Patent Publication Number: US-2021161711-A1

Title: Ophthalmic surgical instruments and snares thereof

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to ophthalmic surgical instruments, and more particularly, to ophthalmic surgical instruments and methods that facilitate the fragmentation and removal of a lens from a lens capsule. 
     Background of Related Art 
     Cataract surgery and other surgical procedures that treat lenticular tissue, such as, for example, the intraocular lens, are performed by making a small incision in the edge of the cornea, which provides access to the anterior chamber and to the anterior surface of the lens capsule. Afterward, a generally circular incision called a capsulorhexis is made through the anterior surface of the lens capsule to provide surgical access to the lens. An ophthalmic surgical instrument may be inserted through the capsulorhexis and used to fragment the cataractous lens to facilitate its removal from the lens capsule. However, during segmentation by the surgical instrument, the distal portion of the lens may be caused to shift undesirably in an upward (i.e., anterior) direction. Such movement may cause trauma to delicate adjacent eye structures such as the lens zonule, lens capsule or, corneal endothelium. 
     Accordingly, a continuing need exists in the surgical arts for improved tools and methods for safely fragmenting and removing a cataractous lens. 
     SUMMARY 
     In accordance with an aspect of the present disclosure, an ophthalmic surgical instrument for severing a lens of an eye is provided and includes an elongated shaft and a wire extending along the elongated shaft. The elongated shaft includes a distal end portion defining a first opening and a second opening. The first and second openings are spaced from one another along a longitudinal axis defined by the elongated shaft. The wire includes a cutting segment extending through the first and second openings. The cutting segment is configured to move between a contracted configuration, and a dilated configuration, in which the cutting segment assumes a diameter approximating a diameter and shape of a lens of an eye. The cutting segment is configured to sever the lens upon moving toward the contracted configuration. 
     In aspects, the distal end portion of the elongated shaft may have a cutting surface that extends longitudinally between the first and second openings. The cutting segment and the cutting surface may be configured to cooperate to apply a cutting force on the lens of the eye upon the cutting segment moving toward the contracted configuration. 
     In aspects, the cutting segment may have a section configured to engage the cutting surface when the cutting segment is in the contracted configuration. 
     In aspects, the cutting segment may have a curvature along a majority of a length thereof. 
     In aspects, the section of the cutting segment may be linear. 
     In aspects, the section of the cutting segment may protrude inwardly toward the cutting surface of the elongated shaft when the cutting segment is in the contracted configuration. 
     In aspects, the elongated shaft may have a distal tip and the first opening may be spaced proximally of the distal tip. 
     In aspects, the second opening may be spaced proximally of the distal tip and distally of the first opening. 
     In aspects, the second opening may be defined in the distal tip and may be spaced distally of the first opening. 
     In aspects, the elongated shaft may have a closed distal tip. 
     In aspects, the cutting segment may have a looped configuration. 
     In aspects, the distal end portion of the elongated shaft may define a third opening disposed between the first and second openings. The third opening may be configured to receive a cutting section of the cutting segment when the cutting segment is in the contracted configuration. 
     In aspects, the wire may have a first end portion fixed relative to the elongated shaft, and a second end portion configured to translate relative to the elongated shaft to transition the cutting segment between the dilated and contracted configurations. 
     In aspects, the first opening may be a proximal opening and the second opening may be a distal opening. The first end portion of the wire may extend through the proximal opening and the second end portion of the wire may extend through the distal opening. 
     In accordance with another aspect of the disclosure, an ophthalmic surgical instrument for severing a lens of an eye is provided and includes a housing and a snare opearbly coupled to the housing. The housing includes a handle body and a hollow, elongated shaft extending distally of the handle body. The elongated shaft has a bottom surface configured to be oriented toward a human eye. The bottom surface defines a proximal opening, and a distal opening spaced distally from the proximal opening. The snare is operably coupled to the housing and includes a looped segment configured to move through the proximal and distal openings between a contracted configuration and a dilated configuration. In the dilated configuration, the looped segment may assume a diameter approximating a diameter and shape of a lens of the human eye. The looped segment is configured to sever the lens upon moving toward the contracted configuration. 
     In aspects, the bottom surface of the elongated shaft may have a cutting surface that extends longitudinally between the proximal and distal openings. The looped segment and the cutting surface may be configured to cooperate to apply a cutting force on the lens of the human eye as the looped segment moves toward the contracted configuration. 
     In aspects, the looped segment may have a cutting section configured to engage the cutting surface when the looped segment is in the contracted configuration. 
     In aspects, the cutting section of the looped segment may be linear. 
     In aspects, the cutting section of the looped segment may protrude inwardly toward the cutting surface of the elongated shaft when the looped segment is in the contracted configuration. 
     In aspects, the elongated shaft may have a closed distal tip. 
     In aspects, the bottom surface of the elongated shaft may define an intermediate opening disposed between the proximal and distal openings. The intermediate opening may be configured to receive the cutting section of the looped segment when the looped segment is in the contracted configuration. 
     In aspects, a majority of the looped segment may be disposed proximally of a distal end of the elongated shaft. 
     As used herein, the terms parallel and perpendicular are understood to include relative configurations that are substantially parallel and substantially perpendicular up to about + or −25 degrees from true parallel and true perpendicular. 
     As used herein, the term “about” means that the numerical value is approximate and small variations would not significantly affect the practice of the disclosed embodiments. Where a numerical limitation is used, unless indicated otherwise by the context, “about” means the numerical value can vary by ±10% and remain within the scope of the disclosed embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure are described herein with reference to the accompanying drawings, wherein: 
         FIG. 1A  is a top view of an ophthalmic surgical instrument in accordance with an embodiment of the present disclosure, illustrating a snare thereof in a contracted configuration; 
         FIG. 1B  is a top view of the ophthalmic surgical instrument of  FIG. 1A , illustrating the snare in a dilated configuration and a pair of stabilization elements in an open configuration; 
         FIG. 2A  is a side cross-sectional view of the ophthalmic surgical instrument of  FIG. 1A , illustrating the snare in the contracted configuration and the stabilization elements in the closed configuration; 
         FIG. 2B  is a side cross-sectional view of the ophthalmic surgical instrument of  FIG. 1A , illustrating the snare in the dilated configuration and the stabilization elements in the open configuration; 
         FIG. 3A  is a top cross-sectional view of the ophthalmic surgical instrument of  FIG. 1A , illustrating the snare in the contracted configuration and the stabilization elements in the closed configuration; 
         FIG. 3B  is a top cross-sectional view of the ophthalmic surgical instrument of  FIG. 1A , illustrating the snare in the dilated configuration and the stabilization elements in the open configuration; 
         FIG. 4A  is a side view of another embodiment of an ophthalmic surgical instrument, illustrating a snare thereof in a contracted configuration; 
         FIG. 4B  is a side view of the ophthalmic surgical instrument of  FIG. 4A , illustrating the snare in a dilated configuration; 
         FIG. 5A  is a side view of yet another embodiment of an ophthalmic surgical instrument, illustrating a snare thereof in a contracted configuration; 
         FIG. 5B  is a side view of the ophthalmic surgical instrument of  FIG. 5A , illustrating the snare in a dilated configuration; 
         FIG. 6  is a side view of yet another embodiment of an ophthalmic surgical instrument, illustrating a snare thereof in a contracted configuration; 
         FIG. 7  is a side view of yet another embodiment of an ophthalmic surgical instrument, illustrating a snare thereof in a dilated configuration; 
         FIG. 8  is a longitudinal cross-sectional view of the snare of  FIG. 7  shown isolated from the remainder of the ophthalmic surgical instrument; 
         FIG. 9  is an enlarged view of the area of detail labeled “ 9 ” in  FIG. 8 ; 
         FIG. 10  is an enlarged view of the area of detail labeled “ 10 ” in  FIG. 8 ; 
         FIG. 11  is a cross-sectional view of an eye; 
         FIG. 12  is a side view of yet another embodiment of an ophthalmic surgical instrument, illustrating a snare thereof in a dilated configuration; 
         FIG. 13  is a bottom view of an elongated shaft of the ophthalmic surgical instrument of  FIG. 12 ; 
         FIG. 14  is a cross-section, taken along line  14 - 14  in  FIG. 13 , of the elongated shaft; 
         FIG. 15A  is a side cross-sectional view of a distal end portion of the ophthalmic surgical instrument of  FIG. 12  illustrating the snare in the dilated configuration; 
         FIG. 15B  is a side cross-sectional view of the distal end portion of the ophthalmic surgical instrument of  FIG. 12  illustrating the snare in a contracted configuration; 
         FIG. 16  is a side view of another embodiment of a snare for use with the elongated shaft of  FIG. 13 ; 
         FIG. 17  is a bottom perspective view of the distal end portion of the elongated shaft of  FIG. 12  illustrating the snare of  FIG. 16  in the contracted configuration; 
         FIG. 18  is a side view of another embodiment of a snare for use with the elongated shaft of  FIG. 13 ; 
         FIG. 19  is a bottom perspective view of the distal end portion of the elongated shaft of  FIG. 13  illustrating the snare of  FIG. 18  in a contracted configuration; 
         FIG. 20  is a bottom perspective view of a distal end portion of another embodiment of an ophthalmic surgical instrument illustrating the snare of  FIG. 19  in a contracted configuration; 
         FIG. 21  is a bottom perspective view of a distal end portion of yet another embodiment of an ophthalmic surgical instrument; and 
         FIG. 22  is a bottom perspective view of a distal end portion of yet another embodiment of an ophthalmic surgical instrument illustrating. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the presently disclosed ophthalmic surgical instruments are described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein and as is traditional, the term “distal” will refer to that portion of the ophthalmic surgical instrument which is further from the user (i.e., closer to the eye) while the term “proximal” will refer to that portion of the ophthalmic surgical instrument which is closer to the user (i.e., further from the eye). 
     The present disclosure provides embodiments of an ophthalmic surgical instrument used to fragment cataractous lenticular tissue prior to its removal from a lens capsule. The ophthalmic surgical instrument includes a handle portion and a snare for enclosing and severing the lenticular tissue. The ophthalmic surgical instrument is constructed so that a distally-extending shaft thereof acts as the stabilization element. In aspects, the shaft defines a pair of first and second openings through which the snare extends. A surface is defined between the first and second openings and acts as a cutting surface against which the snare cuts the lenticular tissue. These and other features and advantages of the various embodiments of the disclosed ophthalmic surgical instruments will be described below. 
     With reference to  FIGS. 1A-3C , an exemplary embodiment of an ophthalmic surgical instrument is illustrated and is generally designated  100 . The ophthalmic surgical instrument  100  generally includes a housing  110 , a snare  112  for severing lenticular tissue, and a pair of stabilization elements, such as, for example, elongated arms  120 ,  122  that selectively expand from a closed or collapsed configuration ( FIGS. 1A, 2A, 3A ) to an open or expanded configuration ( FIGS. 1B, 2B, 3B ). 
     The housing  110  of the ophthalmic surgical instrument  100  has a handle body  114  and first and second levers  116   a ,  116   b  slidably coupled to the handle body  114 . The handle body  114  may be ergonomic and have an elongated configuration. In embodiments, the handle body  114  may assume any suitable shape, such as, for example, rounded, planar, rectangular, or the like. The handle body  114  has a tapered distal end portion  118  dimensioned to assist in positioning the ophthalmic surgical instrument  100  adjacent eye structure. The levers  116   a ,  116   b  may be configured as sliders, buttons, triggers, or the like. In embodiments, the housing  110  may include a cannulated member, such as, for example, a hollow shaft (not shown), extending distally from the distal end portion  118  of the handle body  114  to facilitate entry of the ophthalmic surgical instrument  100  through a standard corneal incision. 
     The snare  112  of the ophthalmic surgical instrument  100  is operably coupled to the first lever  116   a  of the housing  110  and includes a first end portion  112   a  and a second end portion  112   b  ( FIGS. 2A and 2B ). The first end portion  112   a  of the snare  112  is movable relative to the housing  110 , while the second end portion  112   b  of the snare  112  is fixed relative to the housing  110 . In particular, the first end portion  112   a  of the snare  112  is coupled to the first lever  116   a  of the housing via a first actuator rod  124 , such that movement of the first lever  116   a  moves the first end portion  112   a  of the snare  112 , and the second end portion  112   b  of the snare  112  is fixed to an inner tubular structure  126  ( FIGS. 3A and 3B ) formed in the distal end portion  118  of the handle body  114 . It is contemplated that the second end portion  112   b  of the snare  112  may be fixed to the inner tubular structure  126  of the handle body  114  by crimping, welding, adhesives, mechanical interlocks, or any other suitable structure or method. 
     With reference to  FIGS. 2A and 2B , the snare  112  has a looped segment  128  disposed at least partially outside of the housing  110 . The looped segment  128  of the snare  112  is transitionable, via an actuation of the first lever  116   a , between an insertion or contracted configuration, as shown in  FIGS. 1A, 2A, and 3A , and a deployed or dilated configuration, as shown in  FIGS. 1B, 2B, and 3B . For example, a proximal retraction of the first lever  116   a  moves the first end portion  112   a  of the snare  112  proximally away from the second end portion  112   b  of the snare  112 , thereby reducing the diameter of the looped segment  128 . In contrast, a distal advancement of the first lever  116   a  moves the first end portion  112   a  of the snare  112  distally toward the second end portion  112   b  of the snare  112 , thereby increasing the diameter of the looped segment  128  of the snare  112 . The looped segment  128  has a predefined shape dimensioned to closely encircle a lens when the looped segment  128  is in the dilated configuration. 
     In embodiments, at least the looped segment  128  of the snare  112  may be a metal or polymer wire, tether, strap, belt, or the like, with any suitable cross-section configuration configured to sever lenticular tissue during contraction of the looped segment  128  about the lenticular tissue. 
     For an exemplary description of further features of the snare  112  and the mechanism of its operation, reference may be made to U.S. Pat. No. 9,775,743, filed on Sep. 17, 2014, the entire contents of which being incorporated by reference herein. 
     With continued reference to  FIGS. 1B and 2A-3B , the stabilization elements or arms  120 ,  122  of the ophthalmic surgical instrument  100  are disposed on opposite sides of a longitudinal axis “X” defined by the snare  112 . The arms  120 ,  122  are configured to move from the closed configuration ( FIGS. 1A, 2A, 3A ) to the open configuration ( FIGS. 1B, 2B, 3B ) to maintain lenticular tissue in its current location, typically but not always within its lens capsule, as will be described. In embodiments, the arms  120 ,  122  may be configured to move independently of one another. The arms  120 ,  122  are illustrated as being linear, but it is contemplated that the arms  120 ,  122  may assume any suitable shape, such as, for example, wing-shaped, disc-shaped, plate-like, or polygonal. 
     The arms  120 ,  122  may be resiliently-biased toward the open configuration by a biasing member, such as, for example, a coil spring  130 , disposed therebetween. As such, upon moving the arms  120 ,  122  distally out of the handle body  114  or the hollow shaft (not shown) of the housing  110 , the arms  120 ,  122  automatically expand outwardly relative to one another. The arms  120 ,  122  each have a proximal end portion  120   a ,  122   a  pivotably coupled to a hub  132 , and a distal end portion  120   b ,  122   b . In other embodiments, instead of being pivotable, the arms  120 ,  122  may be configured to shift laterally outward from the collapsed configuration to the expanded configuration. 
     The hub  132  couples the arms  120 ,  122  to the second lever  116   b  of the housing  110 . In particular, the housing  110  has a second actuator rod  134  interconnecting the hub  132  and the second lever  116   b . Upon sliding the second lever  116   b  relative to the handle body  114 , the second actuator rod  134  transfers the sliding motion to the hub  132  to axially move the arms  120 ,  122  along the longitudinal axis “X” of the snare  112  relative to the handle body  114  between a proximal position and a distal position. In the proximal position, the arms  120 ,  122  are concealed within the inner tubular structure  126  of the handle body  110  or the hollow shaft when the hollow shaft is used. With the arms  120 ,  122  disposed within the housing  110 , the inner tubular structure  126  of the handle body  119  (or the hollow shaft when used) maintains the arms  120 ,  122  in the collapsed configuration, in which the arms  120 ,  122  are parallel with one another and the longitudinal axis “X” of the snare  112 , therefore assuming a reduced profile. Upon moving the arms  120 ,  122  toward the distal position, the arms  120 ,  122  move distally out of the housing  110  (the handle body  114  and/or the hollow shaft when used) allowing the outwardly-oriented bias of the biasing member  130  to transition the arms  120 ,  122  toward the expanded configuration. In embodiments, rather than automatically moving toward the expanded configuration upon exiting the housing  110 , the arms  120 ,  122  may be expanded manually via a drive mechanism (not shown). 
     As shown in  FIGS. 1B and 3B , in the expanded configuration, the arms  120 ,  122  flare outwardly from opposite sides of the snare  112  to define an angle α between the arms  120 ,  122 . In embodiments, the angle α may be between about 0.1 degrees and about 180 degrees. In embodiments, the angle α may be between about 10 degrees and about 90 degrees. 
     The arms  120 ,  122  together define and reside in a horizontal plane, and the expanded looped segment  128  of the snare  112  defines and resides in a vertical plane that is aligned with the longitudinal axis “X” of the snare  112 . The arms  120 ,  122  remain the horizontal plane throughout their movement between the collapsed and expanded configurations. The arms  120 ,  122  are parallel with the longitudinal axis “X” of the snare  112  while the horizontal plane of the arms  120 ,  122  is perpendicular relative to the vertical plane of the looped segment  128  of the snare  112 . 
     In embodiments, the arms  120 ,  122  may be axially movable in a direction perpendicular to the horizontal plane of the looped segment  128  to adjust a vertical position of the arms  120 ,  122  relative to the housing  110  as well as lenticular tissue. For example, the housing  110  may further include a third lever (not shown) coupled to the hub  132  for moving the arms  120 ,  122  vertically relative to the housing  110 . 
     As best shown in  FIGS. 2A and 2B , each of the arms  120 ,  122  has a posterior tissue-contacting surface  136 . The posterior tissue-contacting surface  136  of the arms  120 ,  122  may define an arcuate recess  138  therein dimensioned to conform to an anterior surface of a lens of an eye. As such, upon deploying the arms  120 ,  122  over a lens, the posterior tissue-contacting surface  136  of each of the arms  120 ,  122  cups the anterior surface of the lens, thereby providing increased surface contact between the arms  120 ,  122  and the lens. It is contemplated that the posterior tissue-contacting surface  136  may have a coating or liner of pliable material, such as an elastomer to help protect vulnerable structures in the eye. 
     In operation, a small incision in the edge of a cornea is made to provide access to an anterior chamber and an anterior surface of a cataractous lens of a patient&#39;s eye “E” ( FIG. 3B ). A capsulorhexis is made through the anterior surface of a lens capsule of the patient&#39;s eye “E,” thereby providing surgical access to the cataractous lens “L.” With the arms  120 ,  122  of the ophthalmic surgical instrument  100  disposed in the proximal position within the housing  110 , and the snare  112  in the insertion configuration, as shown in  FIGS. 2A and 3A , the hollow shaft of the housing  110  is inserted through the corneal incision and the capsulorhexis to position the looped segment  128  of the snare  112  adjacent the anterior surface of the lens “L.” Once in position, the first lever  116   a  is advanced to move the first end portion  112   a  of the snare  112  distally, thereby transitioning the looped segment  128  from the insertion configuration to the deployed configuration, as shown in  FIG. 2B . With the looped segment  128  in the deployed configuration, the snare  112  is rotated about its longitudinal axis “X” (e.g., via rotation of the entire ophthalmic surgical instrument  100  or via a rotation mechanism (not shown) coupled to the snare  112 ) to rotate the looped segment  128  circumferentially about the lens to encircle the lens and position the looped segment  128  so that the vertical plane defined by the looped segment  128  bisects the lens. 
     With the looped segment  128  of the snare  112  in the selected position noted above, the second lever  116   b  of the housing  110  may be advanced to move the arms  120 ,  122  from the proximal position to the distal position. As noted above, as the arms  120 ,  122  move to the distal position, the arms  120 ,  122  automatically transition from the closed configuration to the open configuration, as shown in  FIGS. 1B and 3B . More specifically, the arms  120 ,  122  move distally along the anterior surface of the lens “L” while also expanding relative to one another and the longitudinal axis “X” of the snare  112  to position the posterior tissue-contacting surface  136  ( FIG. 2B ) of each of the arms  120 ,  122  over lateral side portions of the anterior surface of the lens “L.” 
     With the arms  120 ,  122  overlaying and in contact with the anterior surface of the lens “L,” the first lever  116   a  may then be retracted to transition the looped segment  128  from the dilated configuration to the contracted configuration, dividing the lens “L” into two hemispherical sections. During constriction of the looped segment  128  about the lens “L,” the looped segment  128  may exert a proximally-oriented and/or anteriorly oriented force on a distal pole “P” of the lens “L.” However, since the arms  120 ,  122  are in position over the lens “L,” the arms  120 ,  122  resist and/or prevent the distal pole “P” of the lens “L” from shifting proximally out of the lens capsule notwithstanding the proximally-oriented force exerted thereon by the snare  112 . 
     After one or more fragmentations of the lens “L” by the ophthalmic surgical instrument  100 , the fragmented sections of the cataractous lens “L” may then be removed from the eye “E” using any suitable mechanism, such as, for example, an ultrasonic aspirator. 
     In some embodiments, the snare  112  and/or the arms  120 ,  122  may be mechanically powered through an electric motor, a pneumatic power source, a hydraulic power source, magnets, or the like. It is also contemplated that the ophthalmic surgical instrument  100  may be incorporated into a robotic surgical system. 
     With reference to  FIGS. 4A and 4B , another embodiment of an ophthalmic surgical instrument  200  is illustrated, similar to the ophthalmic surgical instrument  100  described above. Due to the similarities between the ophthalmic surgical instrument  200  of the present embodiment and the ophthalmic surgical instrument  100  described above, only those elements of the ophthalmic surgical instrument  200  deemed necessary to elucidate the differences from ophthalmic surgical instrument  100  described above will be described in detail. 
     The ophthalmic surgical instrument  200  generally includes a housing  210  and a snare  212  for severing lenticular tissue. The housing  210  of the ophthalmic surgical instrument  200  has a handle body  214  and a cannulated body, such as, for example, a hollow shaft  226  extending distally from the handle body  214 . The hollow shaft  226  is dimensioned for passage through a corneal incision and has a proximal end  226   a  integrally formed with or attached to the handle body  214 . 
     The snare  212  of the ophthalmic surgical instrument  200  includes a first end portion  212   a  and a second end portion  212   b . The first end portion  212   a  of the snare  212  is movable relative to and within the hollow shaft  226  of the housing  210  via an actuation mechanism (not shown), while the second end portion  212   b  of the snare  212  is fixed relative to the housing  210 . It is contemplated that the first end portion  212   a  of the snare  212  may be axially movable within the hollow shaft  226  via any suitable actuation mechanism, such as, for example, manual actuation or any suitable motorized actuation mechanism. The second end portion  212   b  of the snare  212  may be fixed to an inner surface of the hollow shaft  226  by crimping, welding, adhesives, mechanical interlocks, or any other suitable structure or method. 
     The snare  212  has a looped segment  228  disposed protruding out of a distal end  226   b  of the hollow shaft  226 . The looped segment  228  of the snare  212  is transitionable, via axial movement of the first end portion  212   a  of the snare  212 , between an insertion or contracted configuration, as shown in  FIG. 4A , and a deployed or dilated configuration, as shown in  FIG. 4B . For example, a proximal retraction of a lever (not shown) of the housing  210  moves the first end portion  212   a  of the snare  212  proximally away from the second end portion  212   b  of the snare  212 , thereby reducing the diameter of the looped segment  228 . In contrast, a distal advancement of the lever moves the first end portion  212   a  of the snare  212  distally toward the second end portion  212   b  of the snare  212 , thereby increasing the diameter of the looped segment  228  of the snare  212 . The looped segment  228  has a predefined shape dimensioned to closely encircle a lens when the looped segment  228  is in the dilated configuration. 
     The looped segment  228  of the snare  212  differs from the looped segment  128  of the snare  112  of the ophthalmic surgical instrument  100  of  FIGS. 1A-3B  in that a majority of the looped segment  228  overlaps with the housing  210  (e.g., the hollow shaft  226 ) rather than a majority of the looped segment  228  being disposed distally of the housing  210 . The looped segment  228  has a proximal section  228   a  having a predefined curvature, and a distal section  228   b  having a predefined curvature. The distal section  228   b  of the looped segment  228  is disposed distally of the distal end  226  of the hollow shaft  226 , and the proximal section  228   a  of the looped segment  228  is disposed below the hollow shaft  226  and proximally of the distal end  226   b  of the hollow shaft  226 . 
     The looped segment  228  further includes a pre-bent section  228   c  extending from the second end portion  212   b  of the snare  212 . The pre-bent section  228   c  is disposed distally and outside of the housing  210  and has a smaller radius of curvature relative to the proximal and distal sections  228   a ,  228   b  of the looped segment  228  to position the proximal section  228   a  of the looped segment  228  proximally of and underneath the distal end  226  of the hollow shaft  226  of the housing  210 . The proximal section  228   a , the distal section  228   b , and the pre-bent section  228   c  of the looped segment  228  may be fabricated from the same material or different materials. For example, the pre-bent section  228   c  may be fabricated from a less flexible material than the proximal and distal sections  228   a ,  228   b  of the looped segment  228  to ensure that a majority of the looped segment  228  overlaps with the hollow shaft  226  throughout the transition of the looped segment  228  between the contracted and dilated configurations. 
     The looped segment  228  defines a length “L” parallel with a central longitudinal axis “A” defined by the hollow shaft  226 . The proximal section  228   a  of the looped segment  228  has a length “L 1 ,” which is approximately ½ or more of the overall length “L” of the looped segment  228 , and the distal section  228   b  of the looped segment  228  has a length “L 2 ,” which is less than ½ of the overall length of the looped segment  228 . In embodiments, the length “L 1 ” of the proximal section  228   a  of the looped segment  228  is approximately ¾ of the overall length “L” of the looped segment  228 , and the distal section  228   b  of the looped segment  228  has a length “L 2 ,” which is approximately ¼ of the overall length “L” of the looped segment  228 . In this way, during use of the ophthalmic surgical instrument  200 , a majority of the looped segment  228  overlaps with the housing  210  (e.g., the hollow shaft  226 ), such that the housing  210  is configured to rest on lenticular tissue during its fragmentation to prevent upward movement thereof during constriction of the looped segment  228 . 
     The looped segment  228  is fabricated from shape memory materials, such as, for example, a nickel-titanium alloy to allow the looped segment  228  to move to its predefined, dilated configuration. Other shape memory materials, such as shape memory plastics are also contemplated. In other embodiments, the looped segment  228  may be fabricated from any suitable biocompatible material including, but not limited to, stainless steel, titanium, silicone, polyimide, polyether block amide, nylon, polycarbonate, or combinations thereof. 
     In operation, a small incision in the edge of a cornea is made to provide access to an anterior chamber and an anterior surface of a cataractous lens of a patient&#39;s eye. A capsulorhexis is made through the anterior surface of a lens capsule of the patient&#39;s eye providing surgical access to the cataractous lens. With the snare  212  of the ophthalmic surgical instrument  200  in the insertion configuration, as shown in  FIG. 4A , the hollow shaft  226  of the housing  210  is inserted through the corneal incision and the capsulorhexis to position a distal end portion of the hollow shaft  226  in an overlapping arrangement with the anterior surface of the lens, and position the looped segment  228  of the snare  212  adjacent the anterior surface of the lens. 
     Once the looped segment  228  is in the appropriate position, the first end portion  212   a  of the snare  212  is advanced distally, thereby transitioning the looped segment  228  from the insertion configuration to the deployed configuration, as shown in  FIG. 4B . With the looped segment  228  in the deployed configuration, the snare  212  is rotated about its longitudinal axis “A” (e.g., via rotation of the entire ophthalmic surgical instrument  200  or via a rotation mechanism (not shown)) to rotate the looped segment  228  circumferentially about the lens to encircle the lens and position the looped segment  228  relative to the lens so that the plane defined by the looped segment  228  bisects the lens. Upon rotating the snare  212  to the selected position, the distal end portion of the hollow shaft  226  overlaps with the anterior surface of the lens and a majority of the looped segment  228  of the snare  212 . 
     With the looped segment  228  of the snare  212  disposed about the lens, and the distal end portion of the hollow shaft  226  overlaying and in contact with the anterior surface of the lens, the looped segment  228  is transitioned from the dilated configuration to the contracted configuration, dividing the lens into two hemispherical sections. During constriction of the looped segment  228  about the lens, the looped segment  228  may exert a proximally-oriented and/or anteriorly-oriented force on a distal pole of the lens. However, since the distal end portion of the hollow shaft  226  is in position over the lens, the hollow shaft  226  resists and/or prevents elevation and/or tilting of the distal pole of the lens notwithstanding the proximally-oriented force exerted thereon by the closing snare  212 . 
     After one or more fragmentations of the lens by the ophthalmic surgical instrument  200 , the fragmented sections of the cataractous lens may then be removed from the eye using any suitable mechanism, such as, for example, an ultrasonic aspirator. 
     With reference to  FIGS. 5A and 5B , another embodiment of an ophthalmic surgical instrument  300  is illustrated, similar to the ophthalmic surgical instrument  200  described above. Due to the similarities between the ophthalmic surgical instrument  300  of the present embodiment and the ophthalmic surgical instrument  200  described above, only those elements of the ophthalmic surgical instrument  300  deemed necessary to elucidate the differences from ophthalmic surgical instrument  200  described above will be described in detail. 
     The ophthalmic surgical instrument  300  generally includes a housing  310  and a snare  312  operably coupled to the housing  310  for severing lenticular tissue. The housing  310  of the ophthalmic surgical instrument  300  has a handle body  314  and a cannulated body, such as, for example, a hollow shaft  326  extending distally from the handle body  314 . The hollow shaft  326  is dimensioned for passage through a corneal incision and has a proximal end  326   a  integrally formed with or attached to the handle body  314 , and a closed distal end  326   b . In embodiments, the distal end  326   b  of the hollow shaft  326  may be open. The hollow shaft  326  defines a central longitudinal axis “B” and defines a lateral opening  330  in a lateral side surface  332  thereof. The lateral opening  330  is laterally offset from the central longitudinal axis “B” and defines an axis “C” therethrough that is perpendicular to the central longitudinal axis “A” of the hollow shaft  326 . The lateral opening  330  may be any suitable shape, such as, for example, circular, elongated, square, or the like. 
     The snare  312  of the ophthalmic surgical instrument  300  includes a first end portion  312   a  and a second end portion  312   b . The first end portion  312   a  of the snare  312  is movable relative to and within the hollow shaft  326  of the housing  310  via an actuation mechanism (not shown), similar to the actuation mechanism described above, while the second end portion  312   b  of the snare  312  is fixed relative to the housing  310 . The second end portion  312   b  of the snare  312  may be fixed to an inner surface of the hollow shaft  226  by crimping, welding, adhesives, mechanical interlocks, or any other suitable structure or method. In other embodiments, both the first and second end portions  312   a ,  312   b  may be axially movable. 
     The snare  312  has a looped segment  328  protruding out of the lateral opening  330  in the lateral side  332  of the hollow shaft  226 . The looped segment  328  of the snare  312  is transitionable, via axial movement of the first end portion  312   a  of the snare  312 , between an insertion or contracted configuration, as shown in  FIG. 5A , and a deployed or dilated configuration, as shown in  FIG. 5B . For example, a proximal retraction of a lever (not shown) of the housing  310  moves the first end portion  312   a  of the snare  312  proximally away from the second end portion  312   b  of the snare  312 , thereby reducing the diameter of the looped segment  328 . In contrast, a distal advancement of the lever moves the first end portion  312   a  of the snare  312  distally toward the second end portion  312   b  of the snare  312 , thereby increasing the diameter of the looped segment  328  of the snare  312 . The looped segment  328  has a predefined shape dimensioned to closely encircle a lens when the looped segment  328  is in the dilated configuration. In embodiments, both the first and second end portions  312   a ,  312   b  of the snare  312  may be movable to contract or dilate the looped segment  328 . 
     The looped segment  328  defines a length “L” parallel with a central longitudinal axis “B” defined by the hollow shaft  326 . A majority of the length “L” of the looped segment  328  is in side-by-side, parallel relation with the lateral side  332  of the hollow shaft  326 . Further, a majority of the looped segment  328  (i.e., at least half) is disposed proximally of the distal end  326   b  of the hollow shaft  326 . In this way, during use of the ophthalmic surgical instrument  300 , the hollow shaft  326  hangs over a majority of the looped segment  328 , such that the hollow shaft  326  sits on a lens during lens fragmentation to prevent upward movement of the lens as the looped segment  328  is constricted thereabout. 
     The looped segment  328  includes a proximal section  328   a  disposed proximally of the lateral opening  330 , and a distal section  328   b  disposed distally of the lateral opening  330 . Both the proximal and distal sections  328   a ,  328   b  of the looped segment  328  are disposed proximally of the distal end  326   b  of the hollow shaft  326  when the looped segment  328  is in the contracted configuration, as shown in  FIG. 5A . When the looped segment  328  is in the dilated configuration, the proximal section  328   a  of the looped segment  328  is disposed proximally of the distal end  326   b  of the hollow shaft  326 , whereas a majority, e.g., at least about half, of the distal segment  328   b  is disposed proximally of the distal end  326   b  of the hollow shaft  326 . As such, a majority of the looped segment  328  is disposed alongside the lateral side  332  of the hollow shaft  326  throughout the transition of the looped segment  328  between the contracted and dilated configurations. 
     The looped segment  328  is fabricated from shape memory materials, such as, for example, a nickel-titanium alloy to allow the looped segment  328  to move to its predefined, dilated configuration. Other shape memory materials, such as shape memory plastics are also contemplated. In other embodiments, the looped segment  328  may be fabricated from any suitable biocompatible material including, but not limited to, stainless steel, titanium, silicone, polyimide, polyether block amide, nylon, polycarbonate, or combinations thereof. 
     In operation, a small incision in the edge of a cornea is made to provide access to an anterior chamber and an anterior surface of a cataractous lens of a patient&#39;s eye. A capsulorhexis is made through the anterior surface of a lens capsule of the patient&#39;s eye providing surgical access to the cataractous lens. With the snare  312  of the ophthalmic surgical instrument  300  in the contracted configuration, as shown in  FIG. 5A , the hollow shaft  326  of the housing  310  is inserted through the corneal incision and the capsulorhexis to position a distal end portion of the hollow shaft  326  in an overlapping arrangement with the anterior surface of the lens, and position the looped segment  328  of the snare  312  adjacent the anterior surface of the lens. 
     Once the looped segment  328  is in the appropriate position, the first end portion  312   a  of the snare  312  is advanced distally, thereby transitioning the looped segment  328  from the contracted configuration to the dilated configuration, as shown in  FIG. 5B . With the looped segment  328  in the deployed configuration, the snare  312  is rotated about its longitudinal axis “B” (e.g., via rotation of the entire ophthalmic surgical instrument  300  or via a rotation mechanism (not shown)) to rotate the looped segment  328  circumferentially about the lens to encircle the lens and position the looped segment  328  relative to the lens so that the plane defined by the looped segment  328  bisects the lens. Upon rotating the snare  312  to the selected position, the axis “C” defined through the lateral opening  330  in the hollow shaft  326  extends perpendicularly through a center of the eye, whereby the hollow shaft  326  overlaps with the anterior surface of the lens and a majority of the looped segment  328  of the snare  312 . 
     With the looped segment  328  of the snare  312  disposed about the lens, and the hollow shaft  326  overlaying and in contact with the anterior surface of the lens, the looped segment  328  is transitioned from the dilated configuration to the contracted configuration, dividing the lens into two hemispherical sections. During contraction of the looped segment  328  about the lens, the looped segment  328  may exert a proximally-oriented force on a distal pole of the lens. However, since the hollow shaft  326  is in position over the lens, the hollow shaft  326  resists and/or prevents elevation and/or tilting of the distal pole of the lens notwithstanding the proximally-oriented force exerted thereon by the closing snare  312 . 
     After one or more fragmentations of the lens by the ophthalmic surgical instrument  300 , the fragmented sections of the cataractous lens may then be removed from the eye using any suitable mechanism, such as, for example, an ultrasonic aspirator. 
     With reference to  FIG. 6 , another embodiment of an ophthalmic surgical instrument  400  is illustrated, similar to the ophthalmic surgical instrument  300  described above. Due to the similarities between the ophthalmic surgical instrument  400  of the present embodiment and the ophthalmic surgical instrument  300  described above, only those elements of the ophthalmic surgical instrument  400  deemed necessary to elucidate the differences from ophthalmic surgical instrument  300  described above will be described in detail. 
     The ophthalmic surgical instrument  400  generally includes a housing (not explicitly shown), an elongated shaft  426  extending distally from the housing, and a snare  412  for severing lenticular tissue. The elongated shaft  426  is dimensioned for passage through a corneal incision “E” and has a proximal portion  425  and a distal end portion  426   b  formed with or otherwise coupled to the proximal portion  425 . The proximal portion  425  may include a proximal end portion  426   a  integrally formed with or attached to the handle housing and an intermediate portion  426   c . In aspects, the elongated shaft  426  may be devoid of any intermediate portion, such that the distal end portion  426   b  bends directly from the proximal end portion  426   a . In embodiments, the distal tip of the elongated shaft  426  may be open or closed. 
     The proximal end portion  426   a  of the elongated shaft  426  may have a linear configuration and define a central longitudinal axis “X 1 ,” and the distal end portion  426   b  may also be linear and define a central longitudinal axis “X 2 ,” that is offset from and parallel with the central longitudinal axis “X 1 ” of the proximal end portion  426   a . The distal end portion  426   b  is angled relative to the proximal portion  425  so that upon entry of the distal end portion  426   b  into a corneal incision “E,” the distal end portion  426   b  will be positioned flush with the anterior surface “AS” of the lens “L” rather than at an angle, which would otherwise occur if the distal end portion  426   b  were coaxial with the proximal portion  425 . In aspects, the distal end portion  426   b  or the proximal end portion  426   a  may assume any suitable configuration. For example, the distal end portion  426   b  may be curved along its length (e.g., to match a curvature of a lens). 
     The intermediate portion  426   c  of the elongated shaft  426  extends between the proximal and distal end portions  426   a ,  426   b , and is angled relative to the proximal and distal end portions  426   a ,  426   b . The intermediate portion  426   c  may extend between a bent proximal segment  432  of the elongated shaft  426  and a bent distal segment  434  of the elongated shaft  426 . The intermediate portion  426   c  may have a length of about 2 mm between opposite ends “E” and “F” thereof. The intermediate portion  426   c  has a linear configuration and defines a third central longitudinal axis “X 3 ” that is non-parallel relative to the first and second central longitudinal axes “X 1 ,” “X 2 .” In aspects, the central longitudinal axis “X 2 ” of the intermediate portion  426   c  may be an obtuse angle (e.g., from about 100 degrees to about 170 degrees), an acute angle (e.g., from 10 degrees to about 80 degrees), or a right angle (e.g., about 90 degrees) relative to the first and second central longitudinal axes “X 1 ,” “X 2 .” 
     In aspects, instead of the intermediate portion  426   c  being linear, the intermediate portion  426   c  may be curved along its length, bent at various points along its length, or assume any suitable configuration that positions the distal end portion  426   b  of the elongated shaft  426  on a different plane from the proximal portion  425 . In aspects, the intermediate portion  426   c  may be flexible and/or transitionable between an angled position relative to the proximal and distal end portions  426   a ,  426   b , and a coaxial configuration therewith. In aspects, the intermediate portion  426   c  or various portions of the elongated shaft  426  may be manually transitionable or fabricated from shape memory material that allows the elongated shaft  426  to transition from an otherwise coaxial configuration into the angled configuration as illustrated. 
     The distal end portion  426   b  of the elongated shaft  426  has a length from about 3.5 mm to about 12 mm and, in some aspects, the distal end portion  426   b  may have a length of about 6 mm or about half the diameter of a cornea measured between points “A” and “B.” The distal end portion  426   b  has a bottom portion  436  configured to be oriented toward a human eye, and an upper portion  438  disposed on an opposite side of the distal end portion  426   b . The bottom portion  436  defines an opening  430  therein that is disposed at about a midpoint between opposite ends “C,” “D” of the distal end portion  426   b . The opening  430  may be configured as an arcuate cutout in the bottom portion  436  of the distal end portion  426   b . In aspects, the opening  430  may assume any suitable configuration. The upper portion  438  of the distal end portion  426   b  has an inner surface  440  and an opposed outer surface  442 . The inner surface  440  may form a concave depression  444  and the outer surface  442  may form a convex protuberance  446 . The concave depression  444  and the convex protuberance  446  overlap the opening  430 . The concave depression  444  provides for more space into which the snare  412  may retract, as will be described. 
     The snare  412  of the ophthalmic surgical instrument  400  is movable relative to and within the elongated shaft  426  via an actuation mechanism (not shown), similar to the actuation mechanism described above. The snare  412  has a cutting segment, such as, for example, a looped segment  428  configured to protrude out of the opening  430  when the looped segment  428  is in a dilated configuration. It is contemplated that due to the additional space provided by the concave depression  444  in the distal end portion  426   b  of the elongated shaft  426 , the looped segment  428  of the snare  412  may be entirely or substantially received in the elongated shaft  426  when in the contracted configuration. It is contemplated that a distance of about 0.5 mm may be defined between a point “H” of the upper portion  442  and a point “G” of the convex protuberance  446 . As such, the looped segment  428  may have about 0.5 mm additional space into which it may retract. 
     The looped segment  428  defines a length parallel with the central longitudinal axis “X 2 ” defined by the distal end portion  426   b  of the elongated shaft  426 . Due to the length of the opening  430  of the elongated shaft  426  being substantially smaller than the length of the looped segment  428  in the dilated configuration, a majority of the length of the looped segment  428  overlaps with the bottom portion  436  of the elongated shaft  426  when the looped segment  428  is in the dilated configuration. In this way, during use of the ophthalmic surgical instrument  400 , the bottom portion  436  of the elongated shaft  426  hangs over a majority of the looped segment  428 , such that the elongated shaft  426  sits on a lens “L” during lens fragmentation to prevent upward movement of the lens “L” as the looped segment  428  is constricted thereabout. 
     In operation, a small incision “E” in the edge of a cornea is made to provide access to an anterior chamber and an anterior surface “AS” of a cataractous lens “L” of a patient&#39;s eye. As is typical, the incision “E” is anterior to an anterior surface “AS” of the lens “L.” A capsulorhexis is made through the anterior surface of a lens capsule of the patient&#39;s eye providing surgical access to the cataractous lens “L.” 
     With the snare  412  of the ophthalmic surgical instrument  400  in the contracted configuration, as shown in  FIG. 6 , the elongated shaft  426  is inserted through the corneal incision “E” and the capsulorhexis to position the distal end portion  426   b  of the elongated shaft  426  in an overlapping arrangement with the anterior surface “AS” of the lens “L,” and position the looped segment  428  of the snare  412  anterior to a central location of the anterior surface “AS” of the lens “L.” Due to the distal end portion  426   b  being angled relative to the proximal portion  425 , the distal end portion  426   b  is naturally positioned in flush engagement with the anterior surface “AS” of the lens “L” while the proximal portion  425  extends through the incision “E.” 
     Once the looped segment  428  is in the appropriate position, the looped segment  428  is transitioned from the contracted configuration to the dilated configuration, similar to that shown in  FIG. 5B . With the looped segment  428  in the deployed configuration, the looped segment  428  of the snare  412  naturally encircles the lens, due to the shape memory material from which the looped segment  428  is fabricated, so that the plane defined by the looped segment  428  bisects the lens. With the looped segment  428  of the snare  412  disposed about the lens “L,” and the elongated shaft  426  overlaying and contacting the anterior surface “AS” of the lens “L,” the looped segment  428  is transitioned from the dilated configuration to the contracted configuration, dividing the lens into two hemispherical sections. 
     During contraction of the looped segment  428  about the lens “L,” the looped segment  428  may exert a proximally-oriented force on the lens “L.” However, since the distal end portion  426   b  of the elongated shaft  426  is in position over the lens “L,” the elongated shaft  426  resists and/or prevents elevation and/or tilting of the lens “L” notwithstanding the proximally/anteriorly-oriented force exerted thereon by the closing snare  412 . If the proximal and distal end portions  426   a ,  426   b  of the elongated shaft  426  were coaxial instead of being disposed on different planes, the distal end portion  426   b  would be set at an upward angle relative to the lens “L,” which would result in an unevenly dispersed force being exerted on the lens “L” during contraction of the looped segment  428  about the lens “L.” 
     With reference to  FIGS. 7-10 , another embodiment of a snare  512  of an ophthalmic surgical instrument  500  is illustrated, similar to the snares described above. Due to the similarities between the snare  512  of the present embodiment and the snares described above, only those elements of the snare  512  deemed necessary to elucidate the differences from snares described above will be described in detail. It is contemplated that the snare  512  may be incorporated into the ophthalmic surgical instruments  100 ,  200 ,  300 ,  400  described above or any other suitable hand-held or robotically operated ophthalmic surgical instrument. 
     The ophthalmic surgical instrument  500  generally includes a housing  514 , an elongated shaft  526  extending distally from the housing  514 , and the snare  512  for severing lenticular tissue. The elongated shaft  526  is dimensioned for passage through a corneal incision and has a proximal end portion  526   a  and a distal end portion  526   b  formed with or otherwise coupled to the proximal end portion  526   a . The proximal end portion  526   a  may be integrally formed with or attached to the handle housing  514 . 
     The snare  512  of the ophthalmic surgical instrument  500  is movable relative to and within the elongated shaft  526  via an actuation mechanism (not shown), similar to the actuation mechanisms described above. The snare  512  generally includes a wire  530 , a light source  532 , and a fiber optic cable  534 . The wire  530  has a first end  530   a  configured to be coupled to the actuation mechanism, and a second end  530   b  fixed to or otherwise coupled to the housing  514  or the elongated shaft  526 . In aspects, the second end  530   b  of the wire  530  is fixed to the distal end portion  526   b  of the elongated shaft  526 . 
     The wire  530  has a looped segment  528  configured to protrude out of an opening  536  of the distal end portion  526   b  of the elongated shaft  526  when the looped segment  528  is in a dilated configuration. The looped segment  528  has a cutting segment  538  forming the bottom of the looped segment  528 . The cutting segment  538  may have a different diameter (e.g., smaller) or shape (e.g., sharpened) than the remainder of the looped segment  528 . In aspects, the cutting segment  538  may have the same thickness and shape as the remainder of the looped segment  528 . 
     The wire  530  is fabricated from a pliable, metal material, such as, for example, nickel-titanium or any other suitable superelastic material. In aspects, the wire  530  may be fabricated from any suitable ductile material. The wire  530  defines a channel or bore  540  centrally therethrough. The channel  540  of the wire  530  has a diameter from about 0.025 mm to about 0.178 mm and, in some aspects, about 0.076 mm. The channel  540  is configured to accommodate the fiber optic cable  534  therein. In aspects, rather than the wire  530  having the fiber optic cable  534  disposed therein, an inner surface  542  of the wire  530  that defines the channel  540  may be coated with a material having a high refractive index (e.g., glass, plastic, or a combination thereof) to facilitate passage of light therethrough. 
     The cutting segment or bottom  538  of the looped segment  528  of the wire  530  has a portion, such as, for example, a port  544  defined therein. The port  544  is in communication with the channel  540  to allow light to pass from the channel  540  and out of the cutting segment  538 . The port  544  is formed at a bottom-most apex  546  of the looped segment  528 , such that the port  544  is disposed in overlapping alignment with the opening  536  in the elongated shaft  526  when the looped segment  528  assumes its dilated configuration. In this way, when light is emitted through the port  544 , a clinician may be better able to identify the location of the cutting segment  538  of the wire  530 . The port  544  may be filled with a light-permeable material  548 , such as, for example, glass, transparent ceramics, clear plastics, etc. The light-permeable material  548  allows light to pass through the port  544  while prohibiting fluids and surgical debris from entering the wire  530 . The channel  540  of the wire  530  may be closed at the second end  530   b  thereof or, in some aspects, the wire  530  may have a plug  550  disposed at a location adjacent and proximally of the port  544  to ensure light passes out of the port  544 . In aspects, the wire may have a plurality of ports formed therein. 
     The light source  532  may be an LED, a compact fluorescent lamp, an incandescent light bulb, or any other suitable source of light. The light source  532  is in communication with the channel  540  of the wire  530 . For example, the light source  532  may be attached to the first end  530   a  of the wire  530  and is oriented toward the channel  540 . In some aspects, the light source  532  may be disposed within the channel  540  at any suitable location along the length of the wire  530 . In aspects, the light source  532  may be disposed within or otherwise adjacent the port  544 . The fiber optic cable  534  extends through the channel  540  and has a proximal end  534   a  attached to the light source  532  and a distal end  534   b  terminating adjacent the port  544 . The fiber optic cable  534  is configured to pass light from the light source  532  and to the port  544  of the cutting segment  538 . 
     In operation, a small incision in the edge of a cornea “C” ( FIG. 11 ) is made to provide access to an anterior chamber and an anterior surface “AS” of a cataractous lens “L” of a patient&#39;s eye. As is typical, the incision is anterior to the anterior surface “AS” of the lens “L.” A capsulorhexis is made through the anterior surface “AS” of the lens capsule of the patient&#39;s eye providing surgical access to the cataractous lens “L.” As shown in  FIG. 11 , a portion of the anterior surface “AS” of the lens “L” may be removed to form a cavity “CA.” The cavity “CA” renders the lens “L” more permeable to light, thereby giving a clinician a better view behind the eye. 
     The elongated shaft  526  is inserted through the corneal incision and the capsulorhexis to position the distal end portion  526   b  of the elongated shaft  526  in an overlapping arrangement with the anterior surface “AS” of the lens “L,” and position the looped segment  528  of the wire  530  anterior to a central location of the anterior surface “AS” of the lens “L.” The light source  532  may be activated either prior, during, or after positioning the looped segment  528  adjacent the anterior surface “AS” of the lens “L.” The light emitted from the light source  532  is passed through the length of the wire  530  via the fiber optic cable  534  and out of the bottom  538  of the looped segment  528  via the port  544 . 
     The looped segment  528  of the wire  530  is transitioned from the contracted configuration to the dilated configuration and guided around the lens “L” to position the cutting segment/bottom  538  of the looped segment  528  adjacent a posterior surface “PS” of the lens “L.” The clinician is able to use the light emitted from the port  544  to appropriately position the cutting segment  538  relative to the lens “L.” With the looped segment  528  in the selected position, which is verified using the light transmitted out of the bottom  538  of the looped segment  528 , the looped segment  528  is transitioned from the dilated configuration to the contracted configuration, thereby severing the lens “L.” 
     With reference to  FIGS. 12-15B , another embodiment of an ophthalmic surgical instrument  600  is illustrated, similar to the ophthalmic surgical instruments described above. Due to the similarities between the ophthalmic surgical instrument  600  of the present embodiment and the ophthalmic surgical instruments described above, only those elements of the ophthalmic surgical instrument  600  deemed necessary to elucidate the differences from ophthalmic surgical instruments described above will be described in detail. 
     The ophthalmic surgical instrument  600  generally includes a housing  610  and a snare  612  operably coupled to the housing  610  and configured for severing lenticular tissue. The housing  610  of the ophthalmic surgical instrument  600  has a handle body  614  and a cannulated body, such as, for example, a hollow, elongated shaft  626  extending distally from the handle body  614 . The elongated shaft  626  is dimensioned for passage through a corneal incision and has a proximal end portion  626   a  integrally formed with or attached to the handle body  614 , and a distal end portion  626   b  having a closed distal tip  627 . The distal end portion  626   b  may be bent or curved relative to the remainder of the elongated shaft  626  to more suitably position the distal end portion  626  within a corneal incision. 
     The elongated shaft  626  has an upper surface  632   a  and an opposing bottom surface  632   b  configured to be oriented toward and positioned in contact with an eye. The bottom surface  632   b  of the elongated shaft  626  defines a first opening, such as, for example, a proximal opening  630 , and a second opening, such as, for example, a distal opening  634  therein. The proximal and distal openings  630 ,  634  are in communication with a hollow interior  636  ( FIG. 14 ) of the elongated shaft  626  and are spaced longitudinally from one another along a longitudinal axis defined by the elongated shaft  626 . The proximal and distal openings  630 ,  634  are each disposed proximally of the distal tip  627  and are formed in the distal end portion  626   b  of the elongated shaft  626 . The proximal and distal openings  630 ,  634  are generally oval, but it is contemplated that the proximal and distal openings  630 ,  634  may assume any suitable shape, such as, for example, circular, elongated, square, or the like. In aspects, the distal opening  634  may be shorter or longer than the proximal opening  630 . 
     Due to the proximal and distal openings  630 ,  634  being longitudinally spaced from one another, the bottom surface  632   b  of the elongated shaft  626  has a surface, such as, for example, a cutting surface  638 , disposed between and interconnecting the proximal and distal openings  630 ,  634 . The cutting surface  638  may be arcuate, flat, or assume any suitable shape. 
     The snare or wire  612  of the ophthalmic surgical instrument  600  includes a first end portion  612   a  and a second end portion  612   b . The second end portion  612   b  of the wire  612  is movable relative to and within the elongated shaft  626  via an actuation mechanism (not shown), similar to the actuation mechanisms described above, while the first end portion  612   a  of the wire  612  is fixed relative to the housing  610 . The first end portion  612   a  of the wire  362  may be fixed to an inner surface of the elongated shaft  626  adjacent the proximal opening  630  by crimping, welding, adhesives, mechanical interlocks, or any other suitable structure or method. In other aspects, the second end portion  612   b  of the wire  612  may be fixed whereas the first end portion  612   a  of the wire  612  may be axially movable. In other embodiments, both the first and second end portions  612   a ,  612   b  may be axially movable. 
     The wire  612  has a cutting segment, such as, for example, a looped segment  628  protruding through and out of the proximal and distal openings  630 ,  634  of the elongated shaft  626 . The looped segment  628  of the wire  612  is transitionable, via axial movement of the second end portion  612   b  of the wire  612 , between a dilated configuration, as shown in  FIG. 15A , and an insertion or contracted configuration, as shown in  FIG. 15B . For example, a proximal retraction of a lever (not shown) of the housing  610  moves the second end portion  612   b  of the snare  612  proximally and into the interior  636  of the elongated shaft  626  via the distal opening  634 , thereby reducing the diameter of the looped segment  628 . In contrast, a distal advancement of the lever moves the second end portion  612   b  of the wire  612  distally and out through the distal opening  634  of the elongated shaft  626 , thereby increasing the diameter of the looped segment  628  of the wire  612 . 
     The looped segment  628  has a predefined shape dimensioned to closely encircle a lens when the looped segment  628  is in the dilated configuration. The looped segment  628  defines a length parallel with the longitudinal axis of the elongated shaft  626 . A majority of the length of the looped segment  628  is in side-by-side, parallel relation with the bottom surface  632   b  of the elongated shaft  626 . Further, a majority of the looped segment  628  (i.e., at least half) is disposed proximally of the distal tip  627  of the elongated shaft  626 . In this way, during use of the ophthalmic surgical instrument  600 , the bottom surface  632   b  of the elongated shaft  626  hangs over a majority of the looped segment  628 , such that the elongated shaft  626  sits on a lens during lens fragmentation to prevent upward movement of the lens as the looped segment  628  is constricted thereabout. 
     In operation, a small incision in the edge of a cornea is made to provide access to an anterior chamber and an anterior surface of a cataractous lens of a patient&#39;s eye. A capsulorhexis is made through the anterior surface of a lens capsule of the patient&#39;s eye providing surgical access to the cataractous lens. With the snare  612  of the ophthalmic surgical instrument  600  in the contracted configuration, as shown in  FIG. 15B , the elongated shaft  626  is inserted through the corneal incision and the capsulorhexis to position the distal end portion  626   b  of the elongated shaft  626  in an overlapping arrangement with the anterior surface of the lens, and the looped segment  628  of the wire  612  is positioned adjacent the anterior surface of the lens. 
     Once the looped segment  628  is in the appropriate position, the second end portion  612   b  of the snare  612  is advanced distally and out from within the interior  636  of the elongated shaft  626  through the distal opening  634 , thereby transitioning the looped segment  628  from the contracted configuration to the dilated configuration, as shown in  FIG. 15A . With the looped segment  628  in the dilated configuration, the snare  612  may be rotated about its longitudinal axis (e.g., via rotation of the entire ophthalmic surgical instrument  600  or via a rotation mechanism (not shown)) to rotate the looped segment  628  circumferentially about the lens to encircle the lens and position the looped segment  628  relative to the lens so that the plane defined by the looped segment  628  bisects the lens. Upon rotating or otherwise positioning the snare  612  in the selected position, the lens is disposed between the looped segment  628  and the cutting surface  638  of the bottom surface  632   b  of the elongated shaft  626 . 
     With the looped segment  628  of the snare  612  disposed about the lens, and the elongated shaft  626  overlaying and in contact with the anterior surface of the lens, the looped segment  628  is transitioned from the dilated configuration toward the contracted configuration. As the looped segment  628  moves toward the contracted configuration, a cutting section  640  ( FIGS. 15A and 15B ) of the looped segment  628  cooperates with the cutting surface  638  of the elongated shaft  626  to apply a cutting force on the lens, thereby dividing the lens into two hemispherical sections. Nearing the end of the transition of the looped segment  628  toward the contracted configuration, a distal edge  642  ( FIGS. 15A and 15B ) of the cutting surface  638  may act as a fulcrum allowing the looped segment  628  to be pulled closer to the bottom surface  632   b  of the elongated shaft  626 , causing the cutting section  640  of the looped segment  628  to become taught and straight against the cutting surface  638 . As such, the cutting surface  638  acts in a similar manner as a cutting block or board where the cutting section  640  of the looped segment  628  acts as the knife. 
     With reference to  FIGS. 16 and 17 , another embodiment of a snare, such as, for example, a wire  712  is illustrated, similar to the snare  612  described above. It is contemplated that the snare  712  may be incorporated into the elongated shaft  626  described above. The snare  712  has a looped segment  728  having a curvature along a majority of its length that matches a curvature of a lens of a human eye. The snare  712  differs from the snare  612  in that the looped segment  728  of the snare  712  has a linear, cutting section  740  disposed adjacent the proximal opening  630  in the elongated shaft  626 . 
     Upon transitioning the looped segment  728  to the contracted configuration, as shown in  FIG. 17 , the linear, cutting section  740  of the looped segment  728  extends between the proximal and distal openings  630 ,  634  and engages the cutting surface  638  of the elongated shaft  628 . Due to the cutting section  740  being linear, more of the cutting section  740  contacts the lens as the looped segment  728  moves toward the contracted configuration. 
     With reference to  FIG. 20 , another embodiment of an ophthalmic surgical instrument  600 ′ is illustrated, similar to the ophthalmic surgical instrument  600  described above. The ophthalmic surgical instrument  600 ′ generally includes an elongated shaft  626 ′ and the wire or snare  812  of  FIG. 19  operably coupled to the elongated shaft  626 ′. The elongated shaft  626 ′ has a bottom surface  632 ′ defining a proximal opening  630 ′, a distal opening  634 ′, and an intermediate opening  638 ′ disposed between and spaced from the proximal and distal openings  630 ′,  634 ′. As such, the bottom surface  632 ′ has a first section  632   a ′ extending between and interconnecting the proximal opening  630 ′ and the intermediate opening  638 ′, and a second section  632   b ′ extending between and interconnecting the intermediate opening  638 ′ and the distal opening  634 ′. The first and second sections  632   a ′,  632   b ′ function as support surfaces for the eye during a transition of the looped segment  828  of the snare  812  from the dilated configuration to the contracted configuration, as will be described below. 
     In operation, the elongated shaft  626 ′ is positioned on an anterior surface of a lens of an eye, such that at least the first and second sections  632   a ′,  632   b ′ of the bottom surface  632 ′ of the elongated shaft  626 ′ is in contact with the anterior surface. The looped segment  828  of the snare  812  is transitioned toward the contracted configuration, as shown in  FIG. 20 , to sever the lens of the eye in a similar manner described above. Due to the presence of the intermediate opening  638 ′ in the elongated shaft  626 ′, the cutting section  840  of the looped segment  828  is permitted to cut entirely through the lens as it passes into the intermediate opening  638 ′ in the bottom surface  632 ′. While the looped segment  828  cuts through the lens, the first and second sections  632   a ′,  632   b ′ of the bottom surface  632 ′ exert a reactionary force (in a posterior direction) on the lens to prevent the lens from being lifted, thereby further facilitating cutting of the lens. 
     With reference to  FIG. 21 , another embodiment of an elongated shaft  926  of an ophthalmic surgical instrument is illustrated, similar to the elongated shaft  626  of  FIGS. 13 and 14 . The elongated shaft  926  defines a proximal opening  930  in a bottom surface  932  thereof, and a distal opening  934 . The looped segment  628  of the snare  612  extends through each of the proximal and distal openings  930 ,  934 . The bottom surface  932  has a cutting surface  940  extending between the proximal and distal openings  930 ,  934 . The difference between the elongated shaft  926  and the elongated shaft  626  of  FIGS. 13 and 14  is that the distal opening  934  is defined in a distally-facing surface  936  of a distal tip  927  of the elongated shaft  926 . 
     With reference to  FIG. 22 , another embodiment of an elongated shaft  1026  of an ophthalmic surgical instrument is illustrated, similar to the elongated shaft  626  of  FIGS. 13 and 14 . The elongated shaft  1026  defines a proximal opening  1030  in a bottom surface  1032  thereof, and a distal opening  1034 . The looped segment  628  of the snare  612  extends through each of the proximal and distal openings  1030 ,  1034 . The bottom surface  1032  has a cutting surface  1040  extending between the proximal and distal openings  1030 ,  1034 . The difference between the elongated shaft  1026  and the elongated shaft  626  of  FIGS. 13 and 14  is that the distal opening  1034  has a scooped configuration and extends along a length of an opened distal tip  1027  of the elongated shaft  1026 . 
     It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended thereto.