Abstract:
An ophthalmic apparatus for performing an ocular surgery may include an ophthalmic probe body having an inner cutting member at least partially disposed within and moveable relative to an aspiration tube within the probe body to facilitate flow of aspiration fluid. A motor within the body may be configured to actuate the inner cutting member relative to the aspiration tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present disclosure is a continuation of U.S. patent application Ser. No. 14/244,986, entitled “Minimal Pulsation Ophthalmic Probe,” filed Apr. 4, 2014, the entire disclosure of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure pertains to ophthalmic probes, systems, and methods. More particularly, but not by way of limitation, the present invention pertains to ophthalmic probes, systems, and methods utilizing an aspiration arrangement that may reduce the impact of fluid pulsations. 
       BACKGROUND 
       [0003]    Microsurgical procedures frequently require precision cutting and/or removing various body tissues. For example, certain ophthalmic surgical procedures require cutting and removing portions of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibrils that are often attached to the retina. Therefore, cutting and removing the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself. In particular, delicate operations such as mobile tissue management (e.g. cutting and removal of vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and cutting and removal of membranes are particularly difficult. 
         [0004]    The use of microsurgical cutting probes in posterior segment ophthalmic surgery is well known. These cutting probes typically include a hollow outer cutting member (the needle), a hollow inner cutting member (the cutter) arranged coaxially with and movably disposed within the hollow outer cutting member, and a port extending radially through the outer cutting member near the distal end thereof. Vitreous humor and/or membranes are aspirated into the open port, and the inner member is actuated, closing the port. Upon the closing of the port, cutting surfaces on both the inner and outer cutting members cooperate to cut the vitreous and/or membranes, and the cut tissue is then aspirated away through the inner cutting member. 
         [0005]    The inner cutting member (or cutter) in conventional vitrectomy cutting probe systems typically connects with a larger tube within the probe via a coupling device. With each cutting cycle, the inner cutting member (or cutter), the coupling device, and the larger tube all axially displace by an amount equal to the cutting stroke length, thereby cutting the vitreous that entered the port. However, the cutting motion also results in a change of the internal fluid volume of the ophthalmic probe. This is due to the difference in internal cross-sectional area between the cutter and the larger tube in conjunction with the axial motion of this transition. The volume change may cause pressure pulses and fluid agitation which could result in fluid pumping, and due to the vacuum present, could drive some gas out of solution, thereby producing bubbles. Further, while most of the excess volume may propagate up the aspiration tube, some of the volume may manifest itself as pulses or even a reversal of flow during vitrectomy cutting. It may also create some agitation that results in gas coming out of solution. 
         [0006]    The present disclosure is directed to addressing one or more of the deficiencies in the prior art. 
       SUMMARY 
       [0007]    In some exemplary aspects, the present disclosure is directed to an ophthalmic apparatus for performing an ocular surgery. The apparatus may include an ophthalmic probe body graspable by a user and a cutter extending from the body and comprising an inner cutting member and a needle. The inner cutting member may be at least partially disposed within and moveable relative to the needle, and the inner cutting member may have a lumen having a first diameter. The needle may have a distal end with a port formed therein for receiving patient tissue. An aspiration tube within the probe body may be disposed to extend from the end of the inner cutting member to an aspiration line from the probe body, the aspiration tube having a second diameter greater than the first diameter to facilitate flow of aspiration fluid. A motor within the body may be configured to actuate the inner cutting member relative to the needle and relative to the aspiration tube. 
         [0008]    In an aspect, the inner cutting member is coaxial with the aspiration tube. In an aspect, the aspiration tube is fixed in place so as to be stationary relative to the probe body. In an aspect, the ophthalmic apparatus includes a drive shaft connected to the motor and a coupler coupling the drive shaft to the inner cutting member so that when the motor actuates the drive shaft, the coupler actuates the inner cutting member. In an aspect, the drive shaft is larger than the aspiration tube, the aspiration tube being disposed within the drive shaft. In an aspect, the drive shaft is coaxial with the aspiration tube. In an aspect, the aspiration tube extends through a central portion of the motor. In an aspect, the ophthalmic apparatus includes a cutter seal assembly affixed to the aspiration tube, the cutter seal assembly comprising a seal that prevents the passage of fluid. In an aspect, the motor is affixed directly to the inner cutting member. 
         [0009]    In some exemplary aspects, the present disclosure is directed to an ophthalmic apparatus for performing an ocular surgery and includes an ophthalmic probe body graspable by a user and a cutter extending from the body and comprising an inner cutting member and a needle. The inner cutting member may be at least partially disposed within and moveable relative to the needle. The inner cutting member may have a lumen having a first diameter, the needle having a distal end with a port formed therein for receiving patient tissue. An aspiration tube may be fixed in place relative to the probe body and may extend from the end of the inner cutting member to an aspiration line from the probe body. The aspiration tube may have a second diameter greater than the first diameter to facilitate flow of aspiration fluid. A motor may be disposed within the body and may be coupled to the inner cutting member. The motor may be configured to actuate the inner cutting member relative to the needle. 
         [0010]    In an aspect, the inner cutting member is coaxial with the aspiration tube. In an aspect, the motor is configured to actuate the inner cutting member relative to the aspiration tube. In an aspect, the ophthalmic apparatus includes a drive shaft connected to the motor and a coupler coupling the drive shaft to the inner cutting member so that when the motor actuates the drive shaft, the coupler actuates the inner cutting member. In an aspect, the drive shaft is larger than the aspiration tube, the aspiration tube being disposed within the drive shaft. In an aspect, the drive shaft is coaxial with the aspiration tube. In an aspect, the aspiration tube extends through a central portion of the motor. In an aspect, the ophthalmic apparatus includes a cutter seal assembly affixed to the aspiration tube, the cutter seal assembly comprising a seal that prevents the passage of fluid. In an aspect, the aspiration tube comprises a portion of an aspiration pathway in the probe body, and only the inner cutting member displaces within the aspiration in a manner impacting the volume of the aspiration pathway. In an aspect, the motor is affixed directly to the inner cutting member. 
         [0011]    In some exemplary aspects, the present disclosure is directed to methods of driving an inner cutting member of an ophthalmic probe. The methods may include opening an aspiration port in a needle of a distally protruding cutter by driving a motor to drive an inner cutting member in a proximal direction. The aspiration port, the inner cutting member, and an aspiration tube may form a portion of an aspiration pathway through the ophthalmic probe. The inner cutting member may have a first diameter and the aspiration tube may have a second diameter greater than the first diameter. Driving the inner cutting member in the proximal direction may include moving the inner cutting member relative to the aspiration tube. The method may also include closing the aspiration port to cut tissue in the aspiration port by driving the motor in the ophthalmic probe to drive the inner cutting member in the distal direction relative to the needle and displacing the inner cutting member relative to the aspiration tube. 
         [0012]    In an aspect, the aspiration tube is fixed in place within the ophthalmic probe and the volume of the aspiration pathway in the ophthalmic probe changes only by the volume equal to the axial displacement of the inner cutting member. In an aspect, driving a motor to drive an inner cutting member includes driving a drive shaft connected to the motor, and driving a coupler connected to the drive shaft, the coupler being connected to the inner cutting member at a location distal of the aspiration tube. 
         [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings illustrate embodiments of the devices and methods disclosed herein and together with the description, serve to explain the principles of the present disclosure. 
           [0015]      FIG. 1  is an illustration of an exemplary ophthalmic surgical system according to one aspect of the present disclosure implementing the principles and methods described herein. 
           [0016]      FIG. 2  is a cross-sectional diagram illustrating an ophthalmic probe of the exemplary ophthalmic surgical system of  FIG. 1  according to an aspect of the disclosure. 
           [0017]      FIG. 3  is a cross-sectional diagram illustrating a distal end of a cutter of the exemplary ophthalmic probe of  FIG. 2  according to an aspect of the disclosure. 
           [0018]      FIG. 4  is a detailed view of a portion of the ophthalmic probe of  FIG. 2  according to an aspect of the disclosure. 
           [0019]      FIG. 5  is a cross-sectional diagram illustrating another ophthalmic probe of the exemplary ophthalmic surgical system of  FIG. 1  according to an aspect of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. For simplicity, in some instances the same reference numbers are used throughout the drawings to refer to the same or like parts. 
         [0021]    The present disclosure is directed to surgical devices, systems, and methods for performing ophthalmic surgeries. The surgical devices include, for example, an ophthalmic probe having reduced pulsing and fluid agitation than prior devices. It does this by minimizing the fluid volume displacement during a cutting cycle. That is, in some embodiments of the present disclosure, the ophthalmic probes include a hollow needle connected with a larger tube by a coupling device that does not oscillate with the hollow needle and with the larger tube. Because of this, the fluid volume within the ophthalmic probe is maintained as relatively constant. This relatively constant fluid volume, therefore, more fully reduces a chance of fluid surge or fluid agitation that may result in undesirable fluid resistance or back flow. This also may result in a smoother, more consistent flow, providing predictability and accuracy for an operating surgeon. In turn, this may result in a better patient outcome. 
         [0022]      FIG. 1  illustrates an ophthalmic surgical system, generally designated  10 , according to an exemplary embodiment. The surgical system  10  includes a base housing  12  and an associated display screen  14  showing data relating to system operation and performance during an ophthalmic surgical procedure. The surgical system  10  includes an ophthalmic probe  100  structurally configured in a manner that reduces or minimizes fluid surges during the surgical procedure. In some embodiments, the ophthalmic surgical system  10  is a vitrectomy surgical system used to perform vitrectomy procedures to remove vitreous humor or other tissue from the eye. 
         [0023]    In some embodiments, the surgical system  10  includes a fluidic pressure source and a probe driver disposed in or forming a part of the base housing  12 . In some exemplary embodiments, the fluidic pressure source is a high pressure tank and compressor that provides driving fluidic power to drive the ophthalmic probe  100 . Some exemplary pressure sources are pneumatic pressure sources arranged to provide compressed air to drive the ophthalmic probe  100 . In some embodiments, the pneumatic pressure source is contained on or in the base housing  12 , while in other embodiments, the pressure source is disposed elsewhere in or about the operating room. 
         [0024]    The probe driver may be a pressure pulse generator, such as one or more standard three-way or four-way valves, for example. Some embodiments employ a solenoid that displaces a spool between a charge and a discharge position. The probe driver, sometimes referred to as a pressure pulse generator, cycles to set the cutting rate of the ophthalmic probe  100 . 
         [0025]    The ophthalmic probe  100  and the base housing  12  are in fluid communication with each other along lines  16  representing flow paths or flow lines. Depending on the embodiment, the lines may include a supply line and an aspiration line between the base housing  102  and the ophthalmic probe  100 . The supply line may have a lumen that carries a constant or pulsating pressurized fluid for driving an actuator or motor in the ophthalmic probe  100 . The aspiration line also extends from the base housing  102  to the ophthalmic probe  100  and is used to aspirate fluid and tissue from the probe  100 . 
         [0026]      FIG. 2  illustrates a cross-sectional view of an ophthalmic probe  100  according to an exemplary embodiment of the present disclosure for removing fluid/tissue from a patient&#39;s eye. In some aspects, the ophthalmic probe  100  is an ophthalmic probe usable in vitrectomy procedures. During such procedures, the probe may be used to penetrate the eye globe to access the vitreous humor or other tissue contained therein. The ophthalmic probe  100  may cut the vitreous humor or other tissue and aspirate it to the base housing  12  of the ophthalmic surgical system  10 . It may find particular utility for removing intraocular tissue during an ophthalmic procedure to re-attach a retina of an eye. Although use in an ophthalmic procedure is described, it is to be understood that the ophthalmic probe  100  can be used to cut and aspirate other tissue, such as polyps, fibroids, and other human tissue. 
         [0027]    The ophthalmic probe  100  includes a housing  102 , a motor  104  disposed within the housing  102 , a cutter  105  extending from the housing  102 , and a cutter assembly  108 . 
         [0028]    The housing  102  includes a handle portion  110  and a motor portion  112 . The handle portion  110  includes a handle body  114 . The handle body  114  extends in a proximal direction from a distal end  120  toward the motor portion  112 . An over-molded grip  122  extends about the handle body  114 . The grip  122  may be contoured for comfortable grasping by a user. 
         [0029]    The motor portion  112  is disposed proximal of the handle portion  110 , and includes a rear motor housing  124  and a front motor housing  126 . The rear motor housing  124  includes communication ports  128 ,  130  that provide communication between the ophthalmic probe  100  and the surgical system  10 . It also includes an aspiration port  131  that provides communication between an aspiration pump at the surgical system  10  and the probe  100 . In this embodiment, the communication ports  128 ,  130  are pneumatic ports, and the motor portion  112  is configured to hold a fluidically driven motor, such as, for example, a pneumatically driven motor. It&#39;s worth noting that other embodiments include alternative probe motors. For example, some embodiments include a fluidically driven piston motor in place of a diaphragm. 
         [0030]    The ports  128 ,  130 ,  131  extend from the proximal end of the rear motor housing  124  toward the distal end of the rear motor housing  124 . The front motor housing  126  is disposed distal of the rear motor housing  124  and is arranged to interface with the handle portion  110 . The rear motor housing  124  is configured to provide communication to the surgical system  10 , and the front motor housing  126  cooperates with the rear motor housing  124  to securely support the motor  104  of the ophthalmic probe  100 . 
         [0031]    In this embodiment, the rear motor housing  124  and the front motor housing  126  are shaped to cooperatively form a motor chamber  134 . In this embodiment, the chamber  134  is a transversely extending hollow configured to hold the motor  104  for driving the cutter assembly  108 . The rear motor housing  124  and front motor housing  126  include passages  136 ,  138  that respectively extend between the rear motor housing communication ports  128 ,  130  and the motor chamber  134 . In the embodiment of  FIG. 2 , the ports  128 ,  130  are in fluid communication with opposing sides of the motor chamber  134 , and here, are in communication with the distal and the proximal portions of the motor chamber  134 . As such, the ports  128 ,  130  are in fluid communication with opposing sides of the motor  104 . 
         [0032]    The motor  104  is disposed within the motor chamber  134  and is configured to drive the cutter assembly  108 . In this way, the cutter assembly  108  can be used to cut and aspirate tissue, such as intraocular or other tissue. The motor  104 , in this embodiment is a pneumatically driven motor, formed of a flexible diaphragm  140  and a rigid coupler  142 . It operates by pressure variation between the first and second ports  128 ,  130  and thus, on opposing sides of the motor  104 . The variation in pressure on opposing sides of the motor  104  within the motor chamber  134  causes the diaphragm  140  to vibrate, carrying portions of the cutter assembly  108  in a back-and-forth oscillating motion. 
         [0033]    The distal end of the pneumatic probe  100  includes the cutter  105 . The cutter  105  includes a needle  106  and an inner cutting member  149 . The needle  106  is a hollow cylinder and extends from the housing  102 . It includes a closed end and an outer port that receives tissue, such as ophthalmic tissue, and it cooperates with the cutter assembly  108 . 
         [0034]    A distal end of the cutter  105  is shown in  FIG. 3 . The needle  106  includes a closed end  144  and an outer port  146  that receives tissue, such as ophthalmic tissue. The outer port  146  is in fluid communication with an inner channel  148 . The inner cutting member  149  is located within the inner channel  148  of the needle  106 . The inner cutting member  149  has an inner bore  150 , an open end  152 , and a cutting surface  154 . As will be described below, the inner bore  150  is in fluid communication with the aspiration line of the ophthalmic probe  100 . The aspiration line connects to a vacuum pressure that pulls tissue into the outer port  146  when the inner cutting member  149  is located away from the port  146 . The inner cutting member  149  moves within the inner channel  148  of the needle  106  to cut tissue that is pulled into the outer port  146  by the aspiration system. The ophthalmic tissue received by the outer port  146  is preferably vitreous or membranes. 
         [0035]    It is worth noting that other embodiments have a distal end of the cutter  105  where a distal end of the inner cutting member  149  includes a port extending radially therethrough. As the edges of the radial port of the inner cutting member  149  pass the edges of the outer port  146  of the outer cutting member, the cutting may take place both on the distal stroke and on the proximal stroke, making a dual cutting cutter. One example of such an embodiment is shown in U.S. Pat. No. 5,106,364, incorporated herein by reference. Other arrangements are also contemplated. 
         [0036]    Returning to  FIG. 2 , the cutter assembly  108  includes a drive shaft  156 , a coupler  158 , a stationary aspiration tube  160 , a cutter seal assembly  162 , and the inner cutting member  149 . As shown in  FIG. 2 , the drive shaft  156  connects to and extends from the motor  104  and extends substantially centrally through the body portion  110  toward the distal end of the ophthalmic probe  100 . The drive shaft  156  is a relatively larger diameter tube structurally configured to transmit loading applied by the motor  104  to the coupler  158  and ultimately to the inner cutting member  149 . In this embodiment, the drive shaft  156  is a cylindrical tube, but other shapes are contemplated. For example, the drive shaft  156  may be a square, a triangle, or other shape having a central passage or opening. As will be described further below, the aspiration tube  160  and the cutter seal assembly  162  are disposed within the lumen or tube of the drive shaft  156 . In some embodiments, to reduce mass, the drive shaft  156  is configured of a plurality of longitudinally extending struts or supports, spaced apart by windows or gaps in the drive shaft sidewall. The rigid struts are sufficient to convey oscillating driving force applied by the motor  104  to the distal end of the drive shaft  156 . Other arrangements are also contemplated. The drive shaft  156  is configured to carry driving power from the motor to the coupler  158 . Accordingly, the drive shaft  156  is a rigidly extending structure. 
         [0037]    The coupler  158  is disposed at the distal end of the drive shaft  156  and couples the drive shaft  156  to the cutter inner cutting member  149 . In some embodiments, the coupler  158  is disposed within the drive shaft  156 . In some examples, it protrudes radially from the exterior surface of the inner cutting member  149  to the inner surface of the drive shaft  156 . Like the drive shaft  156 , the coupler  158  is a rigid structure configured to convey the oscillating displacement from the drive shaft  156  to the inner cutting member  149 . It may be solid or may be formed with windows or gaps to decrease its overall weight and decrease its dampening effect on the oscillating motor  104 . In this embodiment, the drive shaft  156 , the coupler  158 , and the inner cutting member  149  are all coaxially aligned in the ophthalmic probe  100 . 
         [0038]    As the drive shaft  156  axially translates in a distal and proximal direction, the coupler  158 , fixed to the drive shaft  156 , also translates in an oscillating manner. Because the inner cutting member  149  is fixed to the coupler  158 , axial displacement or translation of the coupler  158  results in axial displacement or translation of the inner cutting member  149  relative to the needle  106 . 
         [0039]    The stationary aspiration tube  160  and the cutter seal assembly  162  are disposed within the drive shaft  156 . These form a portion of an aspiration pathway through the ophthalmic probe  100 . For example, the aspiration pathway includes the port  146 , the inner cutting member  149 , the aspiration tube  160 , and the aspiration port  131 . In the exemplary embodiment shown, the aspiration tube  160  and the cutter seal assembly  162  are fixed in place relative to the body portion  110  of the ophthalmic probe  100 . As such, as the drive shaft  156 , the coupler  158 , and the inner cutting member  149  oscillate via the motor  104 , the aspiration tube  160  and the cutter seal assembly  162  are substantially fixed in place. 
         [0040]    In the embodiment shown, the aspiration tube  160  is a tube affixed coaxially with the inner cutting member  149  and extends from the inner cutting member  149  to a position proximal of the motor  104 . Accordingly, in the exemplary embodiment in  FIG. 2 , it is also coaxial with the drive shaft  156 . The aspiration tube  160  has a diameter greater than the diameter of the inner cutting member  149  so that the aspirating flow can be more easily induced without the same levels of pressure loss encountered in the smaller diameter inner cutting member  149 . Here, the aspiration tube  160  is coaxially aligned with the aspiration port  131 , and the aspiration tube  160  may be connected directly to the aspiration line of the lines  16  ( FIG. 1 ) connecting the ophthalmic probe to the base housing  12  of the ophthalmic surgical system  10 . 
         [0041]    The cutter seal assembly  162  connects the distal portion of the aspiration tube  160  to the inner cutting member  149 . In this embodiment, the cutter seal assembly  162  is fixed relative to the aspiration tube  60  and, therefore, the inner cutting member  149  moves relative to the cutter seal assembly  162 . The cutter seal assembly also transitions the aspiration pathway from the smaller diameter inner cutting member  149  to the larger diameter aspiration tube  160 . The cutter seal assembly  162  is attached at the distal end of the aspiration tube  160  and is configured to house one or more seals  164  that seal around the inner cutting member  149  to prevent leakage of aspiration fluid from the aspiration pathway and prevent drawing of air into the aspiration pathway from the inner portions of the body portion  110 . In the embodiment shown, the seal  164  is an O-ring, although other seals may be used. In this embodiment, the cutter seal assembly  162  is sized to receive the distal end of the aspiration tube  160  therein, and may be glued, laser or spot welded, or otherwise adhered to the aspiration tube  160 . 
         [0042]    Since the cutter seal assembly  162  is fixed in place relative to the aspiration tube  160 , and the aspiration tube  160  is substantially or completely fixed in place relative to the body portion of the ophthalmic probe  100 , the volume change within the aspiration tube  160  as a result of the oscillating inner cutting member  149  is minimized, resulting in a decreased chance of fluid surge within the aspiration line compared to vitrectomy probes that have a coupler that moves with inner cutting member  149 . This becomes apparent with reference to  FIG. 4 . 
         [0043]      FIG. 4  shows an enlarged view of the cutter seal assembly  162  and a portion of the aspiration tube  160  and the inner cutter member  149 . As can be seen the inner cutting member  149  has a first smaller diameter D 1  and the aspiration tube  160  has a second larger diameter D 2 . In order to reduce pressure loss occurring from long lengths of fluid pathways with minimal diameters, the aspiration pathway is designed to expand to promote more consistent and easier flow. Accordingly, the aspiration flow is configured to expand from the minimal diameter of the inner cutting member  149  to the larger diameter of the aspiration tube  160 . 
         [0044]    In this example, the inner cutting member  149  is disposed at the extreme distal position during a cutting cycle. The dashed lines indicate the position of the inner cutting member  149  at an extreme proximal position during a cutting cycle. The dashed lines also represent the change in volume that occurs locally within the aspiration pathway as a result of the displaced inner cutting member  149  during a cutting cycle. As can be seen in  FIG. 4 , the change in volume that occurs within the aspiration pathway is limited to the volume displaced by the inner cutting member  149 . Because the inner cutting member has a small outer diameter (in the range of about 0.025 to 0.012 in.) and an inner diameter (in the range of about 0.020 to 0.010 in.), and because the cutting cycle axial displacement is often in the range of about 0.010-0.050 in., the total volume displacement is minimal. In some embodiments, the total volume displacement is less than about 9×10 −6  in 3 , and in other embodiments, the total volume displacement is less than about 4×10 −7  in 3 . Yet other values and ranges are contemplated. 
         [0045]    The displacement volume in the aspiration pathway of the ophthalmic probe  100  may be a substantially smaller displacement volume than can be achieved in conventional devices where a coupler is disposed in place of the cutter seal assembly. The conventional coupler fixedly connects to the inner cutting member and therefore moves with the inner cutting member. As both the coupler and the inner cutting member oscillate during a cutting cycle in the conventional device, the fluid volume displacement is much larger than when only the inner cutting member oscillates. The fluid volume displacement in conventional devices may be as much as, for example only, 7-50 times larger (depending on the size of the inner cutting member) than the volume displacement that occurs in the system disclosed herein. This large displacement in prior devices may manifest itself as pulses or fluid surges. In some instances, this may result in a reversal of flow during vitrectomy cutting or in agitation resulting in gas coming out of solution. 
         [0046]    In use, a surgeon sets a cutting rate at the surgical base housing  112 . The fluidic pressure source and the probe driver drive the motor  104  to actuate the cutter assembly  108  at the designated cutting rate. It does this by driving the drive shaft  156  at the designated cutting rate. The drive shaft  156  is rigidly fixed to and drives the coupler  158 . The coupler  158  is rigidly fixed to and drives the inner cutting member  149 . Since the drive shaft  156  and the coupler  158  operate within air, and do not physically contact or disrupt fluid or tissue, the dampening effect is smaller than if the drive shaft  156  and the coupler  158  were to be in contact with the aspiration fluid or if maintained within a fluid chamber. 
         [0047]    Accordingly, during a cutting cycle, when the motor drives the drive shaft and the coupler in the distal direction, the inner cutting member  149  makes a cutting motion in the needle  106  by advancing across the port  146  until it is closed. As this occurs, the proximal end of the inner cutting member  149  moves distally relative to the aspiration tube  160  and the cutter seal assembly  162 . Because only the inner cutting member  149  moves distally, there is very little volume change in the aspiration pathway, and the aspiration flow is only minimally affected. 
         [0048]    When the inner cutting member  149  reaches the distal-most position, the motor drives the cutter assembly  108  in the proximal direction. Again, it does this by moving the drive shaft  156 , the coupler  158 , and the inner cutting member  149  in the distal direction. This opens the port  149  permitting additional fluid and tissue to enter the needle  106 . As the inner cutting member  149  moves in the proximal direction, its volume within the aspiration tube  160  increases as shown in  FIG. 4 . Since the aspiration tube  160  and the cutter seal assembly  162  are fixed in place, only the inner cutting member  149  affects the volume within the aspiration pathway. Because only the inner cutting member  149  moves proximally, there is very little volume change in the aspiration pathway, and the aspiration flow is only minimally affected. 
         [0049]      FIG. 5  illustrates another cross-sectional view of an ophthalmic probe  300  (which in some embodiments is the probe  100 ). The probe  300  includes many features similar to the probe  100  discussed herein. For the sake of simplicity, some reference numbers are used to designate the same or similar parts. For example, the ophthalmic probe  300  includes a housing  102  and a cutter  105  extending from the housing  102 . The probe  300  also includes a motor  301  disposed within a motor chamber  303  in the housing  102 , and includes a cutter assembly  302 . In this embodiment, the cutter assembly  302  includes the stationary aspiration tube  160 , a cutter seal housing portion  304 , and the inner cutting member  149 . The cutter seal housing portion  304  is fixed in place and does not move relative to the stationary aspiration tube  160  and therefore, does not move relative to the probe housing  102 . While the stationary aspiration tube  160  is shown in the cross-sectional view of  FIG. 5  as a separate component from the body  102 , other embodiments have the stationary aspiration tube  160  formed as a part of the body with the stationary aspiration tube  160  being an integral or monolithic portion of the body  102 . 
         [0050]    In this embodiment, the motor  301  is connected directly to the inner cutting member  149  in a manner that drives the inner cutting member  149  in a cutting cycle. Accordingly, only the inner cutting member  149  moves within the aspiration pathway, and therefore, similar to the embodiment in  FIG. 2 , there is very little volume change in the aspiration pathway during a cutting cycle. In this example, the motor  301  is disposed in the distal portion of the probe  300 . Also in this example, the motor  301  is disposed distal of the proximal end of the inner cutting member  149  and is configured to drive the inner cutting member  149 . 
         [0051]    The motor  301  may be similar to the motor  104  and may include a flexible diaphragm and a rigid coupler that operates by pressure variation between the first and second ports  128 ,  130 . The variation in pressure on opposing sides of the motor  301  within the motor chamber causes the diaphragm  140  to vibrate, carrying the inner cutting member  149  in a back-and-forth oscillating motion. Other arrangements are also contemplated. 
         [0052]    Persons of ordinary skill in the art will appreciate that the embodiments encompassed by the present disclosure are not limited to the particular exemplary embodiments described above. In that regard, although illustrative embodiments have been shown and described, a wide range of modification, change, and substitution is contemplated in the foregoing disclosure. It is understood that such variations may be made to the foregoing without departing from the scope of the present disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the present disclosure.