating arm, the binocular viewing assembly disposed on the articulating arm, the articulating arm configured to adjust a position of the binocular viewing assembly and the optical assembly; and an image processing system in communication with the optical assembly and the display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the auxiliary camera, provide output video images based on the received video images, and present the output video images on the display so that the output video images are viewable through the eyepiece, wherein the optical assembly is configured to provide a working distance that is adjustable between about 15 cm and about 45 cm. In some embodiments, the optical assembly is mounted to an isocenter positioning system. In some embodiments, the isocenter positioning system comprises elements configured to allow the optical assembly to be adjusted in three-dimensions such that a field of view of the auxiliary camera always includes a common point. In some embodiments, the isocenter positioning system comprises an isocenter track attached to the binocular viewing assembly, the isocenter track configured to allow the auxiliary camera to be moved to a plurality of locations along the isocenter track and to position the auxiliary camera such that at said plurality of locations said auxiliary camera said remains a fixed distance away from a common point. In some embodiments, said auxiliary camera comprises a Greenough configuration. In some embodiments, said auxiliary camera comprises a pair of optical paths oriented at an angle with respect to each other that converge at said common point established by said isocenter positioning system. In some embodiments, the system further comprises a virtual touch camera configured to image a hand of a user, wherein the image processing system is configured to identify hand gestures based at least partly on the acquired images of the hand of the user to allow the user to interact with a graphical user interface provided on the display. In some embodiments, said hand gestures include gesturing with an optical tool held in said hand. In some embodiments, the system further comprises a virtual touch sensor attached to the binocular viewing assembly, said image processing system being configured to use information from the virtual touch sensor in conjunction with image data from the virtual touch camera to identify gestures to allow the user to interact with a graphical user interface provided on the display. In some embodiments, said binocular viewing assembly is configured not to provide a surgical microscope view via an optical path from said eyepiece through an aperture in said housing. In some embodiments, said auxiliary includes a turning mirror or turning prism configured to reduce the thickness profile of said optical assembly. In some embodiments, said auxiliary camera comprises a pair of optical paths that do not share a common objective lens. In some embodiments, the system further comprises a virtual touch input device configured to receive user input, wherein the image processing system is configured to identify commands based at least partly on the acquired input from the user to allow the user to interact with a graphical user interface provided on the display through a representation of the user&#39;s hand. 
     In accordance with another aspect, a surgical visualization system comprises: A surgical visualization system comprising: a binocular viewing assembly comprising a housing and a plurality of oculars, the plurality of oculars configured to provide display views of at least one display disposed in the housing, the two display views corresponding respectively to a left-eye view and a right-eye view; an optical assembly disposed on the binocular viewing assembly, the optical assembly comprising a left-eye camera and a right-eye camera configured to provide a stereoscopic surgical microscope view of a surgical site; an articulating arm, the binocular viewing assembly disposed on the articulating arm, the articulating arm configured to adjust a position of the binocular viewing assembly and the optical assembly; and an image processing system in communication with the optical assembly and the at least one display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the left-eye camera and the right-eye camera, provide output video images based on the received video images, and present the left-eye output video images via the left-eye display view and the right-eye output video images via the right-eye display view so that the output video images are viewable through the plurality of oculars, wherein the optical assembly provides a convergence angle, the convergence angle being an angle between a left-eye optical path and a right-eye optical path at the surgical site. In some embodiments, the optical assembly is configured to provide a substantially constant convergence angle with changing working distance. In some embodiments, the left-eye camera comprises: a left-eye turning prism configured to direct light from the surgical site along a left-eye lens path; a left-eye lens assembly configured to receive the directed light from the left-eye turning prism and to create a left-eye image; a left-eye image sensor configured to capture the left-eye image and generate a left-eye video image. In some embodiments, the right-eye camera comprises: a right-eye turning prism configured to direct light from the surgical site along a right-eye lens path; a right-eye lens assembly configured to receive the directed light from the right-eye turning prism and to create a right-eye image; a right-eye image sensor configured to capture the right-eye image and generate a right-eye video image. In some embodiments, the left-eye camera and the right-eye camera are configured to acquire video images of the surgical site at a convergence point and wherein a distance from the binocular viewing assembly to the convergence point comprises a working distance. In some embodiments, the optical assembly is configured to provide an adjustable working distance between about 15 cm and about 45 cm. In some embodiments, the left-eye camera comprises a left-eye turning prism and the right-eye camera comprises a right-eye turning prism, the left-eye turning prism and the right-eye turning prism being configured to change their relative orientations thereby changing the convergence angle to provide the adjustable working distance. In some embodiments, the optical assembly is configured to provide a substantially constant convergence angle with changing working distance. In some embodiments, the left-eye camera and the right-eye camera are configured to adjust their relative orientation and position to provide the substantially constant convergence angle. In some embodiments, the left-eye camera comprises a left-eye prism assembly and the right-eye camera comprises a right-eye prism assembly, the left-eye prism assembly and the right-eye prism assembly being configured to adjust their relative orientation and position to provide the substantially constant convergence angle, wherein other elements of the left-eye camera and the other elements of the right-eye camera remain substantially stationary. In some embodiments, the optical assembly is configured to provide a sufficiently narrow convergence angle to provide stereoscopic imagery through an insertion tube. In some embodiments, the insertion tube has a width between about 25 mm and about 50 mm. In some embodiments, the sufficiently narrow convergence angle is also substantially constant with changes in working distance. 
     In accordance with another aspect, a surgical visualization system can comprise: a binocular viewing assembly comprising a housing and an eyepiece, the eyepiece configured to provide a view of a display disposed in the housing; an optical assembly disposed on the binocular viewing assembly, the optical assembly configured to provide a surgical microscope view of a surgical site, the optical assembly comprising a surgical microscope camera; an articulating arm, the binocular viewing assembly disposed on the articulating arm, the articulating arm configured to adjust a position of the binocular viewing assembly and the optical assembly; and an image processing system in communication with the optical assembly and the display, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the surgical microscope camera, provide output video images based on the received video images, and present the output video images on the display so that the output video images are viewable through the eyepiece, wherein the optical assembly is configured to provide a working distance that is adjustable between about 15 cm and about 45 cm. In some embodiments, the optical assembly can be mounted to an isocenter positioning system. In some embodiments, the isocenter positioning system can comprise elements configured to allow the optical assembly to be adjusted in three-dimensions such that a field of view of the surgical microscope camera always includes a common point. In some embodiments, the isocenter positioning system can comprise an isocenter track attached to the binocular viewing assembly, the isocenter track configured to allow the surgical microscope camera to be moved to any location along the isocenter track, wherein the isocenter track orients the surgical microscope camera such that a field of view of the surgical microscope camera includes a common point at any location along the track. In some embodiments, the surgical visualization can further comprise a virtual touch camera attached to the binocular viewing assembly, the virtual touch camera configured to image a hand of a user to allow the user to interact with a graphical user interface provided on the display. In some embodiments, the surgical microscope camera can be also the virtual touch camera. In some embodiments, the surgical visualization can further comprise a: a retractor configured to provide an opening in a surgical site; and a plurality of cameras configured to acquire video images of the surgical site, at least one of the plurality of cameras being disposed on the retractor and configured to acquire video images within the opening provided by the retractor, wherein the image processing system is further configured to: receive video images acquired by the plurality of cameras disposed on the retractor; provide output images based on the received video images from the plurality of cameras; and present the output images from the surgical microscope camera, the output images from the plurality of cameras disposed on the retractor, or a combination of output images from the surgical microscope camera and at least one of the plurality of cameras disposed on the retractor. In some embodiments, the image processor system can be further configured to receive input indicating which output video images to display. 
     In accordance with another aspect, a surgical visualization system can comprise: a binocular viewing assembly comprising a housing and a plurality of oculars, the plurality of oculars configured to provide views of two displays disposed in the housing, the two displays corresponding respectively to a left-eye display and a right-eye display; an optical assembly disposed on the binocular viewing assembly, the optical assembly comprising a left-eye camera and a right-eye camera configured to provide a stereoscopic surgical microscope view of a surgical site; an articulating arm, the binocular viewing assembly disposed on the articulating arm, the articulating arm configured to adjust a position of the binocular viewing assembly and the optical assembly; and an image processing system in communication with the optical assembly and the two displays, the image processing system comprising at least one physical processor, wherein the image processing system is configured to: receive video images acquired by the left-eye camera and the right-eye camera, provide output video images based on the received video images, and present the left-eye output video images on the left-eye display and the right-eye output video images on the right-eye display so that the output video images are viewable through the plurality of oculars, wherein the optical assembly provides a convergence angle, the convergence angle being an angle between a left-eye optical path and a right-eye optical path at the surgical site. In some embodiment, the left-eye camera can comprise: a left-eye turning prism configured to direct light from the surgical site along a left-eye lens path; a left-eye lens assembly configured to receive the directed light from the left-eye turning prism and to create a left-eye image; a left-eye image sensor configured to capture the left-eye image and generate a left-eye video image. In some embodiment, the right-eye camera can comprise: a right-eye turning prism configured to direct light from the surgical site along a right-eye lens path; a right-eye lens assembly configured to receive the directed light from the right-eye turning prism and to create a right-eye image; a right-eye image sensor configured to capture the right-eye image and generate a right-eye video image. In some embodiments, the left-eye camera and the right-eye camera can be configured to acquire video images of the surgical site at a convergence point. In some embodiment, a distance from the binocular viewing assembly to the convergence point can comprise a working distance. In some embodiment, the optical assembly can be configured to provide an adjustable working distance between about 15 cm and about 45 cm. In some embodiment, the left-eye camera can comprise a left-eye turning prism and the right-eye camera comprises a right-eye turning prism, the left-eye turning prism and the right-eye turning prism being configured to change their relative orientations thereby changing the convergence angle to provide the adjustable working distance. In some embodiment, the optical assembly can be configured to provide a substantially constant convergence angle with changing working distance. In some embodiment, the left-eye camera and the right-eye camera can be configured to adjust their relative orientation and position to provide the substantially constant convergence angle. In some embodiment, the left-eye camera comprises a left-eye prism assembly and the right-eye camera comprises a right-eye prism assembly, the left-eye prism assembly and the right-eye prism assembly can be configured to adjust their relative orientation and position to provide the substantially constant convergence angle, wherein other elements of the left-eye camera and the other elements of the right-eye camera remain substantially stationary. In some embodiment, the optical assembly can be configured to provide a sufficiently narrow convergence angle to provide stereoscopic imagery through an insertion tube. In some embodiment, the sufficiently narrow convergence angle can be also substantially constant with changes in working distance. 
     In accordance with another aspect, a medical apparatus can comprise: a surgical retractor; at least one video camera comprising imaging optics and an optical sensor, said at least one camera disposed on said surgical retractor, wherein said imaging optics comprises wafer-scale optics. In some embodiments, the medical apparatus can further comprise a stop forward said imaging optics. In some embodiments, said sensor is proximal said imaging optics with said imaging optics between said stop and said sensor, and wherein said stop the most distal optical element of said camera. In some embodiments, said stop can be just prior to said wafer optics. In some embodiments, the medical apparatus can further comprise a cover plate, said stop disposed between said cover plate and said wafer-scale optics, said cover plate comprising sapphire. In some embodiments, the medical apparatus can further comprise a stop within said imaging optics. In some embodiments, said stop can disposed within said wafer-scale optics. In some embodiments, the medical apparatus can further comprise a movable optical element within said imaging optics. In some embodiments, said movable optical element can be within said wafer-scale optics. In some embodiments, said wafer-scale optics can include a movable optical element configured to be moved to adjust said imaging optics. In some embodiments, the medical apparatus can further comprise an actuator configured to move said a movable optical element to adjust said imaging optics. In some embodiments, said imaging optics can comprise non-wafer-scale lens elements. In some embodiments, said imaging optics can comprise a negative power non-wafer-scale lens element. In some embodiments, said negative power non-wafer-scale lens element can be disposed forward any wafer-scale optics such that said wafer-scale optics is disposed in an optical path between said negative power non-wafer-scale lens element and said optical sensor. In some embodiments, said imaging optics can comprise a negative lens group, a stop, and a positive lens group arranged in an optical path forward of said optical sensor such that said stop and said positive group are disposed between said negative lens group and said optical sensor. In some embodiments, said stop can be between said negative lens group and said positive lens group. In some embodiments, said imaging optics can provide a field of view of at least 70° and up to 125. In some embodiments, said imaging optics can comprise non-wafer-scale optics, a stop, and wafer-scale optics. In some embodiments, said non-wafer scale optics can comprise negative optical power and said wafer-scale optics comprise positive optical power. In some embodiments, said imaging optics can comprise a stack of non-wafer-scale optics lenses having negative power, a stop, and positive lens group. In some embodiments, said imaging optics can comprise a front stop, a positive lens, a negative lens, and a plurality of lenses having positive power disposed in an optical path such that the negative lens is between the positive lens and the plurality of lenses having positive power. In some embodiments, said imaging optics can provide a field of view between about 50°-70°. In some embodiments, said imaging optics can comprise a front stop and four wafer-scale optics lenses. In some embodiments, said imaging optics can comprise no more than four wafer-scale optics lenses. In some embodiments, said imaging optics can provide a field of view between about 50°-70°. In some embodiments, said wafer-scale optics can comprise a stack of wafer scale optics elements having air gaps therebetween, wherein said air gaps are in fluid communication with each other. In some embodiments, said wafer scale optics can comprise fiducials on plates that provide stress to counteract bowing. In some embodiments, said fiducials can be interlocking. In some embodiments, said imaging optics can be configured to be disposed laterally with respect to said optical sensor to provide camera pointing. In some embodiments, the medical apparatus can further comprise actuators to move said imaging optics laterally with respect to said optical sensor to provide camera pointing. In some embodiments, the medical apparatus can further comprise actuators to move said optical sensor laterally with respect to said imaging optics to provide camera pointing. 
     In accordance with another aspect, a medical apparatus can comprise: at least one video camera comprising imaging optics and an optical sensor; and a platform configured to be disposed on a surgical retractor, said at least one video camera disposed on said platform, wherein said imaging optics comprises wafer-scale optics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an embodiment of a surgical visualization. 
         FIGS. 2A-C  show an embodiment of a surgical retractor device having an integrated imaging assembly. 
         FIG. 3A  shows an embodiment of a surgical retractor device having an integrated imaging assembly. 
         FIG. 3B  shows an embodiment of an imaging assembly containing electrical lines and cameras integrated with the retractor blades. 
         FIG. 3C  shows an embodiment of an imaging assembly in which the electrical lines and cameras are integrated into a flexible cable that can be fastened to the retractor frame and retractor blades. 
         FIG. 4A  shows an embodiment of a rotatable stage attached to a retractor frame. 
         FIG. 4B  shows a bottom view of a rotatable stage. 
         FIG. 4C  shows a side view of an embodiment of a camera and prism to be mounted on the inside surface of the rotatable stage. 
         FIG. 4D  shows an enlarged view of a stereo camera pair. 
         FIG. 5  shows an embodiment comprising a plurality of interchangeable retractor blades for a surgical retractor. 
         FIG. 6A  shows an embodiment of a malleable retractor blade with an integrated optical sensor. 
         FIG. 6B  shows an embodiment of a retractor blade that is flexible and has hinges to enable flexure. 
         FIGS. 6C-D  show an embodiment of a rigid articulating retractor blade in a flexed position. 
         FIGS. 6E-G  show an embodiment of a rigid articulating retractor blade in an unflexed position. 
         FIG. 6H  shows an embodiment of a retractor blade stage. 
         FIG. 7  shows embodiments of the distal end of clip-on flexible cable that is attached to a retractor blade. 
         FIG. 8  shows a front surface of a retractor blade or of a flexible cable that can be attached to a retractor blade. 
         FIGS. 9A and 9B  show embodiments of an aggregator, with one or multiple flexible cables in the rolled configuration. 
         FIGS. 10A and 10B  show embodiments of the aggregator, with one or multiple flexible cables in the unrolled configuration. 
         FIG. 11A  shows an embodiment of an aggregator, with one or multiple flexible cables with cutouts in the rolled configuration. 
         FIG. 11B  shows an embodiment of an aggregator, with one or multiple flexible cables with cutouts in the unrolled configuration. 
         FIG. 11C  shows an embodiment of an aggregator, with one flexible cable with cutouts in the unrolled configuration. 
         FIG. 12A  shows an embodiment of a clip-on fastener for fastening the flexible cable to the retractor blade surface. 
         FIG. 12B  shows an embodiment of a hairpin attachment fastener for fastening the flexible cable to the retractor blade surface. 
         FIG. 12C  shows a top view of an embodiment with a dovetail attachment fastener for fastening the flexible cable to the retractor blade surface. 
         FIG. 13A  shows the surgical retractor of  FIGS. 2A-C  with a laser device positioned through the opening. 
         FIG. 13B  shows the surgical retractor of  FIGS. 2A-C  with a needle holder positioned through the opening. 
         FIG. 14  shows an example surgical system including an imaging surgical system having an image processing system and cameras associated with surgical devices. 
         FIG. 15  shows an example output for display of stereo imagery from a proximal stereo camera overlaid with wide field of view imagery from a proximal wide field of view camera. 
         FIG. 16  shows the example output for display of  FIG. 15  with additional imagery from distal cameras displayed as well. 
         FIG. 17  shows an example display incorporating image data from proximal and distal cameras, as in  FIG. 16 , along with a picture-in-picture view of imagery acquired by a camera associated with a surgical tool. 
         FIG. 18  shows an example of using two or more cameras to create a morphed image to provide a central view of a surgical site. 
         FIG. 19  shows an example configuration of proximal cameras that provide a wide field view and a stereo view. 
         FIG. 20A  shows an example configuration of proximal cameras that maintain a desired alignment relative to the gravity vector (a direction associated by the surgeon as opposite to the top of the surgical field as viewed from above the patient&#39;s body) as well as shows rotating or not rotating imagery from a camera associated with a surgical tool. 
         FIG. 20B  shows an example configuration of optical sensors mounted on retractor blades to maintain a consistent horizon between a horizon of acquisition, a horizon of display, and a surgeon horizon. 
         FIG. 20C  illustrates a retractor camera configuration and display wherein the imagery from the retractor cameras is displayed as tiles on the display wherein their displayed location corresponds to their locations on the retractor and/or fields of view with respect to each other and/or the retractor. 
         FIG. 20D  illustrates a retractor camera configuration and display wherein the imagery from the retractor cameras is displayed as tiles on the display wherein their images are rotated via image processing to be more consistent. 
         FIG. 21  shows an example configuration of a proximal stereo camera having a first field of view and a second monocular distal camera having a second field of view. 
         FIG. 21B  illustrates an embodiment of the surgical visualization system having an articulating arm for an imaging system that can be configured to provide imagery similar to a direct-view surgery microscope. 
         FIG. 21C  illustrates an example surgical viewing system attached to an articulating arm, the system including one or more cameras mounted on a viewing platform. 
         FIGS. 21D and 21D-2  illustrates an example surgical viewing system that includes an isocenter positioning system attached to the viewing platform. 
         FIGS. 21E and 21F  illustrate an embodiment of a surgical visualization system having an optical system mounted under the viewing platform. 
         FIGS. 21G-21K  illustrate embodiments of optical assemblies for use in a stereoscopic surgical viewing system, such as those illustrated in  FIGS. 21E-F . 
         FIGS. 21L-21Q  illustrate embodiments of a visualization display with viewing platform attached to a movable arm. 
         FIGS. 22A and 22B  show examples of displaying a composite image by stitching and tiling images from cameras. 
         FIGS. 23A and 23B  show example stitched or tiled displays incorporating image data from a plurality of cameras positioned on retractors. 
         FIG. 24  shows an example graphical user interface that can be used in embodiments of surgical visualization systems. 
         FIG. 24B  shows another example graphical user interface that can be used in embodiments of surgical visualization systems. 
         FIGS. 25A-C  show an irrigation assembly for cleansing an optical sensor. 
         FIG. 26  shows a fenestrated ring configured to cleanse optical sensors. 
         FIG. 27A  shows some embodiments of wafer-scale optics for use with a surgical device. 
         FIG. 27B  shows substrates configured to be interlocked to form wafer-scale optics. 
         FIG. 27C  shows a wafer to be diced to provide a plurality of substrates for forming the wafer-scale optics. 
         FIG. 28  shows an embodiment of an optical prescription for an imaging module having a field of view less than or equal to about 70 degrees. 
         FIG. 29A  shows an embodiment of a wide field-of-view optical assembly with a buried stop for use with a surgical device. 
         FIG. 29B  shows an example embodiment of an optical assembly comprising an afocal module coupled to an optical imaging module for use with a surgical device. 
         FIG. 29C  shows an imaging module comprising interchangeable optical elements configured to change imaging properties of the imaging module. 
         FIG. 29D  shows an example imaging module with optics providing a viewing angle relative to a surgical tool axis. 
         FIG. 30A  shows an embodiment of an imaging stack comprising non-wafer-scale optics in combination with wafer-scale optics. 
         FIG. 30B  shows an example embodiment of an imaging stack comprising a stop between a negative lens group and a positive lens group, wherein the positive lens group has a distortion-correcting lens element. 
         FIGS. 31A and 31B  respectively show top and side views of some embodiments of an imaging module comprising an imaging stack, sensor layer, via layer, and flex layer. 
         FIGS. 32A and 32B  illustrate two embodiments of light guides for use with imaging modules to provide illumination. 
         FIGS. 33A and 33B  illustrate top and side cross-section views, respectively, of a retractor blade with a light guide and illumination source integrated therein. 
         FIG. 34  is a schematic illustration of one embodiment of a hydraulic actuation system. 
         FIG. 35A  is a schematic illustration of another embodiment of a hydraulic actuation system. 
         FIG. 35B  is a schematic illustration of another embodiment of a hydraulic actuation system. 
         FIG. 35C  is a schematic illustration of another embodiment of a hydraulic actuation system. 
         FIG. 36A  is a schematic illustration of a portion of another embodiment of a hydraulic flow circuit. 
         FIG. 36B  is a schematic illustration of a portion of another embodiment of a hydraulic flow circuit. 
         FIG. 37  is a schematic illustration of one embodiment of a hydraulic pressure circuit. 
         FIG. 38  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 39  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 40  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 41  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 42  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 43  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 43A  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 43B  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 43C  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 43D  is a schematic illustration of another embodiment of a hydraulic pressure circuit. 
         FIG. 44A  shows a perspective view of one embodiment of a hydraulic manifold. 
         FIG. 44B  shows an exploded view of the hydraulic manifold of  FIG. 44A . 
         FIG. 44C  shows a rear view of the hydraulic manifold of  FIG. 44A . 
         FIG. 44D  shows a perspective view of one embodiment of a hydraulic manifold. 
         FIG. 44E  shows an exploded view of the hydraulic manifold of  FIG. 44D . 
         FIG. 44F  shows a rear view of the hydraulic manifold of  FIG. 44D . 
         FIG. 45A  shows a perspective cross-section of a hydraulic turbine. 
         FIG. 45B  shows a cross-section of a portion of the hydraulic turbine of  FIG. 45A . 
         FIG. 45C  shows a cross-section of a portion of the hydraulic turbine of  FIG. 45A  and a diverted fluid flow path. 
         FIG. 46  shows one embodiment of an impeller. 
         FIG. 47A  is a schematic illustration of another embodiment of a hydraulic actuation system coupled to a hydraulically actuated surgical device, where the hydraulic actuation system is in a first operating state. 
         FIG. 47B  is a schematic illustration of the hydraulic actuation system of  FIG. 47A , where the hydraulic actuation system is in a second operating state. 
         FIG. 47C  is a schematic illustration of another embodiment of a hydraulic actuation system coupled to a hydraulically actuated surgical device, where the hydraulic actuation system is in a first operating state. 
         FIG. 47D  is a schematic illustration of another embodiment of a hydraulically actuated surgical device. 
         FIG. 47E  is a schematic illustration of an embodiment of a cutting tip of the surgical device embodiment of  FIG. 47D . 
         FIG. 47F  is a schematic illustration of another embodiment of a cutting tip of the surgical device embodiment of  FIG. 47D . 
         FIG. 47G  is a schematic illustration of another embodiment of a cutting tip of the surgical device embodiment of  FIG. 47D . 
         FIG. 48A  is a schematic illustration of another embodiment of a hydraulically actuated surgical device in a first position. 
         FIG. 48B  is a schematic illustration of the embodiment of the hydraulically actuated surgical device of  FIG. 48A  in a second position. 
         FIG. 49A  is a schematic illustration of another embodiment of a hydraulically actuated surgical device in a first position. 
         FIG. 49B  is a schematic illustration of the embodiment of the hydraulically actuated surgical device of  FIG. 49A  in a second position. 
         FIG. 50A  is a schematic illustration of another embodiment of a hydraulically actuated surgical device in a first position. 
         FIG. 50B  is a schematic illustration of the embodiment of the hydraulically actuated surgical device of  FIG. 50A  in a second position. 
         FIG. 51A  is a schematic illustration of another embodiment of a hydraulically actuated surgical device in a first position. 
         FIG. 51B  is a schematic illustration of another embodiment of a hydraulically actuated surgical device in a second position. 
         FIG. 52  is a schematic illustration of another embodiment of a hydraulic actuation system coupled to one or more hydraulically actuated surgical devices. 
         FIG. 53  is a schematic illustration of another embodiment of a hydraulically actuated surgical device. 
         FIG. 53A  is a schematic illustration of an embodiment of a powered drill. 
         FIG. 53B  is a schematic illustration of an embodiment of powered scissors. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is directed to certain embodiments for the purposes of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The described embodiments may be implemented in any device or system that can be configured to provide visualization of a surgical site. Thus, the teachings are not intended to be limited to the embodiments depicted solely in the figures. and described herein, but instead have wide applicability as will be readily apparent to one having ordinary skill in the art. 
     Surgical Field Visualization 
     In order to provide for improved visualization of the surgical site, a surgical device can be provided with multiple cameras integrated therein. For example, the surgical device can be a retractor, and a plurality of cameras may be mounted on or within the retractor. In other embodiments, the surgical device can be a platform having cameras mounted thereon, but may be separate from any retractor used during the surgery. Each of the cameras may capture a distinct view of the surgical site. Imagery from the plurality of cameras may be integrated together, for example, “stitched” together to form composite mosaic imagery that may be displayed disposed over background imagery, or arranged in an array of tiled images shown individually disposed over background imagery for particular emphasis of a surgical work area. Tiled, individual, or composite imagery can provide the user with a view of the area of the body on which surgery is being performed. The user can select the imagery to be displayed and the manner in which it is displayed for enhanced utility during surgery. As used herein, the term imagery and images includes video and/or images captured from one or more cameras. Images from video are often referred to as video images or simply images. The term images may also refer to still images or snap shots. Video feed or video stream may also be used to describe the video images such as video images from a camera. 
     Such cameras can be of particular use when disposed on surgical devices, such as retractors, which are at least partly disposed within the opening through which the surgery is being performed, so as to provide the user with a perspective of being within or just about within the body. Retractors, for example, may be used to hold open a region in the body where surgery is to be performed. This region is formed by making an incision to provide access to the region or surgical site. Accordingly, various embodiments described herein pertain to non-percutaneous procedures, for example, non-laparoscopic. Additionally various embodiments described herein pertain to non-endoscopic procedures. Additionally, various embodiments employ open surgery and cut-down as opposed to percutaneous procedures. Likewise various embodiments employ larger incisions than would be made for arthroscopy, laparoscopy etc. Various embodiments described herein pertain to minimally invasive surgery (MIS) for spine surgery, all of neurosurgery and trans-oral approaches to various cancers such as tongue, tonsils, oral and nasal pharynx and anterior skull base (brain)]. The region may have an area of, for example, from 400 to 2500 mm 2 , 1 to 20 cm 2  or 1 to 10 cm 2  so as to permit the surgeon ready access to the surgical site such that the surgeon can manipulate tools to perform surgery. For example, trans-oral surgeries can retract the mandible, maxilla, and each cheek to provide an approximately 45 by 45 mm working space. A minimally invasive spine surgery can use a tubular retractor having a circular working space with a diameter of approximately 25 mm. The retractor contains blades, fingers, or at least one barrier such as e.g., a tube that holds tissue back to maintain open the surgical site. Multiple cameras located on the retractor at locations within the surgical field or in very close proximity thereto, e.g., within 75 mm of the surgical opening, can provide a useful viewpoint for the surgeon. The cameras may for example be located on the blades, fingers, tubular barrier, or other portion of the retractor close to the surgical field or within the patient and the surgical field. The cameras may include pairs of cameras arranged and/or oriented to provide stereo and thus 3D imaging or single CMOS camera chips with dual optics to provide stereo. The cameras may be located at various locations in relation to surgical devices, for example, the cameras can be located proximally and distally along or near a retractor, wherein the location of the cameras can be configured to facilitate both the progression of surgery and an enhanced view or view selection of an area of interest. 
     In various embodiments, the retractor maintains a central open region that permits the surgeon central access to the surgical field through the opening provided by the retractor and cameras and/or stereo camera pairs disposed on the retractor provide views surrounding the surgical field. Accordingly, the retractor may comprise a plurality of blades or fingers or other members disposed about an open central region. In some embodiments, the retractor comprises a hollow tube that forms a barrier against the tissue surrounding the surgical site. The hollow tube has a central open region that permits central access to the surgical field through the tube. Accordingly, in various embodiments, the retractor is designed to provide the central open region unobstructed by the retractor to permit tools and other surgical devices to have ready access to the surgical site and the central portion of the surgical site. 
     In various embodiments, cameras and/or stereo camera pairs are mounted on the retractor and directed inward toward this central surgical site to provide a view thereof. Accordingly, in various embodiments the cameras and/or stereo camera pairs surround the central portion or are disposed about a portion, for example, ¼, ⅓, ½, ⅔, ¾ or more of the surgical site. The cameras and/or stereo camera pairs may for example be disposed at 3 or 4 or more points, for example up to 6, 8, 10, or more points about the surgical side. For example, the cameras and/or stereo camera pairs may be disposed at positions at 3 o&#39;clock, 6 o&#39;clock, and 9 o&#39;clock, or 3 o&#39;clock, 6 o&#39;clock, 9 o&#39;clock, and 12 o&#39;clock as viewed from above the surgical site. In other embodiments, the cameras and/or stereo camera pairs may be disposed at 2 o&#39;clock, 6 o&#39;clock, and 10 o&#39;clock, or 2 o&#39;clock and 10 o&#39;clock as viewed from above the surgical site. These cameras and/or stereo camera pairs may generally face toward the open central region and thus in some embodiments, at least one camera and/or stereo camera pair has a field-of-view in which another camera and/or stereo camera pair is visible in that field-of-view. Or one or more cameras and/or stereo camera pairs may have a portion of the retractor in their field-of-view in some embodiments. 
     Accordingly, the cameras and/or stereo camera pairs on a retractor or a plurality of retractors may point in different directions or otherwise provide different vantage points. The direction of each camera and/or stereo camera pair may be characterized by its field of view and/or optical axis. The optical axis may extend outwardly along the center of the camera&#39;s and/or stereo camera pair&#39;s field of view. In some embodiments, the optical axes of two or more cameras and/or stereo camera pairs may be non-parallel and thus not point in exactly the same directions. In some embodiments, the optical axes of the cameras and/or stereo camera pairs on the retractor may be at an angle greater than 10, 20, 30, 40, 50, 60, 70, 80 degree&#39;s with respect to each other and may be substantially orthogonal but less than 20, 30, 40, 50, 60, 70, 80, 90, 100 degrees in some embodiments. In some embodiments, the optical axes of the cameras and/or stereo camera pairs on the retractor may be at a larger angle such as greater than 90, 100, 110, 120, 130, 140, 150, 160, or 170, degree&#39;s with respect to each other but less than 100, 110, 120, 130, 140, 150, 160, 170 or 180 degrees in some embodiments. In some embodiments, the optical axes of two cameras and/or stereo camera pairs may be anti-parallel and in various examples may at least be directed in opposite directions. In certain embodiments, these camera and/or stereo camera pairs may be directed at least toward a common central area and may potentially have field-of-views that at least partially overlap. In some embodiments, the centerlines of the field-of-views of two cameras or stereo camera pairs may converge at a point or small central area (e.g., less than 500 mm 2  or less than 100 mm 2 ) within the surgical site. 
     In some embodiments, the projected angle (as seen from directly above the surgical site) between the optical axes of two cameras and/or stereo camera pairs on the retractor may be 0 degrees, however, in various embodiments it may be at least 5, 15, 30, 45, 60, 75, or 90 degrees but less that 100 degrees such as between 5 and 15, 15 and 30, 30 and 45, 45 and 60, 60 and 75, 75 and 90 degrees with respect to one another with the cameras and/or stereo camera pairs facing inward toward the surgical site. More than two cameras and/or stereo camera pairs on the retractor may be oriented such that optical axes of the more than two cameras and/or stereo camera pairs (as seen from directly above the surgical site) is at least 5, 15, 30, 45, 60, 75, or 90 degrees such as between 5 and 15, 15 and 30, 30 and 45, 45 and 60, 60 and 75, 75 and 90 degrees with respect to one another. 
     In some embodiments, the projected angle (as seen from directly above the surgical site) between the optical axes of two cameras and/or stereo camera pairs on the retractor may be at least 95, 105, 115, 125, 135, 145, 155, 165, or 175 degrees but less that 180 degrees such as between 95 and 105, 105 and 115, 115 and 125, 125 and 135, 135 and 145, 145 and 155, or 165 and 175 degrees with respect to one another with the cameras or stereo camera pairs facing inward toward the surgical site. More than two cameras and/or stereo camera pairs on the retractor may be oriented such that optical axes of the more than two cameras or stereo camera pairs (as seen from directly above the surgical site) is at least 95, 105, 115, 125, 135, 145, 155, 165, or 175 degrees but less than 180 degrees such as between 95 and 105, 105 and 115, 115 and 125, 125 and 135, 135 and 145, 145 and 155, 155 and 165, 165 and 175, or 175 and 180 degrees with respect to one another. 
     The cameras and/or stereo camera pairs may be configured to be oriented in such directions. For example, as discussed herein, the cameras may be disposed on platforms that removably attach to the retractor blades in a manner in which the position and/or orientation of the cameras can be altered. For such cameras and/or stereo camera pairs, for example, at least two or more such cameras and/or stereo camera pairs may be configured to be at least 5, 15, 30, 45, 60, 75, or 90 degrees but less than 100 degrees or 95, 115, 130, 145, 160, 175, degrees but less than 180 degrees with respect to one another. The cameras and/or stereo camera pairs can be arranged in many directions to provide a substantially increased range of views of the surgical site for the user. Accordingly, the effective field of view provided by the plurality of cameras and/or stereo camera pairs can be substantially increased. Likewise, although each separate camera and/or stereo camera pair may have a small field-of-view, stitching or tiling images from the different cameras and/or stereo camera pairs together may provide a larger field of view. This wide field-of-view within the surgical site provides enhanced situational awareness for the surgeon. Embodiments described herein can be implemented with virtually any retractor system. For example, suitable retractor systems include the ProView MAP system, DePuy SPOTLIGHTR Access System, Metrx X-Tube Retraction System. 
     In various embodiments, the use of cameras integrated within a retractor can be applied to neurological, spinal, head and neck, oral, and ENT (ear, nose, and throat) surgeries. Additionally, as described in more detail below, a separate camera can be integrated with a surgical tool, such as but not limited to a drill, forceps, scissors, Kerrison, bipolar cautery (RF), confocal imager, or laser delivery system. 
     The cameras may be, for example, Omnivision OV2722 1080P, ⅙ inch. Other configurations are possible. For example, the cameras may include wafer-level optics, conventional optics, molded optics, and combinations thereof. In various embodiments, the camera may include imaging optics comprising a negative distal lens group having one or more lenses that produce a total optical power for that group that is negative and a positive proximal lens group having one or more lenses that produce a total optical power for the group that is positive. In certain embodiments, the camera can include an afocal assembly while in other embodiments the imaging optics are not afocal. In various embodiments, an aperture stop for the imaging optics is between lens elements. For example, the aperture stop may be between the negative lens group and the positive lens group. These lenses may comprise wafer scale optics. In some embodiments, the camera can include wafer-scale optics in combination with non-wafer-scale optics. In some embodiments, the wafer scale optical imaging optics comprises layers comprising, e.g., lens elements, separated by spacers that provide air gaps between the layers. The air gaps between the layers may be in communication with each other and/or air or gas reservoir to reduce the risk of condensation on optical surfaces. 
     The cameras may comprise, for example, CCD or CMOS sensor arrays or other types of detector arrays. A frame grabber may be configured to capture data from the cameras. For example, the frame grabber may be a Matrox Solios eA/XA, 4 input analog frame grabber board. Image processing of the captured images may be undertaken. Such image processing can be performed by, for example, the Matrox Supersight E2 with Matrox Supersight SHB-5520 with two Intel Six Core Xeon E5645 2.4 GHz processors with DDR3-1333SDRAM. This system can be designed to support eight or more camera inputs using two Matrox Solios eA/XA, 4 input, analog frame grabber boards. More or less cameras may be employed. In some implementations, a field programmable gate array (“FPGA”) can be used to capture and/or process imagery received from the cameras. For example, the image processing can be performed by Xilinx series 7 FPGA boards. Other hardware devices can be used as well, including ASIC, DSP, computer processors, a graphics board, and the like. The hardware devices can be standalone devices or they can be expansion cards integrated into a computing system through a local computer bus, e.g., a PCI card or PCIe card. 
     A plurality of illumination sources may be provided to enhance the visualization provided by the cameras. For example, in some embodiments, each camera can have two LEDs associated with it. The LEDs may be positioned on opposite sides of the camera, and may be positioned to illuminate the field of view of the camera. The electronic connections for the cameras and/or LEDs can be provided using coaxial cables or flex cables. Flex cables are stronger and more heat resistant than coaxial in comparable sizes. The use of flex cables can allow for a lower profile system, since the aspect ratio of width and thickness is significantly higher than conventional coaxial or endoscopic approaches. In some embodiments, the illumination element, such as an LED may be directly soldered onto the flex cable. In various embodiments, both the illumination element and the camera may be permanently affixed to the flex cable by soldering. In some cases an assembly of flex cables can be utilized consisting of a flex cable for CMOS sensor or sensors, a flex cable for one or more LED&#39;s, and an EM sensor cable or assembly. Such a combined assembly can be sandwiched as layers in a protective jacket of silicone or epoxy resin or Teflon tubing and be attached, affixed, or be oriented with the axis of the retractor blade. Such an assembly may terminate in an edge connector typically of a male type. 
     In some embodiments, the cameras can be disposed on one or more surgical devices or tools, such as a retractor. The cameras can be positioned and oriented such that one camera is within a field of view of another camera. Similarly, cameras can be positioned and oriented such that other portions of the surgical device can be within a field of view of the camera. Labels, fiducials or color markings can be included on the surgical devices, tools, and/or cameras. The labels or color markings can be configured to be within a field of view of another camera. For example, for a retractor having three blades, each with a camera, each blade may also include a corresponding label or color marking. The blades may be labeled, 1, 2, and 3 (or be marked with red, green, or blue) respectively. Likewise, the view from the camera on blade number 1 (red) would show the blade with the number 2 (green) marking or both the blade with the number 2 (green) and number 3 (blue) markings. The markings should also be visible. Such markings can give the user quick identification of which camera generated the image (e.g., the camera on blade number 1 (red) in this example). The labels or markings thus provide increased or enhanced situational awareness to a user or operator by assisting in understanding the position and/or orientation of a camera associated with respect to a surgical tool or device. In some embodiments, the markings, fiducials or labels can be used in image processing such as in stitching or tiling processes to form a composite image. 
     In certain embodiments, there are an odd number of cameras and/or stereo camera pair provided with the retractor. In some embodiments, the cameras and/or stereo camera pair can be configured to point approximately normal to a retractor axis, and having an odd number of cameras and/or stereo camera pair views can provide for a central camera view providing image data for a central portion of a targeted area and symmetry in the numbers of optical modules views on either side of the central camera view providing image information about peripheral regions. In some embodiments, these sensor module views may be stereoscope views. In such embodiments, an additional camera and/or stereo camera pair can be used to provide a view of a targeted feature, such as a view from a surgical tool (e.g., a cutting tool) and the corresponding area of interest (e.g., area of tissue being cut). In some embodiments, this image of the target features can be displayed in a central portion of a display. The remaining cameras and/or stereo camera pair on the retractor can provide other visual information, such as tool entrance or egress, background or peripheral visual information. 
     In some embodiments, an electrical connector can be included in each blade of a retractor. In some embodiments, each camera module&#39;s connector may be provided at the distal end of an additional run of cabling that attaches to a manifold. Such cabling can be color-coded and/or marked so as to identify or indicate stereoscopic view, field of view differences, etc. The cabling may be plugged into site-specific plugs, which may be unique to the camera type, on a manifold that can, for example, be positioned on the retractor frame near the patient or on a console. In some embodiments, EEPROM tags associated with the different sensors may be used to identify and provide information related to the sensor. In various embodiments, the termination of the cabling is male to facilitate sterilization. 
       FIG. 1  shows one embodiment of a surgical visualization system. As illustrated, the system  1  includes a base  3  from which two articulating arms  5  and  7  extend. The first articulating arm  5  has mounted to its distal end a viewing platform  9 . The viewing platform may include two oculars  11  and be configured similarly to a standard surgical microscope viewing platform. In some embodiments, however, unlike a conventional surgical microscope or a head mounted display the viewing platform  9  is not a direct view devices where the surgeon or other user sees directly through the platform, e.g., an aperture in the platform. As discussed in more detail below, the viewing platform  9  may include displays which received signals from cameras which the surgeon or user employs to view the surgical site. In some embodiments, cameras can be mounted to the viewing platform  9  and the cameras can be configured to provide imagery of the surgical site. Accordingly, the cameras can be used to provide imagery similar to a conventional surgical microscope. For example, the cameras on the viewing platform can be configured to provide a virtual working distance, or a distance from the viewing platform to the patient, that can vary using zooming. The virtual working distance can vary, where the working distance can be at least about 150 mm and/or less than or equal to about 450 mm, at least about 200 mm and/or less than or equal to about 400 mm, or at least about 250 mm and/or less than or equal to about 350 mm. The working distance can be selected and/or changed by the surgeon. In some embodiments, the cameras mounted on the viewing platform  9  can be used to provide gesture recognition to allow a surgeon to virtually interact with imagery provided by the display using the surgeon&#39;s hands, a surgical tool, or both, as described in greater detail herein. The second articulating arm  5  has mounted to its distal end an input and display device  13 . In some embodiments, the input and display device comprises a touchscreen display having various menu and control options available to a user. In some embodiments, the touchscreen can be configured to receive multi-touch input from ten fingers simultaneously, allowing for a user to interact with virtual objects on the display. For example, an operator may use the input device  13  to adjust various aspects of the displayed image. In various embodiments, the surgeon display incorporating a video camera providing a surgical microscope view may be mounted on a free standing articulated arm. The flat panel display touch screen may be positioned on a tilt/rotate device on top of the electronics/fluidics console. 
     A retractor  15  and surgical tool  17  are both connected to the base  3  by electrical cables  19 . In other embodiments, the retractor  15  and surgical tool  17  may be in wireless communication with the base  3 , for example via WiFi (IEEE 802.11a/b/g/n), Bluetooth, NFC, WiGig (IEEE 802.11ad), etc. As described in more detail below, one or both of the retractor  15  and surgical tool  17  may include one or more cameras configured to provide imagery, e.g., image and/or video data. In various embodiments, video data can be transmitted to a video switcher, camera control unit (CCU), video processor, or image processing module positioned, for example, within the base  3 . The video switching module may then output a display video to the viewing platform  9 . The operator may then view the displayed video through the oculars  11  of the viewing platform  9 . In some embodiments, the binoculars permit 3D viewing of the displayed video. As discussed in more detail below, the displayed video viewed through the viewing platform  9  may comprise a composite video formed (e.g., stitched or tiled) from two or more of the cameras on the retractor  15  and/or surgical tool  17 . 
     In use, an operator may use the retractor  15  and surgical tool  17  to perform minimally invasive surgery. The operator may view the surgical site by virtue of the displayed imagery in the viewing platform  9 . Accordingly the viewing platform (surgeon display system)  9  may be used in a manner similar to a standard surgical microscope although as discussed above, the viewing platform need not be a direct view device wherein the user sees directly through the platform  9  to the surgical site via an optical path from the ocular through an aperture at the bottom of the viewing platform  9 . Rather in various embodiments, the viewing platform  9  includes a plurality of displays, such as liquid crystal or light emitting diode displays (e.g., LCD, AMLCD, LED, OLED, etc.) that form an image visible to the user by peering into the ocular. Accordingly, one difference, however, is that the viewing platform  9  itself need not necessarily include a microscope objective or a detector or other image-capturing mechanisms. Rather, the image data is acquired via the cameras of the retractor  15  and/or the surgical tool  17 . The image data can then be processed by a camera control unit, video processor, video switcher or image processor within the base  3  and displayed imagery may then be viewable by the operator at the viewing platform  9  via the display devices, e.g., liquid crystal or LED displays, contained therein. 
     Imaging Assembly 
       FIGS. 2A-C  show one embodiment a surgical retractor device that includes an integrated imaging assembly. In some embodiments, the imaging assembly includes a plurality of integrated cameras. The retractor  100  includes three blades  101 , however, more or less may be included depending on the design. Each of the blades may be attached to an articulable arm  103  that allows for the position of the blades to be adjusted during the operation. For example, following a small incision, the three blades  101  can be arranged in a closed position where each are positioned close to one another. In this closed configuration, the three blades can be introduced through the incision, and then expanded to provide for an operating pathway or working space. In other embodiments 4, 5, 6, 7, 8 or more blades, fingers, retractor members, or other barriers may be employed (or fewer members such as two blades, etc., or even a single member such as a single lumen of a tubular retractor may be used). In various embodiments, the surgical area may be at least 400 mm 2 , for example, have an opening with an areas between 400 and 2100 mm 2 . The working space may be an area centrally located between retractor blades (or within the lumen of a tubular retractor) that allows for surgical tools or other instruments to pass through. As shown, the retractor does not obstruct the center of the retractor (e.g., array of retractor blades, finger, members, etc., or lumen of a tubular retractor) and the open region formed by the retractor and permits unobstructed access to the center of the surgical site for ready access by the surgeon. Each of the blades  101  includes one or more integrated cameras, or cameras with combined stereo paths to one sensor or camera module  105 . In various embodiments the number of camera modules and configurations can vary. In the illustrated embodiment, each camera module  105  includes a camera  107  and one or more, or two illumination sources  109  disposed on opposite sides of the camera  107 . In various embodiments, the number of illumination sources per camera module may vary. In some embodiments, the illumination sources may not be disposed directly adjacent any particular camera. In some embodiments, the illumination sources can be omitted, and the camera module can rely on ambient supplementary or overhead light or directed from a light source located elsewhere. In some embodiments, the orientation of an integrated camera  107  may be substantially fixed with respect to the retractor blade  101  or other surgical tool. In some embodiments, the camera  107  and/or the camera module  105  may be adjustable with respect to the retractor blade  101 . 
     In the illustrated embodiment, the retractor blades  101  are substantially rigid. In various embodiments, the retractor blades may be malleable, and may have a wide range of different structural features such as width, tension, etc. For example, stronger, larger retractor blades may be desired for spinal and trans-oral surgery, while weaker, smaller retractor blades may be desired for neurosurgery. In some embodiments, the retractor can be configured such that different blades can be arranged as desired. 
     Each of the camera modules  105  are in electrical communication with the aggregator  104 . The aggregator  104  is configured to receive input from each of the camera modules  105 , and to connect to external components via electrical cable  108 . For example, the hub or aggregator  104  may receive image data from each of the camera modules  105  and may transmit the image data to an image processing module (not shown). In the illustrated embodiment, the wiring connecting the camera modules  105  with the aggregator  104  is imbedded within the retractor blades  101  and articulating arms  103  and is not visible. In some embodiments, as described in more detail below, cables connecting the camera modules  105  with the aggregator  104  may be adhered (either permanently or non-permanently, e.g., releasably) to the exterior surface of the retractor  100 . In the illustrated embodiment, the hub or aggregator  104  is affixed to an upper surface of the retractor  100 . The aggregator may be positioned at any locations relative to the retractor  100 , or may be disconnected from the retractor  100  altogether. The aggregator may contain camera interface electronics, tracker interface electronics and SERDES to produce a high speed serial cable supporting all cameras in use. The serial cable extending from the aggregator is preferably male terminated to facilitate sterilization. 
     Although the illustrated embodiment shows integrated camera modules  105 , in various embodiments the camera modules  105  may be removably attached to the retractor blades  101 . In some embodiments, the camera modules  105  can be disposed within pre-positioned receptacles on the retractor blades  101  or other surgical device. In some embodiments, the camera modules  105  can be disposed at a plurality or range of locations desired by the user on the retractor blades  101 . In various embodiments, the orientation and position of the sensors can be adjusted by the user, e.g., physician, nurse, technician, or other clinician. In some embodiments, for example, the camera may be disposed on a track such that the camera can slide up and down the retractor, e.g., retractor blade. The height of the camera or camera within or above the surgical site may thereby be adjusted as desired. Other arrangements for laterally adjusting the position of the camera may be used. Additionally, in various embodiments, the cameras may be configured to have tip and/or tilt adjustment such that the attitude or orientation of the camera may be adjusted. The line of sight or optical axis of the cameras can thereby be adjusted to, for example, be directed more downward into the surgical site or be directed less into the surgical sight and more level or angled in different lateral directions. The camera modules  105  can include sensors or markers for, e.g., electromagnetic or optical tracking or use encoders accelerometers, gyroscopes, or inertial measurement units (IMUs) or combinations thereof or any other orientation and/or position sensors, as described in more detail below. Tracking can provide location and/or orientation of the cameras. The images obtained by the cameras may be stitched together or tiled using image processing techniques to render a composite mosaic image. Tracking or otherwise knowing the relative locations of the sensor can assist in image processing and display formatting. Tracking position of cameras can support the touch screen user interface, such that a user can select, position and size (zoom) an image array on surgeon display. 
     In various embodiments, pairs of cameras together provide information for creating a stereo effect or 3-dimensional (3D) image. Pairs of cameras, for example, may be included on each of the blades  101  of the retractor  100 . In certain embodiments, images from separate cameras on separate blades  101  can be assembled to provide the stereo and three dimensional effect. 
     As illustrated, the retractor is configured to hold open tissue so as to produce an open region or cavity centrally located between the blades. Notably, in various embodiments, this open central region is unobstructed by the retractor. In particular, the central portions of the open region would be unobstructed by features of the retractor such that the surgeon would have clear access to the surgical site. The surgeon could thus more freely introduce and utilize his or her tools on locations within the surgical site. Additionally, this may enable the surgeon to use tools with both hands without the need to hold an endoscope. 
     Also as illustrated, the cameras are disposed on the blades of the retractor such that the cameras face inward toward the surgical site that would be held open by the retractor blades. The cameras in this example would be disposed about the central open region held open by the retractor blades so as to provide views from locations surrounding the surgical site. The camera thus would face objects within the surgical site such as structures on which tools would be used by the surgeon to operate. 
     In this particular example, the cameras on two of the blades face each other such that the leftmost blade and the cameras thereon would in the field-of-view of the cameras on the rightmost blade and vice versa. The cameras on the leftmost blade may be anti-parallel to the cameras on the right most blade and have optical axes oriented at an angle, θ, of 180° with respect to each other. The cameras on the remaining blade may be directed orthogonally to the other two blades and thus have optical axes directed at an angle, θ, of 90° with respect to each other. Retractors with cameras can be reaffixed to frame or mounting structure during a procedure and cameras reorient themselves with respect to relative position within an array of cameras through their communication protocol with the aggregator and video switching unit. 
     In some embodiments, the field-of-views of the different cameras, and hence the images produced by the different cameras, may overlap. Image processing may be employed to yield increased resolution at the regions of overlap. Likewise, the number of sensors used may be increased to provide increased field-of-view and/or resolution. Likewise, cameras with overlapping images can be electronically magnified thereby making their images adjacent rather than overlapping. 
       FIG. 3A  illustrates another embodiment of a surgical retractor device  6014  having an integrated imaging assembly shown with a different wiring arrangement than shown in  FIG. 2A . In particular, much of the wiring is exposed as opposed to being buried in the retractor. As illustrated, the imaging assembly  6013  comprises a hub or aggregator  104  and one or more imaging subassemblies  6011 . The imaging assembly contains three imaging subassemblies  6011  although more or less may be included. As illustrated, in some embodiments, the imaging subassemblies  6011  can be integrated within the surgical retractor. Also as illustrated, the imaging subassemblies  6011  can contain electrical signal lines  106  and optics and/or sensor elements. In various embodiments, the electrical signal lines  106  can comprise cables or lines that are exposed and visible as opposed to completely imbedded within the retractor. In other embodiments, different portions of the lines may be buried or embedded within the portions of the retractor and thus not exposed. The electrical signal lines  106  can connect at a first end to an aggregator  104  and at a second end to a camera  6012 . The camera can contain optics (e.g., imaging lenses) and a sensor element (e.g. a two-dimensional detector array such as a CMOS or CCD 2D-array). The electrical signal lines  106  are combined together within the aggregator  104  to a common bus line. The image processing system cable  108  electrically connects to the aggregator  104 , e.g., to the common bus line, at a first end and an image processing unit at a second end (not shown). The imaging subassemblies  6011  can be electrically connected to the aggregator  104  through a male/female connection. In various embodiments, the first end of the electrical signal lines  106  comprises a male connection, while the receiving aggregator  104  connection comprises a female connection. The aggregator  104  (having, for example, female connectors) can be a disposable unit. The imaging subassemblies  6011  (having, for example, male connectors) can be reusable and can be cleaned and/or sterilized. The line  108  can also be terminated by a male connector that plugs into a female connector on the aggregator  104 . Similarly, the long cable  108  can be reusable and sterilizable. 
       FIG. 3B  illustrates another embodiment of an imaging assembly in which the electrical lines or cable, for example, flex cable, and cameras are integrated with the retractor blades or connect to a blade having electrical pathways therein or thereon. In certain embodiments, the retractor blades  7010  can contain varying optics, sensors (e.g., 2D detector arrays), and lighting (e.g., light sources such as LEDs, superluminescent diodes, supercontinuum light sources, or xenon). Additionally, in certain embodiments the retractor blades  7010  can have varying widths, lengths, and strengths. As illustrate, the retractor blades  7010  can be removably attached to the retractor frame  7002 . In the embodiment shown, the retractor blade includes a protruding rail member that slidably fits into a track on an arm of the retractor. Thus the surgeon is able use different retractor blades with different components, sizes, and strengths thereby permitting the surgeon or user the flexibility to provide the suitable retractor blades or optics for a particular medical procedure. 
       FIG. 3C  illustrates an embodiment of an imaging assembly in which the electrical lines and cameras are integrated into a flexible cable that can be readily fastened to the retractor frame and retractor blades. In certain embodiments, the flexible cable  7001  can be affixed to the retractor frame  7002  and the retractor blades  7003  in a manner to be easily affixed and removed. In some embodiments, the flexible cable  7001  can have a distal end  7005 . The distal end  7005  of the flexible cable  7001  can contain optics, sensors, or lighting and combinations thereof. In various embodiments, the flexible cable  7001  can contain a camera  7004 . In certain embodiments, the flexible cable  7001  and the aggregator  7007  can be clipped on to the retractor blades  7003  and retractor frame  7002 , respectively. In one embodiment, the distal end  7005  of the flexible cable  7001  can contain a fastener member  7008  for fastening and unfastening the flexible cable to the retractor frame and/or the retractor blades as shown in  FIG. 3C . The fastener member  7008  can include, for example, a clip, a snap, a strap, a screw, a bolt, a nut, or any combination of these as well as any other method that can facilitate convenient attachment. For example, attachment can be accomplished in under one minute possibly less than 20, 10, 5, 3, or 2 seconds per fastener and may be accomplished in more or less than a second or ½ or ¼ second per arm such that attachment can occur, for example, just prior to and in preparation for surgery. In some embodiments, aggregator  7007  can be permanently attached to the retractor frame  7002 . In such embodiments, the flexible cables  7001  can connect to the aggregator and be removably fastened to the retractor frame  7002  and/or the retractor blades  7003  with a fastening member  7008 . In some embodiments, additional fasteners, not shown, may be located elsewhere, for example, to attach the flex cable  7001  to the retractor arms or other portions of the retractor. 
     The retractor blades  7003  and the flexible cable  7001  can extend into the interior of the body cavity or surgical field opening when the retractor is in use. For example, the retractor blades can be used to hold open the surgical field. The cameras or sensors (e.g., CMOS or CCD detector arrays) integrated into the retractor blades or integrated into the flexible cable and clipped onto the retractor blades can produce images of the surgical field within the body cavity. 
     Rotatable Stage or Frame 
     During surgery it may be desirable to rotate a plurality or array of cameras and/or stereo camera pairs as a group together with respect to the surgical field, patient, or retractor. For example, a surgeon&#39;s positioning relative to the surgical field can vary for different procedures and different surgeons or the positioning of the retractor blades may be set at an angle that does not provide for optimal imaging or image processing. Therefore, it may be useful to rotate or otherwise change the positioning of the plurality of cameras and/or stereo camera pairs without changing the retractor blades positioning. 
     It can be beneficial, for example, that the optics and sensor be in a position to produce an image of the surgical field having vertical and horizontal directions the same or substantially the same as the vertical and horizontal directions that the surgeon associates for the surgical field. If the cameras are not positioned correctly, the image of the surgical field may be rotated on the display such that vertical and horizontal directions on the display do not correspond to vertical and horizontal directions that the surgeon associates with the surgical field as oriented for the surgical procedure. Incorrect positioning or excessive rotation of the surgical field with respect to the vertical and horizontal directions on the display can decouple hand-eye coordination. 
     Accordingly, various embodiments may include a rotatable support for the array of cameras and/or stereo camera pairs that can rotate or move with respect to the retractor blades.  FIG. 4A  illustrates an embodiment of a rotatable stage attached to a retractor frame. In some embodiments, the plurality of cameras can be mounted on a rotatable stage  8005  and the rotatable stage can be coupled to the retractor frame. In some embodiments, the rotatable stage  8005  is fixed to the retractor frame through an attachment post  8006 . The rotatable ring can have a single or multiple attachment posts  8006  supporting the rotatable stage on the retractor frame. The rotatable stage  8005  can move, for example, rotate, with respect to the retractor blades to permit the image formed by the camera to rotate on the display. Accordingly, the image of the surgical field can be rotated such that the directions on the surgical field that the surgeon or operator associate with vertical and horizontal correspond to the vertical and horizontal directions of the display. 
     In certain embodiments, the image visible on the display can be rotated using image processing. For example, the surgeon or user can input to the image processor the amount of rotation that is desired. For example, the user can simply rotate the displayed composite image such as a stitched or tiled image as desired. Accordingly, the user can rotate the displayed image until such the directions on the surgical field that the surgeon or operator associates with vertical and horizontal correspond to the vertical and horizontal directions of the display.  FIG. 4A  shows a plurality of cameras located toward the distal end of the retractor. As illustrated, these cameras are not disposed on a rotating support. In various embodiments, image processing may be employed to rotate the image such as the composite (e.g., stitched or tiled) image formed by these cameras instead of using a rotating support. 
     When stereo camera pairs are disposed on the retractor about the surgical site, having a rotating support for the plurality of stereo camera pairs may, however, be useful.  FIG. 4B , which shows a bottom view of a rotatable stage, illustrates the usefulness of having such a rotating support for certain embodiments having an array of 3D cameras. In the embodiment illustrated in  FIG. 4B , four stereo camera pairs are shown disposed about an annular shaped support. The stereo camera pairs in this example are disposed at 3 o&#39;clock, 6 o&#39;clock, 9 o&#39;clock and 12 o&#39;clock. To provide consistent 3D imaging among the cameras, although the cameras at the 6 o&#39;clock and 12 o&#39;clock positions are arranged along a radial of the annular shaped support, the cameras at the 3 o&#39;clock and 9 o&#39;clock positions are arranged along a tangential direction of the annular shaped support. Such an arrangement of the cameras in the various stereo camera pairs provides for consistent 3D imaging as the left and right camera in the stereo camera pairs will be oriented generally along the same direction, e.g., parallel to the x-axis in this example. This direction may be oriented, for example, along the horizontal direction of the surgical field. In various embodiments, each of the stereo cameras may share a common horizon, even if displayed as a stereo circle composed of right and left eye images. If these camera pairs were mounted on fixed retractor blades, in contrast to the rotatable support, and if the retractor were rotated in the surgical field, the direction along which the left and right cameras are aligned may not necessarily be parallel with the direction that the surgeon associates with either horizontal (or vertical). Accordingly, rotation to provide that the left and right cameras are aligned along a line parallel to the direction the surgeon associates with horizontal (or vertical) may be beneficial. Horizontal alignment in particular may be beneficial for ergonomic considerations. While an operating room microscope can be positioned in an oblique position, looking through it, and holding one&#39;s head in that position for hours, as is sometimes necessary in neurosurgery can be painful for a surgeon. In embodiments in which the retractor and the display are decoupled, ergonomic viewing is possible even if the surgical access is difficult. 
     In an alternative arrangement, the stereo camera pairs are not used at the 3 o&#39;clock and 9 o&#39;clock positions and instead monocular cameras are employed. The stereo cameras at the 6 o&#39;clock and 12 o&#39;clock positions as well as the mono cameras at 3 o&#39;clock and 9 o&#39;clock positions need not be mounted on a rotating support. The mono cameras need not rotate but the 6 and 12 o&#39;clock cameras should ideally be configured ‘in plane’ or their R and L camera views should be parallel with the R and L display views. 
     Also, in some embodiments stereo proximal camera pairs are mount on a rotating supports while distal mono cameras are not mounted on a rotating support in a configuration such as shown in  FIG. 4A . 
     Additionally, in some embodiments, some proximal camera modules include stereo camera pairs and some proximal camera modules include only mono cameras and not stereo camera pairs and a rotating stage need not be used in such a case for the proximal cameras. For example, stereo camera pairs can be positioned at the 6 o&#39;clock and 12 o&#39;clock positions and non-stereo camera were at the 3 o&#39;clock and 9 o&#39;clock positions. Accordingly, in various such embodiments, the stereo camera pair(s) together may be positioned halfway between the other non-stereo cameras and/or the non-stereo cameras may be positioned halfway between stereo camera pair(s). Additionally, in various embodiments, stereo camera pairs are on directly opposite sides of the retractor at locations 180° with respect to each other, such as for example at 3 o&#39;clock and 9 o&#39;clock. 
     However, as shown in  FIG. 4A , in some embodiments a rotating support  8005  is employed. The rotatable stage  8005  can include a ring comprising concentric inner and outer rings. In certain embodiments, the inner ring  8007  can move relative to the fixed outer ring  8008 . The fixed outer ring  8008  can be attached to the retractor frame at one or multiple points of attachment. The inner ring can be rotatably coupled to fit within or on top of the outer ring. The rotatable stage can support cameras, flexible cables, or other components including but not limited to 3D cameras, LEDs, tracking, cleaning, temperature control, heating or therapeutic delivery systems. 
     The rotatable stage can include a ring that is rotated by manual movement, motorized movement, or using other actuators. In some embodiments, the rotatable stage ring can contain a bearing surface between the inner ring and outer ring which allows movement of the rotatable ring. The bearing surface can include a plain bearing, a ball bearing, roller bearing, or any other bearing surface. Additionally, in other embodiments the rotatable stage can contain methods of coupling that allow for translational movement between the inner ring and the outer ring so that the rings can move vertically relative to one another. In some embodiments, the ability to rotate the rotatable stage, ring, or alternative platform, allows the stereo image acquisition horizon to remain horizontal. Further, the rotatable stage can include encoders or other tracking devices as for example those described herein to detect movement of the ring and the placement of the cameras. 
     As illustrated in  FIG. 4B , the stereo camera pairs can be directed downward from the rotating ring as well as inward toward an axis of rotation of the ring and a central open region established by the retractor. Despite being downward directed, in some embodiments, the cameras on the rotatable stage are also in different orientations with respect to each other (e.g. rotated differently) as discussed above. An axis of rotation is defined by the line bisecting the optical axis of the left and right cameras of the first stereo camera pair. In some embodiments, the third stereo camera pair  8011  is rotated 180 degrees relative to the first stereo camera pair  8009 . In some embodiments, the second stereo camera pair  8010  can be rotated 180 degrees relative to the fourth stereo camera pair  8012 . The second stereo camera pair  8010  and the fourth stereo camera pair  8012  can be rotated plus or minus 90 degrees from the first stereo camera pair  8009 . The different configurations of the cameras on the rotatable stage can be advantageous to maintain consistency among the camera images of the different stereo cameras on the rotatable stage. A R and L camera view can be rotated 180 degrees but if so the eye views must be reversed electronically, so that upside down R is now L, etc. 
     In certain embodiments, one or more of the cameras on the rotatable stage can be disposed on the inner surface  8016 , as opposed to the bottom surface, of the rotatable stage. A prism or other reflector may be included to redirect the field-of-view from the camera. For example, the camera can be coupled to a prism, similar to the prisms used in the cylindrical retractor shown in  FIG. 21  and discussed herein, to allow the camera on the inner surface of the rotatable stage to be directed in a downward direction into the surgical field.  FIG. 4C  illustrates an embodiment of a side view of the camera and prism mounted on the inside surface of the rotatable stage. The camera  8015  is disposed on the inside surface  8016  of the rotatable stage, which has a prism  8014  attached thereto and in the optical path of the camera. In particular, the prism has a reflective surface that is disposed in the optical path between the front of the camera or stereo cameras pair and the surgical field. This reflective surface may be oriented at an angle with respect to the retractor to direct the optical path at an angle of between 15 to 75 degrees, e.g., 45° with respect to the rotation axis of the ring. The reflective surface of the prism, for example, may be oriented at an angle of 15 to 30 degrees, e.g., about 22.5° with respect to the axis of rotation of the ring so as to redirect light at an angle of between about 15 and 75 degrees, e.g., about 45°. Such a prism may reduce the profile of structures extending into the otherwise open region provided by the retractor so as to maintain a substantially unobstructed opening for the surgeon to access the surgical site.  FIG. 4D  shows an enlarged view of a stereo camera pair, with intersecting optical axes. In some embodiments a prism having two reflecting surfaces is employed to redirect the optical path. 
     Retractor Blades 
     As discussed above,  FIG. 3B  illustrates an embodiment of an imaging assembly in which the electrical lines and cameras are integrated with detachable retractor blades. In certain embodiments, the retractor blades  7010  can contain varying optics, sensors, and lighting. Additionally, in certain embodiments the retractor blades  7010  can have varying widths, lengths, and strengths. As illustrated, the retractor blades  7010  can be removably attached to the retractor frame  7002  via an attachment system  7011  (e.g., a rail or strip that fits into a track on the retractor arm). The ability to vary the components, sizes, and strengths of the retractor blades allows the surgeon or user the freedom to use various retractor blades or various optics that are appropriate for a particular medical procedure. 
       FIG. 5 , for example, illustrates an embodiment comprising a plurality of interchangeable retractor blades for a surgical retractor. The interchangeable retractor blades can contain various combinations of cameras, lighting sources, sensors, imaging optics, EM tracker sensor and/or other components such as discussed herein. The retractor blade may also have none of these components and may be employed primarily for mechanical purpose such as to hold back tissue in an incision at the periphery. Accordingly, the retractor blades can be of varying widths and strengths. Thus, although in some embodiments, the retractor blades are permanently attached to the retractor frame or frame (they are typically called frames), in some embodiments, the retractor blades  7010  can be removably attached depending on the desired use or imaging required. Such retractor blades can be interchanged to achieve the desired type of retractor blade depending on the procedure to be performed. For example, the retractor blades for spinal or trans-oral procedures can be larger and stronger because of the higher force requirement, while retractor blades for neurosurgery procedures can be weaker and smaller. A surgeon may also switch out retractor blades during a procedure after commencement thereof. In some embodiments, the retractor blades can have aspiration channels or hold aspirators to remove blood and saline or other liquid. Such aspiration channels can be connected by fluidic lines such as lines in the flex cable to a pump or other vacuum source tubing can also send warmed air towards the cameras to prevent fogging. 
     Further, the retractor blades can also be flexible.  FIGS. 6A and 6B  illustrate example embodiments of retractor blades that are flexible.  FIG. 6A  illustrates an embodiment of the pre-flexed retractor blade. In some embodiments, the retractor blade can be made of malleable or flexible material that allows for movement of the retractor blade either prior to use or during use, e.g., during a surgical procedure. The retractor blades of the retractor can be made of a flexible or malleable material which allows for the bending or movement to adjust the shape of the retractor blades but still produce the required stiffness for retractor purposes. In some embodiments, the retractor blades can be made of pre-flexed Nitinol retractor blades and may include one or two cables to straighten out the flex. In certain embodiments, the cable(s) is located on the surface away from the patient. The retractor blade can be allowed to bend or move and this movement can be helpful in the imaging of the surgical field and/or assisting in retraction of the tissue in the surgical area. The flexible retractor blades can be fixed to the retractor unit such as described herein for fixed retractor blades herein. In other embodiments, the flexible retractor blades are clipped onto the retractor unit such as described herein for clip-on retractor blades. In some embodiments, bending or movement of the retractor blade can be controlled remotely, for example by electronic remote control. In some embodiments, the retractor blade may be tilted by at least 10 degrees, 20 degrees, 30 degrees, 40 degrees, or more and less than 90 degrees, less than 80 degrees, less than 70 degrees, less than 60 degrees, or less than 50 degrees via the remote control. In some embodiments, remote control can be provided via a graphic interface. 
     With continued reference to  FIG. 6A , the malleable retractor assembly  350  includes a retractor blade  351  with a push-pull wire  353  attached to the surface of the retractor blade  351 . The wire  353  can rest in a low friction cable guide to enable flexure of the blade  351 . An integrated camera  355  and electromagnetic tracker sensing coil  357  are disposed within the retractor blade  351 . The flexure mechanism can be similar to that used for steerable catheters for interventional procedures. In use, the operator may manipulate the individual retractor blade  351  by use of a small handle  359  that can pull the wire  353  by use of a pulley or other mechanism. For example, the wire  353  can be made of Nitinol, and may be attached to a pulley such that upon rotation of the handle  359 , the retractor blade  351  flexes or extends. In some embodiments, the blade  351  always curves outwards away from the surgical site so as to create a working space for the operator. A set screw (cable clamp)  361  can be employed to fix the axial position of the wire  353 . The set screw  361  can be loosened as desired to axially move the wire  353 , thereby adjusting the flexure of the retractor blade  351 . In other embodiments, two or more wires may be employed and used in conjunction to adjust the flexure of the blade. Also, in other embodiments, the flexible retractor blades can comprise front and rear cables or elastic bands as described more fully below. 
     In various embodiments, the surface of the blade  351  can be coated with PTFE to reduce tissue friction and sticking. In some embodiments, the blade  351  can be coated with a thin layer of elastomeric material or an inflatable balloon to normalize the pressure per area across the entire region of contact with the body. In other embodiments, two wires may be used, one having a distal attachment, the other with a more proximal attachment. For example, the wires may run along the outer curvature of a pre-flexed Nitinol retractor blade. Axially moving one or both wires enables incremental controllable flexure of the blade. 
       FIG. 6B  illustrates an embodiment of a flexible retractor blade with one or more joints. As illustrated, in some embodiments, the flexible retractor blades  9003  can be bent at a joint  9004  or multiple joints within the flexible retractor blade  9003 . Front and rear elastic bands  9001 ,  9002  can be actuated at a proximal end  9005  by one or more motor, piezo, hydraulic actuator, linear actuator, or rotary actuator, or other type of actuator. The flexible retractor blades can have cables or tendon actuation with or without the Nitinol pre-flex retractor blade by the use of, for example, pull-pull cables or lines. 
     Although  FIG. 6B  illustrates an embodiment of a flexible retractor blade with front and rear elastic bands  9001 ,  9002 , in certain embodiments, the front and rear elastic bands of a flexible retractor blade  9003  may comprise an extensor and a flexor cable. The flexor and extensor cables can allow for a greater range of motion, bi-directional flexing, and an S-shape with the two joints flexing in opposite directions. In various embodiments, the force of the tissue being retracted causes the retractor blades to return to an unflexed position once tension on the cable or band is released. 
       FIGS. 6C-6G  illustrate an embodiment of a retractor blade having rigid plates or segments connected by discrete joints. In the illustrated embodiment, retractor blade  9050  includes three plates  9052 ,  9054 , and  9056 . These plates connect to one another at joints  9058  and  9060 . The plates and joints can be manipulated to place the retractor blade in a flexed configuration (as in  FIGS. 6C and 6D ) or in an unflexed configuration (as in  FIGS. 6E-6G ). Internal cables (not shown) may extend within the plates  9052 ,  9054 , and  9056 , and be attached to pinion keys  9062  and  9064 . These pinion keys  9062  and  9064  can be rotated to pull these internal cables. For example, pinion key  9062  may be rotated to pull a first internal cable that extends to the middle plate  9054 . Pinion key  9064  may likewise be rotated to pull a second internal cable that extends to the outermost plate  9056 . Pulling these respective cables causes the plates to rotate with respect to one another about joints  9058  and  9060 . Specifically, rotating pinion key  9062  exerts a pulling force on the first internal cable, which causes the middle plate  9054  to rotate about joint  9058 . Similarly, rotating pinion key  9064  exerts a pulling force on the second internal cable, which causes the outermost plate  9056  to rotate about joint  9060 . Ratchets  9066  and  9068  operate to restrain the rotary position of the pinion keys  9062  and  9064 . Depressing ratchet  9066  releases pinion key  9062 , which releases tension on the internal cable, thereby permitting the middle plate  9054  to rotate back to a position substantially parallel to the innermost plate  9052 . Similarly, depressing ratchet  9068  releases pinion key  9064 , which releases tension on the second internal cable, thereby permitting the outermost plate  9056  to rotate back to a position substantially parallel to the middle plate  9054 . As described elsewhere herein, the retractor blade  9050  may include a camera  9070  thereon. In the illustrated embodiment, the camera  9070  is positioned on the upper surface of the outermost plate  9056 . Cone  9072  illustrates the field of view of the camera  9070 . 
     In use, retractor blade  9050  may be introduced into an incision, with its upper surface facing a working space, and its lower surface facing the surface of the tissue to be retracted. Articulating the retractor blade  9050  (for example by rotating pinion keys  9062  and  9064 ) causes the plates  9052 ,  9054 , and  9056  to exert pressure on the tissue, thereby increasing the size of the working area. In some embodiments, articulation of the retractor blade  9050  can be performed electronically, hydraulically, or by other methods. In some embodiments, the articulation can be controlled remotely. Camera  9070  can be positioned with respect to outermost plate  9056  such that its field of view (represented by cone  9072 ) is directed towards a site of interest within the body. As described elsewhere herein, a plurality of such retractor blades having a plurality of cameras can be used in conjunction to provide for improved visualization of the surgical site. By controlling the position of outermost plate  9056  (for example, by controlling the articulation of retractor blade  9050 ), the position and orientation of the camera  9070  can be controlled. As noted above, this control may be electronic, hydraulic, or otherwise, and may be performed remotely. In some embodiments, articulation or other movement of the retractor blades can be controlled via a graphic user interface, such as provided by a touchscreen, via voice command, etc. Throughout an operation, the position of the camera  9070  may be controlled (e.g., by manually adjusting the retractor blades, by remote electronic control, or other means) to provide a desired field of view. In some embodiments, bending or movement of the retractor blade can be controlled remotely, for example by electronic remote control. In some embodiments, the retractor blade may be tilted backward or forward by at least 10 degrees, 20 degrees, 30 degrees, 40 degrees, or more and less than 90 degrees, less than 80 degrees, less than 70 degrees, less than 60 degrees, or less than 50 degrees via the remote control. In some embodiments, remote control can be provided via a graphic interface. 
     In some embodiments, the retractor blades, finger, member, etc. can be hydraulically manipulated to control the movement of the retractor blades. The retractor can have one or more hydraulic members that are hydraulically actuated to displace tissue or apply pressure. The actuator(s) may comprise one or more linear and/or rotary actuators. A linear actuator may comprise bellows, rolling edge diaphragms, piston-cylinders with hydrostatic bearings, other linear actuators or other actuators including those disclosed herein, known in the art, or yet to be devised. A rotary actuator may comprise displacement type hydraulic motors, vane motors, gerotors, Bourdon tubes, or other rotary actuators known in the art. In some embodiments, a force feedback haptic interface could be used to provide tactile feedback to the user. In some embodiments, a dual bellows actuator&#39;s hydraulic source could supply substantially constant hydraulic force to the hydraulic members. In some embodiments, linear motors could drive master piston-cylinders with hydrostatic bearings for each axis. Other configurations are possible. 
     In some embodiments, the hydraulic member can be the retractor blades, fingers, members, etc. In some embodiments, the retractor can have a mechanical extension to move tissue extending from the retractor or the retractor blade. In such embodiments, the hydraulic member can actuate the mechanical extension to move tissue, apply pressure, and/or other functions that might be necessary for the surgical preparation or procedure. In some embodiments, actuation of the retractor blades can be controlled remotely. 
     In some embodiments, the retractor or retractor blade, finger, member, etc. can contain a positionable tool holder. In certain embodiments, the positionable tool holder can be attached to a retractor blade. In some embodiments, the positionable tool holder can be connected to the retractor base. The positionable tool holder when connected to the retractor base can be out of the field of view of the cameras and does not obstruct the images produced. Additionally, such placement on the retractor unit leaves the surgical field clear and allows the surgeon more room to operate. One example is the inclusion of a large bore suction cannula to remove blood and saline mixture, which is coupled to the positionable tool holder. Another example involves coupling a supplementary light source, such as a fiber optic cable, to the positionable tool holder. 
     As discussed above, in some embodiments, the flexible retractor blades, finger, member, etc. can vary in sizes and toughness or durability to accommodate certain surgical or medical procedures. For example, the retractor blades for spinal or trans-oral procedures can be larger and stronger because of the higher force requirement, while retractor blades for neurosurgery procedures can be weaker and smaller. Additionally, the configurations for achieving and methods of using the flexible characteristics of the retractor blades can vary such as described herein. Further, the flexible retractor blades can have the various optics, sensors, or other lighting, tracking, or imaging components that can be integrated into the retractor blades such as described herein. 
     In certain embodiments, the flexible retractor blades can contain cameras and LEDs, cameras only, LEDs only, or any other combination of components herein described. As discussed above, in some embodiments, the flexible retractor blade can contain one or more components that allow for tracking of the location, orientation, or registration of the attached cameras or combinations thereof. The reconfigurable shape of the retractor blade can makes the use of the tracking particularly useful for touch screen user interface. Accordingly, the flexible retractor blades can incorporate various methods of tracking including: EM trackers, optical tracking, inertial measurement units (IMUs), encoders, and other methods including but not limited to those described herein. The flexible retractor blades can, for example, include encoders, inertial measurement units, such as Hall Effect encoders, to detect the change in position of the flexible retractor blades. In some embodiments, the encoder can supply the user with information such as a measurement of degrees of movement of the flexible retractor blade. The encoders can also provide information to track the location of the retractor blade and for example, the camera(s) located thereon. 
     Further, in some embodiments the flexible retractor blade may be used for mechanical purposes only, such as retraction of tissue, and does not contain any camera, sensors, trackers, or light source components. For example, in some embodiments the flexible nature of the retractor blade can be used to move tissue out of the way. In other embodiments, the flexible nature of the retractor blade can be used to redirect the point-of-view of the camera on the flexible retractor blade. Additionally, in other embodiments, the flexible nature of the retractor blade can be used to both move tissue out of the way and redirect the point-of-view of the camera on the flexible retractor blade. In other embodiments, the flexible retractor blades can have aspiration channels or hold aspirators to remove blood and saline or other liquid. Such aspiration channels can be connected by fluidic lines in the flex cable to a pump or other vacuum source. 
     Multiple flexible or malleable retractor blades can close on a central, axial bullet-tip rod to be used as a dilator and introducer like MetrX. In some embodiments, a dedicated tool may be used to open and close the blades closed on a central, axial rod. 
     In some embodiments, the retractor blade as illustrated and described with reference to  FIGS. 6C-6G  and additional retractor blade embodiments described herein can be assembled onto a retractor blade stage as illustrated in  FIG. 6H . The retractor blade stage  9080  can contain a retractor blade stage ring  9081  and a gear ring  9082 . In some embodiments, the retractor blade stage ring  9081  can be fixed and shaped to receive the gear ring  9082 . In some embodiments, the outer surface of the retractor blade stage ring  9081  can be shaped in an ‘L’ shape and the gear ring  9082  can sit within the recess of the ‘L’. The outer surface of the gear ring  9082  contains teeth and faces the outside of the ring. 
     In some embodiments, the retractor stage ring  9080  can be used to effect a radial movement of the retractor blades. One or more clamps  9083  can be attached to portions of the retractor blade stage ring  9081  and the gear ring  9082 . The clamp  9083  can have a pinion  9084 , a stem  9085 , and a stem ratchet  9086 . The stem  9085  can have an innermost end attached to the proximal end  9052  of the retractor blade  9050 . The stem  9085  can have an outermost end that can pass through the clamp  9083 . In some embodiments, the stem  9085  can move horizontally through the clamp to effect a radial movement of the retractor blade. The clamp  9083  can have a stem ratchet  9086  to engage the teeth of the stem  9085  thereby operating to restrain the radial position of the stem  9085 . For example, depressing the stem ratchet  9084  releases the stem  9085  by disengaging the ratchet  9086  from the teeth of the stem, which releases tension on the stem  9085 , thereby permitting the stem  9085  to move horizontally through the clamp  9083 . The retractor blades can be positioned inside the retractor blade stage  9080  at different distances depending on the positioning of the stem  9085 . Additionally, in some embodiments, the retractor stage ring  9081  can be used to effect a radial movement of a plurality of retractor blades. 
     Additionally, in some embodiments, the retractor stage ring  9081  can be used to effect a rotational movement of a plurality of the retractor blades. In some embodiments, the pinion  9084  can be vertically positioned within the clamp  9083 . The pinion  9084  can have a distal end extending into the clamp and a proximal end that protrudes from the top surface of the clamp. The distal end of the pinion  9084  can have teeth that can engage the teeth on the gear ring  9082 . When the pinion is rotated, the teeth on the pinion  9084  engage with the teeth on the gear ring  9082  and the resulting torque causes the clamp  9083  to rotate on the retractor blade stage  9080 . For example, turning the pinion  9084  causes the clamp  9083  to rotate on the ring  9081 ,  9082 , the stem  9085  that runs through the clamp and connects to the retractor blade rotates with the clamp, and therefore the rotational position of the retractor blade  9050  can be changed by the rotational movement of the clamp  9083  on the ring. Alternatively, in some embodiments, the retractor stage ring  9081  can be used to allow the rotation of each blade individually. 
     Additionally, in some embodiments, the retractor blade stage  9080  can allow for the flexure of the retractor blades. The retractor blades can be flex-finger retractors as described herein with reference to  6 C- 6 G. Alternatively, the flexure retractor blades can be achieved in retractor blades without joints by a tilting of the retractor blade at an angle with respect to the longitudinal axis of the retractor blade stage. The tilt of the retractor blades can assist in the manipulation of tissue or holding of tissue within the surgical area as well as possibly tilt the camera orientation. 
     In some embodiments, the retractor blade stage can allow for rotational, radial, and/or flexure movement of the retractor blades to assist in the appropriate positioning of the retractor blades and this movement can be helpful in the imaging of the surgical field and/or assisting in retraction of the tissue in the surgical area. Alternatively, the retractor blade stage can allow for the rotational movement only and no radial or flexure movement can occur. In some embodiments, the retractor blade stage can allow for the rotational movement and radial movement only and no flexure movement can occur. In some embodiments, the retractor blade stage can allow for the rotational movement and flexure movement only and no radial movement can occur. In some embodiments, the retractor blade stage can allow for the radial movement only and no rotational or flexure movement can occur. In some embodiments, the retractor blade stage can allow for the radial movement and flexure movement only and no rotational movement can occur. In some embodiments, the retractor blade stage can allow for the flexure movement only and no rotational or radial movement can occur. In some embodiments, the retractor blade stage can allow for rotational, radial, and flexure movement of the retractor blades. Moreover, the retractor blade stage can incorporate any of or any combination of the features and/or embodiments of the rotatable stage or frame discussed herein. Further, in some embodiments, the retractor blade stage can incorporate various embodiments of retractor blades described herein. 
       FIG. 7  illustrates embodiments of the distal end of the clip-on flexible cable that is attached to a retractor blade. As illustrated, the clip-on flexible cable can contain various combinations of cameras, lighting sources, sensors, tracking, and/or other components such as described herein. In some embodiments, the flexible cable serves as the platform for these devices (e.g. sensors, lighting, optics, imaging components etc.). In other embodiments, the flexible cable or other cable or lines may connect to a separate platform that supports these devices, including rigid or flexible retractor blades or a separate rigid or flexible platform. 
     The clip-on flexible cable can be interchangeable to provide for different platforms depending on the desired use or imaging required. The clip-on flexible cable can be fastened to the retractor blades with a fastening member which can include, for example, a clip, a snap, a strap, a screw, a bolt, a nut, a magnet, or any combination of these as well as any other method that can facilitate convenient attachment. For example, attachment can be accomplished in under one minute possibly less than 20, 10, 5, 3, or 2 seconds per arm and may be accomplished in more or less than a second or ½ or ¼ second per fastener, which can occur, prior to or during surgery. 
     As described herein, the retractor blade can be made of malleable or flexible material or contain joints that allow for movement of the retractor blade. In some embodiments, the clip-on flexible cable can be configured to move and bend with the retractor blade allowing for movement of the retractor blade and the attached flexible cable either prior to a surgery or procedure or during surgery or a procedure. Rigid, articulated blades with discrete joints, pulled outward via cables for each DOF to retract tissue, tissue pressure “unretracts” when cables are released, as described above with respect to  FIGS. 6C-G . 
     As evident from the discussion above, the imaging assembly can contain an array of cameras on, adjacent to, or integrated as part of the retractor components. The flexible cable and retractor blade on a given retractor arm can incorporate a single camera or a plurality cameras such as proximal and distal cameras. The cameras can include various sensor arrays and lenses in a variety of configurations. In some embodiments, the cameras provide three dimensional (stereo) views. The cameras can, for example include lenses on a sensor array(s) that mimic the convergence of the eye. The cameras can be tilted to create the convergence necessary. For example, in some embodiments, a stereo view can be formed from two sensors and two lenses. Additionally, the stereo can be a single sensor which can be split with two lenses, which may have converging optical axes that mimic the convergence of a surgeon&#39;s eyes. The stereo can be used to provide the surgeon or viewer with a three dimensional view of the operating field. For some views convergence is not required, for many times the focal length in terms of distance the views can be parallel or nearly so. 
       FIG. 8  illustrates a front surface of an example retractor blade or flexible cable that can be attached to a retractor blade. In certain embodiments, the retractor blades or flexible cables can have a proximal camera  8021  which can be located on a proximal portion of the retractor blade or flexible cable, e.g., closer to the entryway into the surgical site or the main body of the retractor. The proximal cameras  8021  on a proximal portion of a retractor blade can include monocular, e.g., 16:9, and/or stereo views. The proximal camera(s)  8021  on the proximal portion of the retractor blade can contain larger sensor arrays and more resolution. In certain embodiments, the retractor blade can have a distal camera  8022  which can be located on a distal portion of the retractor blade, for example, which will be positioned deeper into the surgical site in comparison to the proximal location. The distal camera(s)  8022  on a distal portion of the retractor blade can provide oblique views and/or side views and may contain smaller sensor arrays and need to provide less resolution than the proximal cameras which may provide a more comprehensive view. The distal camera(s)  8022  on the distal end of the retractor blade can be small cameras for oblique and side views within the body cavity near the middle or tip of the retractor blades. Nonetheless, the smaller distal cameras may be stereo. Distal cameras with oblique views make seeing hidden areas possible when line of sight instruments such as operating room microscopes fail. 
     In some embodiments, the cameras on the retractor blades or flexible cable can be tilted, for example, upward or downwards or sideways or combinations thereof. The cameras can be tilted to achieve different orientations of the camera. For example, in some embodiments, the cameras can be tilted with the use of hydraulic balloon actuated pistons thereby orienting the camera in different positions relative to the retractor blade. The tilt of the camera can be changed prior to or during a surgical procedure. For example, the cameras can be positioned on a stage and the stage can be tilted with the use of hydraulic balloon actuated pistons thereby orienting the camera in different positions relative to the retractor blade. In some embodiments, the cameras on the retractor blades can be situated on a track that allows the camera to move vertically (and/or laterally) on the retractor blade thereby changing the position of the camera. Such a vertical position can be set prior to surgery or during surgery. The positioning may be performed manually or be using an actuator, such as a motor or other actuator. 
     In some embodiments, the flexible cable or the retractor blades can contain light sources. The light source can include LEDs and/or multicolor LEDs. A light source such as a single LED or multiple LEDs can be located on, adjacent to, or integrated as part of the retractor blade or flexible cable. The LEDs or other light source can provide illumination of the surgical area as well as possibly color management. The LEDs can provide sufficient brightness for a surgical treatment. In some embodiments, multi-color LEDs can provide color balancing of the image of the surgical area. The intensity of the different colors can be adjusted to provide the desired aggregate color. Through such color management, for example, multi-colored LEDs can be used to control the color temperature of the medical lighting. The color management accomplished with the different color LEDs can allow for precise control of the brightness and color of the light emitted from the LEDs. The control of the color temperature can provide the desired lighting in the surgical field for the surgeons. In the embodiment shown in  FIG. 8  the flexible cable or the retractor blades surface contain an LED  8023  at a distal end of the flexible cable or retractor blade for illumination of the surgical area. 
     As discussed elsewhere herein, the flexible cable or retractor blades can contain a component which allows for tracking of a location and/or orientation, and facilitate registration of the attached cameras. The flexible cable or retractor blades can incorporate various methods of tracking including: EM tracker, optical tracking, inertial measurement units (IMUs), encoders, and other methods as described herein. In some embodiments, the reconfigurable shape of the retractor blade and the flexible cable may increase the usefulness of the tracking for image processing. 
     As discussed above, platforms other than flex cable can be used. 
     Flexible Cable 
       FIG. 3C , described above, however, illustrates an embodiment of a flexible cable  7001  that removably attaches to the retractor blade  7003 . In one embodiment, the flexible cable  7001  connects at its proximal end to the aggregator  7007  and has a distal end  7005  that is attached to the front surface of the retractor blade. 
     The flexible cable  7001  can contain the camera modules, cameras, LEDs, sensors, and/or other components as described herein as well as any signal lines or connectors necessary for their varied operations or use. The flexible cable  7001  can contain the electrical signal lines for the cameras, sensors, or other components. Additionally, in some embodiments, the distal end  7005  of the flexible cable can allow for multiple cameras, sensors, trackers, or LEDs to be positioned in various combinations and varying numbers. In some embodiments, the cameras can be distal relative to the surgeon&#39;s hand and tool handle. Additionally, in some embodiments, the cameras or camera modules can also be distal relative to the tool shaft. 
     The distal end  7005  of the flexible cable can be fastened to the retractor before use through the use of a fastening member which can include, for example, a clip, a snap, a strap, a screw, a bolt, a nut, a magnet, or any combination of these as well as any other method that can facilitate convenient attachment, for example, that can be accomplished in under one minute possibly less than 20, 10, 5, 3, or 2 seconds per arm and may be accomplished in more or less than a second or ½ or ¼ second per fastener, which can occur, for example, prior to surgery. In one embodiment, the distal end  7005  of the flexible cable can be a platform which can be separated from the portion of the flexible cable that connects to the aggregator. The distal end  7005  of the flexible cable can include all functions and components described herein for clip-on flexible cables and retractor blades such as optics, sensors, LEDs, heaters, trackers, and cameras. The distal end  7005  of the flexible cable can be attached to the portion of the flexible cable that connects to the aggregator by a female/male connection port, plug and socket connection, or other hardware interface that allows an electrical signal to pass. In some embodiments, the platform  7005  includes a male connection for ease of cleaning and sterilization. 
     The flexible cable can be made of a material which allows the flexible cable as well as the components on the flexible cable to be rolled or folded into a compact size.  FIGS. 9A and 9B  illustrate embodiments of an aggregator  4007 , with one or multiple flexible cables  4001  in the rolled configuration.  FIGS. 10A and 10B  illustrate embodiments of the aggregator  4007 , with one or multiple flexible cables  4001  in the unrolled configuration. The aggregator  4007  can have one or multiple flexible cables  4001 . The flexible cables  4001  can have a single camera or a plurality of cameras, sensors, LEDs, or camera modules as described herein. 
     In one embodiment, the flexible cable can be split up at the distal end creating multiple extensions.  FIG. 11B  illustrates an embodiment of the flexible cable  4001  with cutouts forming multiple extensions  4003 . The imaging assembly can have only one flexible cable  4001  with multiple extensions  4004  as shown in  FIG. 11C . In various embodiments, the multiple extensions  4003 ,  4004  can be large enough to fit on a single retractor blade. Accordingly, in some embodiments, the multiple extensions  4003 ,  4004  together may have a width smaller than the width of the blade although the multiple extensions can be wider. In certain embodiments, the flexible cable in the unrolled configuration can have multiple extensions  4003 ,  4004  where the extension can have a width such that one extension can be placed on a single retractor blade. Accordingly, in some embodiments, one extension may have a width smaller than the width of the blade. The plurality of extension together however, may be wider than the blade. In various embodiments similar to that shown  FIG. 11B  the multiple extensions  4003  can be small enough so that all extensions  4003  are placed on the same retractor blade, however, the flexible cable with multiple extensions can have a single camera or stereo camera pair on each extension of the flexible cable. In some embodiments, the flexible cable with multiple extensions can have multiple cameras on each extension of the flexible cable. 
     In various embodiments, the flexible cable or other platform can be unrolled by hand. In some embodiments, hydraulics or pneumatics may be used to effectuate unrolling. Fluidic lines in the cable may, for example, be connected to a hydraulic or pneumatic pump source which can be applied to cause the cable to unroll and extend. 
     In various embodiments, the imaging assembly including the aggregator with rolled cables can be provided independent of the retractor unit and clipped-on or otherwise attached to the retractor unit prior to use as described herein. The imaging assembly can be attached at a single attachment point or through multiple attachment points. In various embodiments, for example, the flexible cable clipped on to the retractor frame, arms, and retractor blades. The flexible cables can be attached to the retractor and the retractor blades by a separate attachment mechanism that can be easily attached or removed within seconds. See, for example,  FIG. 3C . 
       FIG. 3B , described above, illustrates an embodiment of the retractor blades with an integrated imaging assembly clipped on to the retractor frame and arms. The retractor blades can be attached to the retractor arms by a separate attachment mechanism that can be easily attached or removed within seconds. In some embodiments, the aggregator is releasably attached via an attachment mechanism to the top surface of the retractor frame. In some embodiments, the imaging assembly can have multiple attachment mechanisms positioned on the aggregator, the flexible cable, the retractor blades or combinations thereof which fasten the imaging assembly to the retractor at various connection points. In certain embodiments, the imaging assembly may have one attachment mechanism and a single connection point on the retractor frame or retractor blades. As discussed above, the attachment mechanisms can include, for example, a clip, a snap, a strap, a screw, a bolt, a nut, a magnet, or any combination of these as well as any other method that can facilitate convenient attachment. For example, that can be accomplished in under one minute possibly less than 20, 10, 5, 3, or 2 seconds per fastener and may be accomplished in more or less than a second or ½ or ¼ second per fastener, which can occur, for example, prior to surgery. 
     A wide variety of fastening systems may be employed. In various embodiments, for example, the distal end  7005  of the flexible cable is fastened to the retractor blade surface or the retractor blades are fastened to the retractor frame through a clip-on mechanism  4011  shown in  FIG. 12A  which can be secured, for example, prior to surgery. 
     In some embodiments, the clip-on attachment mechanism can also resemble a hairpin attachment  4010  as shown in  FIG. 12B . In some embodiments, the hairpin attachment  4010  allows the flexible cable to be releasably and securely attached to the front surface of the retractor blade or the retractor blades to be releasably attached to the retractor frame. Extra fastener components may also be included to reduce risk of inadvertent movement or misalignment. Such clip-on attachment devices may be also used for retractors having different configurations such as for example, cylindrical type retractors such as shown in  FIG. 21 . 
     Additionally, in some embodiments, the flexible cable can be attached to the retractor blades or the retractor blades can be attached to the retractor frame via a dovetail attachment.  FIG. 12C  illustrates an embodiment of a top view of a dovetail attachment mechanism. The retractor blade or retractor frame may, for example, contain a receiving slot  4012  on the inner surface of the retractor blade or retractor frame opening to the interior of the surgical area. Additionally, the flexible cable or retractor blade can contain a first and second edge  4013  and  4014  configured to fit within the receiving slot  4012 . The insertion of the flexible cable or retractor blade into the receiving slot  4012  of the retractor blade or retractor frame provides a secure attachment of the flexible cable to the retractor blades or a secure attachment of the retractor blades to the retractor frame. Further, in some embodiments, the flexible cable can be attached to the retractor blade by insertion into the receiving slot of the retractor blade and also by a clip-on attachment mechanism as described herein. The locations of the receiving slot and edges that are fit therein can be reversed. 
     In certain embodiments, the aggregator with rolled cables can be permanently attached to the retractor frame. In such embodiments, the flexible cable could be rolled out and clipped on to the retractor blades. In some embodiment, the preattached aggregator and flexible cable can be permanently attached to the retractor unit in the unrolled configuration. In some such embodiments, the flexible cable can be permanently attached to the retractor surface and/or the retractor blade surface. 
     A variety of options are thus possible. In certain embodiments, the imaging assembly can be a clip-on imaging assembly which can be clipped on to the retractor and/or the retractor blades. In other embodiments, the retractor blades with integrated components can be permanently attached to the retractor frame along with the flexible cable and aggregator. In some embodiments, the retractor blades with integrated components can be permanently attached to the retractor frame but the flexible cable and aggregator can be clipped on to the retractor unit. In such embodiments, the flexible cable would attach to the integrated retractor blades through a hardware interface (e.g., female and male connectors, respectively) that allows the electrical signal to pass. In some embodiments, the retractors can have different shapes. For example, in some embodiments, the retractors have separate arms similar to that shown in  FIG. 3A . In some embodiments, the retractor can be a cylindrical retractor such as the retractor shown in  FIG. 21 . 
     Surgical Tool with Integrated Camera 
     In some embodiments, a second surgical device, e.g., surgical tool, may be used in conjunction with a first surgical device. For example, as shown in  FIG. 13A , the first surgical device  100  is a retractor with three retractor blades, and the second surgical device  200  can be a surgical laser. The laser  200  also includes an integrated camera module  205  which provides a field of view determined by the position of the distal end  211  of the laser. The laser output aperture  213  is oriented in the same direction as the field of view of the camera module  205  of the surgical laser  200 . In some embodiments, the image obtained from the laser  200  may be associated with the composite image generated by the plurality of cameras integrated within the first surgical device  100 . For example, in some embodiments, the view obtained by camera module on the laser tool may be superimposed over a portion of the composite image generated from the plurality of cameras, e.g., in the retractor  100 . The superimposed image may be positioned so as to indicate the placement of the view with relation to the view of the surgical field provided by the plurality of cameras mounted in the first surgical device. 
     In some embodiments, for example as illustrated in  FIG. 13B , the second surgical device can be a surgical tool such as a needle holder  300 . In various embodiments, the surgical tool can be, for example, drill, Kerrison, a cutting tool, grasping tool, Ronguer, scalpel, scissors, forceps, etc. The surgical tool  300  may have an camera module  305  integrated therein or attached thereto, whose field of view is determined by the position of the tool. For example, CMOS sensors and micro-optics can be incorporated into both power and non-power tools. A flex cable  311  (not shown) extends along the length of the tool  300  and electrically connects to the camera module  305 . In various embodiments, the flex cable  311  can provide electrical connection to the camera module, as well as supplying gas and/or fluid for camera cleansing, as described in more detail below. The additional camera included with the surgical tool may have a different magnification than the cameras on the surgical device, may provide increased resolution, and/or reduced obscuration. As described in more detail below, the video stream from the separate camera on the surgical tool can be superimposed over or otherwise displayed with the composite image generated by, e.g., stitching or tiling images from the plurality of cameras integrated with the surgical device  100 . 
     The tool image can provide an extreme close-up view of the tool-tissue interaction, while the wide-field image can provide a stereo image with situational awareness. The enhanced situational awareness is provided by the wide field-of-view deep within the area proximal to the surgical site, and views of anatomy of interest from more perspectives than a single device such as a microscope or endoscope. This perspective may be from within the body if the plurality of sensors on the first surgical device are within the body or at the surgical opening or within a few to 75 millimeters therefrom. In some cases, this perspective may be conveniently provide with surgical devices that are attached to the body such as by retractors. 
     The CMOS sensors, optics, EM sensor (optional), and tool actuation (if necessary) may be tightly integrated with the second surgical device in order to achieve a sufficiently small package. Power tools can be used, particularly for robotically assisted surgery. Embodiments described herein, however, may be used both in manual and robotic surgery. Electromagnetic tracking sensors, IMUs, and/or one or more cameras may be incorporated into a wide range of tools, including non-powered tools (e.g., pics, knives, curettes, osteotomes, rasps, trocars, dermatomes, retractors, suction cannulas), manually actuated tools (e.g., scissors, forceps (including bipolar cautery/diathermy forceps), clip appliers, Rongeurs, and needle holders), and powered tools (e.g., drills, power Kerrison, power bipolar forceps, harmonic scalpels, ultrasonic tissue removers, and lasers). The applicable tools, however, are not limited to these. 
     As with the first surgical device, pairs of cameras on the second surgical device can provide a stereo or 3D effect. 
     Power tools can provide an integration of the multiple camera system with master-slave surgical robotic systems, as well as decreasing hand fatigue and increasing precision with manual surgery. A proportional foot pedal control may be used, in which increasing depression of the pedal closes the tool proportionally. In some embodiments, hand actuation may be used instead, for example by use of a control lever or push button. In some embodiments, surgical impedance feedback may be provided. For example, sensed actuation pressure (or current if electrically controlled tool) can correspond to the tissue resistance and can be used to drive current/torque to foot pedal to provide surgical impedance feedback. Other configurations can be used to provide tactile feedback corresponding to mechanical forces experienced by the tools to the surgeons controls such as the foot pedal. 
     Tool actuation options include electrodynamic, pneumatic, and hydraulic. Hydraulic actuators advantageously are inexpensive, powerful, and “stiff”, meaning that these actuators are less prone to overshoot than their pneumatic and electrodynamic counterparts. Hydraulic actuators may include but are not limited to a rolling edge diaphragm (fluid is only one side of rolling edge diaphragm), diaphragm with dual actuation (fluid on both sides of diaphragm), as well as a Bourdon tube (axial or helical), or a piston in a cylinder. Master hydraulic actuator options include a brushless DC motor with ball screw linear actuator driving rolling edge diaphragm, and commutated or non-commutated brushless DC motors driving a rolling edge diaphragm. In various embodiments, dual linear actuators can drive dual air cylinders and air over fluid in disposable cassette. Other configurations are possible. 
     Tracking Tools and Optics 
     In various embodiments, cameras can be independently adjustable, either rotatable/articulable within the device, or they may be able to be separately mounted prior to or during insertion of the surgical platform. Multiple cameras can each have a position and/or orientation that is tracked, e.g., electronically or optically. Tracking the position and orientation of the sensors can provide the image processor with real-time, low-latency, 6-DOF (six degrees of freedom) information needed to decrease search and registration times for the purpose of stitching a composite image. Tracking can also be employed to assist in tiling or otherwise arranging images such that the position of the image as displayed is consistent with the arrangement of the locations of the cameras or the field-of-views of the cameras in the surgical site. Tracking options include electromagnetic tracking (as, for example, using NDI Aurora or Ascension medSafe). In such systems, 6-DOF sensors may be less than 1 mm in outer diameter. These systems do not require a line-of-sight, as in optical tracking systems. Electromagnetic tracking sensors can be easily integrated within the surgical devices at relatively low cost. In some embodiments, less than 6 degrees of freedom, e.g., 5-DOF tracking can be employed instead of 6-DOF. In some embodiments, for example, IMUs can be used for 5-DOF tracking. In such 5-DOF tracking, the distance to target is not required to be precise so long as the other distances and positions are known. If the distance to target is a few millimeters closer or further away, the difference in magnification can be negligible. In various embodiments, in which the distance to target must be precise, 6-DOF tracking may be required. 6-DOF tracking may improve integration of the tracking with navigation systems and the GUI. The capability of tracking, and thereby knowing the location and orientation of the camera, can provide the opportunity to tell the camera where it needs to be for an array of images to be aligned in a prescribed manner. For example, a plurality of cameras on malleable retractor fingers by definition are not aligned to an equator. Through tracking, the cameras can offload position derived by sensor and image processing to position adjustment, described in more detail below. 
     Surgical tools can also be tracked. Tracking can provide 6-DOF real-time position and orientation to image process to enable correct positioning of PIP overlay of tool images or alternatively stitching, tiling, and scaling of images into the composite image. EM tracking has significant advantages. Since electromagnetic tracking does not rely on line-of-sight (as opposed to optical tracking), visual obscuration does not interrupt tracking. Particularly in minimally invasive procedures, the presence of various surgical tools within the small incision can provide significant obstacles to optical tracking. The EM tracking may take the form of EM sensor coils, or other techniques. In addition the positions and/or orientations of the cameras and/or the surgical tools can be tracked by using encoders, MEMS IMUs, ultrasonic emitters, optical tracking or other approaches, in some embodiments. 
     Electromagnetic tracker coils can be positioned within sufficient proximity to the each camera and the tracking device included therewith such that the relative location and/or orientation of the cameras can be determined. Such electromagnetic coils can provide 6-DOF position and orientation information, which may then be transmitted to the image processor. The position and orientation information can be used to reduce the computational load required to stitch or tile the various images into the composite image and/or to render the image in stereo key application is touch screen user interface. In some embodiments, cameras can be integrated with retractors that include malleable blades, for example retractors designed for neurosurgery. The position of the cameras individually can therefore provide positional information unavailable when detecting only the position of the retractor blade, since the blade itself can be malleable. In some embodiments, the retractor and its blades can be rigid, and accordingly the tracking requirements may be reduced. 
     In some embodiments, the surgical device and/or any surgical tools can include integrated motion sensors, such as gyroscopes or other MEMS accelerometers. These sensors can measure the physical motion of the cameras due to movement of the device. This motion can be subtracted from the image in order to render a displayed image in which the area of interest is relatively still, despite any movement by the surgical device. 
     Camera connectors can have EEPROM chips to provide information to the image processor about the camera such as the identity, sensor format (e.g., number of horizontal pixels and vertical pixels, etc.) or other information. In the special case of cameras mounted on a tubular retractor for spine surgery or other retractors with fixed camera position, the fixed positions may be made available to the system. 
     If an optical navigation/tracking system is used on retractor, electromagnetic tracking can send tool tracking information to the navigation system to avoid the need for optical recognition features (for example passive reflections of LEDs and/or location of fiducials) on the tool. Electromagnetic trackers can also be positioned on a patient, for example on a bone or anatomic landmarks, as well as being positioned on external fixation systems, for example a cranial fixation system for neurosurgery. The position of the cameras with relation to these external tracked points can be used as input to guide optical navigation systems, for example those provided by Medtronic, Stryker, or BrainLabs. 
     In the case of malleable retractor blades, the position of the cameras integrated therein are not necessarily fixed with respect to the retractor frame. Accordingly, tracking of the cameras may be useful for enabling an image processor to stitch (register) or tile multiple images together in the proper position and orientation without excessive computational load. A 6-DOF electromagnetic sensor can be attached or integrated within the malleable retractor blade near the camera. In some embodiments, the flex circuits for the camera and sensor coil can be integrated together or may be potted together and use the same cable assembly. 
     An alternative approach to tracking camera position can be employed in configurations with retractor blades that can flex only in one plane. An example of such a 1-DOF retractor blade is shown in  FIG. 6A , as described above. With reference to  FIG. 6A , the axial position of the wire  353  can be sensed, for example, by using an optical encoder marking on the wire  353 . A moving 6-DOF electromagnetic sensor outside the surgical site also can be attached to the base of the retractor blade  351  at the proximal end, e.g., at the position of attachment to a retractor frame. Information from the 6-DOF sensor along with the sensed axial position of the wire  353  can provide position and orientation information about the camera  355 . In other embodiments, two wires may be used, one having a distal attachment, the other with a more proximal attachment. For example, the wires may run along the outer curvature of a pre-flexed Nitinol retractor blade. Axially moving one or both wires, each of which may be sensed, enables incremental controllable flexure of the blade. Encoders may be used again for tracking. 
     In other embodiments, particularly when the retractor blades are substantially rigid, the position of the blades can be sensed, and the position of the cameras can be inferred from the blade position. For example, the position of the cameras with respect to the retractor blades on which they are mounted can be known in advance. In use, as the retractor blades are moved, the movement can be tracked. For example, encoders may be positioned within joints of the retractor, such that as the retractor blade is rotated at the joint, the degree of rotation is sensed. Similarly movement of an articulating arm to which the retractor blade is attached can be sensed, and this information can be used to derive the position of the cameras. 
     It is also possible to use optical tracking, where the surgical device includes some kind of identifying markers, and the information is viewed by an overhead camera. The image can then be processed to identify the position and orientation of the surgical tool. The markers, whether shape or color or both, and whether positioned on or within a tool, for example, may provide white balance and intensity information useful for adjusting the sensors or illumination output. In various embodiments, white balancing may be done by inserting the target into the workspace in the field of view of all cameras before surgery. The frame, retractors and assorted cameras could be placed in a holster, whose purpose is multifold, to include but not limited to: authentication, white balance, camera positions with respect to frame, synching camera types to icons in GUI, such as field of view, line of sight, sensor type, stereo pairing, etc. 
     In various embodiments inertial measurement units may be employed to determine movement and/or orientation of the cameras. Such inertial measurement units may be less expensive than potential alternative tracking options. In certain embodiments, IMUs are used to provide 5-DOF as opposed to 6-DOF. 
     In some embodiments, the image obtained from the tool may be blurred or otherwise deteriorated due to operation of the tool. For example, a surgical drill with an integrated camera may produce blurred images due to the rotary motion of the drill. Such image motion can be compensated by the image processor. For example, the torque produced by the rotation of the drill can be proportional to the applied current. In view of the applied current, a feed-forward command can be sent to the image processor to compensate for the blur caused by the rotary motion. 
     In some embodiments, actuation of an electrically powered surgical tool can result in electromagnetic interference with the electromagnetic tracking. In such configurations, optical tracking can be used to supplement electromagnetic tracking as an alternative. Alternatively, a notch filter can be employed to reduce interference from the powered surgical tool with the electromagnetic tracking. The notch filter can be selected such that the stop-band corresponds to the electromagnetic noise produced by the powered surgical tool. The electromagnetic signal used by the trackers may fall outside of the stop-band of the notch filter. Another approach to avoiding deleterious interference with the electromagnetic tracking is for electromagnetic tracking to be suspended during operation of the powered surgical tool. Once operation of the powered surgical tool has ceased, electromagnetic tracking may then re-commence. In various embodiments, a controller can automatically cease electromagnetic tracking when the powered surgical tool is initiated, and similarly can automatically resume electromagnetic tracking when use of the tool ends. Yet another approach involves characterizing the electromagnetic interference caused by a given powered surgical tool, and then using that characterization to subtract out the interference from the electromagnetic tracking signal. For example, in some embodiments, the electromagnetic signatures for a surgical tool may be known in advance, and this signal may be accounted for when electromagnetically tracking the positions of the tool and/or cameras. In other embodiments, the electromagnetic noise caused by the surgical tool may be measured on the fly, and this noise may then be subtracted or otherwise compensated for when calculating the position of the surgical tool and/or cameras. 
     Surgical System Components 
       FIG. 14  illustrates a block diagram of an example surgical system  370  comprising an imaging surgical system  372 , a display system  374 , and a user interface  376 . The surgical system  370  can be used to visualize a surgical site using multiple cameras  378   a  and/or  378   b  associated with a retractor  380 , a surgical tool  382 , and/or auxiliary cameras. Visual information can be presented to a surgeon using the display system  374  to provide visual feedback to the surgeon to enable the surgeon to control the surgical tool  382  using the user interface  376  and/or the tool control  377 . The imaging surgical system  372  can be configured to enhance the situational awareness of the surgeon by displaying imagery (e.g., video and/or still images) of the surgical site where enhancement of the surgeon&#39;s situational awareness occurs based at least in part on multiple points of view of the surgical site, an orientation of the imagery on the display, positions of the imagery relative to one another, stereo and/or layered imagery, information about a position of the surgical tool  382 , imagery of the surgical site from external sources (e.g., MRI, x-ray, CT, or other imaging modality), or any combination of these. The imaging surgical system  372  can be configured to provide imagery of a trajectory of the surgical tool  382 , for example, from entry of the surgical tool  382  at a surgical opening to deep within a convoluted surgical site through the use of multiple views provided by multiple cameras  378   a.    
     The imaging surgical system  372  can include a control system  384  configured to receive input from various systems and/or modules, to process information, to store data, to send output to various systems and/or modules, to receive input from a surgeon or other user, or any combination of these. The control system  384  can include a controller  386 , data storage  388 , a sensor module  390 , an image processing module  392 , a tracking module  394 , and a lighting module  396  which may communicate with one another and/or external systems through communication bus  385 . 
     The control system  384  includes the controller  386  configured to process data and to control communication between the control system  384  and external systems (e.g., the cameras  378   a ,  378   b ; the sensors  398   a ,  398   b ; the lights  399   a ,  399   b ; the display system  374 ; the user interface  376 ; the tool control  377 ; a laptop; a tablet; or any other external system). The controller  386  can be configured to control data communication between control system modules and/or between control system modules and data storage  388 . The controller  386  can be implemented in hardware, software, firmware, or any combination of these. For example, the controller  386  can include logical elements configured to receive imagery from the cameras  378   a ,  378   b  and perform image processing functions on the imagery according to instructions provided by the image processing module  392 . As another example, the controller  386  can include control modules configured to make decisions based on information received from various modules within the control system  384  and/or from external systems. As another example, the controller  386  can include one or more physical processors configured to process information from the user interface  376  or the tool control  377  to send to the surgical tool  382 , to the cameras  378   a ,  378   b , the lights  399   a ,  399   b , or to the display system  374 . As used herein, the term “processor” refers broadly to any suitable device, logical block, module, circuit, or combination of elements for executing instructions. The controller  386  can include any conventional general purpose single- or multi-chip microprocessor such as an Intel® processor, a MIPS® processor, a Power PC® processor, AMD® processor, ARM® processor, or an ALPHA® processor. The controller  386  can include any conventional special purpose microprocessor such as a digital signal processor. The controller  386  and the various illustrative logical blocks, modules, and circuits described in connection with embodiments disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The controller  386  can be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more FPGAs, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some embodiments, the controller  386 , the sensor module  390 , the image processing module  392 , the tracking module  394 , and the lighting module  396  or any combination thereof can be implemented using one or more FPGAs. In some embodiments, the controller  386  and one or more modules can be implemented using one or more FPGAs with associated components. For example, in certain implementations, an FPGA can be configured to provide image processing capabilities as well as video switching, controlling video sent between components of the system  370 , controlling data processing, and/or controlling a flow of data between components of the surgical visualization system  370 . 
     The control system  384  includes data storage  388 . Data storage  388  can be coupled to the other components of the control system  384 , such as the controller  386 , the sensor module  390 , the image processing module  392 , the tracking module  394 , and the lighting module  396 . Data storage  388  can refer to electronic circuitry that allows information, typically computer data, to be stored and retrieved. Data storage  388  can refer to external devices or systems, for example, disk drives or solid state drives. Data storage  388  can also refer to fast semiconductor storage (chips), for example, Random Access Memory (RAM) or various forms of Read Only Memory (ROM) such as an EEPROM, which are directly connected to the one or more processors of the control system  384 . Other types of memory include bubble memory and core memory. In some embodiments, video output from the image processing module and/or other data from components of the surgical visualization system  370  can be stored on data storage  388 . For example, video displayed on the display system  374  can be recorded onto data storage  388 . In some embodiments, data storage  388  is a removable data storage system, such as an external USB hard drive, a flash drive, a memory card, or other similar data storage device. 
     The control system  384  includes sensor module  390  configured to receive and process information from the sensors  398   a ,  398   b  associated respectively with the retractor  380  and the surgical tool  382 . Sensors can include inertial measurement units (IMUs), gyroscopes, magnetometers, accelerometers, thermal sensors such as thermocouples or thermistors, electromagnetic sensors, photosensors, or other such sensors. In some embodiments, the sensor module  390  receives sensor information and processes it to provide feedback to the surgeon through the user interface  376 , the tool control  377 , the display system  374 , or through some other method such as audible or visual signals. For example, the sensor module  390  can receive accelerometer information from a sensor associated with the surgical tool  382  and the image processing module  392  can use this information to display a position of the surgical tool  382  when outputting imagery to be displayed on the display system  374 . In some embodiments, the sensor module  390  receives sensor information and processes it to provide sensor information, for example, to the image processing module  392 , the tracking module  394 , and/or the lighting module  396 . In this way, the control system  384  can use the sensor information to alter operational parameters or control of the surgical system  370  without direct intervention from a user or surgeon. For example, the sensor module  390  can receive temperature information from a thermocouple associated with the surgical tool  382  or camera  378   a  and the control system  384  can decide to implement a cooling procedure if the temperature exceeds a threshold. In some embodiments, sensor information received by the sensor module  390  is stored in data storage  388  for later use and/or analysis. Other uses of sensors in conjunction with operation of the surgical system  370  are described herein. 
     In some embodiments, the retractor  380  and/or surgical tool  382  can be configured to provide an encrypted signal to the control system  384 , for example, to the sensor module  390  or the image processing module  392 . In some embodiments, similar to the encrypted signal, the retractor  380  and/or surgical tool  382  can be configured to provide a header on image data packets to the control system  384 , for example, to the sensor module  390  or the image processing module  392 . Encryption or the header can be provided by the camera chip or a separate chip electrically connected to the optical sensor in the camera. In some embodiments, the header or the encryption of the signal assists the signal processing system in the recognition of the camera once attached or clipped on to the retractor. The header or encryption may also ensure the proper pairing of imaging assembly and retractor base for the appropriate image processing and imaging system configuration. Additionally, the header or encryption can ensure the proper standard and quality of camera is used and complies with appropriate requirements for the image processing herein described. In various embodiments, decryption can be achieved with, for example, a computer processor or other electronics, possibly the image processing module or other signal processing or computing module. In various embodiments, the header can be used to relay non-image information to the various systems for use in control the system, processing imagery received from cameras, displaying output video or images, and the like. 
     The control system  384  includes the image processing module  392  configured to receive image data, process the image data, and to output video or image data for display. The image processing module  392  can be configured to receive image data from the cameras  378   a  and/or  378   b  and/or from other imaging modalities including MRI, CT, X-ray, and the like. In some embodiments, image data from other imaging modalities can be communicated using, for example, the DICOM3 protocol. The cameras  378   a ,  378   b  can include optics, optical sensors such as CCD or CMOS two-dimensional detector arrays, and associated electronics configured to acquire image information of a scene, as described herein with greater detail. The image processing module  392  can be configured to process image data which can include, for example, stitching images, blending images, morphing images, tiling images, performing transformations on the images (e.g., affine transformations, non-linear transformations, etc.), mosaicing images, enhancing resolution of a region using a plurality of images, extracting surgical tool  382  position information, forming stereo images from separate monocular images, or any combination of these or other image processing including but not limited to those described herein. 
     The image processing module  392  can be configured to output video or images for display on the display system  374 , the user interface  376 , or both. In some embodiments, the output video or images can include video from a single camera or a composite video where the video is a result of combining imagery from a plurality of cameras. For example, imagery from multiple cameras can be combined to form a single video by stitching the videos to create a video stream having a wider field of view than provided by any of the multiple cameras used in the stitching. As another example, video from multiple cameras can be combined to enhance a resolution of a region of interest such that the resulting video presents a greater number of pixels per unit of area than any individual input video frame. As another example, multiple cameras can provide multiple viewpoints of an object or area and the video from the multiple viewpoints can be morphed to create video from a virtual viewpoint different from any of the viewpoints of the multiple cameras. 
     In some embodiments, the image processing module  392  outputs video or image data for display where the output includes a plurality of images or video. For example, the image processing module  392  can receive imagery from a plurality of cameras and present these as tiled images or video. In some implementations, the output tiled images or video can be configured to represent information about the input imagery. For example, one or more of the tiled images or video can be presented as a trapezoid or other similar shape to represent an orientation of the camera relative to an object or area being imaged, e.g., to represent that the focal plane of the camera is not parallel to the area or object being imaged. As another example, the output tiled images or video can be positioned to represent their physical arrangement which can include, for example, the relative positions of the cameras providing the imagery and/or the field-of-views of the cameras. In certain implementations, the tiled images or video can be presented with borders around one or more of the images to enhance or help to identify an extent of the corresponding video or images. 
     In some embodiments, the image processing module  392  outputs a combination of any of individual, tiled, and/or stitched imagery. For example, in certain implementations, the image processing module  392  outputs background imagery having a relatively wide field of view where the background imagery is provided by a single camera or where the background imagery is a result of stitching imagery from a plurality of cameras. In some implementations, overlaid on the background imagery, the image processing module  392  can output video having a narrower field of view than the background imagery. For example, the video with a narrower field of view can be a combination of monocular imagery that form a stereo video, an example of which is illustrated in  FIG. 15 . As another example, the imagery with a narrower field of view can be imagery provided by a camera  378   b  on the surgical tool  382 , an example of which is illustrated in  FIG. 16 . In some implementations, overlaid on the background imagery is imagery from a plurality of cameras where the imagery can be tiled and/or stitched, an example of which is illustrated in  FIG. 16 . In some implementations, the image processing module  392  can output a center image or video that can change between imagery provided by camera(s)  378   b  on the surgical tool  382  and imagery provided by distal camera(s)  378 ( a ) on the retractor  380 . For example, imagery from the surgical tool camera(s)  378   a  can be presented as a picture-in-picture overlaid on background imagery and/or with stitched or tiled imagery from retractor camera(s)  378   a , an example of which is illustrated in  FIG. 17 . In some embodiments, imagery from three retractor cameras  378   a  can be displayed as tiled imagery overlaid on background imagery and imagery from the surgical tool camera  378   b  can be displayed as a picture-in-picture-type display over the background imagery. 
     In some embodiments, the image processing module  392  is configured to receive imagery from the cameras  378   a ,  378   b  and to display the received imagery for simultaneous viewing on the display system  374 . In some embodiments, the image processing module  392  is configured to allow a system or user (e.g., a surgeon, an assistant, etc.) to manipulate or interact with the imagery. For example, the image processing module  392  can be configured to provide electronic zoom or magnification according to user input, to system configuration, to camera position, to surgical tool movement or position, or the like. In some embodiments, the image processing module  392  provides feedback to the cameras  378   a ,  378   b  to change a focus, a viewing angle, a zoom factor, or the like. Feedback can be provided by the control system  384 , external systems, and/or the surgeon or other user through the user interface  376 . For example, the surgeon can use the user interface  376  to select images and/or video to view on the display system  374 . The control system  384  can receive input from the surgeon, receive imagery from cameras  378   a  and/or  378   b , process the received imagery, and send the processed imagery to the display system  374 . Functionality and capabilities of the image processing module  392  and image processing of the imaging surgical system  372  in general is described herein. 
     The control system  384  includes tracking module  394  configured to provide and track a location of the retractor  380  and/or the surgical tool  382  during use of the surgical system  370 . The tracking module  394  can be configured to receive information from the sensors  398   a ,  398   b , the sensor module  390 , the image processing module  392 , the user interface  376 , and/or the tool control  376 . The tracking module  394  can process this information to calculate a position of the surgical tool  382 . The tracking module  394  can provide this information to the image processing module  392  for display on the display system  374 . For example, the image processing module  392  can receive surgical tool  382  position information from the tracking module  394  and display the surgical tool  382  on the display system  374  such that the surgical tool  382  is rendered along with imagery of the surgical site in such a way as to provide situational awareness to the surgeon. Surgical tool  382  rendering is described herein with greater detail. The tracking module  394  can incorporate electromagnetic tracking information, EEPROM, radio-frequency identification (“RFID”) information, accelerometer data, gyroscope data, and other such data to calculate a position of the surgical tool  382  and/or other components of the surgical system  370 . In some embodiments, the tracking module  394  provides coarse position information of the surgical tool  382  to the image processing module  392  which can be configured to use the coarse position information to calculate fine position information based at least in part on imagery of the surgical tool  382 . 
     The control system  384  includes lighting module  396  configured to control illumination of the surgical site. The lighting module  396  can control the lights and/or other sources of illumination  399   a ,  399   b  of the imaging surgical system  372  to provide sufficient illumination of the surgical site for the cameras  378   a ,  378   b  to acquire imagery of the site. In some embodiments, the lighting module  396  times or coordinates output of the lights  399   a ,  399   b  such that the lights do not directly illuminate one or more cameras  378   a ,  378   b , as described herein in greater detail. The lights  399   a ,  399   b  can be LEDs or other such sources of visible, infrared, and/or ultraviolet light, as described herein with greater detail. 
     The imaging surgical system  372  includes retractor  380  and/or surgical tool  382 , both of which are described in greater detail herein. The retractor  380  and/or surgical tool  382  can have sensors  398   a ,  398   b , cameras  378   a ,  378   b , lights  399   a ,  399   b , and/or other elements (e.g., a heater) associated therewith each of which can be controlled using the control system  384 , the user interface  376 , the tool control  377 , or other control mechanism. 
     The surgical system  370  can include a display system  374  configured to display information to a user or surgeon. The display system  374  is described herein with greater detail. The surgical system  370  can include a user interface  376  configured to receive input and provide feedback to a user. The user interface  376  can include physical elements configured to receive user input such as, for example, a multi-touch screen, buttons, keyboards, pointer device, switches, knobs, and the like. The user interface  376  can include a display configured to provide visual information to the user and to facilitate interaction with the surgical system  370  and control of the system  370 . In some embodiments, the user interface  376  can be incorporated into the display system  374  such that it both displays information and receives user input. In some embodiments, the user interface  376  displays the graphical user interface on a separate display that is not a part of the display system  374 . In some embodiments, the user interface  376  includes a touch screen interface and/or a gesture recognition system. The user interface  376  can be used to, for example, select imagery to view, zoom-in on imagery, and/or position imagery for display on the display system  374 . In some embodiments, the surgical system  370  can receive input in the form of voice commands. 
     In some embodiments, the display system  374  and the user interface  376  can be combined in a way that allows the surgeon or other user to interact with displayed imagery. In some embodiments, the display system  374  is configured to provide an immersive experience for a user. For example, a virtual display can be used wherein the surgeon viewing displays through binoculars motions with his or her hand in a manner consistent with the imagery seen by the surgeon, and the surgeon&#39;s movements are detected. These movements can be mapped to actions that correspond to manipulating output imagery, cameras, surgical tools, or any combination of these. In some implementations, the binocular presentation can allow for three-dimensional information to be displayed to the user and the user can use hand gestures at the point in space where imagery appears to be to initiate a command. In some embodiments, the gesture recognition can be used in conjunction with a surgical tool  382 . For example, the surgeon can remove the surgical tool  382  from a surgical field and move the tool  382  in such a way that the gesture recognition system correlates the movement to pointing, flicking, dragging, pointer control, and/or stylus functionality. The display system  374  can include image-based or electromagnetic-based motion sensors to detect the gestures of the surgeon. The tracking system used to track the tool, for example, may be used. Such a display system  374  and user interface  376  can allow for a surgeon to interact with the user interface  376  without potential contamination issues that may arise when using a touch-based user interface. 
     The user interface  376  can include a graphical user interface configured to facilitate interaction with the surgical system  370 . The graphical user interface is described with greater detail below with reference to  FIGS. 24 and 24B . In some embodiments, the display system  374  displays the graphical user interface  376 . The user interface  376  can include the tool control  377  where the tool control  377  can be integrated into a unitary user interface  376  or the tool control can be a separate element of the user interface  376 . The tool control  377  can be configured to receive input from a user to manipulate the surgical tool  382 . Examples of the tool control  377  and associated surgical tools include those described herein with reference to  FIGS. 34-53 . 
     Video and Image Control and Processing 
     Surgical visualization systems described herein can include components configured to receive image data, process the image data and other data, and output video and/or images for display. The video and image processing functionality can be provided using any suitable combination of hardware, firmware, and software, such as but not limited to those described herein with reference to  FIG. 14 . For example, a surgical visualization system can include communication buses and/or interfaces to receive image data and one or more micro-processors, FPGAs, ASICs, or the like or combinations thereof that are configured to process received image data to provide output video for display. For ease of description, video and image processing will be described as being performed by an image processing system which can be any suitable system or component of a surgical visualization system that is configured to receive image data, process image data, and output video or images for display, such as for example the image processing module described herein with reference to  FIG. 14 . As part of the description, the image processing system is described as receiving and/or outputting imagery, images, and/or video. The processing of images described herein should be understood to be applicable to video. Any description of processing limited to either images or video should not be construed as limiting the disclosure of the functionality solely to images such as still images or video as video can be interpreted as a series of images. Likewise often the term video images or video image, feed or stream or simply images are used in connection with discussion of video. 
     In some embodiments, the surgical visualization system includes an image processing system configured to output a single image or video stream wherein the single output image is created from a plurality of input images. For example, the image processing system can be configured to receive a plurality of images from cameras associated with a retractor, a surgical tool, another surgical device, or any combination of these. The image processing module can be configured to combine the plurality of images into a single displayed scene. For example, the image processing module can be configured to stitch the images to create a single larger displayed scene by combining images from cameras where the images overlap. In some embodiments, one or more images may be superimposed on or shown forward the stitched image etc. For example, this configuration includes possibly picture-in-picture (PIP) as well as an arrangement of tiled images disposed on the stitched images. 
     Accordingly, the image processing module can be configured to stitch multiple images together to create a single image. Stitching images can provide a wider field of view or field. Stitching images can reduce or eliminate obscuration of a region of interest in the scene by a surgical tool or other device. Stitching images can reduce or eliminate albedo due at least in part to the multiple cameras in the surgical visualization system which provides the surgeon the ability to “look behind” protruding features, such as an aneurysm. Stitching images can reduce image artifacts such as vignetting caused by a retractor tube or blade. These same benefits may be obtained by other arrangements of a plurality of images from different cameras such as tiling images from different cameras. 
     The image processing module can be configured to adjust input images when stitching them together to provide a substantially seamless output image. In some embodiments, direct (e.g., pixel-by-pixel) or feature-based image processing can be used to align images where they overlap. Feature-based image processing can include aligning images based on features within the images. This can include image or shape recognition and matching to align the images. In certain implementations, a target structure with alignment features can be included in a field of view of one or more cameras to assist in feature-based alignment methods. Such a target structure may be provided during initial set-up. The target structure can also include white-balancing features, as described in more detail herein. The target structure may be included on the retractor, might be a component added to the retractor during initialization, or may be a feature of a base, pod, station, or other platform in which or on which the retractor is attached, e.g., rests, during an initialization phase. Similarly, pixel-by-pixel alignment processing can be used, for example, in conjunction with position and orientation information to align pixels based on pixel features to stitch the images together. In some embodiments, stitching images can be simplified where the cameras are identical or have identical sensors, where the relative positions and/or orientations of the cameras are known with relative precision (such by using memory devices or tracking systems as describe above), and their distance to the imaged scene is substantially the same. In some implementations, the cameras can be positioned near a non-planar scene, or a scene that is not flat, and non-linear transformations can be used to stitch images. In some implementations, it may be preferable to use centralized cameras, or cameras that provide imagery of a central portion of a scene (where central can be relative to the output image), as reference images in stitching to reduce cumulative errors across an output image when compared to using a peripheral image as a reference. 
     When stitching images, several techniques can be used to blend overlapping regions of images to provide a substantially visually seamless output image. For example, the image processing system can implement an algorithm to blend image intensities at the seams of stitched images. The algorithm can include blending images using center-weighted averaging (or feathering) wherein pixels near the center of the image are weighted more heavily than pixels near the edge. The algorithm can include using Laplacian pyramid blending and gradient blending to address differences in gain between images at the seams which can result in less blurring than center-weighted averaging. The algorithm can include averaging in the radiance domain appropriate typically where gain differences between images are relatively large. In some embodiments, the image processing system is configured to perform affine transformations on received imagery. 
     The image processing system can be configured to morph multiple images from cameras having different viewpoints to create a single image of a scene wherein the single image appears to include a viewpoint that may differ from the viewpoints of the cameras. For example, the image processing system can receive a first image of a region of interest from a first viewpoint and a second image from a second viewpoint of a region of interest and generate intermediate images from viewpoints that lie between the first and second viewpoints. For example, as illustrated in  FIG. 18 , left and right cameras can be combined to provide a central view from a virtual camera. This approach can be performed for any pair of cameras that image a common region. In some embodiments, more than two cameras are used to reduce or eliminate peripheral ambiguities related to imaging 3-D scenes. This technique can provide, for example, a central view of the surgical site without a central camera, microscope, or endoscope. This technique can be used to simulate camera movement, to provide image data from a viewpoint that is not physically accessible but desirable, to increase image information of a region of interest, or any combination of these. Image morphing can, for example, be accomplished using standard techniques that are known in the art. 
     The image processing system can be configured to display multiple images as individual images where the multiple images are tiled. The tiled images can be purposely tilted and/or distorted based at least in part on an orientation of the camera providing the images. The tiled images can be presented with borders around each image or groups of images. Tiling images can be differentiated from stitching or morphed images because tiled images are not combined to form a unified image of an area of interest or object of interest. However, in some implementations, images can be stitched or morphed and these stitched or morphed images can be output as tiled images. For example, these morphed or stitched images can be included together with other images in a tiled fashion. 
     In some embodiments, positions of cameras can be provided to the image processing system to be used when stitching, morphing, or tiling images from the cameras. In certain implementations, the cameras can have relatively fixed positions, such as when the cameras are associated with a tubular spine surgery retractor. The positions of the cameras can be communicated to the image processing system using any tracking systems and/or memory storage devices (e.g., where the positions of the cameras are fixed). For example, EM or optical tracking, one or more inertial measurement units (IMUs), EEPROMs and/or RFID tags, associated with the retractor, surgical tool, and/or with the cameras may be used. In certain implementations, for example, the cameras can have EM trackers, optical trackers, IMUs etc which communicate their positions and/or orientation during setup to the image processing system. Such information is especially useful if the camera is movable and the camera is reoriented during set up. In some implementations, RFID or EEPROM technology can be used to communicate information about camera field-of-view, resolution, quantity of cameras in use and possibly location and/or orientation. The image processing system can use this tracking information to assist in aligning the images from the various cameras to improve and/or facilitate stitching, morphing, and/or tiling images. In some implementations, the tracking information can provide a coarse position of the cameras and their relative pointing angles, and the image processing system can use this information to calculate a transformation for each received image to stitch them together to provide a substantially seamless display of stitched images. The image processing system, also, can provide greater detail about the positions and/or orientations of the various cameras to the surgical visualization system. Even if the images are not stitched, the images can be arranged in a manner that is consistent with the arrangement and location of the cameras in the surgical field, e.g., on the retractor or their respective field-of-views. 
     The image processing system can be configured to combine images from a plurality of cameras to virtually enhance capabilities of the cameras in the surgical visualization system. For example, the image processing system can create an image of an area of interest having enhanced resolution by combining multiple images of the area of interest. As another example, the image processing system can create a virtual camera having an increased dynamic range by combining image data from cameras having differing gains. 
     In some embodiments, the image processing system can be configured to combine multiple substantially overlaid images to output a single image having a higher resolution than any of the multiple images. In certain implementations, enhancing the resolution in this manner results in an output image where the number of pixels per unit area imaged is greater for the output image than any of the multiple images. In certain implementations, the multiple substantially overlaid images are provided by multiple cameras having fields of view that substantially overlap. In some embodiments, images from cameras having different gain are aligned to provide an aggregate image having increased dynamic range. 
     The image processing system can be configured to provide electronic zoom and/or magnification using image data from a plurality of overlapping cameras. In some embodiments, cameras can be positioned at differing distances from an area or object of interest. As a result of these differing positions, differing views and/or magnifications of the area or object of interest are provided by the cameras. In some embodiments, electronic zoom may be used to normalize magnification levels. For example, images from cameras at different positions can have different magnifications and the image processing system can electronically adjust magnification levels when, e.g., stitching, tiling, and/or morphing the images prior to outputting the images. In some embodiments, the image processing system super-positions images to permit electronic magnification of objects to yield better quality and/or similar-sized images of an area of interest for display. In some embodiments, images that are overlapping can be electronically magnified such that the resulting magnified images provide adjacent views rather than overlapping views. 
     The image processing system can also utilize the differing magnifications resulting from cameras located at different distances to electronically zoom imagery of an area or object of interest. These varied levels of magnification can also be used by the image processing system when morphing images. Cameras that are closer to the area or object of interest present imagery having increased resolution of the area or object of interest which can be advantageous for electronically zooming. The image processing system can use this information to provide electronic zoom capabilities and magnification capabilities. In some embodiments, the image processing system uses superposition of images having differing levels of magnification to provide electronic zoom capabilities based at least in part on the different magnification levels. Accordingly, in some embodiments, the image processing system provides a zoom feature for magnification over an array of cameras having unequal or equalized image magnifications. In some embodiments, the image processing system rotates images to enable this variable magnification and zooming capability. 
     In some embodiments, the image processing system can use camera location information to create a distance guide (e.g., a look-up table) to magnify or de-magnify images corresponding to an area of interest. In some embodiments, the image processing system can use the location information to calculate a magnification of a camera and use this information when combining images from multiple cameras having differing magnifications. In some embodiments, the image processing system can be configured to present images from cameras with different levels of magnification to represent differing distances from an area or object of interest, for example when tiling or with picture-in-picture. 
     In some embodiments, cameras can include MEMS technology to provide zoom functionality by moving and/or positioning the camera optics. The zoom functionality can be used to alter magnification of the images acquired by a camera. The surgical visualization system can include modules and systems that provide feedback to the cameras such that the camera changes magnification levels by changing a focal length or zoom of the camera. For example, the tracking module can provide information about the position of the surgical tool to the image processing system and the image processing system can provide feedback to the camera to alter its magnification factor according to the surgical tool&#39;s distance from a targeted tissue site. Similarly, in some embodiments, cameras can include MEMS technology to provide focusing functionality by moving and/or positioning the camera optics. The focus functionality can be used to change a focal length of the camera optics to account for distance to a targeted site. For example, if the depth of focus of a camera on a surgical tool is not sufficient to maintain focus of targeted tissue when the position of the surgical tool changes, the MEMS system can change the focus of the camera. Thus, as described herein, the surgical visualization system can include methods of electronically zooming and methods of physically zooming cameras. 
     In some embodiments, the surgical visualization system can include cameras at different locations within a surgical site, and particularly at different depths within the surgical site. The image processing system can use the varying depths of field from the cameras at different depths to increase an output depth of field to provide focused imagery of a greater portion of the surgical site. For example, a retractor can have two or more cameras or camera pairs at two or more longitudinal distances along the length of the retractor (e.g. proximal and distal) and the cameras at each level can provide image data to the image processing system. For example, a retractor can have two or more rings or arrays of cameras (e.g. proximal and distal) located on the retractor so as to provide different distances to the same object in the surgical site. The proximal cameras may provide a main larger field of view of the area in the surgical site and the distal cameras may provide a closer-up view(s). The image processing system can combine overlapping image data to provide an output image having a greater depth of focus. An example of a system with cameras located at two depths or longitudinal positions along the length of the retractor is illustrated in  FIG. 21 . Locating cameras at varying distances in the surgical site may potentially provide for increased situational awareness. Locating cameras at varying distances and positions can provide for continuous viewing of a surgical site, and, in some embodiments, the continuous viewing can be provided without a need for repositioning cameras during surgery. For example, where tools or work obscures one or more cameras, imagery from non-obscured cameras can be utilized to provide a view of the surgical site. 
     In some embodiments, image processing can be used to track a position and/or orientation of a surgical tool. For tracking, the surgical tool can include distinguishable or identifiable coloration, patterns, markings, etc. such that the image processing system can identify the surgical tool, calculate its position within the surgical site, and/or calculate an orientation of the surgical tool. 
     In some embodiments, the image processing system receives imagery data from one or more cameras positioned on a retractor and processes this information to identify the surgical tool and prepares a video or image with a model of the surgical tool positioned and/or oriented within the image to represent the position and orientation of the surgical tool. For example, optical tracking of the surgical tool can be accomplished using cameras positioned on a frame of a retractor wherein the surgical tool includes, for example a pattern, e.g., a greycode possibly applied using laser marking with a known pattern around the tool axis. The image processing system can process the images from the cameras to identify the greycode on the surgical tool. Using this information and possibly additional information from one or more other tracking systems or stored data, the image processing system can identify a location and/or orientation of the surgical tool within the surgical site. 
     Accordingly, in some embodiments, a displayed image can be related to a position of the surgical tool. The image processing system can receive tracking information and/or it can extract position information from imagery and configure the output imagery (e.g., position or orient the image relative to a background image or other imagery being displayed) that corresponds to where the surgical tool is currently positioned. The image processing system can be configured to track movement of the surgical tool and integrate this information to smoothly track a position of the surgical tool on the display (e.g., by changing output imagery such that imagery of the surgical tool is presented, for example, as centered on the display system or has a changing location with respect to the background or wide field of view main view remains generally still). The image processing system can also change what images are displayed, for example, tiled, depending on the location of the surgical tool. The image processing system can establish, for example, a centroid of movement for the surgical tool and based on this centroid it can determine whether a movement can be ignored or followed. Such a decision can be based at least in part on dimensions of the surgical site and/or the retractor in use. In addition, the image processing system can be configured to ignore movements that are outliers compared to the centroid distribution, such as when the surgical tool is completely removed from the surgical site. 
     In some embodiments, the image processor can output imagery of the surgical site wherein the output imagery includes a rendering of the surgical tool positioned and oriented within the surgical site according to a measured position and/or orientation. In some embodiments, the rendering of the surgical tool can have a level of opacity that can vary from being completely transparent to being completely opaque and include varying levels of partial transparency/partial opacity therebetween, as described in more detail herein. In some embodiments, the surgical tool can be rendered, e.g., in a picture-in-picture, in a display, as described herein wherein the surgical tool can have a configurable level of transparency (e.g., the surgical tool can be presented as opaque or semi-transparent). By presenting the surgical tool with a level of transparency, a user can view underlying imagery of a surgical site. The transparent rendering described herein can help to overcome a problem in surgical visualization systems where a surgeon&#39;s view of the surgical site is obscured by the surgical tool. This functionality can be provided where multiple cameras acquire images of the surgical site from multiple viewpoints or using a single camera with the position of the surgical tool provided by a tracking system. To provide a rendering of the surgical tool, a computer model (e.g., a CAD model) of a surgical tool can be loaded into the surgical system during initialization or at some other point prior to surgery. In some embodiments, the user can select whether to display the rendering of the surgical tool. In some embodiments, an icon, graphic, or indicator can be provided on a graphical user interface that allows the user to control the rendering of the surgical tool, such as to choose a level of transparency and whether to display the rendering. 
       FIGS. 15 to 17  illustrate example display outputs of the image processing module, suitable for sending to a display system. In some embodiments, the image processing module can be configured to receive video from the plurality of cameras at different positions, process the received video, and output the processed video to the display. The output video can be stitched, tiled, superpositioned, or otherwise combined on the display. The arrangement and/or configuration of the output video can be automatically produced, manually configured, or both. In this way, the surgical visualization system can be configured to display video from multiple cameras for simultaneous viewing. In some embodiments, the display system can be configured to receive processed video from the image processing system and position the output video appropriately with respect to each other for display. 
     As illustrated in  FIG. 15 , the surgical visualization system can include one or more proximal cameras configured to provide a relatively wide field of view of a surgical site. This can provide a background or main view on a display showing the surgical site. The wide field perspective can provide to a surgeon a frame of reference for various areas or objects of interest to enhance a surgeon&#39;s situational awareness. In certain embodiments one camera or camera pair can be to provide the background or main view. In some embodiments, however, the image processing system can provide a wide field of view, for example, by stitching and/or morphing monocular wide field of view camera data, for example, from multiple, e.g., proximal cameras. In some embodiments, the surgical visualization system can include one or more, e.g., proximal (or distal), cameras configured to provide stereo imagery of at least a portion of the surgical site, wherein the cameras acquiring stereo imagery can have a field of view that is less than the field of view of the wide field of view cameras. The image processing system can provide stereo data from adjacent proximal (or distal) cameras or a two-dimensional sensor array with left and right portions dedicated for left and right eye (e.g., each with its own imaging optics) and can super-position the stereo data on the wide field of view or background view. Accordingly, in some embodiments, the display can include a central stereo image overlaid on a wide field of view background image providing peripheral vision information. In some embodiment the wide-field of view background or main view can be stereo and formed from images from proximal (or distal) cameras. Images from the stereo cameras can be displayed on separate displays (e.g. one for each eye) or on the same display (e.g., which is visible to the left and right eye at different times) to create a 3-D visual effect, as described in more detail herein. 
     As illustrated in  FIG. 16 , the surgical visualization system can include one or more distal cameras providing other, possibly smaller, fields of view of the surgical site, where the distal cameras are positioned further within the surgical site. In some embodiments, the distal cameras are configured to provide oblique or side video of the surgical site and can be displayed as tilted to help the surgeon visually interpret the video they provide, such as by providing depth clues to the surgeon. In some embodiments, the video received from the distal cameras can be stitched, tiled, tilted, or otherwise processed and displayed overlaying or overlaid with the video from the proximal wide field of view imagery and/or the proximal stereo imagery. 
     In some embodiments, a plurality of the distal (or proximal) cameras, if not all, are directed at substantially similar inclinations with respect to the surgical device (e.g., retractor) with which they are associated. In some embodiments, the distal (or proximal) cameras are directed normal to an axis of the surgical device. For example, the retractor may have the shape of a right circular cylindrical and have an axis through the center of the circular cross-section. The cameras may be directed toward each other and normal to this axis. Alternatively, the cameras may be directed downward into the surgical site not normal to this axis. The plurality of distal cameras, however, may have substantially similar inclinations or declinations with respect to the axis. In some embodiments, the inclination or declination with respect to the axis can be less than or equal to about 30 degrees, less than or equal to about 45 degrees, less than or equal to about 70 degrees, and/or less than or equal to about 110 degrees. In some embodiments, the inclination or declination with respect to the axis can be greater than or equal to about 0 degrees, greater than or equal to about 30 degrees, greater than or equal to about 45 degrees, and/or greater than or equal to about 70 degrees. 
     In some embodiments, a display of information from distal cameras can be activated according to criteria. For example, initially the proximal camera(s) may be activated and images produced by these proximal cameras displayed. When a tracked surgical tool is inserted into the patient and is at or near a proximal camera at a beginning of a procedure, monocular side views provided by the distal cameras can be displayed on either side of the central stereo view in the display, as illustrated in  FIG. 16 , to provide the surgeon with views of where the tool is to be placed. In some embodiments, the views provided by the distal cameras can be displayed as tiled images. Additionally as the surgeon or user proceeds deeper within the surgical site, the distal camera views can provide oblique views, and as appropriate, can be viewed in tiled or stitched form on either side of the central stereo view in the display. Cameras on the tool may also provide video that may be displayed. A central view of the display can comprise imagery from cameras on the tool or distal cameras and can be configured to switch between sources of imagery for the central view. In some embodiments, camera location information, camera calibration information, and/or area of interest distance and location can be sent to the image processing system. This information may be useful for unwrapping, purposefully distorting, electronically magnifying or de-magnifying a series of images. Such processing may enable a multi-camera viewing display to adjust various fixed camera magnifications and locations within an image. This processing may thereby assist in producing tiled or stitched images where the surgical site is substantially centrally located within a field of vision on the display. The processing may also provide an array of views from distal cameras adjacent to a stereo view from the proximal cameras. 
     Such processing may be employed as well when a user selects one or more camera views. For example, a plurality of thumbnails or windows presenting the video feed or icons representing the video feed from a plurality a cameras may be shown on the display, for example, off to the side of the screen. The user may select from these, for example, by clicking on the icon or thumbnail or enlarging the thumbnail or window. The user may also potentially move these more central video feeds and/or arrange these video feeds in some fashion such as in a manner consistent with the geometric arrangement of the camera or cameras with respect to each other and/or the retractor or surgical site. In some embodiments, when the user identifies a plurality of icons, thumbnails, and/or windows the processor automatically arranges the corresponding video feed in such a geometric arrangement. The user may select video feeds/images from a subset of the total number of cameras on the retractor and/or tool. One or more images may be used as a background over which other images are shown, e.g., as PIP or in a tiled arrangement. The user can for example identify one streaming video window, icon, or thumbnail to be used as the background image. This may be a wide field of view camera or a surgical microscope view (as discussed below). In some embodiments, multiple images are stitched together to obtain this background view. In various embodiments the background view is larger than the tiled or PIP image and may include substantially the entire view provided by the process such as at least 75%, 80%, 90%, 95% or 100% of the screen. In some embodiments, the processor selects which image to show as background. The user may for example identify a plurality of images (e.g., by selecting windows or thumbnails displayed on the display) and the processor may show as default one of those images as a background image. 
     In various embodiments, the display may show a first image or video stream or feed enlarged on the screen, for example, such as at least 75%, 80%, 90%, 95% or 100% of the screen. The user may select a second video from another camera by identifying a streaming video window, icon or thumbnail corresponding to the other camera. The user may enlarge the image from that other camera. The processor may automatically reduce the first image or remove the image altogether when the user enlarges the second image to a certain size. This threshold size may be for example least 75%, 80%, 90%, 95% or 100% of the screen. The user may set this threshold size and/or the processor may have a threshold size for this function. Similarly, the user could select a third video image by identify another camera and by enlarging the images beyond the threshold, the user could cause a window corresponding to the second image to close or be reduced to a thumbnail. The video stream window, icon, or thumbnail for that second image as well as for the first may be available for the user to identify (e.g., by clicking on or enlarging) and to enlarge as a background image. In some embodiments any of these images may be used as background for one or more other images, for example, that are each less than 75%, 80%, 90%, 95% or 100% of the screen. These smaller images may be shown PIP or tiled in front of the other image which is used as background. A wide variety of other capabilities may be integrated in the graphic user interface. In various embodiments, however, the user has the ability to select one or more cameras, represented by icons or thumbnails or windows which show video streams from the cameras, and enlarge and or reposition the images provide by those camera. The user may, for example enlarge and/or position those images more prominently and/or more centrally on the display. The user may arrange the images if images from a plurality of cameras are selected. In some embodiments the processor may automatically (at least as a default) position and/or enlarge to a specific size images that are selected by a user. In some embodiments, a user can select a first video window on a first display and send the first video window to a second display. This can make the system swap the videos such that the video that was previously displayed on the second display is displayed on the first display and vice versa. In some embodiments, this functionality is configured to provide a quick-switching functionality to easily and quickly switch between video feeds. In some embodiments, a mode can be provided wherein by selecting the first video window on a first display, the first video window is sent to a second display; however, the video on the second display remains the second display together with the first video. The user may select which mode by providing different input, for example, clicking versus double clicking, etc. 
       FIG. 19  illustrates an example configuration of proximal cameras that provide a background or main view and a stereo view.  FIG. 19  shows the camera views provided by the camera which may be disposed on the retractor and include a turning mirror such as provided by a prism (e.g., a right angle prism) or other optical element that redirected the image. Such an optical element may be a reflective surface angled, for example, at 45° or other angle with respect to the detector array of the camera.  FIG. 4C  shows an example of such an optical element configured to turn the optical path. Other types of optical elements such as prisms having multiple reflections can be used to redirect or turn the light.  FIG. 21  also shows a tubular retractor having an optical design configured to turning the optical path downward into the surgical site and yet provide a low profile. In particular, using such an optical element such as a turning mirror or prism or other optical element configured to suitably redirect the optical path, may provide the desired camera view while reducing the profile of the camera that would otherwise potentially introduce obstruction and reduce access for surgical tools to the surgical site by the retractor. 
     The background or main view provide by the camera(s) shown in  FIG. 19  can have a relatively larger field of view compared to the stereo field of view and imagery from the cameras can be displayed together (e.g., tiled, stitched, and/or via picture-in-picture). Any number of proximal wide field of view and/or stereo view cameras can be used to provide a desired image quality and display capabilities. 
     The image processing system can be configured to receive image data from proximal and distal cameras having various positions and/or orientations. The image processing module can tile these images for display wherein tiling can include outputting the images without stitching them together. The image processing system can tile the images based at least in part on a region being imaged, a field of view of the camera, camera position, a selection by a user, automated criteria, or any combination of these. A size and/or position of tiled images output to a display can be based at least in part on a field of view, a region being imaged by the camera, camera position, a relative importance of the imagery, a selection by a user, an automated placement, or some combination of these or other criteria. In some embodiments, the image processing system receives camera position and orientation information and uses this information to tile images according to regions the cameras are imaging. In some embodiments, the image processing system processes the imagery to magnify, de-magnify, distort, tilt, or otherwise transform the image prior to tiling the images for display. In some embodiments, the image processing system provides images to the display system which tiles the images on the display according to user selection and/or other criteria. In some embodiments the image processing system provides cues to the view so that the view can readily ascertain the orientation of the cameras. The images may, for example may be modified (e.g. distorted) or a symbol (e.g., an arrow) may be included to show the direction downward into the surgical site. In some embodiments, video data can be received from three or more cameras. A user can select at least two of these cameras for simultaneous viewing. The video from the selected cameras can be presented to the user and in some embodiments the image processing system can arrange and/or orient the video according to physical arrangement of the cameras, fields of view of the cameras, user configuration settings, or the like. The non-selected cameras can be configured to still provide video data to the system, and the video from the non-selected cameras can be obscured, hidden, dimmed, made transparent, or some similar effect or may be located non-centrally (e.g., placed moved off to the side or to another display) so that the video from the selected cameras is more prominent in the display. 
     The image processing system can be configured to output stereo image data using various methods. In some embodiments, images from one or more cameras designated as “left” cameras can be displayed on a “left” display or on a portion of the display system designated as a “left” portion, which are viewed by the left eye and not the right, for example, via the left ocular. Similarly, images from one or more cameras designated as “right” cameras can be displayed on a “right” display or on a portion of the display system designated as a “right” portion which are viewed by the right eye and not the left, for example, via the right ocular. Selective viewing of the left and right images by the left and right eye provides the three-dimensional effect. Accordingly, this method can provide stereo viewing on the display system for the surgeon. Similarly, as illustrated in  FIG. 15 , a divided sensor can be used to acquire stereo data. The appropriate imagery can be displayed on a left-eye display panel and a right-eye display panel. In this way, a right-eye and left-eye view is provided in real-time and the viewer fuses the images in their mind to create a 3-D effect. In some embodiments, the image processing system can process stereo data to output 3-D images to be displayed on a single monitor or display capable of presenting 3-D images. Such displays may, for example, modulate between the left and right image and selectively modulate the oculars through which the viewer sees the display, coordinating the passage of light through the left ocular and blocking of the right ocular at the same time that the display shows the left image. Likewise, the display may coordinate the passage of light through the right ocular and blocking of the left ocular at the same time that the display shows the right image. 
     In some embodiments, stereo data can be overlaid on a background or main view provided by a relatively wide field-of-view camera or cameras. The non-stereo images would be displayed at the same time by both left and right displays or/and at the same time through both left and right oculars. Accordingly, while the stereo portion of the images would be different for the left and right display or images, the non-stereo portions would be the same. 
     In some embodiments, the field of view of the stereo camera or cameras is less than total vision width (e.g., about 170 degrees horizontal and about 110 degrees vertical) and can be less than or equal to about 60 degrees, less than or equal to about 50 degrees, less than or equal to about 30 degrees, between about 30 degrees and about 60 degrees, and/or between about 50 degrees and about 55 degrees full width half maximum (FWHM). In some embodiments, the field of view of monocular cameras providing a wide field of view can be at least about 70 degrees and/or less than about 120 degrees, at least about 90 degrees and/or less than or equal to about 110 degrees, or at least about 70 degrees and/or less than or equal to about 90 degrees FWHM. 
     The image processing system can be configured to process images from a surgical tool and/or images of the surgical tool to provide output imagery that enhances or improves a surgeon&#39;s situational awareness. In some embodiments, cameras associated with a surgical tool can move during surgery and their position and/or their orientation can be transmitted to the image processing system to enable an output display of a close-up of tool-tissue interaction. This output display can be stitched with other imagery from other cameras or it can be provided as its own video stream or imagery such as picture-in-picture or via tiling. The output can be, for example, displayed as a picture-in-picture overlaid on a central scene such as the main or background view where the picture-in-picture display provides a magnified view of a targeted site. This picture-in-picture view can be enlarged or magnified to provide visual feedback to a surgeon to enhance the surgeon&#39;s ability to manipulate the surgical tool in a desired fashion. In certain implementations, an orientation of the picture-in-picture display can remain unchanged throughout the surgery, regardless of any change in orientation of the surgical tool. In such implementations, the image processor may reorient the image based on input from tracking sensors (e.g., IMUs) on the tool so that picture-in-picture image does not move as the tool is moved. In certain implementations, the orientation of the picture-in-picture display does change, for example, with rotation of the surgical tool. 
     In some embodiments, a portion of the surgical tool may be in view of cameras positioned on the retractor during surgery. To reduce or eliminate obscuration of the surgical site due at least in part to the surgical tool, the image processing system can process images from the cameras to output imagery of the surgical site having a variably transparent surgical tool displayed thereon rather than including imagery of the surgical tool itself. For example, a portion of the surgical tool within view of the cameras can be rendered based on CAD models of the tool and 6-degree of freedom tracking information. By providing this variably transparent tool representation, a trajectory of the surgical tool can be monitored on the display system while the tool is being manipulated. In some embodiments, the image of the tool as seen by cameras can be colored in a partially transparent manner when displayed over other views provided by other cameras. The transparency will permit the other camera views to show through and reduce the obscuration provided by the tool. 
     In some embodiments, a camera view from a side that is left (right) of the surgical tool, from the point of view of the surgeon, can be used to reduce or eliminate tool obscuration for right-handed (left-handed) surgeons. This can be done to reduce tool obscuration which can cause retinal rivalry where the surgeon is right-eye (left-eye) dominant. Accordingly, in some embodiment, the user can select a mode, in this example, right hand mode (or left hand mode) and the image processing modulate may select which images to display based on that mode selected without the user necessarily specifying the cameras and/or images. 
       FIG. 17  illustrates an example display incorporating image data from proximal and distal cameras, as in  FIG. 16 , along with a picture-in-picture view of imagery acquired by a camera associated with a surgical tool. The image information from cameras associated with the surgical tool can, for example, be displayed overlaid on the main or background image provided by proximal wide field of view cameras. The picture-in-picture presentation can be in stereo or it can be monocular. In some embodiments, the picture-in-picture display is presented with a different magnification or zoom than the background or main view. In some embodiments, the picture-in-picture display has a level of opacity that allows the surgeon to view image data displayed underneath the picture-in-picture. 
     As discussed above, the cameras can be arranged and positioned to produce an image of the surgical field having vertical and horizontal directions the same or substantially the same as the vertical and horizontal directions that the surgeon associates for the surgical field. If the cameras are not positioned correctly, the image of the surgical field may be rotated on the display such that vertical and horizontal directions on the display do not correspond to vertical and horizontal directions that the surgeon associates with the surgical field as oriented for the surgical procedure. Incorrect positioning or excessive rotation (e.g., greater than 30°) of the surgical field with respect to the vertical and horizontal directions on the display can decouple hand-eye coordination. 
     Accordingly, in various embodiments, the image processing system can display images such that the horizon of the displayed images from the cameras on the retractor remains substantially parallel to the horizon of the acquisition system. In some embodiments, the image processing system rotates and/or repositions acquired images when displays such that the display horizon is parallel to the acquisition horizon which is typically perpendicular to the gravity vector, or in other words, the acquired images are displayed in an upright orientation relative to the horizon. As illustrated in  FIG. 20A , in some embodiments, the surgical visualization system includes a horizon mechanism that rotates to maintain a substantially consistent orientation relative to gravity such that acquisition and display horizons remain substantially parallel with little or no image rotation performed by the image processing system. In some embodiments, the horizon mechanism can include a camera ring associated with the retractor that can be rotated while viewing a sterile alignment and/or white balancing target to address any alignment issues before performing surgery. In some embodiments, imagery from cameras associated with a surgical tool can be rotated when the tool is rotated or they can remain horizontal upon tool rotation, as illustrated in  FIG. 20A . 
     In some embodiments, a visual axis line (the line that is perpendicular to both the visual axes of the surgeon&#39;s eyes) can be parallel to a stereo sensor line (the line perpendicular to both the optical axes of optical sensors providing stereo information). For example, if a z-axis is defined as an axis that generally runs along a spine of a standing surgeon (e.g., the z-axis is parallel to the gravity vector), the visual axis line and the stereo sensor line can be configured to be parallel lines when they are projected onto a plane perpendicular to the z-axis. This allows the visual axis line, the stereo sensor line, or both to rotate about the x-axis, the y-axis, or both (in a Cartesian coordinate system) while maintaining a desired parallel relationship. This parallel relationship can be useful to reduce disorientation of the surgeon when viewing imagery on a display where the imagery is displayed such that the z-axis of the surgeon and the z-axis of the displayed imagery are parallel. In some embodiments, as illustrated in  FIG. 20B , the sensors can be oriented on retractor blades in a parallel fashion (in  FIG. 20B , gravity would be a vector pointing into the page). The sensors on the top and bottom blades can be configured to provide monocular or stereo imagery, and the sensors on the side blades can be configured to provide monocular imagery. In some embodiments, the top and/or bottom blades as well as at least one of the side blades can be configured to provide stereo imagery. In various of these embodiments, the left and right camera apertures for the side blade(s) are arranged to provide consistent stereo perspective as provided by top and/or bottom blades. Accordingly, as shown in  FIG. 20B , the pair of left and right camera apertures may be aligned in a different direction with respect to the length of the retractor blades for the side retractors as opposed to for the top and bottom retractors. Similarly, the left and right camera apertures are aligned in a different direction with respect to the central axis into the surgical site (into the figure) as defined by the retractor as compared to the orientation of the left and right camera apertures for the top and bottom retractors. In particular for the top, bottom and sides, the left and right camera apertures are arranged along the horizontal direction to provide a consistent stereo perspective for each of the retractors. The result, however, is that the cameras are oriented differently on the top and bottom retractor blades as compared to the side retractor blades. 
     This configuration for the top and bottom retractors can be advantageous when it is desirable to conserve space and provide more space for tools in the pathway to the surgical site provided by the retractor. Folded stereo top and bottom cameras, as shown in  FIG. 20B , provide a relatively low profile. Stereo pairs on side cameras cannot typically be made small due at least in part to the horizontal axis being 90 degrees relative to the top and bottom configuration. In some embodiments, side cameras could be made relatively small, if there are no prisms for folding or deviating a line of sight, which can be useful in the 90 degree or opposing view configuration. 
     In various embodiments, the sensors can be oriented such that their optical axes are normal to gravity, parallel to gravity, or have another inclination or declination relative to gravity, as described herein. In some embodiments, the display system can be movable (e.g., using an articulating arm) to allow the surgeon to move relative to the patient, as described herein. The display system can be configured to have motion sensors such that this movement is detected and an alert or warning is provided indicating to the surgeon or other operator that the retractor should be repositioned to maintain a desirable parallel orientation between the surgeon, the display, and the cameras. 
     In some embodiments, the image processing system can provide a default, predetermined, or appropriate image rotation and/or position based at least partly on a position and/or field of view of the camera which is providing imagery. Comparing  FIGS. 20C and 20D , cameras 1-4 provide imagery of an object to a display system. In  FIG. 20C , the image processing system tiles the images from the four cameras in locations on the display corresponding to their locations on the retractor or field of views. The locations on the display can be based at least partly on the positions or field of views of the cameras relative to the object, surgical field or site, to the surgeon, or to another reference frame that is automatically or manually selected. In some embodiments, cameras at opposing positions can be configured to provide stereo video data. For example, Camera 1 and Camera 2 can include cameras configured to acquire stereo data. Additionally, in some embodiments, Camera 1 and Camera 2 can be rotated relative to one another, for example, by 180 degrees. In some embodiments, Camera 3 and Camera 4 can be configured to provide panoramic and/or monocular video. Similar to Cameras 1 and 2, Cameras 3 and 4 can be rotated with respect to one another. In  FIG. 20D , the image processing system positions the tiled images on the display as in  FIG. 20C , but the image processing system also performs a rotation on the imagery (e.g. rotation of the separate images). The rotation can be configured to provide a uniform direction for the displayed object, as illustrated in  FIG. 20D . For example, imagery from camera 1 can be rotated 180 degrees, imagery from camera 2 can be presented without rotation, camera 3 can be rotated 90 degrees, and camera 4 can be rotated 270 degrees. As a result, the object presented in the display will have the same relative orientation. This can facilitate the understanding of the observer as the object has the same orientation in the display even though it is viewed from different viewpoints. In other embodiments not all the images are reoriented. In various embodiments, for example, the images from the video images from camera 2 are rotated 180° with respect to camera 1, or vice versa while the images from camera 3 and 4 are not rotated. In other embodiments, the video images from camera 2 are rotated 180° with respect to camera 1, and the video images of camera 3 is rotated by 90° with respect to camera 4 or vice versa. Other variations are possible. Generally, maintaining camera 2 unrotated may increase the situational awareness or reduce confusion when using the surgical visualization system as camera 2&#39;s horizon may closely align with the horizon of the operator. In some embodiments, camera 2 can provide video data that is enlarged and displayed as a background image for the other three tiled videos from the other cameras. These concepts may apply to more or less number of tile camera views. 
     In some embodiments, the image processing system calculates the position and/or rotation for the displayed images based at least partly on tracking data, information provide with the camera such as memory (EEPROM) storing information regarding that camera, user selection, or a combinations thereof. In some embodiments, the image processing system can perform a default or predetermined rotation and/or positioning of the displayed image based on configuration settings or a configuration of the retractor cameras (e.g. positions and/of field-of-views). In some embodiments, the user can select the position and/or rotation of the tiled images using video windows, icons or thumbnails presented on a graphical user interface. The thumbnails can be rotated reduced-size images that correspond to the video being provided by the retractor cameras. The video windows, icons or thumbnails can remain unrotated, in some implementations, for example, to provide cues as to perspective of the cameras or can be rotated. The rotation of the video in this fashion, as illustrated in  FIG. 20D , can be applied to monocular or stereo imagery. As described above, in various embodiments, the image processor can arrange the videos from the cameras selected by the user for example in an arrangement consistent with the geometrical arrangement of the cameras or their fields of view. The user can, for example, select images or video feeds from cameras by selecting video windows, icons or thumbnails. The processor can automatically enlarge and reposition the videos from these cameras, for example, to improve the ability of the surgeon to see the detail in the video. In some embodiments the processor moves the video to a more central position on the display or to a desired position on the display. In some embodiments, the user enlarges the video manually and/or repositions the video manually, for example, by enlarging the video window, thumbnail or icon and/or repositioning it. Again, the user may enlarge the video to improve ability to see detail in the video and may move the video in a more central position or may move the video to a desired location. In some embodiment, reduced size video windows, thumbnails or icons are on a first touch screen display used as a graphic user interface for the nurse or technician and possibly the surgeon, and the enlarge repositioned images are on a second display, such as the binocular display viewed extensively by the surgeon throughout the procedure. The video streams can thus switch from one display to another in various embodiments depending on the surgeons interested in viewing the display while for example performing a detailed examination of the surgical site, performing tool manipulations in the surgical site, acting upon the surgical site, etc. 
     In some embodiments the group of videos can be rotated as one. For example, the processor provides that a plurality of videos such as those tiled videos shown in  FIGS. 20C and 20D  may be rotated as one. In some embodiments, the user initiates and/or controls the rotation of the videos as a group, although the processing system may do so as well. In some embodiments, the processing system automatically rotates one or more of the individual videos in the group of tiled videos when the group as a whole is rotated. 
     As shown in  FIGS. 20C and 20D , the tiled videos can be configured to be displayed on a background videos that is provided by another camera system, a mosaic of videos, auxiliary cameras, cameras on a surgical tool, a static image, or the like. In various embodiments, as shown in  FIGS. 20C and 20D , tiled videos are spread out, for example, presented more toward the a periphery of the display or in a manner such that the a vacancy is provided in the center of plurality of images and/or of the display. This can allow, for example, for a presentation of an enlarged picture-in-picture videos to be displayed (e.g., a tool image) and/or may be consistent with the concept of a retractor providing an open central pathway providing access to the surgical site. In some embodiments, the surgical tool image can be displayed with the tiled videos from retractor cams and/or with video provided by an auxiliary camera that provides a surgical microscope view, as described herein. In some embodiments, the surgical tool videos can be displayed in a central region overlaid on the tile videos and can have a relatively fixed orientation or the orientation of the video can be adjusted with videos in the tool&#39;s orientation. For example, the surgical tool video can be presented on the display without undergoing any rotation with the image processing system. In some embodiments, the surgical tool camera may present the tool in a fixed position relative to the field of view of the surgical tool camera which will provide orientation cues. 
     Display 
     Embodiments described herein can provide a display having a form factor and articulated arm as well as binocularity that is familiar to surgical microscope users without the associated disadvantages. In contrast to the typical surgical microscope apparatus or endoscope, however, various embodiments described herein can avoid the need for operator control of the optical focus, positioning, distance to target, etc. Embodiments described herein can, for example, provide visualization that is generally always in focus, oriented, and provides a view of virtually the entire surgical field, emphasizing current task space as desired. Embodiments described herein may also avoid the glare/ambient light and view angle problems associated with looking at conventional endoscope flat panel, TV-like displays. Embodiments described herein may also provide a display that is near the surgical site and near the surgeon and oriented to be convenient for the surgeon to view the display while performing surgery, e.g., without having to turn substantially away from the surgical site to view the display. Embodiments described herein can also avoid the vertigo/nausea and weight/bulk on a user&#39;s head, problems which are typical with head-mounted displays. 
     Additionally, embodiments described herein can provide displays having advantages over current robotic-assisted surgery systems, such as the DaVinci. In contrast to the DaVinci approach, embodiments described herein provide a display at the patient, rather than at a remote location across the room. As noted above, embodiments described herein may provide a display that is similar to the operating microscope to which surgeons are familiar and comfortable but more compact and lighter. By providing a display at the patient site, the user is able to visualize body, wound, respiratory movement, endotracheal tube security, IV tubing, central lines, EKG leads, sterility/draping, and other relevant features easily throughout the surgical procedure. In contrast to an operating microscope where many optical elements are aligned from objective to ocular in a conventional manner, the display can be of a more compact form, allowing the surgeon to look under or over the display. Additionally, due to the electronic nature it can be folded in an advantageous manner to allow more working space for the operator&#39;s hands and tools. 
     The composite image described above can be displayed in a variety of ways. For example, a flat screen, curved (e.g. hemispherical) screen, or projection directly into a user&#39;s eyes or glasses may be used. In the case of a flat screen, the display can be, for example, two Ortus Technology, 4.8-inch color LCDs, arranged in landscape orientation with a resolution of 1920×1080, RGB 458 ppi, viewing angle of 160 degrees (horizontal/vertical), color depth of 16.77 million colors, NTSC 72% color gamut, with LED backlight. Different displays in respective left and right optical paths to the eyes can provide stereo and 3-D. A half-silvered mirror beam splitter or multiple mirrors or reflective surfaces (e.g. Wheatstone configuration) can be used to combine images from the displays or portions thereof and/or arrange them adjacent to each other for left and right eye viewing. 
     In some embodiments, an array of multiple, side-by-side emissive OLED displays in Wheatstone or over/under configuration may be used. In some embodiments, a LCoS pico projector array with rear screen or front screen projection may be used to achieve sufficient field of view (“FOV”) and pixel density. Another option is to employ an array of OLEDs projecting on a 3M rear screen. OLED pico projectors have limited brightness, but in configurations in which the display is set up similar to a microscope as discussed below, where little or no ambient light is introduced, the limited brightness presents less of an obstacle. A wide variety of configurations are possible. 
     As referred to above, the display can be enclosed to eliminate stray light, for example in a manner similar to a standard microscope viewing platform. In particular, the use of a microscope-like display can avoid problems associated with insufficient brightness, as the oculars may block out ambient light. 
     As illustrated in  FIGS. 1 and 21B , the surgical visualization system  1  can include a viewing platform  9  with oculars  11  for the surgeon to use to view a display of videos acquired with the various cameras in the surgical visualization system.  FIG. 21B  illustrates an embodiment of the surgical visualization system  1  having an articulating arm  7   b  for an imaging system  18  that can be configured to provide video similar to a direct-view surgery microscope. The imaging system  18  can be configured, then, to provide a surgical imaging system configured to provide an electronic microscope-like view that can comprise video of the work site or operational site from a position above the site (e.g., about 15-45 cm above the surgical cite) or from another desired angle. By decoupling the imagers  18  from the display, the surgeon can manipulate the surgical imaging system to provide a desired or selected viewpoint without having to adjust the viewing oculars. This can advantageously provide an increased level of comfort, capability, and consistency to the surgeon compared to traditional direct-view operating microscope systems. In some embodiments, as described herein, the imagers  18  can be located on the viewing platform  9 , on a dedicated articulating arm  7   b , on a display arm  5 , or detached from other systems. The imagers  18  can comprise a camera configured to be adjustable to provide varying levels of magnification, viewing angles, monocular or stereo imagery, convergence angles, working distance, or any combination of these. 
     The viewing platform  9  can be equipped with wide field-of-view oculars  11  that are adjustable for refractive error and presbyopia. In some embodiments, the oculars  11 , or eyepieces, may additionally include polarizers in order to provide for stereoscopic vision. The display can be supported by an articulated arm  7  or  7   b , such that it may be positioned for the user to comfortably view the display while in position to perform surgery. 
     In some embodiments, the image processing system and the display system are configured to display imagery placed roughly at infinity to reduce or eliminate accommodation and/or convergence when viewing the display. An optical display system comprising a pair of oculars, objectives, and a display resembling a binocular microscope can be employed. The display devices such as liquid crystal displays can be imaged with the objective and the pair of oculars and imaging optics within the display. The objective and the oculars and imaging optics within the display can be configured to produce an image of the displays at infinity. Such arrangements may potentially reduce the amount of accommodation by the surgeon. The oculars can also have adjustments (e.g., of focus or power) to address myopia or hyperopia of the surgeon. Accordingly, the surgeon or other users may view the displays through the oculars without wearing glasses even if ordinarily prescription glasses were worn for other activities. 
     In some embodiments, the viewing platform can include one or more imagers configured to provide electronic microscope-like imaging capabilities.  FIG. 21C  illustrates an example surgical imaging system  51  attached to an articulating arm  7 , the system  51  including one or more cameras  18  mounted on a viewing platform  9 . The cameras  18  can be configured to provide imagery of a worksite. The image data can be presented on a display that the user can view using oculars  11  mounted on the viewing platform  9 . This design can be used to mimic other direct-view microscopes, but it can also be configured to provide additional capabilities. For example, the surgical imaging system  51  can be configured to have a variable working distance without adjusting the viewing platform  9  or the articulating arm  7 . The surgical imaging system  51  can be configured to provide image processing capabilities such as electronic zooming and/or magnification, image rotation, image enhancement, stereoscopic imagery, and the like. Furthermore, the imagery from the cameras  18  can be combined with imagery from retractor cameras, from surgical tool cameras, and the like as described in greater detail herein. 
     In some embodiments, for example, the displays provide video windows, icons and/or thumbnails to identify cameras  18  that provide a surgical microscope view as well as cameras mounted on the retractor. The user may for example select to display either the surgical microscope view or one or more views from the retractor. The user interface may provide an easy way to switch back and forth that may be easier than moving video windows or icons. An icon, button, or other graphic may enable swift switching by the user back and forth between the two types of views. Such flipping back an forth may be useful at the early stage of the procedure when the incision is being made and the retractor is being introduces as well as when tools are being introduce into the surgical site. Flipping back and forth may similarly be useful at the end of the surgical procedure with extraction of items from the surgical site. However, switching back and forth may also be useful in the middle of the procedure. 
     In some embodiments, both the surgical microscope view as well as the retractor camera views may be simultaneously shown. For example, the surgical microscope view may be used as a large wide field of view background and one or more retractor camera views may be use as the foreground for example in PIP or tiled format. 
     Although the discussion and drawings such as  FIGS. 1 and 21B  consider images from retractors, numerous embodiments may involve at least one auxiliary camera  18  and one or more other cameras that are not disposed on retractors but are disposed on other medical devices. These medical devices may include devices introduced into the body such as endoscopes, laparoscopes, arthroscopes, etc. Accordingly, one or more displays such as the at least one display included in the viewing platform  9  may be used to provide a surgical microscope view using one or more cameras such as the auxiliary camera(s)  18  as well as to display views from one or more cameras located on such medical devices other than retractors. In some embodiments, cameras from a variety of sources, e.g., retractors, surgical tools, and other medical devices, in any combination, may be viewed on the display(s) on the surgical platform together with the surgical microscope view from the auxiliary cameras  18 . As discussed above, various embodiments provide the ability to switch between the surgical microscope views and the views provide by cameras associated with other medical devices. Alternatively, the images from the auxiliary camera(s)  18  can be viewed simultaneously with camera view provided by cameras disposed on other medical devices. In some such embodiments, the surgical microscope view may be displayed as a wide field of view background view or main view with other views in the foreground or tiled thereon. As described herein, the displays may provide 3D thus any of the images and graphics may be provided in 3D. 
     In various embodiments a virtual touchscreen may be provided by the auxiliary cameras  18  or other virtual touchscreen cameras mounted to the viewing platform  9 . Accordingly, in some embodiments a user may provide a gesture in the field of view of the auxiliary cameras and/or virtual touchscreen cameras and the processing module can be configured to recognize the gesture as an input. In some embodiments, this camera view can be simultaneously displayed in conjunction with icons, buttons, thumbnails, or other graphics for which gestures may be coordinated to permit the user to provide input. For example, the display(s) in the viewing platform  9  may provide an icon or thumbnail as well as views from the auxiliary camera  18  which show hand gestures or gestures made with a surgical tool held by a surgeon. The surgeon may for example identify a video window, thumbnail, or icon with a gesture of a surgical tool and activate the view of a particular camera such that the view of that camera is enlarged on the screen. In some embodiments, a graphic representation of the surgeon&#39;s hand is shown in the display when the surgeon&#39;s hand is in the field of view of the virtual touchscreen camera(s). In some embodiments, the virtual touchscreen can mimic a multi-touch display, allowing the surgeon to manipulate objects in the virtual environment with their hands and/or fingers. Although the virtual display has been described in the context of the auxiliary cameras  18 , other cameras, e.g., virtual reality input cameras, possibly in addition to the auxiliary cameras  18  may be used. These cameras may be disposed on the viewing platform  9  or elsewhere, such as the additional articulated arm  7   b  shown in  FIG. 21B . In some embodiments, a user may provide a voice command and the processing module can be configured to recognize the voice command as an input. Providing the virtual touch screen can help to create an immersive display experience for a user as it may not be necessary for the user to look away from the display to accomplish a majority of the tasks to be done during a surgical procedure. 
     As described herein the displays may provide 3D thus the virtual reality interface may appear in 3D. This may increase the immersive quality of the viewing experience, enhancing the detail and/or realistic presentation of video information on the display. 
     In some embodiments, as illustrated in  FIG. 21D , the surgical imaging system  51  includes an isocenter positioning system  52  attached to the viewing platform  9 . The isocenter positioning system  52  can include a single track or guide configured to move and orient the cameras  18  such that they are substantially pointed at a single point  53 , the isocenter. In some embodiments, a second track or guide can be attached to the first guide in an orthogonal manner to provide movement along 2 dimensions while substantially maintaining the pointing angle towards the isocenter  53 . Other configurations can be used to provide isocenter pointing capabilities, such as articulating arms, electro-mechanical elements, curved friction plates, etc. In some embodiments, as illustrated in  FIG. 21D-2 , the imaging system is configured to move in an isocenter manner. This can be used to enhance dexterity of the user of the system because hand-eye coordination is increased or maximized. Such enhanced dexterity can be vital for prolonged and/or difficult surgery. In the displayed embodiment, the horizons of the acquisition systems are configured to be horizontal to match the horizon of the display system and the user. As shown in  FIG. 21D-2 , in various embodiments, a stereo imaging system may be maintained in a horizontal configuration as it is moved across a range of locations to avoid confusion for the user viewing the video from the stereo camera. By maintaining a common relative horizon between the display and the acquisition system, the user can relatively easily translate hand motion to manipulation of objects in the display, which may not be the case where translation of the acquisition is accompanied by a relative rotation between the display and the acquisition system. 
     In the embodiments illustrated in  FIGS. 21D and 21D-2 , the isocenter assemblies can be a part of the display system or a separate, independent system. For example, the viewing platform  9  can be mounted on a separate articulated arm from the cameras  18 . Thus, the display and the image acquisition of the surgical imaging system can be decoupled, similar to the embodiment illustrated in  FIG. 21B . By decoupling the isocenter cameras  18  from the display ergonomic benefits are provided such as, for example, the surgeon does not need to be looking through binoculars for an extended period of time or at an uncomfortable position or angle. In various embodiments, a common relative horizon for both the display and the acquisition system is also employed to avoid confusion for the user viewing the video from the stereo camera as stated above. 
     In some embodiments, the distance between the surgical site of interest and the imagers, e.g., the working distance, can be at least about 20 cm and/or less than or equal to about 40 cm, at least about 10 cm and/or less than or equal to about 50 cm, or at least about 5 cm and/or less than or equal to about 1 m. 
     The user can interact with the surgical imaging system  51  to select a working distance, which can be fixed throughout the procedure or which can be adjusted at any point in time. Changing the working distance can be accomplished using elements on a user interface, such as the graphical user interface described herein with reference to  FIGS. 24 and 24B , or using physical elements such as rotatable rings, knobs, pedals, levers, buttons, etc. In some embodiments, the working distance is selected by the system based at least in part on the cables and/or tubing being used in the surgical visualization system. For example, the cables and/or tubing can include an RFID chip or an EEPROM or other memory storage that is configured to communicate information to the surgical imaging system  51  about the kind of procedure to be performed. For an ENT/Head/Neck procedure, the typical working distance can be set to about 40 cm. In some embodiments, the user&#39;s past preferences are remembered and used, at least in part, to select a working distance. 
     In some embodiments, gross focus adjustment can be accomplished manually by positioning the cameras  18  and arm  7 . The fine focus adjustment can be done using other physical elements, such as a fine focusing ring, or it can be accomplished electronically. 
     In some embodiments, the magnification of the surgical imaging system  51  can be selected by the user using physical or virtual user interface elements. The magnification can change and can range between about 1× and about 6×, between about 1× and about 4×, or between about 1× and about 2.5×. Embodiments may be able to change between any of these such as between 2.5× and 6× or between 2.5× and 6×. Values outside these ranges are also possible. For example, the system  51  can be configured to provide magnification and demagnification and image inversion, with a range from about −2× to about 10×, from about −2× to about 8×, from about −2× to about 4×, from about −0.5× to about 4×, or from about −0.5× to about 10×. The surgical imaging system  51  can be configured to decouple zoom features and focus adjustments, to overcome problems with traditional operating room microscopes. In some embodiments, the surgical visualization system  51  can be used to provide surgical microscope views. In some embodiments, the surgical imaging system  51  can decouple instrument myopia by providing an electronic display instead of a direct view of a scene. The electronic displays can be configured to be focused at varying levels of magnification allowing the user to view the displays without adjusting the oculars between magnification adjustments. Moreover, in various embodiments, the oculars can be configured to provide continuous views at infinity. In some embodiments, however, the principal user of the surgical imaging system may select an accommodation level for the oculars, rather than using a relaxed view provide by the electronic displays. The electronic displays, in various embodiments, however, can remain in focus and the ocular adjustments do not affect the focus of the various video acquisition systems. Thus, adjustments by the principal user do not affect the views of the other users of the system viewing, for example, other displays showing the video, as the cameras/acquisition systems can remain focused. In some embodiments, the surgical imaging system  51  can be focused at a relatively close working distance (e.g., a distance with a relatively narrow depth of field) such that the image remains focused when moving to larger working distances (e.g., distances with broader depth of field). Thus, the surgical imaging system  51  can be focused over an entire working range, reducing or eliminating the need to refocus the system after magnification or zoom adjustments are made. 
       FIGS. 21E and 21F  illustrate an embodiment of the surgical imaging system  51  having an optical system  53  mounted under the viewing platform  9 . As illustrated, the optical components are shown as free-standing to show the structure of the components, but in practice the optical components  53  will be mounted within or on a structure attached to the viewing platform. In some embodiments, the optical system  53  and/or the cameras  18  (discussed above) can be modular and can be selected and swapped for use with the surgical imaging system  51 . 
     The optical system  53  is configured to provide stereo image data to the imaging system  51 . The optical system  53  includes a turning prism  54  to fold the optical path underneath the viewing platform  9  to decrease the physical extent (e.g., length) of the imaging system under the viewing platform  9 . 
     In some embodiments, the optical system  53  comprises a Greenough-style system wherein the optical paths for each eye have separate optical components. In some embodiments, the optical system  53  comprises a Galilean-style system wherein the optical paths for each eye pass through a common objective. The Greenough-style system may be preferable where imaging sensors are being used to capture and convey the image data as compared to the Galilean-style system. The Galilean system can introduce aberrations into the imagery by virtue of the rays for each eye&#39;s optical path passing through a periphery of the objective lens. This does not happen in the Greenough-style system as each optical path has its own optics. In addition, the Galilean system can be more expensive as the objective used can be relatively expensive based at least in part on the desired optical quality of the lens and its size. 
     As shown in  FIGS. 21E and 21F , the optical system  53  can include two right-angle prisms  54 , two zoom systems  55 , and two image sensors  55 . This folding is different from a traditional operating room microscope because the optical path leads to image sensors rather than to a direct-view optical system. 
     In some embodiments, the optical system  53  can have a relatively constant F-number. This can be accomplished, for example, by varying the focal length and/or aperture of the system based on working distance and/or magnification. In one embodiment, as the focal length changes, the eye paths can move laterally apart (or together), the prisms  54  can rotate to provide an appropriate convergence angle, and the apertures can change their diameters to maintain the ratio of the focal length to the diameter a relatively constant value. This can produce a relatively constant brightness at the image sensor  56 , which can result in a relatively constant brightness being displayed to the user. This can be advantageous in systems, such as the surgical visualization systems described herein, where multiple cameras are being used and changing an illumination to compensate for changes in focal length, magnification, working distance, and/or aperture can adversely affect imagery acquired with other cameras in the system. In some embodiments, the illumination can change to compensate for changes in the focal length and/or the aperture so as to provide a relatively constant brightness at the image sensors  56 . 
     The optical assembly  53  can include a zoom system  55  configured to provide a variable focal distance and/or zoom capabilities. A Galilean-style stereoscopic system generally includes a common objective for the two eye paths. When this optical system is imaged with image sensors  56 , it can create aberrations, wedge effects, etc. that can be difficult to compensate for. In some embodiments, the surgical imaging system  51  can include a Galilean-style optical system configured to re-center at least one of the stereo paths to a central location through the objective lens, which can be advantageous in some applications. 
     In some embodiments, the real-time visualization system utilizes a Greenough-style system. This can have separate optical components for each stereo path. The optical assembly  53  can be configured to provide variable magnification and/or afocal zoom and can be configured to operate in a magnification range from about 1× to about 6×, or from about 1× to about 4×, or from about 1× to about 2.5×. 
     The distal most portion of the Greenough assembly  53  can be similar in functionality to an objective lens of a typical, direct-view operating room microscope with the working distance set approximately to that of the focal length. The working distance, and in some implementations the focal length, can be between about 20 cm and about 40 cm, for example. In some embodiments the work distance may be adjustable from 15 cm to 40 cm or to 45 cm. Other values outside these ranges are also possible. In some embodiments, the surgical imaging system  51  includes an opto-mechanical focus element configured to vary the focal length of a part of the optical assembly  53  or the whole optical assembly  53 . 
       FIGS. 21G-21K  illustrate embodiments of optical assemblies  53  for use in a stereoscopic surgical imaging system, such as those described herein with reference to  FIGS. 21E-F .  FIG. 21G  illustrates a side view of an example optical assembly  53  configured to use a turning prism  54  to fold an optical path from a tissue  57  to a sensor  56  along a lens train  55  that is situated near or adjacent to a viewing platform  9 . This can advantageously provide a relatively long optical path in a relatively compact distance. 
       FIG. 21H  illustrates a front view of an embodiment of an optical assembly configured to change a convergence angle in a stereoscopic imaging system. The prisms  54  can be the turning prism  54  illustrated in  FIG. 21G . The prisms  54  can be configured to rotate to change a convergence angle, and as a result, a convergence point and/or a working distance. The working distance, which can be a distance from the prisms  54  to the target  57  (e.g., tissue) can be user-selectable or adjustable. In various embodiments, with increased working distance to the target  57 , the convergence angle can decrease. Conversely, when the working distance gets smaller, the convergence angle can increase (e.g., θ1&gt;θ2). This can be advantageous where the lens path  55  is fixed and the working distance is adjustable. The stereo imagery can then be viewed on the display  59  by a user. 
       FIG. 21I  illustrates a front view of an embodiment of an optical assembly  53  that is configured to maintain a substantially constant convergence angle. The optical assembly  53  can include two prisms  54   a  and  54   b  for each optical path, wherein the prisms  54   a ,  54   b  can move and/or rotate. For example, when the working distance decreases the first set of prisms  54   a  can rotate towards one another to decrease an effective distance between the second set of prisms  54   b . The second set of prisms  54   b  can, in turn, rotate to compensate for the changed angle so as to converge on the common target. The second set of prisms  54   b  can direct the light to the first set of prisms  54   a  which can then direct the light down the fixed lens paths  55  (e.g., fixed in their position relative to the viewfinder). By providing a relatively fixed convergence angle, a change in working distance may not require refocusing for the user. Maintaining a constant convergence angle, especially a comfortable angle, may reduce the strain on the user such as a surgeon performing a prolonged, arduous procedure. 
       FIG. 21J  illustrates a front view of an embodiment of an optical assembly  53  configured to provide a substantially narrow convergence angle to be able to view stereoscopic imagery through a narrow insertion tube  60  (e.g., a tube partially inserted into a body during a procedure). A similar assembly  53  can be used as described with reference to  FIG. 21I , and the convergence angle can be maintained substantially constant or at least sufficiently narrow to view through the insertion tube  60 . 
       FIG. 21K  illustrates a front view of an embodiment of an optical assembly  53  configured to provide a substantially constant convergence angle by moving the lens paths  55  laterally, e.g., toward or away from one another. The prisms  54  can be made to have a substantially constant orientation (e.g., no rotation for changing working distances) and compensation for changing working distance can be accomplished by translating the optical paths laterally to separate or join the optical paths. The translation of the optical paths can be accomplished using any suitable means including, for example, electro-mechanical actuators, slides, articulating arms, etc. This can simplify the optical assembly compared to the embodiments having two sets of prisms as only one set of prisms may be used when the lens paths are configured to move. 
     The embodiments of the optical assembly  53  which are configured to maintain a sufficiently narrow convergence angle can be advantageous as they allow stereo access to narrow surgical entries by allowing the angle to decrease and avoid clipping one of the stereo paths. For example, the left and right lens paths can move closer to one another and the prisms can adjust to the proper convergence angle for that distance. As another example, the left and right lens paths can remain fixed and there can be sets of prisms for each path configured to direct the light along the lens paths while maintaining a substantially constant convergence angle. In some embodiments, maintaining a constant convergence angle can be visually helpful to the user when zoom changes, e.g., because the changing depth cues do not confuse the user&#39;s eye and/or brain. In addition, constant convergence may induce less stress on the user. 
     In some embodiments, the surgical imaging systems  51  can include a fiber optic light guide (e.g. fiber optic bundle) that connects to the system  51  and that can provide illumination to the work site. In some embodiments, integrated into the body of the system  51  can be a mixing rod to reduce or eliminate imaging of the pixilated end of the fiber cable onto the surgical site. In some embodiments, the area illuminated by the system can be configured to match that of the imaging area. 
     In some embodiments, the optical assembly  53  can be sterilized by autoclave where the assembly can be made to detach from the viewing platform. In some embodiments, Hall effect switches or sensors can be used for focus and working distance adjustments. 
     The surgical imaging systems  51  can be configured to provide dual zooms, where a first zoom level is for working distance and a second zoom level is for magnification to match what a traditional operating room microscope provides. The dual zooms can be provided by the systems  51  where the optical assemblies  53  include, for example, a sensor, a camera block, a collimating block made up of a telephoto-like assembly of lenses (e.g., 5 or 6 lenses) with a zoom in front or an afocal changer (e.g., configured to adjust the magnification of each lens path&#39;s lenses), a second zoom or afocal assembly (e.g., configured to adjust the working distance), and a prism assembly that deviates the line of sight 90 degrees. Accordingly, various embodiments the surgical imaging system  51  includes one or more cameras that provide both variable work distance as well as a least partially independently variable magnification. 
     In some embodiments, the display can be a curved surface, for example either projection display or recent generation of flexible LCD or OLED displays having high-resolution (e.g., in excess of 300 ppi). A curved display may provide two advantages: the imaging optics for the display can be less complex than for flat panels, and the cone or numerical aperture of each picture element in the display can be directed towards the viewing optics and in the periphery of the display, thereby providing a brighter image less subject to vignetting. 
     In some embodiments, the display can be a volumetric display comprising two or more transmissive display panels having a single backlight wherein the transmissive display panels are stacked to provide different planes of focus for a surgeon. The transmissive displays can be active matrix liquid crystal displays (“AMLCD”) or other types of transmissive displays. The backlight can be a fluorescent lamp, LEDs, or other suitable light source. By having displays positioned in different focal planes, image data from different focal planes may be presented to the surgeon with relatively less image processing and/or compression compared to a system which combines data from multiple focal planes into a single image. In some embodiments, a number of cameras can be positioned at varying depths or having varying focal distances such that the displays at different focal planes are configured to display image data from cameras positioned or focused at different depths to create a display that assists the surgeon in identifying positions of features within displayed images. 
     The display can show, as an overlay, pre-operative CT, MR, or other 3D image datasets from, for example, conventional surgical navigation systems (e.g., the Medtronic StealthStation or Treon, Stryker Surgical Navigation System, or Brainlab, among others). In various embodiments, in addition to images, the display can additionally provide numerical data and/or text. For example, in various embodiments, the display can overlay information such as distance or tool measurements, transparent tool renderings, camera identification information (e.g., the portion of the composite image attributable to a specific optical sensor may generate an identifying border around that portion), up/down orientation, elapsed time, and/or one or more still images captured from one or more optical sensors from a previous time in the operation The tracking system can provide 5-DOF (degrees of freedom) or 6-DOF position and orientation information to conventional surgical navigation systems. Other information, graphic, alpha numeric, or otherwise, can be provided. 
     The tool image can be magnified with respect to the wide-field view image, and change in image scaling will occur as the tool is moved in and out. In some embodiments, a visual metaphor for embodiments of the display is that of a hand-held magnifying glass for inspecting and doing work on a smaller region of a larger workpiece, while seeing the larger workpiece with lower magnification (if any) in more peripheral regions of the visual field to provide situational awareness. Tool images, for example, can be superimposed on the background image thereby blocking that portion of the background image. In various embodiments, the tool images may be stereo. 
       FIGS. 22A and 22B  show examples of displaying a composite image  600  by stitching and tiling images  602   a - c . When tiled, the individual images  602   a - c  may each have a readily discernable border that is displayed against a background scene or color. 
     In the case in which the optical sensors  604   a - c  are pointed downwards or upwards within the surgical device, e.g., at an oblique angle, (for example, the sensors do not form an orthogonal ring of sensors whose chief lines of sight angles are parallel), the images may be rendered as trapezoids. For example, a keystone effect is shown in  FIG. 22B  when optical sensors  604   a - c  are pointed down with an angle, θ, relative to a surface of an object  606 . The composite image,  600 , can comprise trapezoidal images  602   a - c  tiled together without correction for the keystone effect. Trapezoids are powerful monocular clues for direction. The result may reveal the plurality of optical sensors is downwards or upwards, for example. In some embodiments, discontinuities in the tiled image  600  can provide visual cues to the operator to provide additional situational awareness. Other types of direction markings or indicators may be employed. 
     In some embodiments, it is possible for the user to reposition a single optical sensor or optical sensor pair from the array or a modular clip-on optical sensor in such an orientation that the image could not be stitched into the composite image. This image could, in some embodiments, be displayed as a picture-in-picture (PIP) overlaid in a peripheral portion of the composite image in the appropriate location. This PIP can be provided with a clear border so as to indicate that the image is not stitched into the composite image, but rather is a separate overlay. 
       FIGS. 23A and 23B  illustrate a display formed by stitching or tiled imagery from six cameras pointed inward into the surgical field between the surfaces of the retractor. In some embodiments, the cameras are positioned on retractors to image a surgical site such that there is little redundancy between sensors. The image processing module can be configured to stitch or tile imagery from the cameras to provide a relatively wide field of view of the surgical site. The differing positions of the cameras on the retractors in  FIGS. 23A and 23B  correspond to a retractor having an expanded size at a distal end and having the cameras positioned at a proximal end of the retractor ( FIG. 23A ) and a retractor having a cylindrical shape with cameras positioned at a proximal end ( FIG. 23B ). These cameras can be used to create the main or background view shown in  FIGS. 15 to 17 .  FIG. 20  discussed below includes an example retractor that may yield such a distribution of field of views. 
     Visualization Display with Movable Arm 
       FIG. 21L  illustrates a front view of an embodiment of a visualization display with a display support platform attached to a movable arm. The visualization display  5000  includes a housing  5001  and a support pole  5002  from which a movable arm  5003  extends. The movable arm  5003  can have a C-shaped configuration with a distal end  5012  and a proximal end  5013  as shown in  FIG. 21M . The movable arm  5003  can have a display  5004  mounted to the distal end  5012  of the movable arm. The display  5004  can be mounted to the distal end  5012  of the movable arm  5003  through a tilt/rotate device  5007 . The device  5007  can allow the display  5004  to be tipped, tilted, turned, and/or rotated to adjust the platform to achieve the required function and/or user preferences. In some embodiments the device  5007  can be a complex connection allowing for detailed movement, articulation, and positioning of the display. For example, the device  5007  can include one or more hinges, arms, and/or joints (e.g., ball and socket joints). In some embodiments, the movable arm  5003  at its proximal end  5013  can be attached to the support pole  5002 . In some embodiments, the support pole  5002  can be attached to the back surface  5008  of the housing  5001 .  FIG. 21Q  illustrates a perspective view of an embodiment of a visualization display  5000  with an L-shaped support pole  5002 . In some embodiments, the support pole  5002  can be an L-shaped pole with a base  5009  and a stem  5010  as shown in  FIG. 21Q . The base  5009  can attach to the back surface  5008  of the housing  5001  and can extent outward at an angle approximately perpendicular to the back surface  5008  of the housing  5001 . The stem  5010  can extend vertically from the base  5009  at an angle approximately perpendicular to the base  5009 . 
     In some embodiments, the movable arm  5003  can be attached to the support pole  5002  through an attachment mechanism. The attachment mechanism can include, for example, a pivot attachment  5005  and ring  5006 . In some embodiments, the ring  5006  can surround the support pole  5002 , preferably surrounding the stem  5010  of the support pole  5002 . The ring  5006  can rotate about the support pole  5002 , and can move vertically along the support pole  5002 , preferably along the stem  5010 . In some embodiments, a pivot attachment  5005  can be attached to the ring  5006  extending outward from the ring  5006  at an angle approximately perpendicular to the support pole  5002 . In some embodiments, the movable arm  5003  can be attached to the pivot attachments  5005 . In some embodiments, the proximal end  5013  of the movable arm  5003  can be attached to the pivot attachment  5005  at an approximately perpendicular angle. 
     The ring  5006  can be moved vertically along the support pole  5002 . Vertical movement of the ring  5006  can effectuate a vertical movement of the attached movable arm  5003  and the mounted display  5004 .  FIG. 21L  illustrates a front view of the visualization display  5000  showing the movable arm  5003  and the display  5004  are positioned at a vertical position near the top of the stem  5010  of the support pole  5002 .  FIG. 21N  illustrates a front view of the visualization display  5000  similar to that described in  FIG. 21L  except the movable arm  5003  and the display  5004  are positioned at a lower vertical position near the center of the support pole  5002 . The vertical movement up and down the support pole  5002  of the movable arm  5003  and display  5004  can provide for the vertical position of the display  5004  to be adjusted to achieve the desired performance or user preferences. The vertical movement of the display  5004  can allow for accommodation of a surgeon in a seated or standing position. Additionally, the vertical movement of the display  5004  can accommodate the different heights of medical professionals. In some embodiments, the ring  5006  can slide along the support pole  5002 . The ring  5006  can have a locking mechanism (not shown) to fix the ring  5006  to the support pole  5002  at the desired positioning. The locking mechanism can include, for example, a screw, a knob, a clip, clamp, pin, or any combination of these as well as any other method that can facilitate convenient locking or securing known in the art. In certain embodiments, friction between the ring  5006  and support pole  5002  can be adjusted. For example, the friction between the ring  5006  and support pole  5002  can be adjusted through use of surface features (e.g., roughness) and/or mechanical components (e.g., rubber pads or other material additions to effect a change in friction between the support pole  5002  and the ring  5006 ). 
       FIG. 21O  illustrates a top view of an embodiment of a visualization display  5000  with the movable arm  5003  in a rotated position. The movable arm  5003  as illustrated in  FIG. 21M  shows the display  5004  in a first position directly in front of the housing  5001 .  FIG. 21O  illustrates a top view of the visualization display  5000  similar to that described in  FIG. 21M , but  FIG. 21O  shows the movable arm  5003  and the display  5004  rotated to a second position, outward from the housing  5001  and the display  5004  is positioned to the side of the housing  5001 . The movable arm  5003  can rotate about the support pole  5002 , preferably rotating around the stem  5010  of the support pole  5002 . In some embodiments, the movable arm  5003  can rotate up to about 90 degrees clockwise and counterclockwise from its unrotated position or first position where the display  5004  is positioned directly in front of the housing  5001 . In  FIG. 21O , the movable arm  5003  is shown rotated about 45° degrees clockwise from its unrotated position with the display  5004  positioned directly in front of the housing  5001 . In some embodiments, rotating the movable arm  5003  about the stem  5010  can provide the user with more convenient access to the display  5004 . In some embodiments, the visualization display  5000  can contain an internal counter balance similar to surgical microscopes to allow for the rotation of the movable arm  5003  without having to compensate for the additional weight. 
     In some embodiments, the movable arm  5003  can rotate about the pivot attachment  5005 , as illustrated in  FIG. 21P . The rotation about the pivot attachment  5005  can allow for the movable arm  5003  and the display  5004  to rotate from one side of the housing  5001  to the opposite side. For example,  FIG. 21L  shows the movable arm  5003  positioned at a first position, the movable arm  5003  can then be pivoted about the pivot attachment  5005  and  FIG. 21P  shows the movable arm in a second position with the movable arm  5003  directly above the housing  5001 . The movable arm  5003  can continue to pivot about the pivoting attachment  5005  until reaching a third position as shown in  FIG. 21Q  on the opposite side of the housing from the first position. In some embodiments, the movable arm  5003  can be locked in a particular position by a locking mechanism. The locking mechanism can include, for example, a screw, a knob, a clip, clamp, pin, or any combination of these as well as any other method that can facilitate convenient locking or securing known in the art. In some embodiments, the movable arm  5003  can be locked in a particular position by a self-locking mechanism in which the movable arm  5003  can be stabilized when placed at the appropriate position without the need for a locking mechanism. In some embodiments, the rotation of the movable arm  5003  about the pivoting attachment  5005  can facilitate rotation of the movable arm  5003  and display  5004  about the support pole  5002  between one side of the housing  5001  (e.g., the left side with reference to  FIG. 21N ) and another side of the housing  5001  (e.g., the right side with reference to  FIG. 21N ). Such rotation can permit left and right handed users to adjust the position of the display  5004  and can enhance versatility in set up of the display  5004 . In some embodiments, the display  5004  can maintain the display orientation during the rotation of the movable arm  5003  about the pivoting attachment  5005 . For example, in some embodiments, the display orientation can be maintained by turning the display  5004  about the device  5007  (e.g., see  FIG. 21M ). In some embodiments the display orientation can be maintained through image processing. In addition, for use with the surgical visualization system disclosed herein, the display can be, e.g., a computer or instrument display used in other applications more generally. In theory, the applications need not be even medical although anticipate medical applications such as disclosed. 
     Graphical User Interface 
       FIG. 24  illustrates an example graphical user interface that can be used in embodiments of surgical visualization systems described herein. The graphical user interface can be used to receive user input and to display operational information to the user. In some embodiments, the graphical user interface is displayed on a dedicated monitor system separate from the display system used to display images from the cameras associated with the surgical visualization system. In some embodiments, the graphical user interface is incorporated into the same display system that displays image data from the cameras associated with the surgical visualization system, thereby providing a single display system that incorporates user interface elements and display output. In some implementations, both are used, for example to give the surgeon and a nurse or technician access to control system. 
     The GUI can be implemented on a monitor having a sterile touch screen that is accessible to a surgeon, a surgical assistant, a scrub technician, or some other user or operator. The monitor with the GUI can include connectors that provide information to the GUI about the properties and characteristics of the surgical visualization system coupled thereto. The GUI can receive tracking, position, and/or orientation information associated with cameras and surgical devices to display these in correct relative positions and orientations, for example, on a schematic retractor graphic with a 3-D field of view cone being displayed extending into the surgical site. In some embodiments, a small, real-time video window from each camera can be displayed adjacent to a camera icon or included as the icon. The GUI can be used to select one or more cameras to operate and/or to be displayed. The GUI can be used to position and/or orient each camera image on the display system and to determine a size of the displayed image and/or a selected zoom of the image. In some embodiments, if a single camera is selected for viewing the default operation is to substantially fill the display with the selected image. In some embodiments, if two or more cameras are selected for viewing the default operation is to position and orient the displayed images in correct geometric arrangement relative one to another based on the relative locations of the camera or field of views etc. relative to a retractor frame coordinate system. In some embodiments, image data from cameras associated with a surgical tool can be displayed using picture-in-picture techniques, as described herein with reference to  FIG. 17 , and overlaid on a background or main image formed from one or more proximal wide field of view cameras. The picture-in-picture image can be a separate image or video stream from the other imagery. In some embodiments, the GUI can be used to select whether image data from the surgical tool will remain rotationally constant during use or whether it will rotate with tool rotation. 
     Accordingly, in various embodiments, the GUI can include camera selection elements, positioned on the GUI where the camera selection elements can provide a real-time video preview of the imagery acquired by the camera. The GUI can provide a retractor graphic to display relative positions of cameras in the retractor coordinate system. The GUI can provide control over LEDs using LED control element. The GUI can include an orientation icon to control whether the graphics are oriented relative to gravity (as described herein), the patient, the display, the table, etc. or to not orient the graphics (e.g., present imagery from cameras without any relative and/or absolute rotation). The GUI can include an external source control so that imagery from external sources can be incorporated into the display. The GUI can include tool control elements with functionality such as described in detail below. The GUI can provide a method of controlling views on the display through manipulation of graphics on the monitor. For example, windows or thumbnails, presenting real time video from the cameras on the retractor or icons representing such real time video feed, can be moved about such as moved more centrally, arrange with respect to each other, and changed in size, e.g., enlarged, as desired. The video windows or thumbnails themselves may be images from the camera or can be associated with images from the camera. The video windows or thumbnails can be larger in some embodiments. A video camera feed can form the background of the GUI as well. The GUI can provide information to the user about a status of various components such as cameras, LEDs, tools, orientation, and the like. The GUI can be used to select whether displayed imagery, such as the background or main image from a proximal camera, should change to track a position of the surgical tool. In some embodiments, the GUI incorporates information received from a trackball interface that a user can use to control view parameters. Also, the GUI can be split up into different screens that can be selected by the user in some embodiments. 
     The graphical user interface can be used to provide tool and fluidics control functions. In some embodiments, the GUI can be used to turn a drill on or off and to control a pressure associated with the drill. Similarly, the GUI can be used to operate a power Kerrison, a power aneurysm clip applier, power forceps, bipolar &amp; tissue forceps, and/or power scissors controlling a state between on and off and controlling a fluid or air pressure associated with the tool. In some embodiments, the GUI can be used to operate optics pressure washing, changing a state between on, off, standby, or auto. The GUI can be used to control a frequency of washing and a pressure. The GUI can be used to control an air-dry functionality, changing a state between on and off and changing a pressure with which it operates. 
     In various embodiments, virtual display technology is employed for the GUI. For example, images of the user&#39;s hand or a surgical tool may be displayed with the display device interacting with other images, e.g., video windows or icons, displayed by the display device. Similarly, a motion detection system and/or gesture recognition system may be employed to capture and identify movement of the user&#39;s hand or a surgical tool and display the movement and/or gestures on the display device as well as associate those movements/gestures with input instruction. For example, using gesture control the surgeon can select cameras or imagery for viewing, zoom in on a video stream, and/or position video streams on the display. 
     In certain embodiments, for example, the viewing platform  9  shown in  FIG. 21C  with the cameras  18  mounted thereunder can employ one or more of the cameras to act as gesture recognitions cameras  18  to image the surgeon or user&#39;s hand located beneath the viewing platform. The surgeon/user can make gestures or otherwise move his or her hand, which will be imaged by the gesture recognition cameras. The gesture recognition cameras can send signals corresponding to the images of hand movement to the display device that is visible to the surgeon/user peering through the oculars. The image of the hand can be superimposed on images of graphics such as video windows, icons, buttons, etc. in the graphic user interface. The user can thus move his or her hand so that the image of his or her hand, or a representation of the user&#39;s hand, as seen through the ocular, overlaps and/or interacts with (e.g., presses, moves, grabs, etc.) graphics on the GUI presented by the display device as seen through the oculars. Additionally, image recognition and/or gesture recognition processes can be applied to the image of the moving hand to analyze the location, movement, gesture and any combination thereof to discern what instruction is being provide by the user/surgeon. In some embodiments, other types of sensors may be included to assist in identifying the location of the hand and/or the gesture being made. A wide range of configurations are possible. In some embodiments stereo or 3D views may be provided by the one or more cameras. Additionally, although the hand has been discussed as providing the recognizable gesture in this example, the system need not be so limited. 
     One advantage of a gesture recognition based GUI interface is that the surgeon&#39;s hands may have blood or other bio-materials thereon. The virtual type GUI interface reduces the amount of direct contact of the surgeon&#39;s contaminated hands with the visualization equipment and thereby reduces cleaning and/or sterilization requirements. 
     As discussed above, in some embodiments, unlike a conventional surgical microscope, the viewing platform  9  is not a direct view device where the surgeon or other user sees through the platform but is instead an indirect view device. The gesture recognition camera, however can also be used as a scene camera to view the patient and surgical site from above the patient, e.g., above the retractor by between 15-45 cm or more in some examples, as described herein with reference to  FIGS. 21C-21K . The image of the patient and the surgical site can be displayed on the display device and seen through the oculars. Even in embodiments where the gesture recognition system is not employed, one or more cameras  18  beneath the viewing platform  9  can provide views of the patient and surgical site to the display device for viewing through the ocular. In some embodiments, stereo or 3D views may be provided by the one or more cameras. 
       FIG. 24B  illustrates another example embodiment of a graphical user interface for use with the surgical visualization systems disclosed and described herein. The graphical user interface of  FIG. 24B  can be used to display a relative orientation of cameras on a retractor, showing the fields of view as cones on the display. A real-time video feed of the video coming from the respective cameras can be displayed next to or near the respective cameras or elsewhere on the GUI. In various embodiments, real-time video feeds are shown in windows having a reduced-size in comparison to the real-time video used by the surgeon to perform the tool manipulation and examine and interact with the surgical site. Accordingly, these reduced-sized windows may be sufficiently small such that the surgeon may desire to increase their size at a later time to glean sufficient detail from the video to assist in the surgical procedure. The user can manipulate the elements of the display to select cameras for viewing, for adjusting video streams on the display, identifying or verifying alignment of cameras on the retractor, import images or feeds for displaying, select and/or control surgical tools via a toolbar, and the like. 
     In various embodiments such as shown, the GUI includes a model or CAD image of each camera on a graphic, model or CAD depiction of the retractor frame with a conical FOV for each camera, wherein the FOV depiction can be based on tracking information, such as EM tracking information. In some embodiments, the user can verify a placement and/or orientation of the retractor cameras using this GUI as the GUI shows the orientation and FOV. In some embodiments, the user can manually or remotely adjust the placement and/or orientation of the retractor cameras using this GUI or other associated user interface tools. In some embodiments, the FOV displayed for the cameras can be semi-opaque or at least partially transparent to allow a user to see other elements behind the cameras to give a better sense of their relative location and orientation. 
     The GUI includes real-time video feeds corresponding to the video data acquired with the various cameras on the retractor, the surgical tool, and/or auxiliary cameras. The real-time videos can be reduced-size presentations (e.g., reduced-size windows) of the acquired video which can be manipulated to select a video stream for viewing. For example, a user can select a video feed by selecting the appropriate reduced-size window or presentation and placing it on the surgeon&#39;s binocular display (e.g., if the reduced size window is on the separate touchscreen input and display device  13 ) and/or enlarging it on the surgeon&#39;s binocular display  13  (e.g. if the reduced size window and CAD depiction of the retractor frame with a conical FOV&#39;s are on the surgeon&#39;s binocular display). 
     The GUI includes a button or element that allows a user to import imaging data from other imaging modalities. For example, a user can import CT, MR, C-arm, O-arm, and/or ultrasound images as well as images from anatomic databases. These images can be sized and positioned on the screen, similar to the video feeds from the cameras of the surgical visualization system. 
     The GUI includes a positionable tool bar which enables control of optics washing, optics drying, LED cooling, choice and control of tools, and the like. The tools which can be controlled include, but are not limited to, drill, Kerrison, bipolar forceps, scissors, aneurysm clip applier, etc. 
     The GUI can be configured to respond to multi-touch input, allowing the user to virtually manipulate objects or video with their hands. The GUI can also be configured to respond to other methods of input including, for example, voice recognition, gesture recognition, and the like. 
     The use of the GUI can be illustrated by the following example. During the course of a procedure, a binocular surgical display can show one or more real-time video feeds from one or more cameras in a size sufficient for the surgeon to glean detail, which for the sake of this example is referred to as a primary surgical view. See, for example  FIGS. 15, 16, 17, 20B, and 20D . If the user is interested in adjusting the views provided, the user can perform a designated input, via touch input, gesture, voice command, or the like to bring up the GUI illustrated in  FIG. 24B  and select a different camera for presentation. The GUI can then be presented on top of or instead of the primary surgical view (which for the sake of this example is referred to as a display configuration view). The user then manipulates the elements of the GUI of the display configuration to configure the display (e.g., by selecting cameras to view, sizing the camera views, arranging/orienting the camera views, etc.). Other functionality can be provided by the GUI, for example, the user can operate tools, import images, and the like. When finished, the display can revert to the primary surgical view which reflects the changes made by the user on the display configuration view. In some embodiments, actions taken on the display configuration can be configured to immediately trigger actions or results on the primary surgical view. For example, selecting a reduced size window showing a real-time video stream and resizing it about a threshold size can cause the display to show the primary surgical view with the selected camera view full size or enlarged on the surgical view. In this way, for example, the display can be configured to be immersive for the user due at least in part to the ability of the user to perform a majority of the desired functions without looking away from the display. 
     Transparent Rendering of Surgical Tools 
     In conjunction with the tracking information obtained as outlined above, the surgical tools can be rendered transparently or semi-transparently in the composite image. Electromagnetic tool trackers integrated with or fixed to surgical tools can provide position and orientation input to the image processor. This information can be used to enable rendering of tool images as a transparent or semi-transparent overlay on the continuous composite display. The tools can, for example, be rendered as wireframe objects, or can be shown having a ghost-like transparency. This can provide the dual benefits of both indicating the position of the tool and maintaining an unobstructed wide view of the surgical site. In some embodiments, the dimensions and shape of the various tools can be determined and catalogued prior to operation. The image processor may then associate the observed tool with the predetermined size and shape stored in a database or library of tools in order to render a wire-frame or semitransparent image of the tool. 
     Camera Cleaning 
     Positioned within the body, the surface of the cameras or optical elements, such as lenses, can become fogged or otherwise obstructed. To maintain visual clarity, the cameras can be cleansed while remaining in place within the surgical site. One approach to cleansing cameras is to provide pulses of fluid over the surface of the sensor or lens, thereby clearing any obstruction. Cleansing fluids may be, for example, distilled water, deionized water, or saline, among others. In some embodiments, these pulses may be brief, high-pressure, and low-volume. The pulse can be produced in a number of ways, for example by a diaphragm, actuated by a cam and motor in conjunction with a one-way valve. Fluid pressure can be supplied by air pressure in double spike IV bottle. A disposable diaphragm pump can be used to increase pulse pressure. In some embodiments, two pumps can be used to eliminate interruption in pulse pressure. In some embodiments, passive hydraulic amplifiers can be used to increase the fluid pressure. In some embodiments, solenoids, piezoelectric actuators, or other techniques may be used. A rolling edge diaphragm, Bourdon tube, or bellow can likewise be used to produce the pulse. In one embodiment, a reed valve can be configured to alternate between air and saline operating at the natural mechanical resonance frequency of the reed valve and associated fluid and air column dynamics. Pressure may then be maintained in the air and fluid circuits just below valve opening pressure, and an electrical signal may increase pressure until reed valve opened, thus avoiding pulsating fluid tubing. In various embodiments, the fluid can be saline or other biocompatible liquid. In some embodiments, the lens elements are configured such that a stop is affixed to a first lens element wherein the stop covers a large fraction of the first lens element. Additionally, in some embodiments, the lens elements are configured such that a first element comprises a plano window. The stop can be located behind the plano window or more lens elements and can be relatively small. In such embodiments, the light collected by the stop is correspondingly small such that the area of the plano window that should remain clean is relatively small. This configuration can facilitate cleaning the lens system. In some embodiments, the plano window is secured to the lens system using a structure that does not extend over the top of the plano window so as to not interfere with mechanisms configured to clean the lens system. For example, the plano window can have a step edge or be retained by a support member (e.g., a metal ring or an edge of the lens system housing) that extends along a side portion of the plano window without extending beyond the distal face of the plano window through which light is collected for the sensor. 
     In some embodiments, a high-pressure fluid pulse can be followed by a high-pressure pulse of air or gas in order to dry the surface of the camera or lens and prevent salt deposits or image obscuration. Sources for the high-pressure air may be, for example, hospital compressed air nitrogen systems, or compressed air or nitrogen tanks. The air pulse can be actuated similar to the fluid pulse as described above. For example, a diaphragm actuated by a cam and motor in conjunction with a one way valve may be used. In some embodiments, a Venturi effect may be used to generate the post-wash air flow. The Venturi effect depends on the size and shape of the port through which the fluid flows. In general, when a fluid flows through a constricted section of pipe, the pressure is reduced. This low pressure can draw in additional outside air and can cause air flow following the fluid pulse. As discussed in more detail below, a proportional foot pedal can control actuation of the fluid and/or air pulses. 
     In some embodiments, the flex cable may include fluidic channels to convey the air, gas, or liquid to the camera optics to provide for cleaning. Fluidic channels can also transport other fluids such as pharmaceuticals, saline for irrigation, fluorescent dyes, etc. to the surgical site. Fluidic channels can also be provided for aspiration, to provide egress of gases or liquids from the surgical site. The fluidic channel containing flex cable may be an overlay or surrounding member affixed over the electronic flex cable, thereby allowing the fluid-carrying component to be disposable, where as the electronic flex cable with integrated optics module may be sterilizable and reusable. The distal end of the fluidic flex cable can contain an outer housing that is secured over the imaging module. In some embodiments, it is the annular space and shape of the inner surface of said outer housing that directs the fluid and or fluid air pulse over the most distal surface of the optics for cleaning. 
       FIGS. 25A-C  show an embodiment wherein an irrigation pathway  403  is provided by an outer sheath  401  comprising a flex cable  405  including fluidic channel containing flex cable and a portion that covers the sensor and imaging optics  409 . The portion  402  of the sheath  401  that covers the sensor and imaging optics  409  can be shaped to provide conformal fitting yet leave a space  411  between the sheath  401  and the sensor and imaging optics  409  for air flow. A section  410  of the outer sheath  401  forward of the imaging optics can be shaped to direct the fluid across the distal surface of the lens. In some embodiments, the outer sheath  401  that delivers the fluid can be a separable assembly that can be added to or attached to the optical stack  409 . In some embodiments, the fluid is delivered in the flex cable  405  that forms part of this sheath  401 . This flex cable  405  is separate from the flex cable  407  that includes electrical connection for powering and receiving signal from the camera. In some embodiments, when the separable assembly is attached to the optical stack  409  and electric flex cable  407 , the fluidic flex cable  405  assembly sits on top of the electrical flex cable  407  and above the optical stack  409 . In some embodiments, the outer sheath  401  can be designed to snap onto the optical portion creating a seal around the optical stack  409  and then later detached. In various embodiments, the detachable sheath  401  is disposable while the imaging optics  409 , sensor, and flex wire  407  connected thereto are sterilizable. In other embodiments, a fluid nozzle can be positioned on one side of the imaging optics, with an air nozzle on the other side with no sheath. 
     In some embodiments, the outer sheath  401  at the location of the camera and imaging optics  409  includes an inner wall  412  in addition to an outer wall  414 , both shaped as concentric right circular cylinders, one inside the other. In some embodiments, the inner wall  412  which is closest to the imaging optical  409  surrounds the optical stack so as to leave a gap  411  of air between the optical stack  409  and the cylindrical inner wall  412 . This gap  411  advantageously facilitates air flow between the optical elements (e.g., lenses) in the optical stack and thereby reduce the risk of condensation forming on the optical elements. In various embodiments, the outer sheath  401  is configured so as to allow fluid to enter the outer sheath  401  and be directed over the front most surface of the imaging optics  409 . As described above, the delivered fluid can be liquid, or gas, or a combination of both. In some embodiments, the irrigation pathway  403  can also be used to deliver other fluids such as pharmaceutical and fluorescent dies. In some embodiments, the irrigation pathway  403  can be used for aspiration and fluid egress. 
     Other configurations are possible. For example, in some embodiments, the fluid can be delivered by separate fluidic channels of the same flex cable that includes the electrical power and signal lines. 
     An additional approach to cleansing optical sensors and/or lenses is to mechanically ‘squeegee’ the surface. In one embodiment, as illustrated in  FIG. 26 , a fenestrated, rotary ring  501  with silicone rubber surface that can be arranged such that it is normally positioned with holes  503  in front of the cameras  505 . This approach may be particularly useful in embodiments in which the surgical device is a tubular retractor, for example those used in minimally invasive spinal surgery. The cameras  505  can be arranged along the annulus of the retractor. The rotary ring  501  disposed over the cameras  505  may then be rotated such that silicone sweeps across the surface of the cameras  505  or lenses to clean them as a squeegee. The ring  501  may be rotated by a number of mechanisms. In the illustrated embodiment, a gear assembly  507  is disposed at the periphery of the ring  501 . In another embodiment, MEMS or pneumatically actuated individual blades may be arranged adjacent the front surface of a camera module. The blade can be actuated to sweep across the front surface in a windshield-wiper fashion or otherwise, thereby cleansing the camera. 
     Temperature Control 
     In various embodiments it may be advantageous to control the temperature of certain components of the system. For example, heating the cameras to approximately body temperature can reduce fogging effects during surgery. In some embodiments, the flexible cable and/or retractor blades can include a heater to heat the cameras. However, excessive heat—such as from LEDs or from an over-heated cameras—can damage surrounding tissue during use. Accordingly, in some embodiments a thermocouple may be included in the device. For example, a thermocouple may be disposed near the cameras and/or LEDS. In some embodiments, a thermocouple sensor can be used to provide temperature measurement and control of the heated camera or flexible cable. The thermocouple may be configured to provide feedback such that the system provides heating or cooling as appropriate. 
     Heating can be provided in a number of ways. For example, small resistive heaters may be disposed within or near the cameras and/or LEDs. In some embodiments, a metallization disposed within the retractor can provide the heating element. In some embodiments, the metallization can be a part of the flexible cable described above. Similarly, cooling can be provided in a number of different ways. For example, the fluid pulses described above with respect to cleansing of the cameras may also provide cooling effects. Accordingly, should a camera or LED become dangerously hot, a brief, high-pressure pulse of fluid may be dispensed to decrease the temperature. 
     Foot Pedal with Feedback 
     A foot pedal may be used by the operator to actuate surgical tools and/or to actuate cleansing of the cameras. For example, an operator may depress a foot pedal to initiate the pulsing of liquid followed by the pulsing of air over the surface of the cameras. In some embodiments, the liquid pulse and the air pulse may be controlled by separate foot pedals. With respect to surgical tools, a foot pedal may similarly be used for actuation. For example, a cutting tool such as scissors may be moved from an open to a closed position by depressing the foot pedal. A plurality of foot pedals may be provided, each associated with a different surgical tool. In some embodiments, a left foot pedal can provide control of a surgical tool that would manually be controlled by the operator&#39;s left hand, and a right foot pedal can provide control of a surgical tool that would manually be controlled by the operator&#39;s right hand. 
     In some embodiments, the foot pedal may actuate the device proportionally. For example, the degree to which the foot pedal is depressed can control the amount of force applied to the closing of scissors blades or forceps moving elements of an associated surgical tool. In some embodiments, the foot pedal may provide sensory feedback with respect to the actuation of surgical tools. For example, the resistance to the closing of scissor blades can be measured and communicated to the operator by increased resistance to the depression of the foot pedal. Such feedback can provide the operator with a sense of the resistance to cutting, despite the fact that the tool is actuated indirectly via the foot pedal. The position of the foot pedal can be measured in a number of ways, for example by the use of an angular optical encoder and/or a force-sensing resistor. 
     Switching Illumination on and Off 
     As noted above, in some embodiments one or more of the cameras may have associated illumination sources integrated nearby. For example, in some embodiments, each camera can include two adjacent LEDs, each on opposite sides, so that the LEDs illuminate the field of view of the camera. This illumination, however, can be problematic in instances in which one or more of the cameras are oriented so as to at least partially face another camera. For example, if a first camera faces a second camera, adjacent LEDs on the second camera may effectively blind the first camera. The same principle applies to configurations in which the illumination sources are not associated with particular cameras. In any arrangement in which a camera directly images an illumination source, there is a risk of blinding the camera, or at least degrading the quality of the image. 
     To address this shortcoming, the illumination sources and the cameras can be carefully timed or synched to avoid a camera directly imaging an active illumination source. For example, an illumination source that is in the field of view of a camera can be controlled such that it is off or blocked while the camera is on, and conversely the illumination system can be on while the camera is off or blocked. This arrangement can be toggled rapidly, effectively strobing both the camera and the illumination source so as to reduce or eliminate the time during which the camera directly images an active illumination source. The camera and illumination source can be electronically controlled to allow for automatic and rapid strobing. At a sufficiently high strobing frequency, the effect can be undetectable by an observer. The composite image generated by stitching the views of the plurality of cameras can avoid any particular camera being blinded by the presence of an active illumination source in its field of view. 
     As noted above, in some embodiments described herein there may be many cameras, and additionally there may be many illumination sources. The strobing principle noted above can be applied to such configurations in a similar fashion. For example, by appropriately timing each of the illumination sources and each of the cameras, images can be captured in which the active unblocked illumination sources are imaged less often, or in some embodiments not at all. Such timing can be realized in a number of different approaches. For example, in one embodiment, each camera and its associated illumination source(s) can be turned on while all other cameras and illumination sources are turned off. When one camera and its illumination source(s) are then turned off, a next camera and its illumination source(s) can then be turned on. This can continue at a rapid pace such that each camera is active for a brief time in a given cycle. The cycle can be repeated continuously so that the composite image can effectively provide continuous wide field-of-view visualization. 
     In other embodiments, the strobing can be applied only to those cameras which directly image or have an illumination source in the field-of-view of the camera. In some embodiments, optical recognition, positional tracking, or other techniques can be used to determine when a camera is positioned to image an illumination source. In some embodiments, once this condition has been determined, that camera may be modulated, synched, or strobed (e.g., switched on and off or blocked during intervals of time and unblock during other intervals) in coordination with the associated illumination source, which also may be modulated or strobed (e.g., switched on and off or blocked for certain intervals of time and unblocked during other intervals). This approach can be applied to configurations containing many cameras and many illumination sources. As noted above, the strobing may be affected continuously and rapidly, such that an observer is unable to detect the strobing, however, in other embodiments the rate of modulation or strobing need not be so fast as to be undetectable by the eye. In some embodiments, the rates of modulation, for example, may be below the absolute threshold of seeing, or below a difference threshold, where the measure or sensation of 2 or more individual image modulations are not detected by the user. Moreover, brief flashes of the light sources and/or short activation periods for the sensors need not be used. Yet, in such embodiments, the illumination may alternated in synchrony with the operation of image sensors that are in the field-of-view of the light sources and vice versa. 
     In addition to direct blinding of a camera by an illumination source, specular reflections from instruments in the field of view of one or more cameras may reduce image quality. For example, a particular sensor may receive an unwanted specular reflection from a particular tool originating at a particular illumination element. In various embodiments, there are at least two possible responses: strobing and synching of the offending illumination source and sensor, and/or an area-of-interest calculation to reduce blooming or oversaturation in a portion of a sensors image, in particular a CMOS sensor. As the tools, sensors, and illumination sources can be known through tracking, in various embodiments a global response to blooming may take the form of look up table or global ray tracing algorithm to minimize over saturated areas within an image or array of images as the tools are used within the illuminated scene. 
     White Balancing 
     As discussed elsewhere herein, a composite image can be formed by stitching together multiple, separate images from a plurality of cameras. The images obtained from the separate cameras may, however, have different optical properties depending on a variety of factors. For example, the images obtained may vary in saturation, brightness, contrast, etc. depending on the camera and the configuration thereof and the conditions under which the images are recorded. Stitching together images of varying optical properties can create a patchwork effect in which the composite image can be degraded by the stark contrast in optical properties from a region captured by one camera to the next. 
     In order to counterbalance such effects, the images recorded from the separate cameras can be balanced or normalized. One such approach involves white balancing of the images from the cameras. For example, a white or neutral colored object, such as a cylindrical fixture, can be inserted into the surgical space observable by some or all of the cameras. The color of this object can be used to normalize the optical properties (color gamut and gain) of the sensors and the different images, thereby allowing for a more seamless composite image generated by stitching or tiling. In some embodiments, a multiple camera array can color balance composite images, wherein color balancing can include a global adjustment on one or more primary colors, red for example. Much of the surgical scene is dominated by red and its corresponding channel may be adjusted for continuity. 
     In some embodiments, the cameras could white balance on the mechanism, that holds the array of cameras inside a tubular retractor where one camera image intersects another. Various other approaches can be used to normalize the images obtained from the plurality of cameras. The resulting composite image can therefore appear seamlessly stitched, such that the user is unable to readily determine the borders between one image and the next. Note that in some embodiments, the images may be tiles such that discontinuities and/or gaps may exist in the composite image as a result of regions of the surgical site not imaged by the cameras. 
     In some embodiments, the item or mechanism used for color- or white-balancing can include a target to assist in aligning images from various cameras. In some embodiments, the target can be a mechanism that is used prior to inserting the retractor into the surgical site. For example, the mechanism can include a cylindrical or conical element with a substantially uniform color (e.g., white) and an asymmetric pattern. The retractor having a plurality of cameras can be positioned on the mechanism such that the cameras image the mechanism. The image processing module can calibrate the cameras based at least in part on the imagery of the mechanism where calibration information can include white balancing and/or alignment information. The white balance can be based at least in part on differences in color of the images of the mechanism between the cameras. Alignment information can be based at least in part on aligning the asymmetric pattern of adjacent images. For example, the white-balancing/alignment mechanism can be a uniformly white cylinder having asymmetric horizontal and/or vertical lines. The image processing system can use these features to align the images received from the various cameras by aligning the features within the composite image. Such a system can be used in association with a surgical tool as well. For example, the surgical tool can have a known color and/or pattern and the image processing system can process images of the surgical tool to calculate a position and/or orientation of the surgical tool as well as use the features of the surgical tool to align images from multiple cameras and/or color- or white-balance the images. 
     Example Embodiments of Imaging Modules 
       FIG. 27A  shows some embodiments of an imaging module  700  comprising wafer-scale optics (or wafer level optics) for use with a surgical device. The imaging module  700  can include a stop  702  at a distal end of the module. In some embodiments, the stop  702  has a value at least about 2.8 and/or less than or equal to about 3.3. The imaging module  700  can include one or more regions of material  704   a - d  configured to act as optical elements, such as lenses. The elements  704   a - d  can be configured to direct light and/or control distortion in the imaging module  700 . In some embodiments, the elements  704   a - d  may comprise optically transparent material such as but not limited to plastic or glass (e.g., molded glass). The elements may comprise, for example, monomers, polymers, or other compositions. In some embodiments, the elements  704   a - d  comprise resin. In some embodiments, the elements  704   a - d  comprise acrylic, benzyl (meth)acrylate, (meth)acrylic acid copolymers or multicomponent copolymers comprising benzyl (meth)acrylate, (meth)acrylic acid or other materials. The elements may also comprise a wide range of other materials instead. As an example, and without limitation, elements  704   a - d  can have a refractive index that is at least about 1.5 and/or less than or equal to about 1.7, or at least about 1.52 and/or less than or equal to about 1.65. As an example, some elements  704   a - d  can have a relatively high dispersion and can have an Abbe number that is, without limitation, at least about 50, at least about 55, or at least about 60. Some elements  704   a - d  can have a relatively low dispersion and can have an Abbe number that is, without limitation, less than or equal to about 30, less than or equal to about 25, or less than or equal to about 20. For some examples of wafer-scale optics (or wafer level optics), see U.S. Patent Pub. Nos. 2011/0063734 to Sakaki and 2012/0134028 to Maruyama. 
     The imaging module  700  can include structural elements  706   a  and  706   b  configured to separate optical elements, provide mechanical durability, provide support to optical elements, maintain one or more gaps  712  in the imaging module, or any combination of these. In some embodiments, the structural elements  706   a  and  706   b  can comprise a material that has a relatively low index of refraction, that has a low coefficient of thermal expansion, that is relatively impervious, or any combination of these properties. The structural elements  706   a  and  706   b  can be borosilicate glass, low-iron crown glass, or other similar material. For example, the structural elements  706   a  and  706   b  can be SCHOTT MEMpax®, BOROFLOAT® 33 borosilicate glass, D 263 T® eco borosilicate glass, AF 32® eco aluminoborosilicate glass, or B 270® low-iron crown glass supplied by Schott North America, Inc. or Duryea, Pa. Other materials, however, may also be used. 
     As an example, and without limitation, typical values for coefficients of thermal expansion for structural elements  706   a  and  706   b  can be between about 2×10 −6  K −1  and 9.9×10 −6  K −1 . As an example, and without limitation, typical values for refractive indices for structural elements  706   a  and  706   b  can be between about 1.4 and 1.6 As an example, and without limitation, typical values for Abbe numbers for structural elements  706   a  and  706   b  can be between about 50 and 70. Value outside these ranges, however, are possible. 
     The imaging module  700  can include an image sensor  708 , as described more fully herein. The imaging module  700  can be electrically and/or physically coupled to cable  710 . In some embodiments, cable  710  is a flex cable, as described more fully herein. In some embodiments, the module  700  has a field of view that is about 70 degrees. 
     In some embodiments, the imaging module  700  includes a moving element configured to adjust a position and/or orientation of one or more lens elements. For example, the moving element can include a piezo, motor, or other transducer or actuator configured to translate one or more lens elements in one or more directions. 
     The imaging module  700  comprising wafer-scale optics can be manufactured using processes utilized in semiconductor wafer manufacturing. In some embodiments optically transparent material is deposited on a surface of a substrate or structural support element ( 706   a ,  706   b ) such as a circular wafer like the wafers used for semiconductor device fabrication and is shaped to form a lens ( 704   a - 704   d ). The optically transparent material may be shaped, for example, by imprinting, embossing, or molding using a master. The master may be formed, in part by ion etching in certain embodiments. In some embodiments, material is added to the optically transparent material disposed on the substrate, material is removed from the optically transparent material disposed on the substrate, or as mentioned above, the optically transparent material disposed on the substrate is shaped. In some embodiments, ion milling may be employed. In some embodiments, multiple layers maybe be formed and joined during manufacturing. For example, multiple substrates or structural support elements  706   a ,  706   b  may be provided, and lenses ( 704   a - 704   d ) formed thereon. The substrate or structural support elements  706   a ,  706   b  can be stacked. In some embodiments, lenses  704   a  are formed on a wafer which is cut to create separate support elements  706   a  having lenses disposed thereon. Similarly, lenses  704   b  are formed on a different wafer which is cut to produce separate support elements  706   b  having lenses thereon. Support elements  706   a  having lenses  704   a  thereon can be stacked on support elements  706   b  also having lenses  704   b  thereon. Additional layers may be added as well. 
     Likewise, the wafer scale optics shown in  FIG. 27A  comprises a plurality of substrates stacked on top of each other with spaces therebetween. Lenses having one planar surfaces adjacent to the planar surface of the substrate and one curved surface can, for example, refract and bend light. As shown, such lenses having one planar surface formed on a substrate and one curved surface can be formed on both sides of a substrate (which as shown has two planar surfaces). Accordingly, in some embodiments, two curved surface are provide for a given substrate. 
     For example, as illustrated in  FIG. 27B , a first layer  740  can be formed having a first thickness, d 1 , and interlocking features  742 . The first layer  740  may comprise the structural support element  706   a  having layer of material formed thereon and patterned to produce the interlocking features  742 . A second layer  744  can be formed having a second thickness, d 2 , and interlocking features  746  that are complementary to the first layer interlocking features  742 . The second layer  744  may comprise the structural support element  706   b  having a layer of material formed thereon and patterned to produce the interlocking features  746 . The layer of material that is deposited may comprise monomer, polymer, glass or other material. The first and second layers  740 ,  744  can be stacked and interlocked to produce a portion of a wafer-scale optics or/wafer level optics element. The first thickness, d 1 , and the second thickness, d 2 , can be different. The height of the interlocking features  742  and  746  can also be different. In some embodiments, multiple layers (e.g., two, three, four, five or more layers) are stacked to form the imaging module  700 . 
     In some embodiments, wafers  750  such as illustrated in  FIG. 27C  are diced up to form the structural support elements  706   a ,  706   b  after having the elements  704   a ,  704   b  formed thereon thereby producing the separate multiple wafer-scale optics elements  752  that are stackable. To align the wafer-scale optics elements  752 , fiducials features  754  can be included. In some embodiments, these fiducial features comprise the interlocking features  742 ,  746  discussed above. Accordingly, fiducials  754  on a proximal surface of a first wafer can be configured to mate with complementary fiducials  754  on a distal surface of a second wafer such that the wafers interlock when aligned. In some embodiments, adhesives are included when stacking the layers. The adhesives can be UV-cured adhesives, thermal-cured adhesives, or other types of adhesives. The plurality of the wafer-scale optics elements  752  can be aligned and locked together as described. In some embodiments, wafers  750  such as illustrated in  FIG. 27C  are diced and then stacked. Alternatively, the wafers  750  can be stacked and then diced. Combinations of these approaches may also be used. 
     In certain embodiments, the fiducials  754  can provide stress relief to the imaging module  700  thus formed. The structural support elements  706   a ,  706   b , having lenses  704   a ,  704   b  formed thereon may be subject to stress that causes the structural support element  706   a ,  706   b  to bow or otherwise misshapen. This stress may be caused at least in part, for example, by differing coefficients of thermal expansion of various components of the wafer-scale optics elements  752  such as of the structural support element  704  and the lens  706 . In various embodiments, the fiducials  754  can be used to apply forces on proximal and distal surfaces of the wafers and structural support element  706   a ,  706   b  thus assisting the structural support element  704  and the lens  706  thereon to substantially to retain its shape. In some embodiments, the fiducials  754  comprise monomers, polymers, glass, or other material deposited on proximal and/or distal surfaces of a wafer  750 . The fiducials  754  can be configured to reduce or eliminate stress-induced warping due at least in part to differing coefficients of thermal expansion of various elements on the wafer and/or in the imaging module  700 . In various embodiments, the stress contributed by the fiducial layers  754  on opposite sides of the structural support element  704  largely offset each other to reduce the amount of bowing. In some embodiments, the amount of material forming the fiducial  754  may exceed the amount of material forming the lens such that the stress induced by the fiducial on both proximal and distal sides of the structural support element exceeds and overwhelms the stress induced by the lens. In some embodiments, the stress induced by the lens  704  and the fiducials on the same side of the support element  706  is substantially similar to the stress induced by the fiducial layer on the opposite side of the support element  706 . 
     In certain embodiments, the structural elements  706   a ,  706   b  (referring to  FIG. 27A ) in the imaging module  700  comprise substrates having one or more holes  714  extending from a proximal surface to a distal surface of the substrate. The holes  714  in the substrate can allow fluids to communicate between regions or gaps  712  between the structural elements  706   a  and  706   b . The holes  714  can be formed by drilling through the substrate or using a chemical machining process during manufacture or may be formed using other techniques. With reference to  FIG. 27C , the holes  714  can be cut in the plurality of wafers  750 . As described above, the wafers  750  can be cut and the substrates  706  formed therefrom can be stacked and interlocked, creating compartments  712  between the substrates  706  that otherwise would provide a barrier preventing fluidic communication between compartments. The holes  714 , however, thus can provide for fluidic communication between these compartments. Fluidic communication can reduce or eliminate condensation on optical elements in the imaging module  700 , e.g., on the lenses  704  during use or procedures where elements are exposed to fluids and/or changes in temperature that facilitate or promote the formation of condensation. 
       FIG. 28  shows some embodiments of an optical prescription for an imaging module  800  having a field of view less than or equal to about 70 degrees. The imaging module  800  can include a stop  801  on a distal portion of the imaging module in combination with four or more lenses. In some embodiments, the imaging module  800  includes the stop  801 , a positive lens, a negative lens, and a plurality of positive lenses. The imaging module  800  can be relatively compact while providing a moderate field of view and resulting in relatively low distortion (e.g., less than about 10% distortion). In some embodiments, the first element  802  is a positive lens having a relatively high index of refraction and relatively moderate dispersion. The first element  802  can be combined with a lens having a relatively high index of refraction and relatively high dispersion. Lens elements  806  and  808  can be positive lenses and configured to shorten an optical path and correct for distortions introduced by previous lens elements. The imaging module  800  can comprise wafer-scale optics. The imaging module  800  can be used with a surgical device. 
     As shown in  FIG. 28 , the imaging module  800  comprises lens elements  802 ,  804 ,  806 ,  808 ,  810 , and can be configured to form an image at  812 . The respective lens elements can have properties, such as distal and proximal radii, thickness, distance to the next element, index of refraction (n), Abbe number (V), and the like. Table 1 lists example values for various properties of the optical elements  802  through  810 . For reference, a distal surface of a lens element is the surface furthest from the image  812 , and a proximal surface of the lens elements is the surface closest to the image  812 . Furthermore, a thickness is the distance from the distal surface to the proximal surface in a particular lens element. Finally, the column labeled distance in the table refers to the distance from the proximal surface of the element in that row to the next element (i.e., the element in the next row). In the example shown in  FIG. 28  and Table 1, the stop is at the first surface and has an aperture of 0.125. The values in the table are normalized to produce an effective focal length of 1. Note that in this design, the aperture stop is in front and the lens, in order, from front to back are positive, negative, positive, and positive. This design may be suitable for providing fields-of-view less than 70 degrees, e.g., between 50-70 degrees. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Lens 
                   
                   
                 Thick- 
                   
                   
                   
               
               
                 Element 
                 Distal R 
                 Proximal R 
                 ness 
                 Distance 
                 n 
                 V 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Element 802 
                 0.823 
                 −3.216 
                 0.235 
                 0.089 
                 1.79 
                 47.5 
               
               
                 Element 804 
                 −1.04 
                 1.04 
                 0.07 
                 0.13 
                 1.76 
                 26.5 
               
               
                 Element 806 
                 −2.94 
                 −0.8 
                 0.255 
                 0.012 
                 1.79 
                 50.0 
               
               
                 Element 808 
                 1.3 
                 6.055 
                 0.44 
                 0.341 
                 1.79 
                 50.0 
               
               
                 Element 810 
                 infinity 
                 n/a 
                 0.25 
                 0.04 
                 1.52 
                 58.6 
               
               
                   
               
            
           
         
       
     
     In certain embodiments, the imaging module  700  includes a lens group comprising two or more lenses ( 806 ,  808 ) at a proximal end that concentrate or focus light, similar to a condenser lens group. In some embodiments, this group comprises two positive power lenses. In some embodiments, these lenses may comprise positive power lens  806  having a concave distal surface and a convex proximal surface and a positive power lens  808  having a convex distal surface and a concave proximal surface as shown. Accordingly, the vertices of these lenses  806 ,  808  may face each other and be in close proximity or even be in contact with each other. Although the stop is shown forward the first lens  802 , in certain embodiments, the stop  702  can be located between lens elements. 
       FIG. 29A  shows some embodiments of a wide field-of-view imaging module  900  with a buried stop  904  for use with a surgical device. Advantageously, some embodiments include the buried stop  904  allowing for a relatively wider field of view. In some embodiments, aspheres and/or more elements are included in the imaging module  900  to correct for distortion. In various embodiments, the imaging module  900  may include imaging optics comprising a negative distal lens group  902  having one or more lenses that produce a total optical power for that group that is negative and a positive proximal lens group  906  having one or more lenses that produce a total optical power for the group that is positive. The negative distal lens group  902  can be relatively strongly curved. A plano-concave lens can be used to facilitate fabrication, alignment, and/or cleaning, among other advantageous features. In some embodiments, the negative distal lens group  902  can include a plano-concave lens that has a relatively large negative optical power, a relatively high index of refraction, and a relatively moderate dispersion. In certain embodiments, the negative distal lens group  902  has a relatively high index of refraction and a relatively high dispersion. Some examples of lens elements suitable for use in the negative distal lens group  902  are SF10, SF14, SF57, supplied by Schott North America, Inc. of Duryea, Pa., and LAH58, LAF-21, LAFN31, LASF41, and LASF44 supplied by Ohara of Rancho Santa Margarita, Calif. In some embodiments, the negative distal lens group  904  includes lens elements configured to correct for distortion introduced by lens elements having a relatively strong curvatures or a relatively high negative optical power. In certain embodiments, the positive proximal lens group  906  is configured to correct for distortions introduced by the negative distal lens group  904 . The imaging module  900  can include a stop  904  wherein the negative distal lens group  902  is on a distal side of the stop  904  and the positive proximal lens group  906  is on a proximal side of the stop  904 . In some embodiments, the stop  904  can have an f-stop value that is, for example, at least about 3 and less than or equal to about 10 and may be at least about 4 and less than or equal to about 8. In some embodiments, the imaging module  900  can include one or more afocal lens groups but may be non-afocal as well. The imaging module  900  can include a camera  908 , as described more fully herein. The imaging module  900  can be configured to have a wide field-of-view. For example, the imaging module  900  can be configured to have a field-of-view that is at least about 90 degrees and/or less than or equal to about 120 degrees. 
     In some embodiments, the wide field-of-view imaging module  900  comprises non-wafer-scale optics combined with wafer-scale optics on a distal side of the stop  904 . The wide-field of view imaging module  900  can include additional optics on a proximal side of the stop  904 . In certain embodiments, the negative distal lens group  902  comprises non-wafer-scale optics and the positive proximal lens group  906  comprises wafer-scale optics. In some embodiments, the negative distal lens group  902  comprises wafer-scale optics having a stack of negative lens elements on a distal side of the stop  904 . The wide field-of-view imaging module  900  can include optics on a proximal side of the stop  904  comprising wafer-scale optics or non-wafer-scale optics. 
       FIG. 29B  shows an example embodiment of an optical assembly  950  comprising an afocal module  955  coupled to an optical imaging module  960  for use with a surgical device. The afocal module  955  can be added to an existing optical imaging module  960  to create a combined optical assembly  950  configured to achieve desired optical properties. The previously existing optical imaging module  960  may comprise, for example, a wide field-of-view, imaging module that otherwise would form an image on the sensor  975  In some embodiments, the optical assembly  950  has a different field of view than the optical imaging module  960  due at least in part to the afocal module  955 . For example, when compared to the optical module  960 , the combination of the afocal module  955  and the optical module  960  can have a broader or narrower field of view as determined, at least in part, to the optical properties of the afocal assembly  955 . In some embodiments, the optical assembly  950  includes an optical filter. The optical filter can be included between the afocal module  955  and the optical module  960 , the optical filter can be part of the afocal module  955 , or the optical filter can be a part of the optical module  960 . The optical assembly  950  has a stop  970  located in the optical module  960 . In some embodiments, the stop  970  can be located in the afocal assembly  955  or between the afocal assembly  955  and the optical module  960 . 
     The afocal assembly  955  includes optical elements  957   a ,  957   b . A first optical element  957   a  can have a negative optical power. A second optical element  957   b  can include optical elements that, when combined with the first optical element  957   a , form an afocal module  955 . The optical elements  957   a ,  957   b  can be wafer-scale optics, non-wafer-scale optics, or a combination of these. The second optical element  957   b  of the afocal assembly  955  includes a lens element  965  having a configuration wherein a central circular portion  966  has a negative optical power and an annular peripheral portion  968  has a positive optical power. The lens element  965  can be configured to alter a direction of propagation of peripheral rays more than of central rays. The lens element  965  can be used to correct for distortions introduced by the first optical element  957   a . The lens element  965  can be positioned to increase or maximize corrections to distortions. For example, the lens element  965  can be positioned near the image plane  975  or near the first optical element  957   a . The lens element  965  can be positioned before the stop  970 . 
     As shown, the optical element  957   b  includes lens on the proximal and distal sides thereof. The lens shown on the distal side may comprise a positive power lens in some embodiments. Other configurations, however, are possible. 
     The optical elements  957   a ,  957   b  can be aspherical, spherical, or have another shape. The optical module  960  can include one or more optical elements  962  wherein the optical elements comprise wafer-scale optics, non-wafer-scale optics elements such as glass, or a combination of these. In some embodiments, the afocal module  955  comprises non-wafer-scale optics optical elements made of glass. In some embodiments, the optical module  960  comprises wafer-scale optics. The optical assembly  950  can thus be configured as a combination of non-wafer-scale optics optical elements and wafer-scale optics. The afocal module  955  can include spherical lens elements. The lens elements of the afocal module  955  can comprise materials having a relatively high index of refraction (e.g., without limiting the indices of refraction, typical values can be between about 1.55 and about 1.7) and relatively high dispersion (e.g., without limiting the Abbe number, typical values can be at least about 50, 55, or 60) or materials having a relatively low index of refraction (e.g., without limiting the indices of refraction, typical values can be between about 1.3 and about 1.6) and relatively low dispersion (e.g., without limiting the Abbe number, typical values can be less than or equal to about 30, 25, or 20). In some embodiments, the optical assembly  950  can have a relatively low f-number compared to other wafer-scale optical assemblies wherein the f-number is set to provide a relatively greater depth of field compared to wafer-scale optics suitable for use where the subject is relatively far from the image sensor. In some embodiments, adding the afocal module  955  to the optical module  960  reduces the focal length, thereby increasing the field of view. Although module  955  has been described as an afocal module  955 , this module need not be afocal. 
     As described above, the module  955  may advantageously be added to a pre-existing optical imaging module  960 . In this manner, the field-of-view may be altered. For example, the pre-existing optical imaging module  960  may have a modest field-of-view, e.g. of between 50°-70°. However, addition of the add-on module  955  may increase the field-of-view to beyond 70° such as to 90°-120°. 
       FIG. 29C  shows an imaging module  980  comprising optical elements  982   a  and  982   b  configured to change properties of the imaging module  980 . For example, a first interchangeable optical element  982   a  can comprise a plano-plano block having an optical path length of d. This block provides for a substantially straight linear optical path as shown. A second interchangeable optical element  982   b  can comprise a block having features  983  that change the direction of the optical path within the interchangeable optical element  982   b . These features  983  may comprise, for example, refractive surfaces that redirect light towards a side of the optical element  982   b . These refractive index surfaces comprise interfaces between different section (three shown) of the prism  982   b  optical elements. Although three are shown, more or less may be included. The second interchangeable optical element  982   b  can have an optical path length of d, same as the first interchangeable optical element  982   a . By switching between interchangeable optical elements  982   a  and  982   b  (e.g., at the manufacturing stage), a viewing angle of the imaging module  980  can be changed. Having similar optical path lengths reduces the design implications of the change. The imaging module  980  can include a first negative lens or lens group  984  that can be moved or reoriented when changing between interchangeable elements  982   a ,  982   b . In some embodiments, the negative lens or lens group  984  can be a part of the interchangeable optical element  982   a ,  982   b . The imaging module  980  includes a proximal positive lens group  986 . The lens group  986  can have a total power that is positive or negative and may comprise wafer-scale optics. 
       FIG. 29D  shows an example imaging module with optics providing a viewing angle relative to a surgical tool axis. The example imaging module can be used with a stereo optical sensor to provide a narrow profile along a surgical device (e.g., a retractor blade) while providing a viewing angle, θ, that is not parallel to the axis of the surgical device nor parallel to the surgical device. This can allow for the use of a relatively large image sensor with little or minimal obstruction of a surgical site due to an imaging module protruding from a surgical device such as a retractor. The imaging module can include a sensor, wherein the sensor can be configured for monocular imaging or the sensor can be a divided sensor configured to provide stereo imagery. The imaging module can include a prism configured to direct light to the sensor where the incoming optical axis is substantially parallel to an axis of the surgical device. The imaging module can include optics configured to focus light from the surgical site onto the sensor. The imaging module can include redirection optics configured to direct light from a region of interest to the prism where the light comes generally from an angle, θ, relative to the axis of the surgical device. Accordingly, the imaging module can provide a viewing angle, θ, that is at least about 30 degrees, at least about 45 degrees, at least about 70 degrees relative to the axis of the surgical device. In some embodiments, an auto focus mechanism can be added between the sensor and the prism which can allow a user to control a focus of the imaging module and/or a faster f-number. 
     In various embodiments other types of prism elements may be used instead of the prism element  982   b  shown in  FIG. 29C . For example, the prism element may be formed by cementing together smaller prism sections to create a “compound” or “compact” prism or alternatively may the prism element may comprise a deviating prism that is a single homogenous piece of transparent material having outer surface shaped to obtain the desired beam direction. This material may be glass in various embodiments. An optical element that redirect light using multiple and in some embodiments an even number of reflections, e.g., 2, reflections can offer benefits with respect to parity or inverting and/or re-orienting an image upright. 
     Such interchangeable optical elements  982   a ,  982   b  can be used for cameras on surgical tools to change the view of the camera from directly in front of the camera, for example, directly forward the distal end of the tool. Instead, a view angle towards the side of the tool can be provided by interchanging the optical element  982   a ,  982   b.    
       FIG. 30A  shows some embodiments of an imaging stack  1000  comprising non-wafer-scale optics  1002  in combination with wafer-scale optics  1004  and  1006  for use with a surgical device. The imaging stack  1000  includes a cover glass  1001 . The cover glass  1001  can be made of a material having desirable optical and/or mechanical properties, such as sapphire. The cover glass  1001  can be a plano-plano optical element having a stop  1012  bonded thereto or formed thereon. The combination of the cover glass  1001  and stop  1012  can provide for a relatively small area of the cover glass  1001  to be exposed, thereby facilitating cleaning. In some embodiments, the non-wafer-scale optics  1002  include one or more components made of glass, polycarbonate, sapphire, or other material having desired optical properties. In some embodiments, the non-wafer-scale optics  1002  have one or more lenses that produce a total optical power that is negative. For example, the non-wafer-scale optics  1002  can include a lens with a negative optical power having a relatively strong curvature typically not produced for wafer-scale optics. The imaging stack  1000  can include a first wafer-scale optical element  1004 . The first wafer-scale optical element  1004  can include one or more components  1008  configured to provide optical correction, provide a desired focal length, provide an afocal system, or the like. In some embodiments, the one or more components  1008  are configured to compensate for distortion in a wide field-of-view system. The first wafer-scale optical element  1004  can include registration marks, structures, fiducials, or features  1010  configured to aid in subsequent image processing or mounting/registering non-wafer-scale optics  1002  with minimal or reduced active optical alignment and increased alignment precision. In some embodiments, the combination of non-wafer-scale optics  1002  and first wafer-scale optical element  1004  provides a total optical power that is negative. The imaging stack  1000  can include a positive proximal wafer-scale optical group  1006  having one or more optical elements that produce a total optical power for the group that is positive. 
       FIG. 30B  shows some embodiments of an imaging stack  1000  comprising non-wafer-scale optics  1002  in combination with wafer-scale optics  1004  and  1006  for use with a surgical device. In some embodiments, the imaging stack  1000  includes a stop  1012  positioned between the first wafer-scale optical element  1004  and the positive proximal wafer-scale optical group  1006 . The positive proximal wafer-scale optical group  1006  can include an optical element  1009  wherein a radial central portion  1011  of the optical element  1009  has a negative optical power and a radial peripheral portion  1013  of the optical element  1009  has a positive optical power. In some embodiments, the optical element  1009  can be configured to alter a direction of propagation of peripheral rays more than of central rays. The optical element  1009  can be used to correct for distortions introduced by optical elements in the non-wafer-scale optics  1002 , the first wafer-scale optics, and/or the positive proximal wafer-scale optical group  1006 . The optical element  1009  can be positioned to increase or maximize corrections to distortion. The imaging stack  1000  includes an image plane  1010 . 
     In some embodiments, wafer scale optics (or wafer level optics) may include an aperture therein provided, for example, by the manufacturer. Nevertheless, in various embodiments, another aperture that can be used as the stop can be placed between a non-wafer scale optical element and the wafer scale optics having the aperture therein. For example, a stop may be included between a negative power distal lens group comprising one or more non-wafer scale optical element and a proximal lens group comprising wafer scale optics. 
     In some embodiments, the cameras and/or optical systems described herein can include MEMS configured to change optical properties of the optical system, such as, for example, a focal length, a magnification, a pointing angle, a field of view, or any combination of these. In some embodiments, an actuator can be used to drive a low power optical element substantially along the optical axis. The optical element can be driven at a rate such that the full sinusoidal cycle of focus is completed at a greater rate than the human critical flicker fusion rate (e.g., about 60 Hz). This can increase a depth of field of the camera or optical system. The actuator can include, for example, a voice coil, a moving magnet, a piezo, or other such actuators. In some embodiments, increasing the depth of field in this manner can be accomplished using COTS MEMS auto-focus modules driven by a sine wave having a frequency that is greater than or equal to about 60 Hz. In some embodiments, the auto-focus actuator can be driven such that the focal plane or median of increased depth of focus volume tracks a desired portion of a surgical tool, such as a tip of the surgical tool, where a position of the surgical tool is acquired using any of the tracking methods described herein, such as EM tracking. 
     In some embodiments, cameras can be positioned at different depths within the surgical site along a retractor. The image processing system can use the varying depths of field from the cameras at different depths to increase an output depth of field to provide focused imagery of a greater portion of the surgical site. For example, a retractor can have two or more rings of cameras and the cameras at each level can provide image data to the image processing system. The image processing system can combine overlapping image data (e.g., by tiling and/or stitching images) to provide an output image having a greater depth of focus. An example of a system with cameras at two depths is illustrated in  FIG. 21 . 
     In some embodiments, surgical devices, such as surgical tools or retractors, can include right-angle prisms to direct light from a scene onto an optical sensor. This can be used so that the optical sensor and associated optics can be housed within the surgical device or other protective housing thereby providing increase working room for the surgeon that is not obstructed by cameras and to reducing possible damage to cameras from use. 
     In some embodiments, LEDs associated with cameras can produce a light cone that is substantially similar to the field of view of the associated camera. Such a light beam may be used in set-up to position and/or orient the cameras. This process may be employed when the cameras are in the initialization platform. 
       FIGS. 31A and 31B  respectively show top and side views of some embodiments of an imaging module  1100  comprising an imaging stack  1106 , sensor layer  1114 , via layer  1104 , and flex layer  1110 . The via layer  1104  can include vias configured to permit liquid or electrical cables to pass through. The via layer  1104  can be coupled to the flex layer  1110 , which can comprise a flex cable according to some embodiments described herein. The flex layer  1110  can include a plurality of channels  1112  configured to transmit liquid or house electrical cable. The imaging module  1100  can include an image stack  1106 , such as imaging stacks described herein with specific reference to  FIGS. 27A-30B . The imaging module  1100  can include a sensor layer  1114  configured to house an image sensor, as described more fully herein. The vias  1102  on the via layer  1104  can be configured to transmit liquid to or from the flex layer  1110 . In some embodiments, the vias  1102  are coupled to or combined with cleaning systems as described herein. The vias  1108  can be configured to pass electrical cables from the flex layer  1110  to the sensor layer  1114 . In some embodiments, the flex layer  1110  comprises more than one flex cable with at least one flex cable configured to house electrical cables and at least one flex cable configured to transmit fluid to and from the imaging module  1100 . 
     As noted above, in some embodiments, illumination sources such as LEDs may be positioned near the optical sensors. For example, in the case of a retractor, in some embodiments optical sensors positioned on the retractor blades may each have one or more corresponding LEDs positioned adjacently. However, in other embodiments, the LEDs need not be positioned adjacent the optical sensors. For example, the LED or other illumination source may be positioned at some distance from the optical sensors, but light may be directed from the LED to an area near the optical sensor using a one or more light guides or mixers. 
       FIGS. 32A and 32B  illustrate two embodiments of light guides/mixers for use with imaging modules. As shown in  FIG. 32A , a light guide  1201  has an illumination source  1203  disposed adjacent the first end  1205  of the light guide  1201 . In various embodiments, the light guide  1201  can be made of resin, glass, plastic, or any other transparent material suitable for propagation of light therein. The thickness of the light guide  1201  can decrease from the first end  1205  to the second end  1207 , creating a tapered profile. In various embodiments, light entering the light guide  1201  at the first end  1205  propagates through the body of the light guide  1201  by total internal reflection. In implementations in which the light guide  1201  is tapered, light guided in the light guide  1201  will propagate by total internal reflection until it is ejected by the light guide  1201  at an oblique angle relative the light guide  1201 . In some implementations, the rearward surface  1211  of the light guide  1201  can have a reflective surface so as to reflect light emitted from the light guide plate  1201  such that the light is turned and output from through light guide  1201  and emitted from the forward surface  1213 . In various embodiments, the reflective surface can be metallic. In some embodiments, a film having a lower index of refraction than that of the light guide  1201  may be positioned over the rearward surface  1211  to support the propagation of light therein. 
     As shown in  FIG. 32A , light can be emitted from the forward surface  1213  of the light guide  1201  along the length of the light guide  1201 . In various embodiments, the light emitted from the forward surface  1213  can be substantially uniform across the entire length of the light guide  1201 . In some embodiments, the light emitted from the forward surface  1213  can be emitted across substantially the entire forward surface  1213 . In some embodiments, the emitted light may exhibit directionality. In other embodiments, the emitted light may be dispersed substantially uniformly. 
       FIG. 32B  shows a light guide  1201  and illumination source  1203  similar to that of  FIG. 32A . However, as shown in  FIG. 32B , the light guide  1201  has a substantially rectangular profile along part of its length, with a tapered profile near the second end  1207 . Additionally, a reflective layer  1215  is disposed over a portion of the forward surface  1213  of the light guide  1201 . The reflective layer  1215  can be, for example, a metallic layer. In other embodiments, the reflective layer  1215  can be replaced with a dielectric film that is substantially non-transmissive. In various embodiments, a reflective opaque layer is used for the layer  1215 . As a result of the reflective layer  1215 , light propagating within the light guide  1201  that would otherwise be emitted from the forward surface  1213  is reflected by the reflective layer  1215  and continues to propagate within the light guide  1201 . As illustrated, the reflective layer  1215  does not extend along the full length of the light guide  1201 . The portion of the forward surface  1213  nearest the second end  1207  of the light guide  1201  is not covered by a reflective layer  1215 . As a result, light propagating within the light guide plate  1201  can be emitted from the forward surface  1213  in the region not covered by the reflective layer  1215 . In other embodiments, the light guide  1201  may be tapered along part of its length such that the thickness increases from the first end  1205  towards the second end  1207 , until it the portion nearest  1207 , at which point the thickness decreases as with the illustrated embodiment. 
     In contrast to  FIG. 32A , the light guide of  FIG. 32B  emits light from the forward surface  1213  only in one region of the light guide  1201 . Accordingly, the emitted light can be directed to a specific region, resulting in a spotlight effect depending on the directionality of the emitted light. As noted above, the configuration illustrated in  FIG. 32A  can provide substantially uniform emission across the entire forward surface  1213  of the light guide, resulting in a wider floodlight effect. 
     In either of the illustrated embodiments, the illumination source  1203  may include one or more light emitters such as light emitting diodes. In some embodiments, the illumination source  1203  can include multiple LEDs of different colors. For example, in various embodiments the illumination source  1203  can include red, green, and blue LEDs. Light from each of the different colored LEDs propagates through the light guide  1201  and in the process the light is mixed. As a result, light emitted from the forward surface  1213  can be mixed, for example such that the red, green, and blue light produces an emitted white light from the forward surface  1213  of the light guide  1201 . In various embodiments, additional colors, such amber, near infrared, or other colors can be added. The inclusion of amber light may provide additional color between green and red where the LED spectrum from phosphor whites or discreet RGB modules may have a gap. 
     In some embodiments, an optical film may be positioned over the forward surface  1213  of the light guide  1201 . For example, a diffusing film can be positioned to aid in color mixing and/or to provide a more uniform emission profile. In some embodiments, the optical film can have other properties, for example the optical film can operate to focus the direction of the emitted light over a narrower range. In various embodiments, an optical film comprising a color filter can be positioned over the forward surface of the light guide. As with the reflective layer  1215  illustrated in  FIG. 32B , in various embodiments any additional optical film may not necessarily extend across the entire forward surface of the light guide. In various embodiments, the film could have a diffractive or other pattern for improving or modifying the output distribution. 
     Although the illustrated embodiments show a tapered light guide, in various embodiments the light guide may assume other profiles. For example, in some embodiments the light guide can be substantially rectangular in profile, and may include light-turning features on one or more surfaces to redirect light propagating within the light guide such that the light is emitted out the forward surface. Such light-turning features may be prismatic (e.g. facets) or diffractive (e.g., a holographic film), and may be formed integrally with the light guide or may be included in a separate optical film placed over one or more surfaces of the light guide. In various embodiments, the light guide  1201  can include prismatic light-turning features to redirect light out of the light guide  1201 , rather than relying solely on the tapered profile. 
       FIGS. 33A and 33B  illustrate top and side cross-section views, respectively, of a retractor blade with a light guide and illumination source integrated therein. As shown, the distal portion of one retractor blade  1217  can have positioned thereon a light guide  1201  with an illumination source  1203  positioned adjacently. In the illustrated embodiment, the illumination source  1203  comprises three separate LEDs. As noted above, in various embodiments, different color LEDs such as red, green, and blue LEDs may be used to inject light into the light guide  1201 , where it is then mixed and ejected as white light. In some embodiments, red, green, and blue LEDs may be used in conjunction with an amber LED. Such combination may provide a desirable look for red tissue that is viewed by the cameras. In some embodiments, white LEDs may be used. Light sources other than LEDs may also be used. As described above, light from the illumination source  1203  propagates in the light guide  1201  until emitted from the forward surface of the light guide  1201 . 
     The retractor blade  1217  may be used in conjunction with multiple other retractor blades, each similarly equipped with an illumination source  1203  coupled to a light guide  1201 . Each retractor blade may include one or more optical sensors (not shown). Each light guide  1201  on a retractor blade  1217  can provide illumination for a certain area, depending on the orientation of the retractor blade and the properties of the light guide and illumination source. The light guide  1201  may be imbedded within or incorporated as part of the retractor blade or may be removably attached thereto. For example, the light guide may be included with a support component such as a slide or finger that is removably attached to the retractor blade  1217 . Although the embodiment illustrated in  FIGS. 33A and 33B  is a retractor blade, the illumination system can be used in conjunction with any number of surgical devices. 
     Positioning the LEDs at a distance from the optical sensors and using light guides to direct light from the illumination sources can provide several advantages. For example, illumination sources such as LEDs are subject to rising temperature during operation. Positioning such illumination sources in portions of the surgical device, which will be introduced into a patient&#39;s body, presents the danger of increased temperature damaging nearby tissue. Fluids also coming in contact with the LEDs may become heated. In such a configuration, an illumination source providing a broad flat light (i.e. having a relatively low level of illumination per area) may produce similar illumination levels at the surgical site that a plurality of smaller, hotter illumination sources would. Additionally, heat management devices, such as external heat sinks, can disadvantageously add bulk to the illumination source, thereby reducing the working area available to the user. Additionally, as noted above, the use of light guides can allow for mixing of light from the illumination source prior to emission from the light guide. For example, in various embodiments the illumination source can comprise multiple LEDs of different colors. In some embodiments, for example, red, green, blue and possibly amber light emitted from LEDs can propagate through the light guide and be mixed therein, such that substantially white light is emitted from the light guide and directed towards the surgical site. By adjusting the properties of the light guide and the number, intensity, and/or color of the LEDs, the properties of emitted light from the light guide towards the surgical site can be controlled. 
     Embodiments of Hydraulic Actuator Circuits 
     Hydraulic actuator circuits can be used in combination with surgical tools and corresponding imaging systems to perform various functions within the surgical systems. For example, without limitation, the hydraulic actuator circuits can power the surgical tools, provide cooling to components within the imaging systems, and/or clean components within the system. In some embodiments, using hydraulic actuator circuits and subcomponents thereof to power the surgical tools can create reduced or minimal electromagnetic interference with tracking tools. For example, electromagnetic fields that may otherwise interfere with electromagnetic tracking need not be inserted into the body proximal to the retractor blade and surgical access site and the tracking elements associated with cameras on the retractor blades and/or tracking elements on the surgical tools. Although in some embodiments electrical motors and devices may be employed to drive hydraulic components, such electrical motors and devices can be located a distance from the tracking devices included on the retractor and/or the surgical tools so as to reduce or eliminate electromagnetic interference. In various embodiments, the tracking devices and/or the optical sensors may include shielding such as a casing or shield comprising metal or Mu-metal. 
     In some embodiments, the components of the hydraulic circuit (e.g., pumps, valves, surgical tools, manifolds) can be made or at least partially constructed from non-metal materials (e.g., polymers) and/or non-ferrous materials. Hydraulic actuator circuits can include many inexpensive and/or disposable components (e.g., molded components and/or subcomponents). In some configurations, hydraulic actuator circuits can operate at low noise volumes compared to pneumatic drills, reducing or minimizing irritation and potential ear damage for the surgeons and medical staff. The components of the hydraulic actuation circuits can be constructed from a combination of computer numerical control (CNC) parts and molded parts. 
       FIG. 34  illustrates an embodiment of a hydraulic actuator circuit  1500 . The circuit  1500  preferably includes a hydraulic pressure source. In some embodiments, the hydraulic pressure source is a fluid interface chamber  1502 . Portions of or the entire fluid interface chamber  1502  can be disposable and/or non-autoclavable. The fluid interface chamber  1502  can be pre-loaded with a hydraulic fluid  1504  (e.g., saline). As discussed in the present disclosure, the term “hydraulic fluid” can refer to saline (e.g., a physiological saline) and/or to any other physiologically compatible fluid (e.g., fluid suited to interaction with the interior of the body of a patient). Other fluids can be used in the fluid interface chamber  1502  (e.g., distilled water, oil). A pneumatic fluid source  1510  (e.g., a hospital nitrogen system, a nitrogen tank, etc.) can be actuated to exert pressure on the hydraulic fluid  1504  within a cavity  1508  of the housing  1506 , thereby pressurizing the fluid  1504 . The pneumatic fluid source  1510  can be controlled via user input (e.g., a treadle, button, dial, etc.) and/or via automatic control (e.g., a pre-programmed computer). 
     The fluid interface chamber  1502  can output hydraulic fluid  1504  (e.g., saline) to a tool-powering apparatus. For example, the fluid interface chamber  1502  can output saline to a saline turbine  1512  configured to power a hydraulic drill or other tool, as further discussed below. In one embodiment, the fluid interface chamber  1502  can output saline in a pulsed manner to cause rotation of the saline turbine  1512  (e.g., via the impingement of the fluid flow stream with one or more vanes of the saline turbine  1512 ). In some embodiments, the saline turbine  1512  and/or powered drill/tool are disposable and/or non-autoclavable. The saline input into the turbine  1512  can cool the turbine  1512 . The turbine  1512  can include a hydrostatic bearing. In some embodiments, leakage of saline from the turbine  1512  via the hydrostatic bearing or otherwise can irrigate the surgical field. In some embodiments, the saline turbine  1512  can operate at low noise volumes (e.g., compared to pneumatic drills) at high operation speeds (e.g., speeds exceeding 40,000 rpm). However, the turbine  1512  can operate at other speeds. The saline turbine  1512  can be lightweight, can have a high torque to mass ratio, and can operate without producing FR losses, thus reducing heating within the hydraulic actuator circuit  1500 . Preferably, the saline turbine  1512  can be an impulse turbine. In some embodiments, the saline turbine  1512  is a vane motor, or a Tesla turbine. 
     In the preferred embodiment, the exhaust fluid  1514  can be output from the turbine  1512  to a hydraulic manifold  1516 . The manifold  1516  can distribute the exhaust fluid  1514  amongst one or more manifold outputs. For example, a portion of the exhaust fluid  1514  can be directed through a first manifold outlet  1517  to be used to wash optics such as imaging optics included in cameras on the retractor blades or surgical tools, for example, as discussed above. The manifold  1516  can include one or more pumps and/or valves. For example, fluid directed toward the first manifold outlet  1517  can be manipulated by a linear actuator compressing an elastomeric valve or a multi-lobed cam on a brushless DC motor or a proportional solenoid array to produce tube compression and/or compression of blisters on the manifold  1516  to produce optics washing pulses. In some embodiments, air or other gases can be input into the manifold  1516  to dry the optics after washing. The optics can be sterilized before, after, or during washing. A portion of the fluid  1514  can be directed through a second manifold outlet  1518  to cool LEDs used to provide illumination to the surgical site to facilitate imaging by cameras on the retractor and or surgical tools and viewing by the surgeon and a portion of the fluid  1514  can be directed through a third manifold outlet  1519  toward hydraulics for a power Kerrison or rongeur. The manifold  1516  can include more than or less than three manifold outlets depending on the specific application of the hydraulic circuit  1500 . In one embodiment, the manifold  1516  can include one or more valves (not shown) that can be selectively actuated to direct exhaust fluid  1514  to one or more manifold outlets, while not directing exhaust fluid to other manifold outlets. For example, the valves can be selectively actuated (e.g., via a controller based on user inputs or based on an automatic control algorithm implemented by the controller) so that exhaust flow is directed to the first and second manifold outlets  1517 ,  1518 , but not the third manifold outlet  1519 , or so that exhaust flow is directed to the third manifold outlet  1519 , but not the first and second manifold outlets  1517 ,  1518 . The manifold may comprise flexible plastic and may be ultrasonically welded or adhesive bonded to make channels with edge connectors for tubing in some embodiments.  FIG. 35A  illustrates an embodiment of a hydraulic circuit  1520  which includes a pump  1522 . The pump  1522  can be a roller pump configured to pressurize exhaust fluid  1514  from the turbine  1512 . In some embodiments, a roller pump can reduce the overall envelope size of the system. The pump  1522  can include a roller  1524  configured to compress a flexible tube  1526  in a rotational manner such that fluid entering the pump  1522  via the pump inlet  1528  is compressed and/or accelerated through the flexible tube  1526  to the pump outlet  1530  as the roller  1524  rotates. The flexible tube  1526  and/or other components of the pump  1522  can be disposable. Pressurized fluid exiting the pump outlet  1530  can be directed to the fluid interface chamber  1502  and/or to the turbine  1512 . In some embodiments, a bi-directional valve is located between the pump outlet  1530  and the fluid interface chamber  1502  and turbine  1512 . Such a valve can be manually or automatically controlled (e.g., via a computer controller) to direct flow to the fluid interface chamber  1502  and/or to the turbine  1512 . In some embodiments, the hydraulic circuit  1520  or portions thereof can be configured be releasably installed within a cassette assembly. The cassette assembly can be disposable and can provide a condensed volume in which portions of or the entire hydraulic circuit  1520 . Similar or identical cassette assemblies can be used in conjunction with the hydraulic circuits described herein. 
     According to some variants, as illustrated in  FIG. 35B , a hydraulic circuit  1540  can include a proportioning valve  1534  configured to automatically direct a desired proportion of the hydraulic fluid output by the fluid interface chamber  1502  directly to one or both of the turbine  1512  and the hydraulic manifold  1516 . The proportional valve  1534  can be inexpensive and/or disposable. In some embodiments, the proportional valve  1534  is non-autoclavable. The proportioning valve  1534  can be driven by a proportional solenoid or non-commutated linear motor (e.g., with either moving a coil or moving magnet).  FIG. 35C  illustrates a hydraulic circuit  1580  that includes a bellows actuator  1536  for use as a hydraulic pressure source. The bellows actuator  1536  can include a bellows (e.g., a metal bellows) actuated at least in part by a linear actuator  1542 . The linear actuator  1542  can be controlled by a motor  1544  (e.g., a brushless motor) or other controller device. The bellows actuator  1536  can perform many or all of the functions previously described with respect to the fluid interface chamber  1502 . For example, the bellows actuator  1536  can provide pressurized hydraulic fluid (e.g., saline) to the proportioning valve  1534  and/or turbine  1512 . The bellows actuator  1536  can include a return spring that biases the bellows  1536  to an expanded position. In one embodiment, a controller (e.g., a computer controller) can control the operation of the motor  1544  (e.g., based on user input, such actuation of a foot pedal, push button, lever, voice command, etc.), thereby controlling the operation of the bellows actuator  1536  to provide a desired fluid flow and/or pressure to the proportioning valve  1534 . 
     The hydraulic circuit  1580  can include a second hydraulic pressure source. For example, the circuit  1580  can include an IV bag pressurized fluid source  1546 . The IV bag source  1546  can output fluid to a directional valve  1548 . The directional valve  1548  can be constructed inexpensively and/or can be disposable. The directional valve  1548  directs the output fluid from the IV bag source to a pump  1522  and/or to a check valve  1552 . The check valve  1552  can be configured to permit fluid flow from the directional valve  1548  to the bellows actuator  1536  while preventing fluid flow through the check valve  1552  from the bellow actuator  1536  to the directional valve  1548 . Fluid directed to the pump  1522  can be pressurized within the pump  1522  and output to the hydraulic manifold  1516 . In some embodiments, the bellows actuator  1536  and fluid interface chamber  1502  are interchangeable structurally and/or functionally within the hydraulic circuits  1500 ,  1520 ,  1540 ,  1580 . 
       FIG. 36A  illustrates an embodiment of an LED cooling system  1600 . The cooling system  1600  can include a pump  1522  that is similar or identical to the pump  1522  described above. The system  1600  can include a fluid input  1610  via a vent line for saline priming. A pinch valve  1608  (e.g., a solenoid pinch valve) or other valve can be positioned at or near the fluid input  1610 . The pinch valve  1608  can be configured to selectively inhibit fluid flow into the LED cooling system  1600 . The pinch valve  1608  can be manually and/or automatically controlled (e.g., via an electronic or computer controller). 
     The cooling system  1600  can be used to cool one or more LEDs  1602  used to provide illumination to the surgical site to facilitate imaging by cameras on the retractor and or surgical tools and viewing by the surgeon. In this example, 6 LEDs  1602  are shown. Fewer or more LEDs  1602  are possible. The fluid (e.g., saline) received into the system  1600  via the input  1610  (e.g., received via the manifold described above) can be passed through, over, and/or past the LEDs  1602  to cool the LEDs  1602 . The pump  1522  can be used to pump the fluid past the LEDs  1602 . In some embodiments, the pump  1522  pumps the fluid back to the hydraulic actuator circuits and/or to an optics washing circuit via a cooling system outlet  1612 . A second pinch valve  1609  can be positioned within the cooling system  1600  to selectively inhibit the fluid output from the first pinch valve  1608  from accessing the pump  1522  without passing by/through the LEDs  1602 . Accordingly, the cooling of the LED provide by the hydraulic system can be switched on or off. The pinch valves  1608 ,  1609  can be configured in some embodiments, so that a portion of the fluid that flows into the LED cooling system  1600  can exit the system  1600  via the cooling system outlet  1612  without passing through the pump  1522  or past the LEDs  1602 . 
     In some embodiments, as illustrated in  FIG. 36B , the cooling system  1600  includes hydraulic pressure source. The hydraulic pressure source can be, for example, a saline bag pressure compression system  1630 . The compression system  1630  can include a bag  1632  pre-charged with hydraulic fluid (e.g., saline) and disposed in a housing, for example via fluid flow from fluid input  1610 . The compression system  1630  can have a driven compressing element  1634  (e.g., a plate, piston) configured to compress the bag  1632 . The compressing element  1634  can be driven by a motor or other actuator (e.g., other electrical, mechanical or pneumatic actuator). For example, the actuator can be a motor  1638  configured to drive a Acme or preferably ball screw  1636 . The screw  1636  can couple with the compressing element  1634  and can move the compressing element  1634  toward and/or away from the bag  1632  upon input from the motor  1638 . The compression system  1630  or other hydraulic pressure source can provide pressurized hydraulic fluid to the cooling system  1600 . In some embodiments, a portion of the fluid output from the compression system  1630  is directed to the hydraulic actuator circuits and/or to an optics washing circuit via the cooling system outlet  1612 . The pinch valve  1608 ,  1609  can be configured to selectively inhibit access to the fluid input  1610  by the fluid output from the compression system  1630 . 
     In some embodiments, the hydraulic pressure source of the hydraulic pressure circuits and/or LED cooling systems can be a rolling edge diaphragm, a syringe (e.g., a disposable syringe) or any other suitable hydraulic pressure source or combination or pressure sources (e.g., a syringe in combination with bellows). The hydraulic pressure source(s) can be free from valves. 
     As illustrated in  FIG. 37 , a hydraulic pressure circuit  2000  for use with surgical tools or otherwise can include a fluid source  2010 . The fluid source  2010  can include a fluid reservoir  2012  (e.g., an IV bag or other fluid container). The fluid source  2010  can be gravity-driven. In some embodiments, the hydraulic pressure circuit  2000  includes a fluid source actuator configured to force fluid from the fluid source  2010 . In some embodiments, the fluid source  2010  includes a hydraulic pump  2014  (e.g. a roller (peristaltic) pump, a linear actuator pump, a gear pump, a radial piston pump, a screw pump, and/or an axial piston pump) fluidly connected to the reservoir  2012 . The hydraulic pump  2014  can be configured to force fluid out of and/or into the fluid reservoir  2012 . One or more feedback sensors (e.g., pressure transducers  2018 ) can be connected to the fluid reservoir  2012  to monitor the fluid pressure within the fluid reservoir  2012  and/or within the fluid lines connected to the reservoir  2012 . 
     The hydraulic pressure circuit  2000  can include a hydraulic manifold  2020 . In some embodiments, the hydraulic manifold  2020  is housed at least partially within a cassette assembly, an example of which will be discussed below. The hydraulic manifold  2020  can include one or more external connectors  2002 . The external connectors  2002  can be configured to facilitate fluid communication between the hydraulic manifold  2020  and other components of the hydraulic circuit  2000 . For example, an external connector  2002  can provide a fluid interface between the hydraulic manifold  2020  and one or more fluid lines of the fluid source  2010 . 
     In some embodiments, the external connectors  2002  define one or more fluid inlets and/or fluid outlets into and out of the hydraulic manifold  2020 . For example, the external connector  2002  configured to connect to the fluid source  2010  can define a fluid inlet into the hydraulic manifold  2020 . The hydraulic manifold  2020  can include one or more external connectors  2002  configured to facilitate fluid connection between the hydraulic manifold  2020  and a tool assembly  2080 . For example, the hydraulic manifold  2020  can include a tool fluid outlet and a tool fluid inlet to facilitate fluid transfer to and from the tool assembly  2080 . In some cases, a long flexible tube  2084  (e.g., a seven foot flexible tube) can be used to fluidly connect the hydraulic manifold  2020  to the tool assembly  2080 . In some embodiments, the hydraulic manifold  2020  includes external connectors  2002  configured to form one or more LED fluid inlets and one or more LED fluid outlets to facilitate fluid transfer between the hydraulic manifold  2020  and an LED assembly  2060 . In some embodiments, the LED assembly  2060  can be fluidly connected to the fluid source  2010 , with or without the use of external connectors on the LED assembly  2060  and the fluid source  2010 . 
     The external connectors  2002  can be configured to reduce the time and effort associated with fluidly connecting and/or disconnecting the components of the hydraulic pressure circuit  2000  (e.g., the fluid source  2010 , the hydraulic manifold  2020 , the LED assembly  2060 , and/or the tool assembly  2080 ) to each other. For example, the connectors  2002  can comprise tapered connectors onto which tubing (e.g., flexible plastic tubing) can be pressure-fit. In some embodiments, the connectors  2002  can comprise male and/or female luer connectors (e.g., ANSI-compliant connector interfaces) configured to connect with a corresponding connector on a fluid conduit. In some embodiments, the connectors  2002  include internal and/or external threading configured to releasably engage with external and/or internal threading on a fluid conduit. 
     According to some variants, one or more valves  2032  can be positioned on or within the hydraulic manifold  2020  to control and/or limit the fluid flow through one or more fluid conduits within the hydraulic manifold  2020 . The one or more valves  2032  can be, for example, two-way two position valves  2032  (e.g., pinch valves). In some embodiments, the hydraulic manifold  2020  can include one or more proportioning valves  2034  (e.g., proportional two-way two position valves, diaphragm-type valves, and/or spindle valves) configured to control and/or limit fluid flow through one or more fluid conduits within the hydraulic manifold  2020 . In certain cases, a valve  2032 ,  2034  is positioned on each fluid channel within the hydraulic manifold  2020  (e.g.,  FIG. 37 ). The valve  2032 ,  2034  can act as on/off valves to provide pulsed flow through one or more of the fluid conduits in the hydraulic manifold  2020 . 
     In some embodiments, the hydraulic manifold  2020  includes one or more fluid actuators. For example, the hydraulic manifold  2020  can include one or more bellows actuators  2022 . Other types of fluid actuators such as master-slave balloon pumps, axial pistons, and peristaltic pumps can also be used in addition to or instead of the bellows actuators  2022  to pressurize hydraulic fluid within the hydraulic pressure circuit  2000 . Although the following discussion will refer to bellows actuators  2022  as the fluid actuator, the concepts disclosed herein could also apply to other types of fluid actuators disclosed above. The bellows actuators  2022  can be configured to increase fluid pressure within the fluid conduits of the hydraulic manifold  2020 . The bellows actuators  2022  can include a bellows  2028 . One or more linear actuators  2026  can be configured to compress and decompress the bellows  2028 . The one or more linear actuators  2026  can be manipulated by one or more motors  2024  (e.g., brushless motors, stepper motors). 
     Fluid can be provided to the bellows actuators  2022  from the fluid source  2010 . One or more valves  2032 ,  2034  can be positioned in the fluid paths between the fluid source  2010  and the bellows actuators  2022 . The bellows actuators  2022  can output high pressure fluid to the tool assembly  2080  and/or to the LED assembly  2060 . In some embodiments, the hydraulic manifold  2020  includes two or more bellows actuators  2022 . In some cases, the use of two or more bellows actuators  2022  can provide continual pressurization of fluid travelling from the bellows actuators  2022  to the tool assembly  2080  and/or to the LED assembly  2060 . For example, the compression strokes of the linear actuator  2026  of the bellows actuators  2022  can be timed such that, at a given moment in the operation of the hydraulic pressure circuit  2000 , at least one of the linear actuators  2026  is operating in a compression stroke. 
     Pressurized fluid output from the bellows actuators  2022  to the tool assembly  2080  can pass through a proportioning valve  2034 . The proportioning valve  2034  can control the amount of fluid and/or the pressure of the fluid that passes from the bellows actuators  2022  to the tool assembly  2080 . In some cases, the proportioning valve  2034  can control the operating speed and/or operating power of the tool assembly  2080 . As will be explained in more detail below, pressurized fluid from the bellows actuators  2022  can be passed through a nozzle  2086  and impeded upon a turbine or other drive source for a tool  2082  (e.g., a hydraulic drill or other surgical tool). In some embodiments, the nozzle  2086  intensifies the velocity of the pressurized fluid. At least a portion of the fluid used to drive the tool  2082  can be collected and/or redirected back to the bellows actuators  2022  in order to reenergize the fluid. In some embodiments, a hydrophobic filter  2088  can be positioned in a branch of the fluid channel through which fluid returning from the tool assembly  2080  to the bellow actuators  2022  flows. The hydrophobic filter  2088  can allow air or other gases from the fluid channel to exit the hydraulic pressure circuit  2000  while preventing the hydraulic fluid (e.g., the water, saline, and/or oil) from exiting the hydraulic pressure circuit  2000 . In some embodiments, a one-way valve can be positioned in the return fluid channel between the tool assembly  2080  and the bellow actuators  2022  to inhibit air or other gases from entering the hydraulic pressure circuit  2000  through the hydrophobic filter  2088 . 
     In some embodiments, a portion of the fluid exiting the fluid source  2010  can be directed to the LED assembly  2060 . This portion of fluid can be directed through the hydraulic manifold  2020  before it reaches the LED assembly  2060 . This portion of fluid can bathe the LEDs  2062  and can provide conductive and/or convective cooling for the LEDs  2062 . In some embodiments, the LED assembly  2060  includes a roller pump or other source of fluid pressurization that pulls fluid onto and around the LEDs  2062  from the hydraulic manifold  2020  and/or from the fluid source  2010 . After passing over/around the LEDs  2062 , the cooling fluid can be directed via a fluid conduit back to the fluid source  2010 , as illustrated in  FIG. 37 . 
     In some embodiments, a portion of the fluid exiting the bellows actuators  2022  is directed to one or more nozzles  2066  in or on the LED assembly  2060 . An on/off valve can be positioned on or around the fluid conduit between the bellows actuators  2022  and the LED assembly  2060 . The on/off valve can be configured to provide a pulsed pressure for washing the LEDs  2062 . The fluid used to wash the LEDs  2062  can be redirected to the fluid source  2010 . 
     In some embodiments, the pressure and pulse rate of the fluid washing and air drying of the LEDs  2062  can be further controlled through the addition of a check valve near the nozzles  2066 . In some embodiments, when a pressure differential across the check valve (e.g., the ratio of the upstream fluid pressure to the downstream fluid pressure) reaches a predetermined level, the check valve can open to release a stronger pulse and higher pressure of fluid for washing the LEDs than would be achieved with the pulsing regulated by valves at the cassette. The check valve can be a duck billed valve, a diaphragm check valve, lift check valve, or any other check valve known in the art. In some embodiments, a T connector can be used near the nozzle connecting the air line and the saline line to the nozzle, thereby allowing for the air and saline to share the same nozzle. Additionally, in some embodiments, the two saline lines from the fluid source and/or pistons can be connected by a T connector to connect the two fluid lines to the nozzle. A check valve can be positioned near the nozzle to facilitate a pressure buildup on the upstream side of the check valve. In some embodiments, such a buildup of pressure can release a high pressure pulse of fluid for washing the LEDs. Alternatively, in some embodiments, a T connector can be used to connect a fluid line, from the fluid source and/or the pistons, and an air line. The air line can contain a high pressure and low pressure air source. The low pressure combined with the fluid line can exert a force to open the check valve near the nozzle. In some embodiments, a subsequent higher pressure blows air through the nozzle to allow for drying of the LEDs through the same nozzle as washing. In some embodiments, the pulse of fluid for washing the LEDs can have a pressure ranging from about 60 psi to about 125 psi. 
     Additionally, in some embodiments, the LED assembly  2060  can be cooled by a refrigeration system. In some embodiments, the refrigeration system can comprise a micro miniature refrigerator (Joule Thomson effect) cooler to circulating saline and cool the LEDs  2062 . The temperature change in the compressed gas system when the gas or fluid is forced through a valve can allow for the cooling of the gases or fluids if kept insulated so that no heat is exchanged with the environment. 
       FIG. 38  illustrates an embodiment of a hydraulic pressure circuit  2100 . Some numerical references to components in  FIG. 38  are the same as or similar to those previously described for the hydraulic pressure circuit  2000  (e.g. hydraulic manifold  2120  v. hydraulic manifold  2020 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2100  of  FIG. 38  shows certain variations to the hydraulic pressure circuit  2000  of  FIG. 37 . 
     In some embodiments, the hydraulic pressure circuit  2100  includes an air pump  2190 . The air pump  2190  can be configured to provide pressurized air, via a fluid conduit, to the nozzles  2166  of the LED assembly  2160 . In some embodiments, the pressurized air can be used to dry the LEDs  2162  before or after washing the LEDs. A filter  2192  (e.g., a hydrophobic and/or antimicrobial filter) can be positioned between the air pump  2190  and the nozzles  2166 . 
     The hydraulic pressure circuit  2100  can include a balloon  2170 . The balloon  2170  can be used as a slave actuator to power a tool (e.g., a Kerrison). For example, the balloon  2170  can be used to power tools that require high pressure (e.g., 100-150 psi) actuators. In some embodiments, as discussed below, one or more tools are actuated via pneumatic actuators. 
       FIG. 39  illustrates an embodiment of a hydraulic pressure circuit  2200 . Some numerical references to components in  FIG. 39  are the same as or similar to those previously described for the hydraulic pressure circuit  2100  (e.g. hydraulic manifold  2220  v. hydraulic manifold  2120 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2200  of  FIG. 39  shows certain variations to the hydraulic pressure circuit  2100  of  FIG. 38 . 
     In some cases, the hydraulic pressure circuit  2200  can include an air accumulator  2294  located between the air pump  2290  and the nozzles  2066  of the LED assembly  2060 . The air accumulator  2294  can provide a pre-loaded source of air for use in drying the LEDs  2266  and can help reduce lag between the operation of the air pump  2290  and the delivery of air to the nozzles  2066 . 
     A hydraulic pump  2236  (e.g. a roller (peristaltic) pump, a linear actuator pump, a gear pump, a radial piston pump, a screw pump, and/or an axial piston pump) can be positioned within the hydraulic manifold  2220 . The hydraulic pump  2236  can be positioned and configured to increase the fluid pressure and/or fluid velocity of fluid output from the fluid source  2210 . In some embodiments, the hydraulic pump  2236  pulls fluid from the fluid source  2210 . Fluid from the hydraulic pump  2236  can be directed toward the bellows actuators  2222  and/or toward the LED assembly  2260 . In some embodiments, positioning the hydraulic pump  2236  within the hydraulic manifold  2220  can eliminate the need for a nurse or other practitioner to handle the hydraulic pump  2236  during assembly and/or disassembly of the hydraulic pressure circuit  2200 . 
       FIG. 40  illustrates an embodiment of a hydraulic pressure circuit  2300 . Some numerical references to components in  FIG. 40  are the same as or similar to those previously described for the hydraulic pressure circuit  2200  (e.g. hydraulic manifold  2320  v. hydraulic manifold  2220 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2300  of  FIG. 40  shows certain variations to the hydraulic pressure circuit  2200  of  FIG. 39 . 
     The hydraulic pressure circuit  2300  can include a second hydraulic pump  2338  (e.g. a roller (peristaltic) pump, a linear actuator pump, a gear pump, a radial piston pump, a screw pump, and/or an axial piston pump). The second hydraulic pump  2338  can be positioned on or within the hydraulic manifold  2320 . In some embodiments, the second hydraulic pump  2338  is positioned on the fluid path through which the fluid exiting the tool assembly  2380  is directed as the exiting fluid is redirected to the bellows actuators  2322 . The second hydraulic pump  2338  can be configured to increase the pressure and/or velocity of said exiting fluid. In some embodiments, the second hydraulic pump  2338  pulls fluid from the tool assembly  2380  after the fluid has been used to power the turbine or other power source for the tool  2382 . 
       FIG. 41  illustrates an embodiment of a hydraulic pressure circuit  2400 . Some numerical references to components in  FIG. 41  are the same as or similar to those previously described for the hydraulic pressure circuit  2300  (e.g. hydraulic manifold  2420  v. hydraulic manifold  2320 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2400  of  FIG. 41  shows certain variations to the hydraulic pressure circuit  2300  of  FIG. 40 . 
     In some embodiments, the hydraulic pressure circuit  2400  includes a second tool  2486 . The second tool  2486  can be, for example, a hydraulically-driven Kerrison. In some embodiments, the second tool  2486  is driven by fluid by a bellows actuators  2422 . The hydraulic manifold  2420  can include a proportioning valve  2434  positioned on the fluid path between the bellows actuators  2422  and the second tool  2486 . This proportioning valve  2434  can control the amount of fluid and/or the pressure of the fluid that passes from the bellows actuators  2422  to the second tool  2486 . In some cases, the proportioning valve  2434  can control the operating speed and/or operating power of the second tool  2486 . Additional proportioning valves  2434  can be positioned on the fluid paths of the fluid returning from the tool  2482  to the bellows actuators  2422 . These proportioning valves  2434  can be configured to control the rate at which fluid is returned to the bellows actuators  2422  from the tool  2484 . In some embodiments, one or more of the valves  2432  in the hydraulic manifold  2420  can be interchangeable with a proportioning valve  2434 . 
     In some embodiments, the hydraulic pressure circuit  2400  includes a pneumatic tool assembly  2450 . The pneumatic tool assembly  2450  can include a pneumatic tool  2453  (e.g., micro-scissors, micro-forceps). The pneumatic tool  2453  can be powered by the air pump  2490 . In some embodiments, the pneumatic tool assembly  2450  includes a pneumatic module  2451  which can include a three-way valve  2456  (e.g., a three-way, two position valve) positioned between the air pump  2490  and the pneumatic tool  2453 . The three-way valve  2456  can be configured to selectively direct air or other gases from the air pump  2490  to the pneumatic tool  2453 . In some embodiments, the pneumatic tool assembly  2453  includes a fluid conduit extending between the pneumatic tool  2453  and the three-way valve  2456  and configured to facilitate passage of air or other gases from the pneumatic tool  2453  to the three-way valve  2456 . 
       FIG. 42  illustrates an embodiment of a hydraulic pressure circuit  2500 . Some numerical references to components in  FIG. 42  are the same as or similar to those previously described for the hydraulic pressure circuit  2400  (e.g. hydraulic manifold  2520  v. hydraulic manifold  2420 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2500  of  FIG. 42  shows certain variations to the hydraulic pressure circuit  2400  of  FIG. 41 . 
     In some embodiments, the pneumatic module  2551  can include an air accumulator  2558 . The air accumulator  2558  can be positioned along the fluid path between the air pump  2590  and the nozzles  2566  of the LED assembly  2560 . The air accumulator  2558  can be configured to reduce lag between the production of pressurized gas by the air pump  2590  and delivery of said pressurized gas to the nozzles  2566 . Positioning the air accumulator  2558  outside the hydraulic manifold  2520  can simplify the structure and design of the hydraulic manifold  2520  unit (e.g., the cassette in which the hydraulic manifold  2520  may be housed). 
       FIG. 43  illustrates an embodiment of a hydraulic pressure circuit  2600 . Some numerical references to components in  FIG. 43  are the same as or similar to those previously described for the hydraulic pressure circuit  2500  (e.g. hydraulic manifold  2620  v. hydraulic manifold  2520 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2600  of  FIG. 43  shows certain variations to the hydraulic pressure circuit  2500  of  FIG. 42 . 
     In some embodiments, the air accumulator  2658  can be positioned on or in the fluid path between the air pump  2690  and the pneumatic tool  2653 . The air accumulator  2690  can reduce the lag between the production of pressurized gas from the air pump  2658  and the delivery of said pressurized gas to the pneumatic tool  2653  and/or to the nozzles  2666  of the LED assembly  2660 . Various pneumatic indicators  2655  can be positioned around and/or within the pneumatic assembly  2650  to provide visual indication of the status of various pneumatic components within the pneumatic assembly  2650 . 
     In some cases, the second tool  2686  can be configured to redirect at least a portion of the fluid used to power the second tool  2686  back to the hydraulic manifold  2620 . For example, a fluid line can extend from the second tool  2686  to the hydraulic manifold  2620  such that fluid exhausted from the second tool  2686  can be directed to the bellows actuators  2622  to reenergize said exhausted fluid. 
     The hydraulic manifold  2620  can include a fluid-air separator  2637 . The air separator  2637  can be configured to remove air and other gases from the fluid line onto which the air separator  2637  is installed. For example, the fluid-air separator  2637  can be positioned and configured to remove air and other gases from the fluid that is directed toward the bellows actuators  2622  from the tool  2682  and/or from the second tool  2686 . Such air-gas mixtures can result from actively scavenging low velocity hydraulic fluid and air from the tool  2682  and/or second tool  2686  via annular vents around the turbines of the tools or otherwise after the hydraulic fluid is used to power the tool  2682  and/or second tool. Removal of gases from the fluid lines of the hydraulic manifold  2620  can improve the performance of the hydraulic components of the hydraulic pressure system  2600  (e.g., the tools  2682 ,  2686 ). In some embodiments, the hydraulic manifold  2620  includes a pressure compensation source  2639  (e.g., a master-slave balloon) configured to regulate the pressure in one or more of the fluid lines of the hydraulic manifold  2620 . 
     In some embodiments, one or more of the valves within the hydraulic pressure circuits described above can be a consumable valve (e.g., the valve can be one-time use and/or disposable). For example, one or more of the valves within the hydraulic manifolds can be a consumable check valve configured to be discarded after use. Use of disposable valve can reduce the part and maintenance costs associated with the hydraulic pressure circuits. For example, the reusable valves or other reusable components of the hydraulic manifold (e.g., valves, housings, fluid lines, pumps) could be constructed from polymers, elastomers, and/or other low-cost materials. 
       FIG. 43A  illustrates an embodiment of a hydraulic pressure circuit  2700 . Some numerical references to components in  FIG. 43A  are the same as or similar to those previously described for the hydraulic pressure circuit  2600  (e.g. hydraulic manifold  2720  v. hydraulic manifold  2620 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2700  of  FIG. 43A  shows certain variations to the hydraulic pressure circuit  2600  of  FIG. 43 . 
     In some embodiments, the hydraulic pressure circuit  2700  can include a pneumatic pressure assembly  2765 . The pneumatic pressure assembly  2765  can function as a pressure source for the hydraulic fluid of the hydraulic pressure circuit  2700 . In some embodiments, the pneumatic pressure assembly  2765  is used in combination with mechanical actuators (e.g., bellows similar to or the same as bellows  2628 ) to pressurize the hydraulic fluid within the hydraulic pressure circuit  2700 . In some embodiments, the pneumatic pressure assembly  2765  is used instead of such mechanical actuators to pressurize the hydraulic fluid within the hydraulic pressure circuit  2700 . 
     The pneumatic pressure assembly  2765  can include one or more pneumatic actuators. The pneumatic actuators can be configured to pressurize air or other gases within the pneumatic pressure assembly  2765 . For example, the pneumatic pressure assembly  2765  could include one or more linear actuators  2726 ,  2726 ′ driven by one or more motors  2724 ,  2724 ′. The linear actuators  2726 ,  2726 ′ can be used to increase and decrease the pressure of a pneumatic fluid within a pneumatic actuator chamber  2723 ,  2723 ′. For example, the linear actuators  2726 ,  2726 ′ can be used to increase and decrease the size (e.g., the volume) of the pneumatic actuator chambers  2723 ,  2723 ′ to effect changes in pressure for the pneumatic fluid within the actuator chambers  2723 ,  2723 ′. 
     In some embodiments, the pneumatic pressure assembly  2765  includes one or more pneumatic pressure sources. The one or more pneumatic pressure sources can be in fluid communication with the actuator chambers  2723 ,  2723 ′. For example, the pneumatic pressure assembly  2765  can include a pump  2796 . The pump  2796  can be configured to provide pressurized pneumatic fluid (e.g., air and/or other gases) to the actuator volumes  2723 ,  2723 ′. The pump  2796  can be configured to pressurize the pneumatic fluid to pressures above atmospheric (e.g., 60 psi). In some configurations, one or more valves  2727 ,  2727 ′ can be positioned in the fluid path(s) between the pump  2796  and the chambers  2723 ,  2723 ′. In some embodiments, the use of the pump  2796  can reduce or eliminate a need to connect the pneumatic pressure assembly  2765  and/or hydraulic pressure system  2700  to a hospital compressed air system. The valves  2727 ,  2727 ′ can be configured to selectively allow and/or constrict fluid communication between the pump  2796  and the chambers  2723 ,  2723 ′. In some embodiments, the valve  2727 ,  2727 ′ are three way, two position valves. Many different types of valves are possible (e.g., one-way check valves, pincher valves, solenoid valves, etc.). 
     The pneumatic actuator chambers  2723 ,  2723 ′ can be in fluid communication with secondary pneumatic actuator chambers  2723   a ,  2723   a ′. In some embodiments, one or more valves  2729 ,  2729 ′ can be positioned in the fluid path(s) between the actuator chambers  2723 ,  2723 ′ and the secondary pneumatic actuator chambers  2723   a ,  2723   a ′. The valves  2729 ,  2729 ′ can be configured to selectively allow and/or constrict fluid communication between the actuator chambers  2723 ,  2723 ′ and the secondary pneumatic actuator chambers  2723   a ,  2723   a . In some embodiments, the valve  2729 ,  2729 ′ are three way, two position valves. Many different types of valves are possible (e.g., one-way check valves, pincher valves, solenoid valves, etc.). 
     The secondary pneumatic actuator chambers  2723   a ,  2723   a ′ can be positioned at least partially within the hydraulic manifold  2720 . Pressure within chambers  2723   a ,  2723   a ′ can exert force upon floating piston heads  2726   a ,  2726   a ′. In some embodiments, the secondary chambers  2723   a ,  2723   a ′ do not include floating piston heads and the pressurized pneumatic fluid interacts directly with the hydraulic fluid in the chambers  2723   a ,  2723   a ′. The floating piston heads  2726   a ,  2726   a ′ can define an interface between the pneumatic fluid of the pneumatic pressure assembly  2765  and the hydraulic fluid F of the hydraulic manifold  2720  and hydraulic pressure circuit  2700 . Exertion of force upon the floating piston heads  2726   a ,  2726   a ′ by the pneumatic fluid within the chambers  2723   a ,  2723   a ′ can cause the floating piston heads  2726   a ,  2726   a ′ to increase the pressure of the hydraulic fluid F on the side of the floating piston heads  2726   a ,  2726   a ′ opposite the chambers  2723   a ,  2723   a ′. In embodiments without piston heads, introduction of pressurized pneumatic fluid into the chambers  2723   a ,  2723   a ′ can increase the pressure of the hydraulic fluid F within the chambers  2723   a ,  2723   a ′. In some embodiments, the floating piston heads  2726   a ,  2726   a ′ in combination the pressurized pneumatic fluid within the secondary pneumatic actuator chambers  2723   a ,  2723   a ′ can perform the same or a similar function as performed by the bellows actuators described above and below. In some embodiments without floating piston heads, the pressurized pneumatic fluid acting directly on the hydraulic fluid within the chambers  2723   a ,  2723   a ′ can perform the same or a similar function as performed by the bellows actuators described above and below. 
     In some embodiments, the pneumatic pressure assembly  2765  includes one or more pneumatic indicators  2725 ,  2725 ′,  2725   a ,  2725   a ′. In some embodiments, pneumatic indicators  2725   a ,  2725   a ′ are redundant backup indicators in the case of malfunction and/or failure of the indicators  2725 ,  2725 ′. The indicators can be configured to monitor the pressure within the fluid lines connecting the pneumatic actuator chambers  2723 ,  2723 ′ with the secondary pneumatic actuator chambers  2723   a ,  2723   a ′. The indicators can be operably coupled (e.g., electrically connected via wired and/or wireless connections) with the motors  2724 ,  2724 ′ and/or with the linear actuators  2726 ,  2726 ′. In some embodiments, the indicators  2725 ,  2725 ′,  2725   a ,  2725   a ′ are operably coupled with the pump  2796  and/or other pneumatic pressure source. 
     According to some configurations, the pneumatic pressure assembly  2765  can operate in the following manner. During a compression stroke, the linear actuator  2726  can be configured to compress the pneumatic fluid within the chamber  2723  (e.g., in response to input from the motor  2724 ) to maintain a predetermined pressure (e.g., 120 psi) within the fluid line connecting the chamber  2723  with the secondary chamber  2723   a . The indicator  2725  can monitor the pressure within the fluid line and can communicate (e.g., via an operable connection such as a wired or wireless electrical connection) with the motor  2724  to ensure that the pressure within the fluid line remains at or above a minimum acceptable pressure. 
     The valve  2729  can be configured to permit fluid communication between the chamber  2723  and the secondary chamber  2723   a  during the compression stroke of the linear actuator  2726 . Compression of the pneumatic fluid within the chamber  2723  during the compression stroke can cause an increase in pressure within the secondary chamber  2723   a . Increase in pressure of the pneumatic fluid in the secondary chamber  2723   a  can force the floating piston  2726   a  to (or can directly, in the case of a piston-less embodiment) compress the hydraulic fluid F, thus pressuring the fluid F for use in the hydraulic pressure circuit. 
     Upon completion of the compression stroke of the linear actuator  2726 , the valve  2729  can cut off fluid communication between the chamber  2723  and the secondary chamber  2723   a  and allow the secondary chamber  2723   a  to vent to ambient. At this point, the pneumatic fluid within the secondary chamber  2723   a  can vent to atmosphere and the hydraulic fluid F provided by the return lines from the tool  2782  and/or second tool  2786  and/or from the fluid reservoir  2712  can increase the pressure on the hydraulic side of the floating piston  2726   a . Such an increase in pressure can cause the piston  2726   a  to move and reduce the volume of the secondary chamber  2723   a . In embodiments without piston heads in the chambers  2723   a ,  2723   a ′, the introduction of hydraulic fluid F from the return lines from the tool  2782  and/or second tool  2786  and/or from the fluid reservoir  2712  can force the pneumatic fluid out from the chambers  2723   a ,  2723   a′.    
     Concurrent with the venting of the secondary chamber  2723   a , the valve  2727  can be opened to permit fluid communication between the pump  2796  and the chamber  2723 . The pump  2796  can provide pneumatic fluid (e.g., air and/or other gases) at a pressure above ambient (e.g., 60 psi) to help facilitate retraction of the linear actuator  2726 . In some embodiments, the motor  2724  can act in combination with or instead of the pump  2796  to quickly retract the linear actuator  2726 . Upon refilling of the chamber  2723  with pneumatic fluid (e.g., upon completion of the expansion stroke of the linear actuator  2726 ), the valve  2727  can cut off fluid communication between the pump  2796  and the chamber  2723 . In some embodiments, the valve  2727  can be configured to facilitate venting of the pressurized fluid from the pump  2796  to ambient. Although the operation of the pneumatic circuit  2765  has been described in the context of one linear actuator  2726 , all or at least most of the functions described with regard to linear actuator  2726  and its corresponding valves and chambers equally describe the functioning of linear actuator  2726 ′ and its corresponding valves and chambers (e.g., chambers  2723 ′ and  2723   a ′, valves  2727 ′ and  2729 ′, piston  2726   a ′). In some embodiments, the use of more than one linear actuator  2726  and corresponding valves and chambers can facilitate substantially continual pressurization of the hydraulic fluid F in the hydraulic pressure circuit  2700 . For example, while the linear actuator  2726  is in the compression stroke, the linear actuator  2726 ′ can be configured to operate in the expansion stroke such that, upon completion of the compression stroke of the linear actuator  2726 , the compression stroke of the linear actuator  2726 ′ can begin. 
       FIG. 43B  illustrates an embodiment of a hydraulic pressure circuit  3000 . Some numerical references to components in  FIG. 43B  are the same as or similar to those previously described for the hydraulic pressure circuit  2700  (e.g. hydraulic manifold  3020  v. hydraulic manifold  2720 ). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  3000  of  FIG. 43B  shows certain variations to the hydraulic pressure circuit  2700  of  FIG. 43A . 
     In some embodiments, the fluid lines connecting the various components of the pneumatic pressure assembly  3065  can include one or more release valves  3067  configured to open if the pressure within a given fluid line rises above a predetermined maximum (e.g., 150 psi). The release valves  3067  can be positioned on the fluid lines between the valves  3027 ,  3027 ′ and the chambers  3023 ,  3023 ′. In some embodiments, the fluid line connecting the pump  3096  with the chambers  3023 ,  3023 ′ can include a venting valve  3061  configured to selectively vent to atmosphere. Such a venting valve  3061  can improve the safe operation of the pneumatic pressure assembly  3065  and can allow the pump  3096  to continue safely running throughout the use of the pneumatic pressure assembly  3065 . In some embodiments, the fluid line connecting the pump  3096  with the chambers  2723 ,  2723 ′ can include a venting valve and/or pressure relief valve  3069  configured to open and vent to atmosphere upon detection of a predetermined maximum pressure (e.g., 70 psi). 
     In certain configurations, the pump  3096  can be in fluid communication with and supply pressurized pneumatic fluid to the air accumulator  3058  of the pneumatic assembly  3050 . A pressure regulator  3069   a  can be positioned on the fluid line between the pump  3096  and the accumulator  3058  to regulate the pressure within the line. In some embodiments, one or more pneumatic indicators  3055 ,  3063  can be positioned on the fluid line between the pump  3096  and the air accumulator  3058 . In some embodiments, such an arrangement can eliminate the need for a second pump  2790  and can simplify the overall design of the hydraulic pressure circuit  3000 . The pneumatic assembly  3050  can include one or more vent valves  3034   c  (e.g., valves configured to vent to atmosphere) configured to reduce the risk of over-pressurizing the pneumatic assembly  3050 . In some embodiments, a pair of pneumatic indicators (e.g., pressure sensors)  3055   a ,  3055   b  are positioned on the fluid lines between the air accumulator  3058  and the vent valve  3034   c  and between the air accumulator  3058  and the pneumatic tool  3053 . A restriction  3057  (e.g., an orifice) between the two pneumatic indicators  3055   a ,  3055   b  can help to detect an open pneumatic line. In some embodiments, a restriction  3057  can help prevent sudden reaction in the pneumatic tool  3053  when the vent valve  3034   c  is opened to vent the pneumatic assembly  3050 . 
     One or more of the valves (e.g., valves  3027 ,  3027 ′,  3029 ,  3029 ′,  3034   a ,  3034   b ,  3034   c ) in the pneumatic pressure assembly  3065  and/or in the pneumatic assembly  3050  can be spring-driven. For example, the valves can be biased to the open/venting configuration in the default position. In some embodiments, such a configuration can help reduce the risk of over-pressurization of the pneumatic pressure assembly  3065  and/or of the pneumatic assembly  3050  and can ensure venting of the assemblies  3065 ,  3050  upon shut down of the assemblies  3065 ,  3050 . 
     One or more of the valves  3034  on the cassette  3020  can be diaphragm valves formed by an elastomeric element. The valves  3034  can be used to control the first tool  3082  and/or second tool  3086  (e.g., a Kerrison and/or drill). The valves  3034  can be actuated by non-disposable linear electromagnetic actuators. 
       FIG. 43C  illustrates an embodiment of a hydraulic pressure circuit  2800 . Some numerical references to components in  FIG. 43C  are the same as or similar to those previously described for the hydraulic pressure circuit  3000  (e.g. linear actuators  2824 ,  2824 ′ v. linear actuators  3024 ,  3024 ′). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2800  of  FIG. 43C  shows certain variations to the hydraulic pressure circuit  3000  of  FIG. 43B . 
     For example, the hydraulic pressure circuit  2800  can include a hydraulic pump  2814  (e.g., a peristaltic pump) or other fluid pressurizing component to inhibit fluid backflow into the fluid source  2812  from the secondary chambers  2823   a ,  2823   a ′. One way valves  2832  can be positioned in the fluid paths between the fluid source  2812  and the secondary chambers  2823   a ,  2823   a ′ to selectively permit refilling of one or more of the secondary chambers  2823   a ,  2823   a ′ from the fluid source  2812 . 
     The pneumatic pressure assembly  2865  can include two or more linear actuators  2824 ,  2824 ′ configured to translate within two or more chambers  2823 ,  2823 ′. The fluid lines between the chambers  2823 ,  2823 ′ and the secondary chambers  2823   a ,  2823   a ′ can include air inlet valves  2827 ,  2827 ′. In some embodiments, the inlets to the secondary chambers  2823   a ,  2823   a ′ include three-way solenoid valves  2832   a ,  2832   a ′ configured to selectively allow fluid ingress/egress two and from the secondary chambers  2823   a ,  2823   a ′. The three-way solenoid valves  2832   a ,  2832   a ′ can be configured to vent the fluid lines between the chambers  2823 ,  2823 ′ and the secondary chambers  2823   a ,  2823   a ′. Pinch valves  2832 ′ or other valves can be used to selectively permit passage of pressurized hydraulic fluid from the secondary chambers  2823   a ,  2823   a ′ to the remaining hydraulic circuit (e.g., via fluid path  2899 ). 
       FIG. 43D  illustrates an embodiment of a hydraulic pressure circuit  2900 . Some numerical references to components in  FIG. 43D  are the same as or similar to those previously described for the hydraulic pressure circuit  2800  (e.g. secondary chambers  2923   a ,  2923   a ′ v. secondary chambers  2823   a ,  2823   a ′). It is to be understood that the components can be the same in function or are similar in function to previously-described components. The hydraulic pressure circuit  2900  of  FIG. 43D  shows certain variations to the hydraulic pressure circuit  2800  of  FIG. 43C . 
     For example, the pneumatic pressure assembly  2965  can include a single pneumatic actuator chamber split into a first pneumatic actuator chamber  2923  and a second pneumatic chamber  2923 ′. A single linear actuator  2924  can be transitioned back and forth (e.g., right and left in  FIG. 43D ) to alternately compress and expand the first and second chambers  2923 ,  2923 ′. A pump  2996  can be used to provide compressed pneumatic fluid to the chambers  2923 ,  2923 ′ during their respective expansion strokes via valves  2995 ,  2995 ′ (e.g., solenoid valves). In some embodiments, the pneumatic circuit  2965  includes a pressure chamber  2997  configured to store pre-compressed pneumatic fluid for distribution to the chambers  2923 ,  2923 ′. 
     As explained above, portions of or the entire hydraulic manifold  2020 ,  2120 ,  2220 ,  2320 ,  2420 ,  2520 ,  2620  ( 2020  hereinafter for simplicity) can be housed within a cassette containment apparatus. For example, as illustrated in  FIG. 44A , a cassette housing  2021  can include a number of external connectors  2002 . One or more valves  2032  (e.g., pinch valves, diaphragm valves, elastomeric valves) can be attached to the cassette housing  2021 . In some embodiments, the valve assembly  2032  on the cassette housing  2021  can have a flexible pad  2041 , a cavity  2040 , a valve opening  2038 , and a pincher or valve stem actuator  2039 . The valve stem actuators  2039  can be fixed to a console into or onto which the cassette is connected. The valve stem actuators  2039  can be fixed to a console into or onto which the cassette is connected. In some embodiments, the valve stem  2039  can exert a downward force on the flexible pad  2041  thereby compressing the flexible pad  2041  into the cavity  2040  of the cassette housing  2021  above the valve opening  2038  and toward the valve opening  2038 . The valve opening  2038  can be fully obstructed, partially obstructed, or fully open at varying amounts depending on the compression of the flexible pad  2041  by the valve stem  2039 . The degree of obstruction of the valve opening  2038  by the flexible pad  2041  can regulate, direct, or control the flow of fluid into the valve. For example, the valve stem  2039  can be used to pulse the flow of fluid through a valve opening  2038 . In some embodiments, the valve stem  2039  can be used to accelerate fluid flow through a valve opening  2038  (e.g., the valve stem  2039  can constrict the valve opening  2038  and act as a nozzle). 
     In some embodiments, the valve opening  2038  can be obstructed by the flexible pad  2041  and can allow for precise control of the degree and period of obstruction by the valve stems  2039  depression onto to the flexible pad. The flexible valve opening can allow for the flow of fluid through the valve to be obstructed at such varying degrees or with a pulsing flow thereby allowing for a fluid flow through the valve to be sustained at a wide range of desired flow rates by controlling the frequency and distance of depression of the flexible pad  2041  by the valve stem  2039 . For example, the valves  2032  in and on the cassette housing  2021  can act as diaphragm valves to flex flexible pads on the top of the cassette housing  2021  and throttle the substantially constant high pressure hydraulic fluid supplied from the bellows or other hydraulic pressure source. In some embodiments, the valve stem  2039  can be depressed into the flexible pad  2041  by mechanical or hydraulically driven forces, or other forces known in the art or described herein. In some such configurations, pressurized hydraulic fluid can be proportionally directed to the various subsystems and fluid pathways of the hydraulic pressure circuit (e.g., the hydraulic tools, LED arrays). In some configurations, the cassette housing  2021  is a substantially closed container. In some embodiments, the cassette housing  2021  has one or more opened portions. 
     As illustrated in  FIGS. 44B and 44C , the cassette assembly  2021  can include a cassette cap portion  2021   a  and a cassette body  2021   b . The cassette cap portion  2021   a  can include one or more flexible pads  2041 , one or more valves  2032 , and one or more cavities  2040 . Additionally, the pinchers or valve stem actuators  2039  can be included in the cassette assembly  2021 . The cassette body  2021   b  can include one or more cylindrical containers configured to house the bellows  2028  of the bellows actuators  2022 . In some embodiments, the cassette assembly  2021  includes a plurality of tubing sections  2023  configured to connect various components and external connectors  2002  to one another. One or more of the components of the cassette assembly  2021  and/or of the hydraulic manifold  2020  can be consumable. For example, as explained above, the valves, fluid lines, body, cap portion, bellows, and/or ports of the cassette assembly  2021  can be consumable. The use of consumable parts can reduce the amount of assembly required hydraulic manifold  2020  and can reduce the likelihood of introducing contaminants to the hydraulic pressure circuit  2000  and can reduce or eliminate the cleanup process required for the hydraulic pressure circuit  2000  after use. 
       FIGS. 44D-44F  illustrate an embodiment of a cassette assembly configured to contain the at least a portion of the hydraulic manifold  2720 ,  3020 . The cassette housing  3021  can include one or more connector interfaces  3002 . The cassette housing  3021  can be a substantially closed container. In some embodiments, the cassette  3021  is at least partially open on one or more side. 
     In some embodiments, the cassette housing  3021  includes a cassette cap portion  3021   a  and a cassette body  3021   b . The cassette cap portion  3021   a  can define one or more cap fluid channels  3057   a  configured to provide fluid communication between fluid lines and connectors/ports in and on the cassette  3021 . In some embodiments, the fluid channels can contain the cavity  2040  in which the flexible pads  2041  are depressed into by the valve stem  2039  as described herein. Fluid channel caps  3059  can be positioned on top of the cap fluid channels  3057   a  to inhibit fluid from leaking from the channels  3057   a . In some embodiments, the fluid channel caps can be a flexible pad  2041  used for the valve assembly as described herein. The fluid channel caps  3059  can be constructed from a flexible or semi-flexible material (e.g., elastomers, polymers, etc.). Valves stems  2039  can be used to flex the caps  3059 . The valves stems  2039  can be used to close off or open the connectors/ports in the cassette  3021 . In some embodiments, the valve stems  2039  act as diaphragm valves and restrict the flow paths in the fluid channels  3057   a  without completely closing off the connectors/ports. In some such configurations, the valves stems  2039  act as proportional valves to selectively distribute hydraulic fluid flow between the various components and subsystems of the hydraulic pressure circuit  3000  (e.g., the hydraulic tools, the LED array, etc.). One or more flexible and/or rigid tubing sections  3057  can be used to connect fluid connectors/ports (e.g., connectors interfaces  3002 ) within the cassette  3021 . The secondary chambers  3023   a ,  3023   a ′ can, in some embodiments, be housed at least partially within the cassette  3021 . 
     As explained above, the tool  2082 ,  2182 ,  2282 ,  2382 ,  2482 ,  2582 ,  2682  (hereinafter  2082  for simplicity) can be driven by a hydraulic turbine. In some embodiments, as illustrated in  FIGS. 45A and 45B , a hydraulic turbine  2070  includes a turbine housing  2071 . In some cases, at least a portion of a nozzle frame  2072  is housed within the turbine housing  2071 . In some embodiments, stator vanes can be used in conjunction with and/or in place of the nozzle frame  2072 . The nozzle frame  2072  can include one or more turbine nozzles  2073 . In some embodiments, the turbine nozzles  2073  are positioned in a circumferential array, as illustrated in  FIG. 45A . Each of the turbine nozzles  2073  can have a nozzle inlet  2074  and a nozzle outlet  2075 . In some embodiments, the nozzles  2073  have substantially constant cross-sectional areas from nozzle inlet  2074  to nozzle outlet  2075  (e.g., drill hole-type nozzles). For example, circular nozzles can be used. 
     The relative areas of the nozzle inlet  2074  and the nozzle outlet  2075  can vary. For example, the nozzle outlet  2075  can have an area that is greater than or equal to approximately 125% of the area of the nozzle inlet  2074  and/or less than or equal to about 600% of the area of the nozzle inlet  2074 . In some embodiments, the area of the nozzle outlet  2075  is approximately 300% of the area of the nozzle inlet  2074 . 
     As illustrated in  FIG. 45B , the profile of the nozzle  2073  can widen between the nozzle inlet  2074  and the nozzle outlet  2075 . The rate at which the turbine nozzle  2073  widens between the nozzle inlet  2074  and the nozzle outlet  2075  can vary. For example, the nozzle  2073  can flare out in the direction of the nozzle outlet  2075 . In some embodiments, the profile of the nozzle  2073  narrows between the nozzle inlet  2074  and the nozzle outlet  2075 . In some embodiments, the nozzles  2073  have substantially constant cross-sectional areas from nozzle inlet  2074  to nozzle outlet  2075  (e.g., drill hole-type nozzles). In some embodiments, the nozzle inlet  2074  can be tapered or flared in such that an opening into the nozzle inlets  2074  is wider or larger than a midsection of the nozzles  2073 . 
     In some embodiments, hydraulic fluid is directed through the nozzle frame  2072  toward an impeller  2076 . The impeller  2076  can include a plurality of impeller blades  2077  around the outer periphery of the hub of the impeller  2076 . The impeller blades  2077  can rotate within a blade cavity  2077   a . The impeller  2076  can be integral with or otherwise rotationally coupled with an output shaft  2079  for driving the tool  2082 , which can be a drill or other rotational tool. The outer diameter of the hub of the impeller  2076  can be smaller than the outside diameter of the array of hydraulic nozzles  2073 . For example, the outer diameter of the hub of the impeller  2076  can be greater than or equal to approximately 15% of the outer diameter of the hydraulic nozzles  2073  and/or less than or equal to approximately 75% of the outer diameter of the hydraulic nozzles  2073 . In some cases, the outer diameter of the impeller  2076  can be greater than or equal to 0.5 inches and/or less than or equal to approximately 1.5 inches. Many variations sizes and relative sizes of the components of the hydraulic turbine  2070  and its subcomponents are possible. 
     In some cases, the impeller blades  2077  are oriented at an angle offset from the central axis of the impeller  2077 . The hydraulic nozzles  2073  can be configured to turn the flow of hydraulic fluid from an axial direction A to nozzle direction  2078  as the flow is passed through the nozzle frame  2072  toward the impeller  2076 . The nozzle direction  2078  can be selected to be at an angle θ T  offset from axial A such that the nozzle direction  2078  is substantially perpendicular to the faces of the impeller blades  2077 . The closer nozzle outlets are to the plane of the impeller blades  2077  and the more radially-directed the flow from the nozzles, the more torque can be imparted upon the impeller blades  2077 . For example, the nozzle outlets can be positioned close to the impeller blades  2077  in the axial direction and can direct hydraulic fluid at a highly-radial angle toward impeller blades  2077  whose surfaces are close to parallel to the rotation of axis of the impeller  2076 . 
     In some cases, utilizing a plurality of circumferentially-distributed turbine nozzles  2073  to drive a plurality of impeller blades  2077  can increase the torque output of impeller  2076  as compared to a configuration wherein only one turbine nozzle  2073  is utilized. In some such configurations, the outer diameters of the nozzle frame  2072  and impeller  2076  can smaller than a single-nozzle configuration of equal output torque. 
     In some embodiments, the hydraulic turbine  2070  can be configured to operate at rotational speeds of 40,000 rpm to 60,000 rpm, though higher and lower rpm values may be possible. The hydraulic turbine  2070  can be configured to operate at operating pressures between 70 psi and 190 psi, though greater and lesser operating pressures are possible. In some embodiments, the operating pressure of the hydraulic turbine  2070  is designed to be approximately 120 psi. 
     As illustrated in  FIG. 46 , an impeller  2076 ′ can be designed to have bucket-shaped impeller blades  2076 ′. The bucket-shaped impeller blades  2077 ′ can be oriented at an angle of approximately 45° from the axial direction A. Many variations of the impeller blade  2077 ′ angles are possible. Additionally, many different shapes of blades  2077  are possible, such as Pelton or Turgo shaped blades. 
     As illustrated in  FIG. 45C , the hydraulic turbine  2070  can be designed to collect the hydraulic fluid that has already impacted the impeller blades  2077 ,  2077 ′ (hereinafter  2077  for simplicity). For example, an exhaust angle can be calculated to represent the angle at which hydraulic fluid reflects off of the impeller blades  2077  after impact with the impeller blades  2077 . One or more vacuum ports  2093  can be positioned on or in the turbine housing  2071  to extract the fluid F 1  that is reflected off of the impeller blades  2077  and redirect the fluid F 1  into a bypass channel  2095 . In some embodiments, the vacuum source can be an external pump (e.g., a peristaltic pump) or the vacuum can be the result of a Venturi effect created by the diversion of fluid. For example, in some embodiments, the vacuum source can be provided by diverted, high velocity fluid F 2  directed to bypass the impeller  2076 . In some embodiments, one or more ports  2093  in the hydraulic turbine housing  2071  (e.g., on the side of the housing closer to the impeller  2076  than to the nozzle frame  2072 ) can create fluid communication between the reflected fluid F 1  in the blade cavity  2077 A and the diverted high velocity fluid F 2  in the bypass channel  2095 . The pressure differential between the two fluid bodies (e.g., lower pressure in fluid F 2  and higher pressure in fluid F 1 ) will pull the reflected fluid F 1  out of the housing  2071  and into the diverted fluid path  2095 . Removal of the reflected fluid from the housing  2071  can increase the performance of the turbine  2070  by reducing the viscous drag on the impeller from undiverted fluid F 1 . For example, the viscous frictional losses that would be otherwise incurred from interaction between the reflected fluid F 1  and the impeller  2076  and/or output shaft  2079  can be reduced. The diverted high velocity fluid F 2  and scavenged reflected fluid F 1  can be diverted back to the cassette  2020  for re-pressurization. In some embodiments, scavenging reflected fluid F 1  and diverting it back to the cassette  2020  can reduce the amount of hydraulic fluid (e.g., saline) required to operate the tools and/or other components of the system. 
     In some embodiments, multiple impellers  2076  (e.g., multiple turbine wheels) can be utilized in the same turbine housing  2071 . In some such embodiments, the overall diameter of the turbine  2070  and/or some of its components can be reduced relative to a single-impeller turbine  2070  without sacrificing output torque. 
     Some instruments such as surgical tools use torque or mechanical force to translate manual input into tool actuation. For example, a Kerrison for bone removal generally includes a handle mechanically coupled to a head including a stationary portion and a movable portion. When a user squeezes the handle, the movable portion moves closer to the stationary portion in a cutting manner (e.g., in a shearing manner), for example to remove bone by trapping the removed bone between the stationary portion and the movable portion (e.g., within a channel between the stationary portion and the movable portion). Other examples of tools include an aneurysm clipper, a rongeur, forceps, scissors, and the like, although many other hand-operated tools are known to those skilled in the art. Referring again to the Kerrison, the pace and force of the squeezing translates to the pace and force of the cutting, and this phenomenon is also applicable to other hand-operated tools. This translation can be disadvantageous, for example varying based on each user, being too slow or too fast or having variable speed, lacking force or imparting too much force or having variable force, etc. Additionally, periodic use of such manually operated tools (e.g., during a lengthy operation or procedure) can lead to hand fatigue of the surgeon or user. Manual actuation leads to inadvertent movement of the tool tip. 
       FIGS. 47A and 47B  schematically illustrate an example embodiment of a system  1700  for hydraulically actuating instruments. The system  1700  includes a user interface  1702 , a drive system  1704 , a pusher member  1706  (e.g., piston, plunger), a fluid reservoir  1708 , a first inflatable element  1710 , a housing  1712 , a fluid conduit  1714 , a second inflatable element  1716 , a chamber or housing  1718 , a piston  1720 , and an instrument  1722 . In some embodiments, a shaft  1726  can extend away from the piston  1720  to actuate any number of tools, such as a Kerrison, standard forceps, micro forceps, bipolar forceps, ronguer, clip appliers, scissors, or any other desired tool, as will be described in greater detail below. The system  1700  allows the user to actuate the instrument  1722  by operation of the user interface  1702 . The user interface  1702  is not mechanically coupled to the instrument  1722 , so the forces on the user interface  1702  are not necessarily directly translated to the forces on the instrument  1722 . 
     Any of the tool embodiments disclosed herein, including any of the Kerrison, standard forceps, micro forceps, bipolar forceps, ronguer, clip appliers, or scissors embodiments disclosed herein, can be configured to be anatomically designed to fit snugly in a particular orientation relative to a user&#39;s hand. Configuring the tools for a predetermined orientation in a user&#39;s hand can dictate the orientation (rotational orientation or otherwise) of the tool relative to a reference point or surface, such as a ground surface. In this configuration, a CMOS sensor supported by the tool will always be oriented right side up (i.e., in the proper orientation), thereby eliminating the need for PIP image rotation. PIP computation will then be translational and scaling only. 
     Operation of the user interface  1702  sends a signal to the drive system  1704 . The user interface  1702  may include a proportional foot pedal, a push button, lever and the like. In some embodiments, the user interface  1702  is analog, where different levels of operation of the user interface  1702  cause different responses by the drive system  1704 . In some embodiments, the user interface  1702  is digital, where the drive system  1704  responds the same regardless of the level of input on the user interface  1702 . In some embodiments, the user interface  1702  includes a single direction, for example a pedal that may be operated only forward. In some embodiments, the user interface  1702  includes a plurality of directions, for example a pedal that may be operated forward or backward. The user interface  1702  may be biased (e.g., by a resilient force such as a spring) to a particular orientation, for example to a resting point opposite the single direction or to a point between a plurality of directions. 
     In response to the signal sent from the user interface  1702 , the drive system  1704 , which may for example comprise a linear actuator, drives a pushing member or plunger  1706  by way of a proportional solenoid, Acem or ball screw, and the like. In some embodiments, the drive system  1704  converts random forces on the user interface  1702  into uniform, known, and/or predictable forces on the pushing member  1706 . The drive system  1704  may increase accuracy of the instrument  1722 . In some embodiments, rather than a user attempting fine control by different forces squeezing on a handle, the drive system may respond to operation of the user interface in fine increments. For example, each operation of the user interface  1702  may cause a partial actuation of the instrument  1722  (e.g., advancing a movable portion of a Kerrison 1 mm for each interaction with the user interface  1702 ). 
     The fluid reservoir  1708  is fluidly coupled to the first or master inflatable element  1710 . The fluid reservoir  1708  may comprise a mass of fluid such as saline, deionized water, etc., for example, contained in an intravenous bag positioned higher than the first inflatable element  1710  such that gravity causes fluid to flow from the fluid reservoir  1708  into the first inflatable element  1710 , or may comprise a pressurized canister and the like. After inflating or priming the first inflatable element  1710 , the fluid reservoir  1708  may be disconnected from the first inflatable element  1710  (e.g., physically disconnected from the first inflatable element  1710  or fluidly disconnected by closing a valve between the fluid reservoir  1708  and the first inflatable element  1710 ). The first inflatable element  1710  includes a defined volume to contain an amount of fluid in an inflated state. In some embodiments, the first inflatable element  1710  includes an inflatable balloon similar to those used for percutaneous transluminal angioplasty or kyphoplasty. Certain such balloons are generally inexpensive, disposable, sterile, and/or are not susceptible to overinflation. The pusher member  1706  and the first inflatable element  1710  may be at least partially contained by a housing  1712 . The housing  1712  may include apertures for connection to the fluid reservoir  1708  and the fluid conduit  1714 , and for the shaft of the pusher member  1706  and/or to allow air and/or fluid to enter and exit the chamber as the air and/or fluid is displaced by inflation or deflation of the first inflatable element  1710 . The fluid conduit  1714  is in fluid communication with the first inflatable element  1710  and the second or slave inflatable element  1716 . 
     As illustrated in  FIG. 47B , with the first inflatable element  1710  at least partially inflated by a fluid such as saline, for example after being primed by the fluid reservoir  1708 , the user interface  1702  is actuated, which causes the drive system  1704  to move the pusher member  1706  to compress the first inflatable element  1710  within the housing  1712 , for example against a platen. Although illustrated as compressing the first inflatable element  1710  radially inwardly (e.g., widthwise), longitudinal compression is also possible. Although illustrated as compressing the first inflatable element  1710  in a single direction, a plurality of plungers or other compression mechanisms are also possible. For example, drive system  1704  may cause longitudinal compression of the first inflatable element  1710  from each end. For another example, drive system  1704  may cause inflation of a toroidal element around the first inflatable element  1710 . Fluid flows out of the first inflatable element  1710  through the fluid conduit  1714  and into the second inflatable element  1716 . As the fluid enters the second inflatable element  1716 , the second inflatable element  1716  inflates within the chamber  1718 . The chamber  1718  may restrict inflation of the second inflatable element  1716  to be substantially linear or substantially in a single direction (e.g., towards the piston  1720 ). During inflation of the second inflatable element  1716 , the second inflatable element  1716  pushes the piston  1720 . The piston  1720  is coupled to the instrument  1722  or may even be part of the instrument  1722 . As illustrated in  FIGS. 47A and 17B , the instrument  1722  is coupled to the chamber  1718 . In some embodiments, the instrument  1722  is spaced from and/or separate from the chamber  1718 . The chamber  1718  may include apertures for connection to the fluid conduit  1714 , and for the shaft of the piston  1720  and/or to allow air and/or fluid to enter and exit the chamber as the air and/or fluid is displaced by inflation or deflation of the second inflatable element  1716 . 
     The instrument  1722  may comprise any instrument actuatable by motion of the piston  1720  caused by the second inflatable element  1716 . For example, the instrument  1722  may comprise a Kerrison, an aneurysm clip applier, a rongeur, a tissue cutter, scissors, forceps, and other surgical instruments. The instrument  1722  may be a non-surgical instrument, for example used for machinery, plumbing, electrical, and the like. As described herein, hydraulic power can inhibit or eliminate interference with electromagnetic tracking, so the instrument  1722  may comprise any instrument used in a setting in which reduction of interference with electrical devices may be advantageous. In embodiments in which the instrument  1722  comprises a Kerrison, the Kerrison may include a D-shaped cutting surface, for example to cut bone without a twisting motion. In some embodiments, the cut bone fragments can accumulate in a Kerrison lumen proximal to the cutting surface (e.g., for later extrusion for removal such as by a screw auger), and the like. 
     The second inflatable element  1716 , the chamber  1718 , and the piston  1720  may provide certain advantages over other systems. For example, if the system  1700  did not include the second inflatable element  1716  such that fluid flowed from the fluid conduit  1714  directly into the chamber  1718 , the chamber  1718 , including interaction between the chamber  1718  and the piston  1720 , would need to be fluid-tight, but such systems are prone to leakage, especially at high pressure. A fluid-tight piston  1720  may also cause stiction issues, leading to the use of higher pressure, which can disadvantageously lead to leakage. Lubricants that may reduce these disadvantages are generally not biocompatible. Stiction may also lead to difficulty in precise movement of the piston  1720 . By contrast, a system  1700  comprising a second inflatable element  1716  can allow the piston  1720  to generally fit in the chamber  1718 , but does not require a fluid-tight fit. This can reduce or eliminate issues with stiction. Because the fluid is contained within the second inflatable element  1716 , issues with leakage of the chamber  1718  may be reduced or eliminated. Distal mechanisms such as diaphragms and bellows may also have issues. For example, a diaphragm generally has less range of motion than an inflatable element  1716 . For another example, bellows are generally expensive and therefore are possibly not disposable. By contrast, inflatable elements  1716  such as balloons may have a high range of motion and/or be readily disposable. 
     In some embodiments, the second inflatable element  1716  comprises an expandable elastomer (e.g., comprising flexible polyvinyl chloride (PVC), cross-linked polyethylene, polyurethane, polyethylene terephthalate (PET), nylon, and/or other polymers). Nylon may be weaker and less compliant than PET, but may be softer and still thin and strong compared to other materials. Advantages provided by PET over other materials can include tensile strength and/or maximum pressure rating. In some embodiments, the second inflatable element  1716  includes an inflatable balloon such as those used for percutaneous transluminal angioplasty or kyphoplasty. In some embodiments, the second inflatable element  1716  is the same or substantially the same as or includes at least one property (e.g., volume, radius, and/or length in an inflated state, type of material, etc.) as the first inflatable element  1710 . In embodiments in which the second inflatable element  1716  is the same or substantially the same as the first inflatable element  1710 , actions on the first inflatable element  1710  by the drive system  1704  may cause an equal but opposite effect on the second inflatable element  1716 . This may be useful, for example, to visualize on the first inflatable element  1710  what is happening to a non-viewable second inflatable element  1716 . The use of a first inflatable element  1710  can provide a defined volume, for example to inhibit or prevent overinflation of the second inflatable element  1716 . In some embodiments, at least one of the first inflatable element  1710 , the second inflatable element  1716 , the housing  1712 , and the chamber  1718  comprises a lubricious coating, for example to reduce friction between the first inflatable element  1710  and the housing  1712  and/or between the second inflatable element  1716  and the chamber  1718 . In some embodiments, at least one of the first inflatable element  1710  and the second inflatable element  1716  comprises an abrasion and puncture-resistant coating, for example to increase reliability. 
     Although illustrated in  FIGS. 47A and 47B  as having both ends as square ends, the either or both of the ends of the first inflatable element  1710  and/or the second inflatable element  1716  may be any appropriate shape including, for example, conical sharp corner, conical radius corner, spherical end, and/or offset neck. For example, the first inflatable member  1710  may include two offset necks (e.g., as in offset or directional balloons) such that the connections to the fluid reservoir  1708  and the fluid conduit  1714  do not move during inflation and deflation of the first inflatable element  1710 . Although illustrated in  FIGS. 47A and 47B  as having a uniform longitudinal profile, the first inflatable element  1710  and/or the second inflatable element  1716  may include longitudinal tapers, steps, combinations thereof, and the like. Although the first inflatable element  1710  is illustrated in  FIGS. 47A and 47B  as inflating and deflating only radially and the second inflatable element  1716  is illustrated in  FIGS. 47A and 47B  as inflating and deflating in all directions, the first inflatable element  1710  and/or the second inflatable element  1716  may be designed to inflate and/or deflate in a single dimension or direction (e.g., a single longitudinal direction, radially, etc.) or in all dimensions. 
     In some embodiments, the system  1700  optionally does not include the first inflatable element  1710 . For example, upon receiving a signal from the user interface  1702 , the drive system  1704  may cause fluid to flow into the second inflatable element  1716  by operating a valve, advancing a piston within a cylinder (e.g., advancing the pusher member  1706  within a fluid-tight housing  1712  in fluid communication with the fluid conduit  1710 ), or otherwise causing fluid to flow through the fluid conduit  1714 . 
     In some embodiments, a biasing element such as a metal spring or a resilient elastomeric member can be positioned between the pusher member  1706  and the housing  1712  and/or between the piston  1720  and the chamber  1718 . Such biasing element(s) can cause the system  1700  to be in a default state when a user in not interacting with the user interface  1702 . For example, the pusher member  1706  can be biased away from the first inflatable element  1710  (e.g., the pusher member  1706  being between a negative biasing element and the first inflatable element  1710 ), and the force of the biasing element on the pusher member  1706  provides available volume for at least partial inflation of the first inflatable element  1716 . For another example, the piston  1720  can be biased towards the second inflatable element  1716  (e.g., the piston  1720  being between a positive biasing element and the second inflatable element  1716 ), and if the force of the biasing element on the piston  1720  is sufficient to cause at least partial deflation of the second inflatable element  1716 , the second inflatable element  1716  can be biased to a deflated state and the instrument  1722  can be biased to a first state or open state in which inflation of the second inflatable element  1716  is not providing force to the piston  1720 . 
     In some embodiments, as illustrated in  FIG. 47C , a spring member  1724  (which can be a metal spring member, an elastomeric spring member, or any other suitable axially resilient member) can be positioned between the piston  1720  and the chamber  1718  to cause the piston  1720  to return to the default or initial position of the piston. In this arrangement, when the piston  1720  is in the default position (i.e., where the spring member  1724  is substantially fully expanded), a cutting head  1728  of the Kerrison attached to the shaft  1726  will be in an open or retracted position so as to be spaced apart from the fixed cutting surface  1730  of the Kerrison. As the second inflatable element  1716  is expanded, the piston  1720  will be forced toward a first end  1720   a  of the housing  1718  against the bias of the spring member  1724 , causing the cutting head  1728  of the Kerrison to move toward the fixed surface  1730  of the Kerrison, to effect the cutting of the bone or other tissue to be cut with the Kerrison. 
     Additionally, with reference to  FIGS. 47D-47G , the Kerrison can have a variety of cutting head configurations. For example, with reference to  FIGS. 47E-47G , in any of the embodiments disclosed herein, the cutting head  1728  can have a circular shaped cross-section (as in  FIG. 47E ), the cutting head  1728  can have a C shaped cross-section (as in  FIG. 47F ) or a closed D shaped cross-section (as in  FIG. 47G ). Other shapes and designs are possible. 
     Additionally, in any of the Kerrison embodiments described herein, the fixed cutting surface  1730 ′ can be generally vertically oriented. As shown in  FIG. 47D , the fixed cutting surface  1730  can also be angulated (for example, angled at approximately 45 degrees, or from approximately 35 degrees or less to 55 degrees or more). 
     In any of the tool embodiments disclosed herein, including without limitation the Kerrison, the housing supporting or comprising the tool can be configured to have a port or lumen therein arranged to facilitate the removal of tissue and bone extracted from the surgical site. For example, the Kerrison can have a side port or opening located proximal of the cutting head  1728 ,  1728 ′, though which cut tissue can be removed (e.g., pushed through port or opening as cutter withdraws and Kerrison returns to the default position). In some embodiments, a source of suction, or a source of saline and suction, can be supplied to the port. Additionally, the removal port or lumen of the housing can also support a mechanical removal mechanism, such as but not limited to a screw type auger (which can be hydraulically actuated, via for example a gear motor, gerotor, or vane motor  1512  discussed above), to facilitate removal of bone debris and extracted tissue from the surgical site. In some embodiments, the removed tissue can be extracted to a waste reservoir supported by or tethered to the housing of the tool. In another embodiment, the movable cutting head of the Kerrison can be a generally cylindrical tube that can be actuated (in the matter described above) to slidably move against the fixed cutting surface  1730 . For example, said cylindrical tube can be slidable within an outer housing of the Kerrison when a force is exerted thereon via the expansion of the second inflatable element  1716 , as discussed above. 
     Additionally, in any of the tool embodiments disclosed herein, including without limitation the Kerrison, the housing supporting or comprising the tool can be configured to have a suction port and a source of saline so that the tool and/or the surgical site can be flushed with saline and the saline and debris can removed via the suction line simultaneously or sequentially with the flushing. In some embodiments, the saline can be provided through the conduit used to provide saline to the second inflatable element, through the same or a different lumen of such conduit. 
     Additionally, the saline source or conduit and/or the suction source or conduit can be separate from the tool so that it can be independently positioned. In some embodiments, the saline source or conduit and/or the suction source or conduit can be tethered to the tool. 
     Any of the hydraulic system embodiments disclosed herein can be configured to incorporate or use any suitable surgical tools, including without limitation scissors, micro-scissors, forceps, micro-forceps, bipolar forceps, clip appliers including aneurysm clip appliers, ronguers, and, as described, Kerrison tools. 
     For example,  FIGS. 48A and 48B  show an embodiment of a hydraulic scissors tool  1732  that can be used with any of the hydraulic system embodiments disclosed herein, including system  1700 . The scissors tool can have other configurations than shown in  FIGS. 48A and 48B , and can but is not required to have an adapted version of or some similar components as a commercially available non-hydraulically operated scissors tool. 
     In use, the second inflatable element  1716  can be actuated, as described above, to move the hydraulic micro-scissor tool  1732  from a first, open position, as shown in  FIG. 48A , to a second, closed position, as shown in  FIG. 48B . In particular, in some embodiments, the second inflatable element  1716  can be inflated to advance the piston  1720  toward the second end of the housing  1718 . The piston can have one or more channels  1721  formed therein. Each blade  1733  of the scissors can have a pin, dowel, tab, or other protrusion  1734  supported at an end thereof, the pins  1734  each being configured to translate along the length of the channels  1721 . In this arrangement, as the piston  1720  is advanced toward the scissors  1732 , the pins  1734  will move along the length of the channels  1721  and move inwardly, causing the blades  1733  of the scissors  1732  to come together, as illustrated in  FIG. 48B . The scissors can be in a fixed axial position relative to the piston  1720  to effect the relative motion between the piston  1720  and scissors  1732  that operates the scissors. A spring or other biasing mechanism (for example, between the end of the housing and the piston) can be used to return the piston back to the retracted position to return the scissors to an open arrangement or state. 
       FIGS. 49A and 49B  show another embodiment of a hydraulic scissors tool  1732 ′ that can be used with any of the hydraulic system embodiments disclosed herein, including system  1700 . The scissors tool can have other configurations than shown in  FIGS. 49A and 49B , and can, but are not required to, have an adapted version of or some similar components as a commercially available non-hydraulically operated scissors tool. With reference to  FIGS. 49A and 49B  a first scissors blade  1733   a  can be fixed or otherwise attached to the housing  1718 , and the second scissors blade  1733   b  can be caused to move relative to the first scissors blade  1733   a  by moving the piston  1720  relative to the end of the housing, thereby causing a pin or other protrusion  1734  in the end of the handle  1733   b  to translate within the channel  1721 , as described above with reference to  FIGS. 48A and 48B . A spring or other biasing mechanism (for example, between the end of the housing and the piston) can be used to return the piston back to the retracted position to return the scissors to an open arrangement or state. 
       FIGS. 50A and 50B  show another embodiment of a hydraulic scissors tool  1732 ″ that can be used with any of the hydraulic system embodiments disclosed herein, including system  1700 . The scissors tool can have other configurations than shown in  FIGS. 50A and 50B , and can, but is not required, to have an adapted version of or some similar components as a commercially available non-hydraulically operated scissors tool. With reference to  FIGS. 50A and 50B , a first scissors blade  1733   a  can be fixed or otherwise attached to the housing  1718 , and the second scissors blade  1733   b  can be caused to move relative to the first scissors blade  1733   a  by moving the piston  1720  and shaft  1726  relative to the end of the housing. The end of the shaft  1726  can have a slanted, curved, or angulated shape or surface that, when translated relative to the second blade  1733   b , can cause the second blade  1733   b  to rotate relative to the first blade  1733   a , causing the cutting action. As with the other embodiments disclosed above, in some embodiments, a spring member or other biasing mechanism  1724  can be positioned between the end of the housing  1718  and the piston  1720  to bias the piston  1720  to the first, retracted position, thereby biasing the scissors to an open position. 
     Any other desired tool, such as a micro-scissors, forceps, micro-forceps, bipolar forceps, clip appliers including aneurysm clip appliers, ronguers, and, as described, Kerrison tools, can be configured to work with any embodiments of the hydraulic system disclosed herein. Further as described above, any of the tools and configurations that provide actuation may be configured differently. 
     Additionally, the chamber or housing  1718  and shaft  1726  can be configured and adapted to work with and/or interchangeably support any suitable tool, including without limitation scissors, micro-scissors, forceps, micro-forceps, bipolar forceps, clip appliers including aneurysm clip appliers, ronguers, and, as described, Kerrison tools. For example, with reference to  FIGS. 51A-51B , the system  1700  can be configured such that any of the aforementioned tools, or other suitable tools (represented schematically by the box  1740  can be removably attached to an end portion  1718   a  of the chamber  1718 . In some embodiments, the tool  1740  can have an attachment element  1742  that can be removably coupled with an end portion  1718   a  of the chamber  1718 . Any of the tools used in this configuration can be modified from their standard form, as necessary, to be actuated with the linear moving shaft  1726  or with a configuration similar to any other embodiment disclosed herein, such as without limitation the embodiments shown in  FIGS. 48A-50B . 
     In some embodiments, the attachment element  1742  for each of the tools can be threadedly secured, or otherwise removably coupled, to the end portion  1718   a  of the chamber  1718 . However, the system  1700  can be configured such that the tool is integrally formed or otherwise non-removably secured to the chamber  1718 . Any desired tools, including without limitation scissors, micro-scissors, forceps, micro-forceps, bipolar forceps, clip appliers including aneurysm clip appliers, ronguers, and, as described, Kerrison tools, can be similarly adapted to be removably or non-removably coupled with the chamber  1718 . Though in some embodiments, the surgical devices or tools can be modularly coupled to the hydraulic actuation system, in other embodiments the surgical devices or tools can at least partially incorporate one or more components (e.g., chamber  1718 , second inflatable element  1716 ), so that the tool and such components are part of a single piece. 
     The chamber  1718  can be contoured and shaped to fit comfortably within the hand of a surgeon, so that the surgeon can accurately control the positioning and orientation of the tool. This chamber or housing  1718  is not required to be cylindrical, but can have any suitable shape. For example, in some embodiments, the housing  1718  can have an ovular cross-sectional shape or any anatomically or aesthetically desirable shape. Additionally, the size of the housing  1718  can be varied depending on the size requirements of the second expansion element  1716 , the amount of force required to be exerted on the tool by the second expansion element and piston  1720 , and other factors such as gripability and comfort for the user of the device. 
     Further to the description above, the operation of the tool attached to the housing  1718  can be controlled by the positioning and orientation of the tool and by operation of the user interface, such as the user interface  1702  discussed above. In some embodiments, the user interface can define a variety of different positions to enable the surgeon to accurately control the amount of extension of the shaft  1726  and, hence, the state of the tool. Additionally, a spring mechanism or member can be positioned within the chamber of any tool disclosed herein to bias the piston  1720  and shaft  1726  toward a first or retracted position. In this configuration, when the linear actuator is moved toward the relaxed state, by operation of the user interface and the drive system  1704 , the spring mechanism can cause the piston to compress the second inflatable element of any tool disclosed herein to force the fluid within the second inflatable element through the conduit  1714  and back into the first inflatable element. 
     Some embodiments of the system  1700  can have a manifold  1760  in fluid communication with the conduit  1714 , the manifold being configured to divert the fluid supplied through the conduit  1714  through any desired number of sub conduits. For example, with reference to  FIG. 52 , six or more sub-conduits  1764  can be in coupled with the manifold  1760 . Each of the different sub-conduits  1764  can be used to provide fluid to any desired number of tools connected to the sub-conduits, each sub-conduit  1764  being configured to couple with one tool. For example, a first sub-conduit  1764  can be coupled with a Kerrison, a second sub-conduit  1764  can be coupled with a rongeur, a third sub-conduit  1764  can be coupled with micro-scissors, a fourth sub-conduit  1764  can be coupled with micro-forceps, and so on. In some embodiments, a first pneumatic port is directed toward powering scissors and forceps, a first hydraulic port is used to power a drill, and a second hydraulic port is used to power a Kerrison, with individual tubing for each flow path. In some such embodiments, individual tools can be replaced without replacing other tools or tubing associated with other tools. 
     Each of the variety of tools connected to the conduits can have a secondary inflation element, a chamber, a piston, and any other components used to independently operate such tool, similar to that described in the embodiments above. 
     Additionally, though not required, each of the different sub-conduits  1764  can have a flow valve  1762  associated therewith to independently control the flow of fluid through such sub-conduits  1764 . A user interface can be used to independently control the operation of the plurality of flow valves  1762  (e.g., via a controller, such as a computer controller) such that a surgeon or other user can electronically control the flow of fluid through the sub-conduits  1764  using a control panel or other user interface. In this configuration, the surgeon or user can control the flow of fluid into and out of the sub-conduits  1764  and, hence, into and out of the second inflation elements  1716 , of the respective tools, to exchange fluid between the primary or first inflation element  1710  of the system and the second inflatable elements  1716 . 
     For example, in use, a user may wish to perform an operation with a Kerrison coupled with a first sub-conduit  1764 , but not a ronguer (e.g., a second Kerrison) coupled with a second sub-conduit  1764 . Even though both such tools may be attached to the system, the user can essentially restrict the flow of fluid from the first inflatable element to the ronguer by closing the valve associated with the sub-conduit connected to the ronguer. The valve associated with the first sub-conduit can be opened such that any fluid advanced into the manifold from the first inflation element can fill the second inflation element of the Kerrison to operate the Kerrison. 
     In some embodiments, the system can be coupled with a source of saline at the hospital or other facility to prime or prefill the first inflatable element. Alternatively, the system can be prefilled with saline such that the first inflatable element has enough saline or other desired fluid therein to completely fill all of the second inflatable elements in communication therewith. Though several embodiments of hydraulically actuated surgical devices or tools are described above, one of skill in the art will recognize that the hydraulic actuation systems described herein (e.g., master-slave balloon hydraulic system, vane motor hydraulic system) can be used to actuate a variety of surgical tools by using a hydraulically generated force or torque to turn, pivot, or otherwise move one mechanical component relative to another to perform a desired surgical procedure (e.g., cut, hold, press). 
     In some embodiments, a hydraulically powered or actuated drill can be adapted to be used with any of the pressurized hydraulic systems disclosed herein, including without limitation any of the saline systems pre-charged by a bag compressor and/or roller pump, or otherwise, as discussed above. With reference to  FIG. 53 , some embodiments of the drill  1850  can have a housing  1852 , a drill chuck or other suitable connector  1854  for receiving and supporting a drill bit or other desired rotary bit  1856  therein, a turbine  1860  rotationally coupled with the chuck  1854 . A first inlet fluid flow path or conduit  1862  connectable to a first or inlet conduit  1864  can direct a fluid, such as saline, toward the turbine  1860  with a level of fluid flow velocity sufficient to rotate the turbine and, hence the chuck and rotary bit  1856  at the desired velocity. In some embodiments, the drill can have a hydrostatic bearing coupled with the turbine. In some embodiments, the drill can have an air bearing coupled with the turbine. The air bearing and/or hydrostatic bearing can function as a thrust bearing. In some embodiments, the turbine used for the drill or any desired rotational tool can be arranged similarly as compared to the impeller  2076  and nozzle frame  2072  described above, which can reduce the diameter or size of the turbine or impeller and the rotational tool. In this case, the output shaft  2079  can be coupled with a drill chuck or with a drill bit or other rotational tool. 
     A controller attached to a flow valve in the inlet line or conduit  1862  or  1864  can be used to adjust the velocity of the flow against the turbine  1860 . In some embodiments, a valve and valve controller (not illustrated) can be supported by or within the housing  1852  such that a surgeon can quickly and easily change the velocity of the drill by adjusting the valve in communication with the inlet flow conduit  1862 . A flow meter can be used to measure a flow velocity within the fluid flow path. 
     In some embodiments, the outlet channel and conduit  1866 ,  1868  can have the same cross-sectional size as the inlet conduit and channel, respectively. In some embodiments, the outlet channel and conduit  1866 ,  1868  can have a larger cross-sectional size as compared to the inlet conduit and channel, respectively, to reduce pressure buildup in the outflow portion of the flow pathway. 
     The inlet and outlet lines can each have a one-way flow valve and quick connector thereon to permit the drill to be removed from the hydraulic lines or system without the substantial loss of hydraulic fluid. Couplings  1870 ,  1872  can be positioned at the rear end of the housing  1852  to removably couple the inlet and outlet conduits with the housing  1852 . 
     A saline or hydraulically powered tool, such as any of the tools described herein, can have several advantages. First, they can be configured to work with EM tracking without interference to the EM tracking, which electric powered drills other tools will not. Accordingly, the surgical tool, such as a disposable or non-disposable hydraulic drill or Kerrison could include or have attached thereto (e.g., via clip-on connector) an electromagnetic tracker sensor. Accordingly, the surgical tool, such as a disposable or non-disposable hydraulic drill or Kerrison could include or have attached thereto (e.g., via clip-on connector) an optical sensor such as a CCD or CMOS camera sensor or detector array. Additionally, such saline or hydraulically powered tools are lightweight, generate very little or no heat, use hydrostatic bearings, and produce little noise during use. 
     The hydraulic system may also be used for other purpose such as cleaning optics and/or cooling light emitters for illuminating a surgical site. 
     As illustrated in  FIG. 53A , a powered drill  1850 ′ (e.g., a hydraulically or electrically powered drill) can include a camera  1854   a . The camera  1854   a  can be positioned on the chuck  1854 ′ and/or on the handle  1857  of the drill  1850 ′. The camera  1854   a  can be fixed in position rotationally (e.g., with respect to the axis of the rotary bit  1856 ′. The handle  1857  can include a waist portion to inhibit axial movement of the hand of a surgeon or other practitioner during use of the drill  1850 ′. In some embodiments the drill  1850 ′ include a tactile feature  1857   a  (e.g., a faceted ring, a nub, a protrusion, a roughened portion) fixed in a rotational position on the handle  1857 . The tactile feature  1857   a  can provide the practitioner with a tactile indication of the orientation of the camera  1854   a.    
     In some embodiments, as illustrated in  FIG. 53B , a set of powered (e.g., hydraulically, pneumatically, and/or electrically powered) scissors  1950  comprises handles  1958  and a body  1957 . A blade coupler  1954  can be coupled with the body  1957  and can provide mechanical coupling between the body  1957  and a set of blades  1956 . In some embodiments, the powered scissors  1950  include a camera  1954   a  mounted in a fixed rotational position (e.g., with respect to an axis of the blade coupler  1954 ). In some embodiments, the coupler  1554 ′ can be rotated (e.g., using a gnarled ring fixed thereto) to rotate the orientation of the blades  1956  with respect to the handles  1958 . In various embodiments, the orientation of the camera with respect to the handles  1958  remains intact. The powered scissors  1950  can also include a tactile feature  1957  configured to provide the user of the scissors with tactile confirmation of the alignment of the camera  1954   a . This tactile feature may, include but is not limited to a facet, dimple or other surface. 
     A wide range of embodiments are therefore possible. Various embodiments may comprise, for example, a retractor having plurality of cameras that form images and an image processing module and display configured such that the user selects which images formed by the cameras are displayed. These images may be video streams. In some embodiments, the user may enlarge one or more of the images and/or display the one or more images more centrally. For example, the user may select icons that represent the images and enlarge and place the image more central or at a desired location. These icons may actually show the images, which as stated above may comprise a video stream. The images or video stream may be real time. 
     Various embodiments may comprise, for example, a retractor having plurality of cameras having respective field-of-views and that are configured to obtain images as well as an image processing module and display configured to display the images tiled in a geometric arrangement that is consistent with the field-of-views and/or positions of the cameras. As described above, these images may be video streams. The geometric arrangement may include position and/or orientation of the images. 
     Various embodiments may comprise, for example, a retractor and plurality of cameras, wherein the retractor is configured to hold open a surgical site and the plurality of cameras are inwardly facing toward the surgical site. The retractor may, for example, comprise a plurality of blades having the cameras disposed thereon wherein the blades hold back tissue to hold open the surgical site. In some embodiments, the cameras face downward and inward into the surgical site. In some embodiments, the retractor includes proximal and distal cameras. 
     Various embodiments may comprise, for example, a surgical device such as a retractor and plurality of cameras comprising at least one distal camera and at least one proximal camera. In some embodiments, the plurality of cameras comprise a plurality of distal cameras and/or a plurality of proximal cameras. In some embodiments, the proximal cameras can be disposed more toward the end of a retractor blade and the distal cameras can be disposed more toward the distal end of the retractor. In some embodiments, the cameras face inward and possible downward into the surgical site held open by the retractor. 
     Various embodiments may comprise, for example, a surgical devices such as a retractor, a plurality of cameras, and a tracking system, wherein the plurality of cameras comprises a first and a second camera and the tracking system is configured to track a first movement of the first camera and a second movement of the second cameral wherein the movements are different. For example, the movements may be in different directions and/or to different extents. 
     Various embodiments may comprise, for example, a surgical device such as a retractor having a plurality of cameras that form images and an image processing module and display configured to display at least one of the images and a tool rendered as partially transparent. 
     Various embodiments may comprise, for example, a surgical device such as retractor having a plurality of cameras that form images, and an image processing module and a display configured to display an image morphed from at least two of the images. 
     Various embodiments may comprise, for example, a surgical devices such as retractor having a plurality of cameras that form images, and an image processing module and a display configured to display at least two of the images, wherein the at least two images are from cameras disposed on opposite sides of the surgical device (e.g. retractor) and wherein the imaging processing module flips one of the two images. 
     Various embodiments may comprise, for example, a surgical device having a plurality of cameras that form images, and a binocular display with at least one internal display device coupled to the cameras to display images from the cameras. In some embodiments, the binocular display is disposed on an articulated arm. In some embodiments, the binocular display comprises a pair of oculars attached to a housing containing the internal display device. In some embodiments, the binocular display comprises a non-direct view microscope comprising at least one camera coupled to the binocular display (e.g., disposed at the bottom of the housing) to provide images of the region below the binocular display. The images of the region below the binocular display may be displayed on the at least one internal display device. The non-direct view microscope may further comprise a variable zoom to alter the work distance of the non-direct view microscope. The variable zoom may comprise a two stage zoom providing one control for changing the work distance and one control for changing the magnification. In some embodiments, virtual reality gesture recognition may be provided to receive input from gestures made below the binocular display. In some embodiments, the camera below the binocular display may be used for such gesture recognition. In some embodiments, the camera further comprises an additional sensor (e.g. below the housing) for providing the gesture recognition. 
     Accordingly, various embodiments may comprise, for example, a surgical device having a plurality of cameras that form images, and a display with at least one internal display device coupled to the cameras to display images from the cameras and at least one sensor underneath to provide a virtual reality graphic user interface. In some embodiments the sensor comprises an optical detector array for imaging. In some embodiments, the sensor comprises a distance measuring device. 
     Various embodiments may comprise, for example, a retractor having plurality of cameras that form images and an image processing module and display configured to provide a main wide field of view image with plurality of narrow field of view tiled images superimposed thereon. The user may select which images formed by the cameras are displayed. These images may be video streams. The images or video stream may be real time. 
     Various embodiments may comprise, for example, a retractor having plurality of cameras that form images and an image processing module and display configured to provide a composite main wide field of view image produced from plurality of images (e.g., stitched or tiled) with an image (e.g., picture-in-picture image) superimposed thereon. The user may select which images formed by the cameras are displayed. These images may be video streams. The images or video stream may be real time. 
     Various embodiments may comprise, for example, a retractor having plurality of cameras that form images and an image processing module and display configured to provide a main wide field of view image from the retractor camera with an image superimposed thereon from a camera disposed on a surgical tool. The user may select which images formed by the cameras are displayed. These images may be video streams. The images or video stream may be real time. 
     Various embodiments may comprise, for example, a retractor having a plurality of cameras that form images and an image processing module and display configured to provide multiple images from cameras on the retractor as icons showing images that can be enlarged and/or arranged by a user. These images may be video streams. The images or video stream may be real time. 
     Various embodiments may comprise, for example, a retractor having a plurality of cameras that form images, a surgical tool, and an image processing module and display configured to display camera images, wherein movement of the tool triggers selection of different sets of camera images. For example, the movement may comprise movement of the tool to different locations, e.g., to different depths within the surgical site. These images may be video streams. The images or video stream may be real time. 
     Various embodiments may comprise, for example, a retractor having a plurality of cameras and a surgical tool having at least one camera that form images. 
     Various embodiments may comprise, for example, a multiple pump hydraulic system for driving surgical tools, wherein the multiple pumps provide substantially constant pressure to the system. The tools may be used in conjunction with a surgical device such as a retractor having cameras and a possible tracking system for tracking the cameras and/or tool. Proportional valves may be used to portion out pressurized fluid from the multiple pumps to the hydraulic tools. The multiple pumps may combine pneumatics and hydraulics. The multiple pumps may be included in a disposable cassette. 
     Various embodiments may comprise a retractor, use a retractor, or are configured to be used with a retractor and not an endoscope, laparoscope, or arthroscope. Similarly, many embodiment comprise retractors or use retractors or are configured to be used with retractors wherein cameras are disposed on the retractors, not endoscope, laparoscope, or arthroscope. 
     In various embodiments the retractor fits in an opening in a manner to provide ample room for the surgeon to operate but does not provide a gas seal for pumping up a cavity as may a laparoscope. Similarly, in many embodiments the retractor does not maintain alignment of the layers of tissue that are cut through to form the incision. 
     In various embodiments, the retractor is not employed as a fulcrum for surgical tools. 
     In various embodiments the camera(s) can be positioned on top of the retractor near and above the body surface or on the retractor at a depth within the surgical site (e.g., at the far distal end of the retractor into the deepest portion of the surgical site, or elsewhere on the retractor such as more proximal). 
     Many embodiments are employed for spine surgery, neurosurgery, head and/or neck surgery, and ear nose and throat surgery and many embodiments involve the cutting and extraction of bone, for example, through the pathway provided by the retractor. 
     Various embodiments, however, may be used with devices other than retractors. 
     Many other embodiments are possible, including numerous combinations of the above recited features. 
     CONCLUSION 
     Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. 
     Certain features that are described in this specification in the context of separate embodiments also can be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment also can be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations may be described as occurring in a particular order, this should not be understood as requiring that such operations be performed in the particular order described or in sequential order, or that all described operations be performed, to achieve desirable results. Further, other operations that are not disclosed can be incorporated in the processes that are described herein. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the disclosed operations. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single product or packaged into multiple products. Additionally, other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.