Patent Publication Number: US-2021186624-A1

Title: Head tracking control for ophthalmic surgery

Description:
TECHNICAL FIELD 
     The present disclosure relates to ophthalmic surgery and surgical equipment, and more specifically, to a head tracking control system to improve visualization for ophthalmic surgery and associated methods. 
     BACKGROUND 
     Ophthalmic surgery is surgery performed on the eye or any part of the eye. Ophthalmic surgery saves and improves the vision of tens of thousands of patients every year. However, given the sensitivity of vision to even small changes in the eye and the minute and delicate nature of many eye structures, ophthalmic surgery is difficult to perform and the reduction of even minor or uncommon surgical errors or modest improvements in accuracy of surgical techniques can make an enormous difference in the patient&#39;s vision after the surgery. 
     One type of ophthalmic surgery, vitreoretinal surgery, encompasses various delicate procedures involving internal portions of the eye, such as the vitreous humor, the retina, epiretinal membranes, and the internal limiting membrane. Different vitreoretinal surgical procedures are used, sometimes with lasers, to improve visual sensory performance in the treatment of many eye diseases, including epimacular membrane, diabetic retinopathy, vitreous hemorrhage, macular hole, detached retina, vitreomacular traction syndrome, macular schisis, and complications of cataract surgery, among others. 
     During ophthalmic surgery, such as vitreoretinal surgery, an ophthalmologist typically uses an optical, surgical microscope with oculars to view a magnified image of the eye undergoing surgery. A surgical microscope may provide intraoperative viewing of optical images of an eye, and optionally illumination of the eye for ophthalmic surgery. The patient typically lies supine under the surgical microscope during ophthalmic surgery and a speculum is used to keep the eye exposed. Depending on the type of optical system used, the surgeon has a given field of view of the fundus, which may vary from a narrow field of view to a wide field of view that can extend to peripheral regions of the fundus. 
     More recently, ophthalmic surgeons may use an ocular-free digital image system to aid visualization during ophthalmic surgery such as NGENUITY® (Novartis AG Corp., Switzerland). These systems may include a 3D high dynamic range (“HDR”) camera system with a pair of complementary metal-oxide-semiconductor (CMOS) sensors that allow the surgeon to view the retina on a display screen using polarized glasses, digital oculars or a head-mounted display. The display screen provides relief from having to view the surgery using oculars and allows others in the operating room to see exactly as the surgeon does. The system also allows for improved images under high magnification, and increased depth of field compared to a conventional optical, analog surgical microscope. In addition, an ophthalmic surgical microscope or digital image system may include a foot pedal located on the floor, which may provide for foot-actuated control of various visualization displays during ophthalmic surgery. However, when performing ophthalmic surgery, a hand-, voice, or foot-actuated command to control displays or equipment may not be desirable or practical. 
     SUMMARY 
     The present disclosure provides a head tracking control system that improves visualization for ophthalmic surgery. The head tracking control system includes at least one marker positioned on a head of a surgeon. The head tracking control system also includes an infrared camera including at least two infrared sensors and that detects infrared light reflected off the at least one marker and sends a signal corresponding to the detected light to a processor. The infrared camera also executes instructions on the processor to detect a movement of the at least one marker. The head tracking control system also includes an intelligent tracking system that executes instructions on the processor to determine if the detected movement of the at least one marker corresponds to a defined head movement of the surgeon. The head tracking control system also includes an ophthalmic surgical microscope that includes the processor. If the detected movement of the at least one marker corresponds to the defined head movement of the surgeon, the processor executes instructions to control the ophthalmic surgical microscope. 
     The head tracking control system and its methods of use may include the following additional features: i) the defined head movement of the surgeon may be a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof; ii) the intelligent tracking system may include a noise detection system that includes a microphone and determines if the detected movement of the at least one marker corresponds to a quiet head movement of the surgeon; a motion thresholding system that determines if the detected movement of the at least one marker corresponds to a deliberate head movement of the surgeon; and a motion recognition system that determines if the detected movement of the at least one marker corresponds to an uncommon head movement of the surgeon; iii) a head movement that is not the defined head movement may be ignored by the head tracking control system; iv) the defined head movement may be a displacement along an x-axis, a displacement along a y-axis, a pitch movement, or any combination thereof; v) the system may further include a motorized microscope head support, and the processor may control the ophthalmic surgical microscope by executing instructions to move the motorized microscope head support along a microscope movement x-axis, a microscope movement y-axis, or any combination thereof; vi) the system may further include an objective, and the processor may control the ophthalmic surgical microscope by executing instructions to move the objective; vii) the at least one marker may be an active infrared marker, a passive infrared marker, a fiducial marker, disposed in a cap, attached by adhesive, marked in pen, or any combination thereof. 
     The present disclosure further provides a head tracking control system that includes a 3-axis gyroscope and a 3-axis accelerometer positioned on the head of a surgeon and that detect a head movement of the surgeon and send a signal corresponding to the detected movement to a processor. The head tracking control system also includes an intelligent tracking system that executes instructions on the processor to determine if the detected head movement of the surgeon corresponds to a defined head movement of the surgeon. The head tracking control system also includes an ophthalmic surgical microscope that includes the processor. If the detected head movement of the surgeon corresponds to the defined head movement of the surgeon, the processor executes instructions to control the ophthalmic surgical microscope. 
     The head tracking control system and its methods of use may include the following additional features: i) the defined head movement of the surgeon may be a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof; ii) the intelligent tracking system may include a noise detection system that includes a microphone and determines if the detected head movement of the surgeon corresponds to a quiet head movement; a motion thresholding system that determines if the detected head movement of the surgeon corresponds to a deliberate head movement; and a motion recognition system that determines if the detected head movement of the surgeon corresponds to an uncommon head movement; iii) a head movement that is not the defined head movement may be ignored by the head tracking control system; iv) the defined head movement may be a displacement along an x-axis, a displacement along a y-axis, a pitch movement, or any combination thereof; v) the system may further include a motorized microscope head support, and the processor may control the ophthalmic surgical microscope by executing instructions to move the motorized microscope head support along a microscope movement x-axis, a microscope movement y-axis, or any combination thereof; vi) the system may further include an objective, and the processor may control the ophthalmic surgical microscope by executing instructions to move the objective. 
     The present disclosure further provides a head tracking control system that includes at least one marker positioned on a head of a surgeon. The head tracking control system also includes an LED driver that emits near-infrared light. The head tracking control system also includes a digital micromirror device that modulates the near-infrared light emitted by the LED driver and projects the modulated light at the at least one marker. The head tracking control system also includes a three-dimensional scanning camera that detects distortions in the modulated light reflected off the at least one marker, sends a signal corresponding to the distortions to a processor, and executes instructions on the processor to detect a movement of the at least one marker. The head tracking control system also includes an intelligent tracking system that executes instructions on the processor to determine if the movement of the at least one marker corresponds to a defined head movement of the surgeon. The head tracking control system also includes an ophthalmic surgical microscope that includes the processor. If the movement of the at least one marker corresponds to the defined head movement of the surgeon, the processor executes instructions to control the ophthalmic surgical microscope. 
     The head tracking control system and its methods of use may include the following additional features: i) the defined head movement of the surgeon may be a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof; ii) the intelligent tracking system may include a noise detection system that includes a microphone and determines if the detected movement of the at least one marker corresponds to a quiet head movement of the surgeon, a motion thresholding system that determines if the detected movement of the at least one marker corresponds to a deliberate head movement of the surgeon, and a motion recognition system that determines if the detected movement of the at least one marker corresponds to an uncommon head movement of the surgeon; iii) a head movement that is not the defined head movement may be ignored by the head tracking control system; iv) the defined head movement may be a displacement along an x-axis, a displacement along a y-axis, a pitch movement, or any combination thereof; v) the system may further include a motorized microscope head support, and the processor may control the ophthalmic surgical microscope by executing instructions to move the motorized microscope head support along a microscope movement x-axis, a microscope movement y-axis, or any combination thereof; vi) the system may further include an objective, and the processor may control the ophthalmic surgical microscope by executing instructions to move the objective; vii) the at least one marker may be an active infrared marker, a passive infrared marker, a fiducial marker, disposed in a cap, attached by adhesive, marked in pen, or any combination thereof. 
     The present disclosure further provides a visualization system that includes a head tracking control system including a processor and at least one marker positioned on a head of a surgeon. The visualization system further includes a surgeon head movement detection device that detects infrared light reflected off the at least one marker and sends a signal corresponding to the detected light to the processor, and executes instructions on the processor to detect a movement of the at least one marker. The visualization system further includes an intelligent tracking system that executes instructions on the processor to determine if the detected movement of the at least one marker corresponds to a defined head movement of the surgeon. The visualization system further includes a surgical camera that moves with six degrees of freedom, and is controlled by the processor if the movement of the at least one marker corresponds to the defined head movement of the surgeon. 
     The visualization system and its methods of use may include the following additional features: i) the surgical camera may be a component of an NGENUITY® 3D Visualization System; ii) the defined head movement of the surgeon may be a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof; iii) the intelligent tracking system may include a noise detection system that includes a microphone and determines if the detected movement of the at least one marker corresponds to a quiet head movement of the surgeon; a motion thresholding system that determines if the detected movement of the at least one marker corresponds to a deliberate head movement of the surgeon, and a motion recognition system that determines if the detected movement of the at least one marker corresponds to an uncommon head movement of the surgeon; iv) a head movement that is not the defined head movement may be ignored by the head tracking control system; the defined head movement may be a displacement along an x-axis, a displacement along a y-axis, a pitch movement, or any combination thereof; v) the at least one marker may be an active infrared marker, a passive infrared marker, a fiducial marker, disposed in a cap, attached by adhesive, marked in pen, or any combination thereof. 
     The present disclosure further provides a method for controlling an ophthalmic surgical microscope by detecting a surgeon head movement using a head tracking control system; determining if the head movement is a quiet head movement; determining if the head movement is a deliberate head movement; determining if the head movement is an uncommon head movement; and if the head movement is a quiet head movement, a deliberate head movement, and an uncommon head movement, allowing the head tracking control system to control the ophthalmic surgical microscope. 
     The present disclosure further provides a method for controlling a visualization system by a surgeon by making a defined head movement; detecting the defined head movement using a surgeon head movement detection device; determining a corresponding movement of a surgical camera; and moving the surgical camera in response to the defined head movement. The defined head movement of the surgeon may be a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. The surgical camera may move with six degrees of freedom. The surgical camera may be a component of an NGENUITY® 3D Visualization System. 
     Aspects of the head tracking control system and its methods of use may be combined with one another unless clearly mutually exclusive. In addition, the additional features of the head tracking control system and its associated methods described above may also be combined with one another unless clearly mutually exclusive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, which are not to scale, in which like numerals refer to like features, and in which: 
         FIG. 1  is a schematic representation of the six degrees of freedom of surgeon head gestures and a frame of reference; 
         FIG. 2  is a schematic representation of a head tracking control system, including an ophthalmic surgical microscope, a headband, an infrared camera, an intelligent tracking system, and a motorized microscope head support; 
         FIG. 3  is a schematic representation of a process flow for controlling an ophthalmic surgical microscope using a head tracking control system; 
         FIG. 4  is a schematic representation of a head tracking control system, including an ophthalmic surgical microscope, a headband, a 3-axis gyroscope and a 3-axis accelerometer, an intelligent tracking system, and a motorized microscope head support; 
         FIG. 5  is a schematic representation of a head tracking control system, including an ophthalmic surgical microscope, a headband, a three-dimensional scanning camera, a light emitting diode (LED) driver, a digital light processing controller chip, a digital micromirror device, a lens, an intelligent tracking system, and a motorized microscope head support; 
         FIG. 6  is a schematic representation of a head tracking control system as a component of an NGENUITY® 3D Visualization System (Novartis AG Corp., Switzerland); 
         FIG. 7  is a schematic representation of a computer system, including a head tracking control system; 
         FIGS. 8A-8C  are schematic representations of a medical system, including a head tracking control system; and 
         FIG. 9  is a flow diagram illustrating a method of controlling a visualization system using a head tracking control system. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure provides systems including head tracking control to improve visualization for ophthalmic surgery and associated methods. 
     Ophthalmic surgeons face unique challenges when visualizing the eye. During ophthalmic surgery it may be desirable for a surgeon to control a number of pieces of equipment, visualization systems, and surgical instruments. For example, in order to perform any of a variety of surgical procedures, a surgeon may desire to control the positioning or focus of a visualization system. 
     The present disclosure relates to surgeon head tracking control of a visualization system for ophthalmic surgery. During ophthalmic surgery, the surgeon is typically engaged with full attention and is using both hands to operate on the patient. Accordingly, the ability of the surgeon to provide continuous user input to, for example, position or focus a visualization system may be limited. Hand-operated selection controls for the visualization system (such as panel mounted controls, touch screen controls, focus rings, or any combination thereof) may be unsuitable or impossible for the surgeon to operate while performing surgery. A voice-operated selection control of the visualization system may also be unsuitable due to concerns about reliability, language customization, and a slow speed of voice recognition. Therefore, voice-operated controls may be particularly useful for selecting options involving a single command, rather than for continuously positioning or focusing a visualization system, which may involve rapid and repetitive user input. 
     A visualization system may include image acquisition positioning that is controlled by a foot pedal device. However, foot pedal control may result in inadvertent surgeon hand motion, which in turn may disrupt delicate surgical procedures. Furthermore, ophthalmic surgical systems typically include a first foot pedal for control of the ophthalmic surgical system, and optionally a second foot pedal to control a laser. As a surgeon only has two feet, it may be difficult to activate a third pedal for further control of positioning or focus of a visualization system. A head mounted display with head motion sensing may also be used to control a visualization system. This may be undesirable, however, as a head mounted display can cause nausea, vertigo, spatial disorientation, and fatigue. Use of a head mounted display also adds weight on the surgeon&#39;s head, which may cause cervical spine disease. Certain head tracking control systems for ophthalmic surgery also may not distinguish between head movements that are intended to control the visualization system and head movements that are instinctively made by the surgeon, for example head movements that are made while talking, and not intended to control the visualization system. 
     The head tracking control systems and methods of the present disclosure may provide for improved control of a visualization system for ophthalmic surgery. In particular, the head tracking control systems and methods of the present disclosure may provide for faster, safer, sterile, and more comfortable surgical procedures as compared to certain other control systems. The head tracking control systems and methods disclosed herein may provide hands-free control of a visualization system for ophthalmic surgery. This in turn may allow greater ease of use while providing for safer and more sterile surgical procedures. The head tracking control systems and methods disclosed herein may provide improved control of a visualization system as compared to certain other control systems by providing improved comfort for a surgeon. In particular, the head tracking control systems and methods disclosed herein may use a headband, hat or cap, as compared to certain other control systems that use a heavier head mounted display. This in turn may decrease nausea, vertigo, spatial disorientation, fatigue, and the weight on the head of the surgeon during surgery. 
     The head tracking control systems and methods disclosed herein may enable improved positioning and focus of a visualization system as compared to certain other control systems. In particular, the head tracking control systems and methods disclosed herein may allow improved control of a visualization system as compared to certain other control systems by limiting the types of head movement that may control a visualization system. For example, the head tracking control systems and methods of the current disclosure may only allow head movements of a surgeon that are defined head movements to control a visualization system. The head tracking control systems and methods of the present disclosure may also improve visualization for ophthalmic surgery as compared to certain other control systems by obeying the horizontal meridian. This may improve the ease of use and the responsiveness of the head tracking control system. The head tracking control systems and methods disclosed herein may allow improved control of a visualization system as compared to certain other control systems by providing a microphone to monitor the vocal gestures of the surgeon. By doing so, the systems and methods may allow the head tracking control system to ignore any head movement of the surgeon while they are, for example, speaking, coughing, or sneezing. The head tracking control systems and methods disclosed herein may allow improved control of a visualization system as compared to certain other control systems by ignoring head movements of the surgeon that are not deliberate, for example, fast or small head movements. The head tracking control systems and methods disclosed herein may allow improved control of a visualization system as compared to certain other control systems by ignoring common head movements, for example, a yaw head movement. A yaw head movement may be commonly associated with a surgeon speaking to other staff in the operating theatre. 
     The systems and methods disclosed herein may improve visualization for ophthalmic surgery by providing a head tracking control system that tracks the position of the head of surgeon using optical tracking, at least one 3-axis gyroscope sensor and at least one 3-axis accelerometer sensor, optical three-dimensional scanning, or any combination thereof. The systems and methods disclosed herein may include a headband, hat, or cap, or any combination thereof, positioned on the head of a surgeon. This may result in a reduced weight on the surgeon&#39;s head during surgery. The headband, hat, or cap may include at least one marker. The movement of the at least one marker may be detected by the head tracking control system, and in response to the movement instructions may be executed to control the visualization system. 
     Referring now to  FIG. 1 , head gestures used by surgeon  101  to control a visualization system may include six degrees of freedom on separate axes. Rotational degrees of freedom may include pitch  110 , yaw  120  and roll  130 . Translational degrees of freedom may include x  140 , z  150  and y  160 . Pitch  110 , yaw  120  and roll  130  may all be zero when the surgeon has his or her head level and pointing directly forward. Pitch  110  may be rotational motion about lateral x-axis  111 . Pitch  110  may be positive when surgeon  101  points his or her head upwards, and may be negative when surgeon  101  points his or her head downwards. Yaw  120  may be rotational motion about vertical z-axis  121 . Yaw  120  may be positive when surgeon  101  turns his or her head to their right, and may be negative when surgeon  101  turns his or her head to their left. Roll  130  may be rotational motion about longitudinal y-axis  131 . Roll  130  may be positive when surgeon  101  banks his or her head to their right, and may be negative when surgeon  101  banks his or her head to their left. 
     Translation x  140 , z  150  and y  160  may be zero when the surgeon has his or her head in a neutral, un-extended position. Translation x  140  may be displacement along x-axis  111 . Translation x  140  may be positive when surgeon  101  displaces his or her head to their left, and may be negative when surgeon  101  displaces his or her head to their right. Translation z  150  may be displacement along z-axis  121 . Translation z  150  may be positive when surgeon  101  displaces his or her head upwards, and may be negative when surgeon  101  displaces his or her head downwards. Translation y  160  may be displacement along y-axis  131 . Translation y  160  may be positive when surgeon  101  displaces his or her head forward, and may be negative when surgeon  101  displaces his or her head backward. 
     Referring now to  FIG. 2 , head tracking control system  200  may include ophthalmic surgical microscope  201 , headband  230 , infrared camera  250 , and motorized microscope head support  265 . Ophthalmic surgical microscope  201  may include microscope body  205 , binoculars  210 , and objective  220 . Objective  220  may be placed in an optical path  225  (dotted line) and may represent a selectable objective to provide a desired magnification or field of view of the fundus of eye  10 . Objective  220  may be moved closer or away from eye  10  to change the focus of ophthalmic surgical microscope  201 . Ophthalmic surgical microscope  201  may include illumination source  226 . Illumination source  226  may be an endoilluminator (not shown). Alternatively, illumination source  226  may be provided by an ophthalmic surgical microscope, such as ophthalmic surgical microscope  201 , or another ophthalmic visualization system, such as the NGENUITY® 3D Visualization System (Novartis AG Corp., Switzerland). 
     Binoculars  210  may be used in conjunction with microscope body  205  and may be positioned in optical path  225 . Optical path  225  may extend through binoculars  210  to the eye of surgeon  101 . Portions of eye  10  suitable for viewing using ophthalmic surgical microscope  201  may include the retina, macula (for example, the foveola, fovea centralis, para fovea, and perifovea), cornea, iris, lens, lens capsule, optic disc (for example, the optic cup), one of more layers of the retina, vitreous, vitreous body, retinal pigment epithelium, choroid, or any portion in which a surgical instrument is also viewed. 
     Ophthalmic surgical microscope  201  may further include various other electronic and mechanical components in different implementations. Accordingly, while the particular optical design discussed with reference to  FIG. 2  is specific to an ophthalmic visualization system that includes ophthalmic surgical microscope  201 , one skilled in the art will appreciate that alternative optical arrangements to support other ophthalmic visualization systems are within the scope of the disclosure. 
     During surgery, surgeon  101  may use ophthalmic surgical microscope  201  to view at least a portion of eye  10 . Eye  10  may be illuminated by illumination source  226 . Ophthalmic surgical microscope  201  may have an exemplary field of view that includes XY plane  266 . XY plane  266  may be formed by microscope movement x-axis  211  and microscope movement y-axis  231 . XY plane  266  may be a horizontal plane that is about parallel to the floor of the operating room. XY plane  266  may be a plane that is about horizontal above eye  10  during surgery. Objective  220  may be moved closer or away from eye  10  along focus z-axis  221  to change the focus of ophthalmic surgical microscope  201 . In another example, the focus of ophthalmic surgical microscope  201  may be changed opto-mechanically by moving optical elements called cells, or the entire microscope closer or away from eye  10 . 
     Head tracking control system  200  may track the position of the head of surgeon  101  using optical tracking. In particular, head tracking control system  200  may track the position of the head of surgeon  101  using infrared camera  250  and headband  230 . Infrared camera  250  may be a camera that detects infrared light, which may be light having a wavelength in the range of 0.7-1000 microns. Headband  230  may be positioned on the head of surgeon  101 . Headband  230  may alternatively be a hat or cap. Headband  230  may include at least one marker  235 . During surgery, the position of the at least one marker  235  may be tracked using infrared camera  250 . 
     Marker  235  may be an active infrared marker. An active infrared marker may include an infrared light emitting element, and may include at least one light emitting diode (LED). In one example, marker  235  may include six active beacons. The inclusion of six active beacons may allow marker  235  to be tracked as a rigid body with six degrees of freedom. In another example, marker  235  may include six LEDs. The LEDs may be flashed in a time synchronous controlled sequence. In another example, marker  235  may include at least one passive infrared marker, and may include at least one passive reflective marker. Marker  235  may include six passive infrared markers. The inclusion of six passive markers may allow marker  235  to be tracked as a rigid body with six degrees of freedom. Marker  235  may function as a fiducial. Marker  235  may function as a fiducial in a captured image, in real space, or a combination thereof. Marker  235  may be disposed in a cap, attached by adhesive, marked in pen, marked by any other means, or any combination thereof. Marker  235  may be placed in any orientation necessary such that its position may be tracked in six degrees of freedom. 
     Infrared camera  250  may be mounted on the top of ophthalmic surgical microscope  201 . Infrared camera  250  may alternatively be positioned in any suitable location to track the at least one marker  235 . For example, infrared camera  250  may be positioned in the range of from about 2 feet to about 6 feet from marker  235 . Infrared camera  250  may detect reflected infrared light, may detect emitted infrared light, or a combination thereof. Infrared camera  250  may have a field of view that is wide enough to include the at least one marker  235 . Infrared camera  250  may include at least infrared sensors  252  and  253 . Infrared sensors  252  and  253  may be photodetectors that detect infrared light. Infrared sensors  252  and  253  may be two paired area array infrared sensors. Infrared sensors  252  and  253  may be active infrared image sensors, time-of-flight range sensors, infrared sensitive CMOS sensors, infrared sensitive CCD sensors, or any combination thereof. In an alternative example, infrared camera  250  may be substituted for three line scan infrared cameras. Infrared camera  250  may use infrared sensors  252  and  253  to detect infrared light reflected off the at least one marker  235 . Alternatively, infrared camera  250  may use infrared sensors  252  and  253  to detect infrared light emitted by the at least one marker  235 . Infrared camera  250  may include active infrared illuminator  256 , which may emit infrared light in the thermal part of the infrared spectrum. Infrared camera  250  may use infrared sensors  252  and  253  to detect infrared light emitted by active infrared illuminator  256  and reflected off the at least one marker  235 . 
     Head tracking control system  200  may include image processing system  270 . Digital images captured by infrared sensors  252  and  253  may be processed by image processing system  270 . Image processing system  270  may include processor  280 . Infrared sensors  252  and  253  may detect infrared light reflected off the at least one marker  235  and send a signal corresponding to the detected light to processor  280 . 
     Processor  280  may include, for example, a field-programmable gate array (FPGA), a microprocessor, a microcontroller, a digital signal processor (DSP), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. 
     Processor  280  may include any physical device able to store and/or execute instructions. Processor  280  may execute processor instructions to implement at least a portion of one or more systems, one or more flow charts, one or more processes, and/or one or more methods described herein. For example, processor  280  may execute instructions to track the position of the head of surgeon  101 . Processor  280  may be configured to receive instructions from memory medium  281 . In one example, processor  280  may include memory medium  281 . In another example, memory medium  281  may be external to processor  280 . Memory medium  281  may store the instructions. The instructions stored by memory medium  281  may be executable by processor  280  and may be configured, coded, and/or encoded with instructions in accordance with at least a portion of one or more systems, one or more flowcharts, one or more methods, and/or one or more processes described herein. 
     A FPGA may be may be configured, coded, and/or encoded to implement at least a portion of one or more systems, one or more flow charts, one or more processes, and/or one or more methods described herein. For example, the FPGA may be configured, coded, and/or encoded to track the position of the head of surgeon  101 . An ASIC may be may be configured to implement at least a portion of one or more systems, one or more flow charts, one or more processes, and/or one or more methods described herein. For example, the ASIC may be configured, coded, and/or encoded to track the position of the head of surgeon  101 . A DSP may be may be configured, coded, and/or encoded to implement at least a portion of one or more systems, one or more flow charts, one or more processes, and/or one or more methods described herein. For example, the DSP may be configured, coded, and/or encoded to track the position of the head of surgeon  101 . 
     A single device may include processor  280  and image processing system  270 , or processor  280  may be separate from image processing system  270 . In one example, a single computer system may include processor  280  and image processing system  270 . In another example, a device may include integrated circuits that may include processor  280  and image processing system  270 . Alternatively, processor  280  and image processing system  270  may be incorporated into a surgical console. 
     Processor  280  may interpret and/or execute program instructions and/or process data stored in memory medium  281 . Memory medium  281  may be configured in part or whole as application memory, system memory, or both. Memory medium  281  may include any system, device, or apparatus configured to hold and/or house one or more memory devices. Each memory device may include any system, any module or any apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). One or more servers, electronic devices, or other machines described may include one or more similar such processors or memories that may store and execute program instructions for carrying out the functionality of the associated machine. 
     Infrared sensors  252  and  253  may detect infrared light reflected off the at least one marker  235  at detection points  254  and  255 , respectively, and send a signal corresponding to detection points  254  and  255  to processor  280 . The relative position of detection points  254  and  255  on each of infrared sensors  252  and  253 , respectively, may define the three-dimensional location of the at least one marker  235 . Infrared sensors  252  and  253  may be placed in any relative orientation suitable to define the three-dimensional location of the at least one marker  235 . 
     The position of marker  235  may be tracked using infrared camera  250  in real time. As used herein, “real time” may refer to the updating of information at the same rate as data is received. In the context of the head tracking control systems and methods of the present disclosure, “real time” may mean that image data is acquired, processed, and transmitted from a photosensor at a high enough data rate and a low enough delay that when the data is displayed, objects more smoothly without user-noticeable judder or latency. For example, this may occur when new images are acquired, processed, and transmitted at a rate of at least 30 frames per second and displayed at about 60 frames per second, and where the combined processing of the signal has less than about a 1/30 th  second of delay. 
     Infrared camera  250  may detect infrared light reflected off the at least one marker  235  using infrared sensors  252  and  253  and send a signal corresponding to the detected light to processor  280 . Infrared camera  250  may further execute instructions on processor  280  to detect a movement of the at least one marker  235 . The movement of the at least one marker  235  may be analyzed by intelligent tracking system  271 . The movement of marker  235  detected by infrared camera  250  may correspond to a head movement of surgeon  101  that is pitch  110 , yaw  120 , roll  130 , x  140 , z  150 , y  160 , or any combination thereof. The head movement of surgeon  101  may be described by Cartesian co-ordinates corresponding to x-axis  111 , z-axis  121  and y-axis  131 . 
     Intelligent tracking system  271  may execute instructions on processor  280  to determine if the movement of the at least one marker  235  corresponds to a defined head movement of surgeon  101 . Intelligent tracking system  271  may include noise detection system  272 , motion thresholding system  273 , and motion recognition system  274 . Intelligent tracking system  271  may allow head tracking control system  200  to control ophthalmic surgical microscope  201  when surgeon  101  makes a defined head movement. A defined head movement may include a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. A defined head movement may correspond to a characteristic movement of marker  235  detected by infrared camera  250 . 
     A quiet head movement may include a head movement that is not accompanied by a noise from surgeon  101 . The noise may include speech, a sneeze, a cough, a sigh, or any combination thereof. Speech by the surgeon may include communicating with others in the operating room. Quiet head movements may be detected by noise detection system  272 . Noise detection system  272  may be communicatively coupled to microphone  260 . Microphone  260  may be worn by surgeon  101 . Microphone  260  may be a wireless microphone. Microphone  260  may be a head mounted microphone. A head movement may be a quiet head movement if little or no signal is detected from microphone  260  at about the same time as a movement of marker  235  is detected by infrared camera  250 . Noise detection system  272  may determine if a head movement is a quiet head movement and send a signal corresponding to the determination to processor  280 . Processor  280  may execute instructions to control ophthalmic surgical microscope  201  in response to the quiet head movement. 
     A deliberate head movement may include a head movement that is made with purpose by surgeon  101 , for example, a head movement that is not an instinctive head movement. A deliberate head movement may include a head movement that is slower than an instinctive head movement, a head movement that is larger in magnitude than an instinctive head movement, a head movement that is smoother in motion than an instinctive head movement, or any combination thereof. A deliberate head movement may be a head movement that is slower than a head movement that occurs at 2 Hz. Alternatively, a deliberate head movement may be a head movement that is slower than a head movement that occurs at 4 Hz. A deliberate head movement may be a head movement that is larger in magnitude than a head movement of 1 mm, as measured by movement of a particular point on the surgeon&#39;s head through three-dimensional space. Alternatively, a deliberate head movement may be a head movement that is in the range of from about 1 mm to about 16 mm, as measured by movement of a particular point on the surgeon&#39;s head through three-dimensional space. A deliberate head movement may be a head movement that is smoother in motion than a head movement that accelerates the head faster than 1 m/s 2 . A deliberate head movement may be a head movement that is smoother in motion than a head movement that accelerates the head faster than 2 m/s 2 . Deliberate head movements may be detected by motion thresholding system  273 . A head movement may be a deliberate head movement if the movement of marker  235  detected by infrared camera  250  is slow, large in magnitude, smooth, or any combination thereof. Alternatively, a head movement may be a deliberate head movement if the movement of marker  235  detected by infrared camera  250  is slow, large in magnitude, and smooth. Motion thresholding system  273  may determine if a head movement is a deliberate head movement and send a signal corresponding to the determination to processor  280 . Processor  280  may execute instructions to control ophthalmic surgical microscope  201  in response to the deliberate head movement. 
     An uncommon head movement may include a head movement that is not commonly made by a surgeon during surgery. For example, an uncommon head movement may include a translation x  140  or y  160 . Common surgeon movements that occur frequently during surgery may include yaw  120 , for example, to address other staff in the operating room. Uncommon head movements may be detected by motion recognition system  274 . A head movement may be an uncommon head movement if the movement of marker  235  detected by infrared camera  250  corresponds to a head movement that is not commonly made by a surgeon during surgery. Motion recognition system  274  may determine if a head movement is an uncommon head movement and send a signal corresponding to the determination to processor  280 . Processor  280  may execute instructions to control ophthalmic surgical microscope  201  in response to the uncommon head movement. 
     Intelligent tracking system  271  may allow head tracking control system  200  to control ophthalmic surgical microscope  201  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, and an uncommon head movement. Alternatively, intelligent tracking system  271  may allow head tracking control system  200  to control ophthalmic surgical microscope  201  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. A surgeon head movement that is not a defined head movement may be ignored by head tracking control system  200 . 
     Ophthalmic surgical microscope  201  may execute instructions on processor  280  in response to a defined head movement of surgeon  101 . For example, processor  280  may execute instructions to move motorized microscope head support  265  in response to the defined head movement of surgeon  101 . The movement of motorized microscope head support  265  may be described by a two-dimensional Cartesian co-ordinate system of microscope movement x-axis  211  and microscope movement y-axis  231 . 
     For example, a movement of the at least one marker  235  that corresponds to a defined head movement of x  140  by surgeon  101  may be detected by infrared camera  250  and a signal corresponding to the detected movement may be sent to processor  280 . Processor  280  may execute instructions to move motorized microscope head support along microscope movement x-axis  211 . This may change the field of view that includes XY plane  266  observed by surgeon  101  along microscope movement x-axis  211 . Similarly, a movement of the at least one marker  235  that corresponds to a defined head movement of y  160  by surgeon  101  may be detected by infrared camera  250  and a signal corresponding to the detected movement may be sent to processor  280 . Processor  280  may execute instructions to move motorized microscope head support along microscope movement y-axis  231 . This may change the field of view that includes XY plane  266  observed by surgeon  101  along microscope movement y-axis  231 . 
     Alternatively, processor  280  may execute other instructions to control ophthalmic surgical microscope  201  in response to a defined head movement of surgeon  101 . For example, a movement of the at least one marker  235  that corresponds to a defined head movement that includes z  150  and pitch  110  by surgeon  101  may be detected and a signal corresponding to the detected movement may be sent to processor  280 . Processor  280  may execute instructions to change the focus of ophthalmic surgical microscope  201  by moving objective  220 . Objective  220  may be moved along focus z-axis  221 . If z  150  and pitch  110  are positive, processor  280  may execute instructions to move objective  220  away from eye  10  along focus z-axis  221  within surgical microscope  201 . If z  150  and pitch  110  are negative, processor  280  may execute instructions to move objective  220  closer to eye  10  along focus z-axis  221 . Processor  280  may execute instructions to control ophthalmic surgical microscope  201  in any manner useful for ophthalmic surgery in response to any appropriate defined head movement of surgeon  101 . Such instructions may be unique and programmable to accommodate the preference of individual ophthalmic surgeons. 
     The instructions executed by processor  280  to control ophthalmic surgical microscope  210  may be movement instructions. Movement instructions may have a parameter of velocity, which may be measured, for example, in units such as mm/second or μm/second. The velocity of the movement instructions may be fixed or variable. The velocity of the movement instructions may vary according to the position of the corresponding movement. For example, the velocity of movement instructions to move motorized microscope head support  265  in response to the defined head movement of surgeon  101  may vary according to the position of motorized microscope head support  265 . A movement of the at least one marker  235  that corresponds to a defined head movement of y  160  by surgeon  101  may be detected by infrared camera  250  and a signal corresponding to the detected movement may be sent to processor  280 . Processor  280  may execute movement instructions to move motorized microscope head support along microscope movement y-axis  231 . Motorized microscope head support  265  may move from start point  261  to end point  262 . As motorized microscope head support  265  moves away from start point  261 , the velocity of the movement instructions may increase with increasing distance from start point  261 . This increase may continue until motorized microscope head support  265  reaches a point equidistant between start point  261  and end point  262 . The velocity of the movement instructions may then decrease with decreasing distance of motorized microscope head support  265  to end point  262 . Accordingly, the movement instructions may be configured to result in a slow ramping up and ramping down of the velocity of the movement of motorized microscope head support  265 . The movement instructions may also be configured to result in any velocity of movement of a component of ophthalmic surgical microscope  210  that improves visualization for ophthalmic surgery. 
     Head tracking control system  200  may include control device  282 . Control device  282  may adjust, for example, the settings of intelligent tracking system  271 , the sensitivity of microphone  260 , the velocity of movement instructions executed by processor  280 , any other surgeon specific settings of head tracking control system  200 , or any combination thereof. 
       FIG. 3  depicts a process flow  300  for controlling an ophthalmic surgical microscope using a head tracking control system. Process flow  300  may include detecting a surgeon head movement in step  301 . The head movement may be detected by an infrared camera such as infrared camera  250 . Process flow  300  may further include determining if the head movement is a quiet head movement in step  310 . A noise detection system, such as noise detection system  272 , may detect if a head movement is a quiet head movement. If the head movement is not a quiet head movement, in step  340  the head tracking control system, such as head tracking control system  200 , may not control the ophthalmic surgical microscope, such as ophthalmic surgical microscope  201 . If the head movement is a quiet head movement, process flow  300  may include determining if the head movement is a deliberate head movement in step  320 . A motion thresholding system, such as motion thresholding system  273 , may detect if a head movement is a deliberate head movement. If the head movement is not a deliberate head movement, in step  340  the head tracking control system may not control the ophthalmic surgical microscope. If the head movement is a deliberate head movement, process flow  300  may include determining if the head movement is an uncommon head movement in step  330 . A motion recognition system, such as motion recognition system  274 , may detect if a head movement is an uncommon head movement. If the head movement is not an uncommon head movement, in step  340  the head tracking control system may not control the ophthalmic surgical microscope. If the head movement is an uncommon head movement, process flow  300  may include allowing the head tracking control system, such as head tracking control system  200 , to control the ophthalmic surgical microscope. 
     In process flow  300 , a surgeon head movement that is a quiet head movement, a deliberate head movement, and an uncommon head movement may allow the head tracking control system to control the ophthalmic surgical microscope. Alternatively, a surgeon head movement that is a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof, may allow a head tracking control system to control the ophthalmic surgical microscope. 
     Referring now to  FIG. 4 , head tracking control system  400  may include ophthalmic surgical microscope  201 , headband  430 , 3-axis gyroscope  457 , 3-axis accelerometer  458 , and motorized microscope head support  265 . 
     Head tracking control system  400  may track the head movement of surgeon  101  using at least one gyroscope sensor and at least one accelerometer sensor. For example, head tracking control system  400  may include 3-axis gyroscope  457  and 3-axis accelerometer  458  mounted on headband  430 . Headband  430  may be positioned on the head of surgeon  101 . 3-axis gyroscope  457  and 3-axis accelerometer  458  may be wirelessly communicatively coupled to processor  480 . In another example, head tracking control system  400  may include a vibrating structure gyroscope sensor. Head tracking control system  400  may include a gyroscope sensor contained on a single chip. Head tracking control system  400  may include an accelerometer sensor contained on a single chip. Headband  430  may alternatively be a hat or cap. 
     3-axis gyroscope  457  may be a 3-axis gyroscope sensor that may detect the angular velocity of the head of surgeon  101  wearing headband  430 . 3-axis gyroscope  457  may also detect the rotational motion pitch  110 , yaw  120 , roll  130  of the head of surgeon  101 . 3-axis accelerometer  458  may be a 3-axis accelerometer sensor that may detect the acceleration of the head of surgeon  101  wearing headband  430 . 3-axis accelerometer  458  may also detect translation x  140 , z  150 , y  160  of the head of surgeon  101 . 
     During surgery, 3-axis gyroscope  457  and 3-axis accelerometer  458  may detect the head movement of surgeon  101  and send a signal corresponding to the detected movement to processor  480 . The head movement of surgeon  101  may be analyzed by intelligent tracking system  271 . The head movement of surgeon  101  detected by 3-axis gyroscope  457  and 3-axis accelerometer  458  may correspond to a head movement that is pitch  110 , yaw  120 , roll  130 , x  140 , z  150 , y  160 , or any combination thereof. The head movement of surgeon  101  may be described by Cartesian co-ordinates corresponding to x-axis  111 , z-axis  121  and y-axis  131 . The head movement of surgeon  101  may be tracked using 3-axis gyroscope  457  and 3-axis accelerometer  458  in real time. 
     Intelligent tracking system  271  may execute instructions on processor  480  to determine if the head movement of surgeon  101  corresponds to a defined head movement. Intelligent tracking system  271  may include noise detection system  272 , motion thresholding system  273 , and motion recognition system  274 . Intelligent tracking system  271  may allow head tracking control system  400  to control ophthalmic surgical microscope  201  when surgeon  101  makes a defined head movement. A defined head movement may include a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. A defined head movement may correspond to a characteristic head movement of surgeon  101  as detected by 3-axis gyroscope  457  and 3-axis accelerometer  458 . 
     Intelligent tracking system  271  may allow head tracking control system  400  to control ophthalmic surgical microscope  201  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, and an uncommon head movement. Alternatively, intelligent tracking system  271  may allow head tracking control system  400  to control ophthalmic surgical microscope  201  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. Accordingly, a surgeon head movement that is not a defined head movement may be ignored by head tracking control system  400 . 
     Ophthalmic surgical microscope  201  may execute instructions on processor  480  in response to a defined head movement of surgeon  101 . For example, processor  480  may execute instructions to move motorized microscope head support  265  in response to the defined head movement of surgeon  101 . The movement of motorized microscope head support  265  may be described by a two-dimensional Cartesian co-ordinate system corresponding to microscope movement x-axis  211  and microscope movement y-axis  231 . Alternatively, processor  480  may execute other instructions to control ophthalmic surgical microscope  201  in response to a defined head movement of surgeon  101 . 
     Referring now to  FIG. 5 , head tracking control system  500  may include ophthalmic surgical microscope  201 , headband  530 , three-dimensional scanning camera  550 , LED driver  556 , digital light processing controller chip  557 , digital micromirror device  558 , lens  559 , and motorized microscope head support  265 . 
     Head tracking control system  500  may track the head movement of surgeon  101  using optical three-dimensional scanning to provide a digitized three-dimensional scan of the head of surgeon  101 . Three-dimensional scanning may be performed using structured light, which may be provided by digital micromirror device  558 . Three-dimensional scanning using structured light is an optical method where a series of patterns may be projected upon the head of surgeon  101 . Three-dimensional scanning camera  550  may detect distortions in the patterns of structured light reflected off the head of surgeon  101 . Image processing and triangulation algorithms, which may be performed by image processing system  270 , may convert these distortions into a three-dimensional point cloud. The point cloud may be used to determine a head movement of surgeon  101 . 
     Digital light processing controller chip  557  may control an array of reflective aluminum mirrors disposed on digital micromirror device  558 . LED driver  556  may emit near-infrared light (for example, wavelengths in the range of from 700 nm-2500 nm). In an alternative configuration, LED driver  556  may be substituted for a lamp or laser. Digital micromirror device  558  may modulate the amplitude, direction, phase, or any combination thereof, of incoming light emitted by LED driver  556 . Light emitted by LED driver  556  and modulated by digital micromirror device  558  may pass through lens  559 . 
     Head tracking control system  500  may include headband  530 . Headband  530  may be positioned on the head of surgeon  101 . Headband  530  may alternatively be a hat or cap. Headband  530  may include at least one marker  535 . Marker  535  may include six passive infrared markers. The inclusion of six passive markers may allow marker  535  to be tracked as a rigid body with six degrees of freedom. During surgery, the position of the at least one marker  535  may be tracked using three-dimensional scanning camera  550  using optical three-dimensional scanning. Marker  535  may function as a fiducial. Marker  535  may function as a fiducial in a captured image. Marker  535  may also function as a fiducial in real space. Marker  535  may be disposed in a cap, attached by adhesive, marked in pen, marked by any other means, or any combination thereof. Marker  535  may be placed in any orientation necessary such that its position may be tracked in six degrees of freedom. 
     Three-dimensional scanning camera  550  may detect structured light reflected off the at least one marker  535  and send a signal corresponding to the detected light to processor  580 . Three-dimensional scanning camera  550  may further execute instructions on processor  280  to detect a movement of the at least one marker  535 . The movement of the at least one marker  535  may be analyzed by intelligent tracking system  271 . The movement of marker  535  detected by three-dimensional scanning camera  550  may correspond to a head movement of surgeon  101  that is pitch  110 , yaw  120 , roll  130 , x  140 , z  150 , y  160 , or any combination thereof. The head movement of surgeon  101  may be described by Cartesian co-ordinates corresponding to x-axis  111 , z-axis  121  and y-axis  131 . The head movement of surgeon  101  may be tracked using three-dimensional scanning camera  550  in real time. In another example, three-dimensional scanning camera  550  may be a LIPSedge™ AE400 stereo camera (LIPS Corp., Taiwan). 
     Intelligent tracking system  271  may execute instructions on processor  580  to determine if the movement of the at least one marker  535  corresponds to a defined head movement of surgeon  101 . Intelligent tracking system  271  may include noise detection system  272 , motion thresholding system  273 , and motion recognition system  274 . Intelligent tracking system  271  may allow head tracking control system  500  to control ophthalmic surgical microscope  201  when surgeon  101  makes a defined head movement. A defined head movement may include a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. A defined head movement may correspond to a characteristic movement of marker  535  detected by three-dimensional scanning camera  550 . 
     Intelligent tracking system  271  may allow head tracking control system  500  to control ophthalmic surgical microscope  201  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, and an uncommon head movement. Alternatively, intelligent tracking system  271  may allow head tracking control system  500  to control ophthalmic surgical microscope  201  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. Accordingly, a surgeon head movement that is not a defined head movement may be ignored by head tracking control system  500 . 
     Ophthalmic surgical microscope  201  may execute instructions on processor  580  in response to a defined head movement of surgeon  101 . For example, processor  580  may execute instructions to move motorized microscope head support  265  in response to the defined head movement of surgeon  101 . The movement of motorized microscope head support  265  may be described by a two-dimensional Cartesian co-ordinate system corresponding to microscope movement x-axis  211  and microscope movement y-axis  231 . Alternatively, processor  580  may execute other instructions to control ophthalmic surgical microscope  201  in response to a defined head movement of surgeon  101 . 
     Head tracking control system  200 , head tracking control system  400 , or head tracking control system  500  may be used, at least in part, as a component of the NGENUITY® 3D Visualization System (Novartis AG Corp., Switzerland) in visualization system  600 , as depicted in  FIG. 6 . Visualization system  600  may include headband  630 , surgeon head movement detection device  650 , intelligent tracking system  271 , surgical camera  660 , patient table  665 , surgical camera system  685 , and display  690 . Surgeon head movement detection device  650  may be a device such as infrared camera  250 , 3-axis gyroscope  457  and 3-axis accelerometer  458 , three-dimensional scanning camera  550 , or any combination thereof. 
     Headband  630  may be positioned on the head of surgeon  101 . Headband  630  may alternatively be a hat or cap. Headband  630  may include at least one marker  635 . During surgery, the position of the at least one marker  635  may be tracked using surgeon head movement detection device  650 . Marker  635  may be an active infrared marker. An active infrared marker may include an infrared light emitting element, and may include at least one light emitting diode (LED). In one example, marker  635  may include six active beacons. The inclusion of six active beacons may allow marker  635  to be tracked as a rigid body with six degrees of freedom. In another example, marker  635  may include six LEDs. The LEDs may be flashed in a time synchronous controlled sequence. 
     Marker  635  may be a passive reflective marker. Marker  635  may include six passive infrared markers. The inclusion of six passive markers may allow marker  635  to be tracked as a rigid body with six degrees of freedom. Marker  635  may function as a fiducial. Marker  635  may function as a fiducial in a captured image. Marker  635  may also function as a fiducial in real space. If at least part of head tracking control system  400  is included as a component of visualization system  600 , headband  630  may include a 3-axis gyroscope and a 3-axis accelerometer, such as 3-axis gyroscope  457  and 3-axis accelerometer  458 , instead of marker  635  (not shown). 
     Surgical camera  660  may be positioned above patient table  665 . Surgical camera  660  may be a digital camera, an HDR camera, a 3D camera, a surgical camera, or any combination thereof. Surgical camera  660  may move with six degrees of freedom. Surgical camera  660  may also utilize optomechanical focus system  661 , zoom system  662 , and variable working distance system  663 . Surgical camera  660  may be communicatively coupled with surgical camera system  685  and display  690 . Surgical camera system  685  may include image processing system  670 , processor  680 , and memory medium  681 . 
     Display  690  may be a head-up display mounted on support member  698  and mount base  699 . Support member  698  and mount base  699  may be adjustable to change the distance between display  690  and the surgeon. Display  690  may also be ceiling mounted. Display  690  may be communicatively coupled with surgical camera system  685 . Display  690  may be a picture-in-picture display. In another example, surgical camera  660  may be a 3D HDR camera and display  690  may be a 3D  4 K OLED surgical display. Display  690  may display a 3D surgical image of an eye. Processor  680  may be an ultra-high-speed 3D image processor, which may optimize 3D HDR images in real time. 
     Surgical camera  660  may be communicatively coupled with surgical camera system  685  and display  690 . Display  690  may receive information from surgical camera  660  via surgical camera system  685 . Display  690  may display a digital image of an eye captured by surgical camera  660 . 
     Surgeon head movement detection device  650  may detect a head movement of surgeon  101  and send a signal corresponding to the detected head movement to processor  680 . The head movement of surgeon  101  may be analyzed by intelligent tracking system  271 . The head movement of surgeon  101  may be pitch  110 , yaw  120 , roll  130 , x  140 , z  150 , y  160 , or any combination thereof. The head movement of surgeon  101  may be described by Cartesian co-ordinates corresponding to x-axis  111 , z-axis  121  and y-axis  131 . 
     Intelligent tracking system  271  may execute instructions on processor  680  to determine if the head movement of surgeon  101  corresponds to a defined head movement. Intelligent tracking system  271  may include noise detection system  272 , motion thresholding system  273 , and motion recognition system  274 . Intelligent tracking system  271  may allow a head tracking control system to control surgical camera  660  when surgeon  101  makes a defined head movement. A defined head movement may include a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. A defined head movement may correspond to a characteristic movement of marker  635  detected by surgeon head movement detection device  650 . 
     Processor  680  may execute instructions to move surgical camera  660  in response to the defined head movement of surgeon  101 . Movement of surgical camera  660  may be described by Cartesian co-ordinates corresponding to x-axis  611 , z-axis  621  and y-axis  631 . Visualization system  600  may maintain a relative pose in six degrees of freedom (x, y, z, pitch, yaw, and roll) between the head of surgeon  101  (x-axis  111 , z-axis  121  and y-axis  131 ) and surgical camera  660  (x-axis  611 , z-axis  621  and y-axis  631 ). In this way, surgical camera  660  may function as if it were attached to the head of surgeon  101  when a head tracking control system is activated. The surgical camera  660  may be a distance  666  from the head of surgeon  101 . Distance  666  may be in a range of from about 175 mm to about 300 mm. When the head tracking control system is activated, surgeon  101  may move his head as if it were surgical camera  660 . The head tracking control system may be activated, for example, by a foot pedal. 
     Intelligent tracking system  271  may allow a head tracking control system to control surgical camera  660  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, and an uncommon head movement. Alternatively, intelligent tracking system  271  may allow a head tracking control system to control surgical camera  660  if surgeon  101  makes a defined head movement that is a quiet head movement, a deliberate head movement, an uncommon head movement, or any combination thereof. Accordingly, a surgeon head movement that is not a defined head movement may be ignored by a head tracking control system in visualization system  600 . A defined head movement when controlling surgical camera  660  may be different to a defined head movement when controlling ophthalmic surgical microscope  201 . 
     In another example, processor  680  may execute instructions to allow navigation on display  690  in response to a defined head movement of surgeon  101 . Display  690  may display a virtual display of a surgical procedure. A head movement of surgeon  101  that is pitch  110  or yaw  120  may be used to navigate around the virtual display. Alternatively, a head movement of surgeon  101  that is pitch  110  or yaw  120  may be used to execute commands of yes and no, respectively to navigate on display  690 . 
     Head tracking control system  200 , head tracking control system  400 , or head tracking control system  500  may be used in combination with a computer system  700 , as depicted in  FIG. 7 . Computer system  700  may include a processor  710 , a volatile memory medium  720 , a non-volatile memory medium  730 , and an input/output (I/O) device  740 . Volatile memory medium  720 , non-volatile memory medium  730 , and I/O device  740  may be communicatively coupled to processor  710 . 
     The term “memory medium” may mean a “memory”, a “storage device”, a “memory device”, a “computer-readable medium”, and/or a “tangible computer readable storage medium”. For example, a memory medium may include, without limitation, storage media such as a direct access storage device, including a hard disk drive, a sequential access storage device, such as a tape disk drive, compact disk (CD), random access memory (RAM), read-only memory (ROM), CD-ROM, digital versatile disc (DVD), electrically erasable programmable read-only memory (EEPROM), flash memory, non-transitory media, or any combination thereof. As shown in  FIG. 7 , non-volatile memory medium  730  may include processor instructions  732 . Processor instructions  732  may be executed by processor  710 . In one example, one or more portions of processor instructions  732  may be executed via non-volatile memory medium  730 . In another example, one or more portions of processor instructions  732  may be executed via volatile memory medium  720 . One or more portions of processor instructions  732  may be transferred to volatile memory medium  720 . 
     Processor  710  may execute processor instructions  732  in implementing at least a portion of one or more systems, one or more flow charts, one or more processes, and/or one or more methods described herein. For example, processor instructions  732  may be configured, coded, and/or encoded with instructions in accordance with at least a portion of one or more systems, one or more flowcharts, one or more methods, and/or one or more processes described herein. Although processor  710  is illustrated as a single processor, processor  710  may be or include multiple processors. One or more of a storage medium and a memory medium may be a software product, a program product, and/or an article of manufacture. For example, the software product, the program product, and/or the article of manufacture may be configured, coded, and/or encoded with instructions, executable by a processor, in accordance with at least a portion of one or more systems, one or more flowcharts, one or more methods, and/or one or more processes described herein. 
     Processor  710  may include any suitable system, device, or apparatus operable to interpret and execute program instructions, process data, or both stored in a memory medium and/or received via a network. Processor  710  further may include one or more microprocessors, microcontrollers, FPGAs, DSPs, ASICs, or other circuitry configured to interpret and execute program instructions, process data, or both. 
     I/O device  740  may include any instrumentality or instrumentalities, which allow, permit, and/or enable a user to interact with computer system  700  and its associated components by facilitating input from a user and output to a user. Facilitating input from a user may allow the user to manipulate and/or control computer system  700 , and facilitating output to a user may allow computer system  700  to indicate effects of the user&#39;s manipulation and/or control. For example, I/O device  740  may allow a user to input data, instructions, or both into computer system  700 , and otherwise manipulate and/or control computer system  700  and its associated components. I/O devices may include user interface devices, such as a keyboard, a mouse, a touch screen, a joystick, a handheld lens, a tool tracking device, a coordinate input device, or any other I/O device suitable to be used with a system. 
     I/O device  740  may include one or more buses, one or more serial devices, and/or one or more network interfaces, among others, that may facilitate and/or permit processor  710  to implement at least a portion of one or more systems, processes, and/or methods described herein. In one example, I/O device  740  may include a storage interface that may facilitate and/or permit processor  710  to communicate with an external storage. The storage interface may include one or more of a universal serial bus (USB) interface, a SATA (Serial ATA) interface, Ethernet, a PATA (Parallel ATA) interface, and a small computer system interface (SCSI), among others. In a second example, I/O device  740  may include a network interface that may facilitate and/or permit processor  710  to communicate with a network. I/O device  740  may include one or more of a wireless network interface and a wired network interface. In a third example, I/O device  740  may include one or more of a peripheral component interconnect (PCI) interface, a PCI Express (PCIe) interface, a serial peripheral interconnect (SPI) interface, and an inter-integrated circuit (I2C) interface, among others. In a fourth example, I/O device  740  may include circuitry that may permit processor  710  to communicate data with one or more sensors. In a fifth example, I/O device  740  may facilitate and/or permit processor  710  to communicate data with one or more of a display  750  and head tracking control system  200 , among others. As shown in  FIG. 7 , I/O device  740  may be coupled to a network  770 . For example, I/O device  740  may include a network interface. 
     Network  770  may include a wired network, a wireless network, an optical network, or any combination thereof. Network  770  may include and/or be coupled to various types of communications networks. For example, network  770  may include and/or be coupled to a local area network (LAN), a wide area network (WAN), an Internet, a public switched telephone network (PSTN), a cellular telephone network, a satellite telephone network, or any combination thereof. A WAN may include a private WAN, a corporate WAN, a public WAN, or any combination thereof. 
     Although  FIG. 7  illustrates computer system  700  as external to head tracking control system  200 , head tracking control system  200  may include computer system  700 . For example, processor  710  may be or include processor  280 . 
       FIGS. 8A-8C  illustrate examples of medical system  800 . As shown in  FIG. 8A , medical system  800  may include head tracking control system  200 . Alternatively, medical system  800  may include head tracking control system  400  or head tracking control system  500 . As illustrated in  FIG. 8B , medical system  800  may include head tracking control system  200  and computer system  700 . Head tracking control system  200  may be communicatively coupled with computer system  700 . As shown in  FIG. 8C , medical system  800  may include head tracking control system  200 , which may include computer system  700 . 
       FIG. 9  presents a flow diagram for a method of controlling a visualization system using a head tracking control system. In step  900 , a surgeon makes a defined head movement, which may be a head movement that is a quiet head movement, a deliberate head movement, and an uncommon head movement. In step  910 , the defined head movement may be detected by a surgeon head movement detection device, such as surgeon head movement detection device  650 . The defined head movement may be pitch  110 , yaw  120 , roll  130 , x  140 , z  150 , y  160 , or any combination thereof. In step  920 , a corresponding movement of a surgical camera, such as surgical camera  660 , may be determined. The corresponding movement of the surgical camera may be in six degrees of freedom. Alternatively, the corresponding movement of the surgical camera may be in less than six degrees of freedom. For example, head tracking control system  200  may detect a defined head movement of the surgeon in six degrees of freedom, but may control ophthalmic surgical microscope  201  in three degrees of freedom. In step  930 , the surgical camera may move in response to the defined head movement of the surgeon. 
     Head tracking control system  200 , head tracking control system  400 , head tracking control system  500 , visualization system  600 , computer system  700 , medical system  800 , and components thereof may be combined with other elements of visualization tools and systems described herein unless clearly mutually exclusive. For instance, the infrared camera and active infrared illuminator may be used with other visualization systems described herein. 
     The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. For example, although a head tracking control system is most commonly needed to improve control of a visualization system for ophthalmic surgery, if it were useful in another procedure, such as a purely diagnostic procedure not otherwise considered to be surgery, the systems and methods described herein may be employed.