Patent Publication Number: US-2005131434-A1

Title: Reciprocating instrument for separating a cornea to form a corneal flap

Description:
FIELD OF THE INVENTION  
      The present invention relates to an instrument for separating the cornea of an eye to form a flap in the surface of the cornea. More particularly, the present invention relates to an instrument that has a reciprocating wire that is adapted to separate an epithelial layer from the remainder of the cornea to form an epithelial flap in the surface of the cornea.  
     BACKGROUND OF THE INVENTION  
      The cornea consists of three regions, the epithelial sheet, the stroma, and the endothelial lining. The epithelial sheet is the outermost region. It consists of between five to eight layers of cells and makes up approximately 10% of the thickness of the cornea. Moreover, the epithelial sheet is renewable, in other words, capable of re-growth. In addition, the epithelial sheet is filled with thousands of tiny nerve endings, making the cornea extremely sensitive to pain when the epithelial sheet is, for example, scratched. The stroma is the middle region. It is located behind the epithelial sheet and makes up approximately 90% of the thickness of the stroma. The endothelial lining is the innermost region. It is a single layer of cells located behind the stroma.  
      During refractive eye surgery, the shape of the stroma is changed. For example, in Photo Refractive Keratectomy (“PRK”) the shape of the stroma is changed with an excimer laser. First, however, the cells in the epithelial sheet are killed or removed using a laser, a chemical, or a scraping device. After the PRK, the epithelial sheet grows back over the stroma. However, during this time period, the patient may experience pain and/or poor vision. In addition, regression might occur. Regression is the growth of the epithelial sheet in a pattern which restores, or nearly restores, the shape of the cornea prior to the PRK.  
      In Laser Assisted In Situ Keratomileusis (“LASIK”), the shape of the stroma is also changed using an excimer laser. In LASIK, a microkeratome is used to hinge back the outermost 20-30% of the cornea. The excimer laser is then used to change the shape of the exposed stroma. Because LASIK maintains the epithelial sheet, LASIK tends to avoid the problems discussed above in regard to PRK. However, LASIK is dependent on the use of the microkeratome, which may jam, shred, or lose the corneal flap. Moreover, a suction device must be used in conjunction with the microkeratome, increasing intra ocular pressure up to approximately 100 mm Hg. For some vulnerable patients, the increase in intra ocular pressure can harm their eyes.  
      In Laser Epithelial Keratomileusis (“LASEK”), the epithelial sheet is loosened with an alcohol solution, then rolled back to expose the stroma. The excimer laser is then used to change the shape of the stroma and the loosened epithelial sheet is repositioned over the stroma. However, in LASEK, the patient experiences a slow return to clear vision and must wear a contact lens on the affected eye for a number of days. The slow return to clear vision is due to the use of the alcohol solution, which kills some of the epithelial cells. Moreover, the presence of dead epithelial cells renders the cornea vulnerable to infection, a situation that is enhanced because of the post-operative use of a contact lens.  
      Additional devices have been developed to separate the epithelial sheet. For example, a subepithelial separator, which is a microkeratome-based device, uses a blunt blade and low suction to mechanically separate a hinged epithelial sheet without alcohol. The sheet is then reflected nasally onto a contact lens. After ablation of the exposed cornea, the sheet is replaced along with a contact lens. This type of device is preferably to the use of alcohol, since the mechanical separation takes place under the basement membrane, thus preserving the integrity of the epithelial flap.  
      However, with a conventional subepithelial separator, the use of a small knife or blade is generally required. It is very difficult to maintain the proper blade sharpness with these types of blades. If the blade is too sharp or not sharp enough, it is difficult to predict the type of cut that will result and whether or not the blade will cut deep enough or too deep. It is generally very important that the stroma is not cut during this type of procedure. Additionally, blades can be very expensive to purchase and maintain.  
      Accordingly, a need exists for an improved instrument for forming an epithelial flap.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide an instrument adapted to form a flap in the surface of the cornea.  
      Another object of the present invention is to provide a reciprocating instrument adapted to form an epithelial flap in the surface of the cornea of the eye.  
      Yet another object of the present invention is to provide an instrument that has a reciprocating wire that is adapted to form an epithelial flap in the surface of the cornea of the eye.  
      The foregoing objects are basically attained by a device for forming a flap on the surface of a cornea of an eye, including a head portion adapted to reciprocate, and a wire attached to the head portion and adapted to separate the cornea into first and second surfaces, which form a flap in the cornea of the eye.  
      The foregoing objects are further attained by a device for forming a flap in the surface of a cornea of an eye, including first member having a head portion, with a reciprocating member coupled to the head portion. A first arm and a second arm are coupled to the reciprocating member, and a wire extends between the first and second arm and are adapted to separate the cornea into first and second surfaces.  
      By forming an instrument for forming epithelial flaps in this manner, precise epithelial flaps that remain intact can be inexpensively and effectively formed.  
      Other objects, advantages, and salient features of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Referring to the drawings which form a part of this disclosure:  
       FIG. 1  illustrates a side elevational view of the preferred embodiment of the present invention, including the reciprocating member and the positioning member coupled together and positioned relative the eye of a patient;  
       FIG. 2  is a top view of the present invention of  FIG. 1 ;  
       FIG. 3  is a side view in section of the present invention forming an epithelial flap in the surface of the cornea of an eye;  
       FIG. 4  is a side elevational view of the eye of  FIG. 3  with an epithelial flap formed therein;  
       FIG. 5  is a bottom view of the present invention, including the reciprocating member and the positioning member coupled together;  
       FIG. 6  is a top perspective view of the reciprocating member and the positioning member of  FIG. 5  detached from one another;  
       FIG. 7  is a partial top view of the positioning member of  FIG. 5 ;  
       FIG. 8  is a partial side view of the positioning member of  FIG. 7 ;  
       FIG. 9  is a partial bottom view of the positioning member of  FIG. 8 ;  
       FIG. 10  is a partial front view of the positioning member of  FIG. 9 ;  
       FIG. 11  is a partial top perspective of the positioning member of  FIG. 10 ;  
       FIG. 12  is a partial bottom view of the reciprocating member of  FIG. 5 ;  
       FIG. 13  is a partial top perspective view of the reciprocating member of  FIG. 12 ;  
       FIG. 14  is a partial side view of the reciprocating member of  FIG. 13 ;  
       FIG. 15  is a partial side perspective view of the view of the reciprocating member of  FIG. 14 ;  
       FIG. 16  is a partial top perspective of the positioning member of  FIG. 15 .  
       FIG. 17  is a side view of a second embodiment of the present invention, wherein the positioning member is coupled or affixed to the reciprocating member;  
       FIG. 18  is a third embodiment of the present invention, wherein a blank or lens is positioned overlying the epithelial flap;  
       FIG. 19  is a bottom perspective view of a cutting device used to form a groove in the cornea;  
       FIG. 20  is a side view of the cutting device of  FIG. 19  being applied to surface of the cornea; and  
       FIG. 21  is a top view of the cornea of the eye of  FIG. 19 , showing the groove formed by the cutting device.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As illustrated in  FIGS. 1-6  the present invention relates to an instrument  10  for forming an epithelial flap  12  in the surface  14  of the cornea  16  of an eye  18 . Instrument  10  includes a reciprocating or first member  20  and a positioning or second member  22 , which couple together. The positioning member is adapted to be positioned on the surface  14  of the cornea  16  and position the reciprocating member  20  an appropriate distance from the surface of the cornea, when the positioning member and the reciprocating member are coupled together. Once the reciprocating member and the positioning member are coupled together and properly positioned on the eye, the reciprocating wire  24  is activated and the reciprocating member  20  is moved relative to the positioning member  22  ( FIG. 3 ), with the wire  24  reciprocating or cutting through the surface  14  of the cornea  16  and forming the desired flap  12 .  
      As shown in  FIGS. 7-11 , the positioning member  22  has a handle  26  and a head portion  28 . Handle  26  is preferably a metal cylindrical handle that is coupled to head portion  28 . Preferably handle  26  is coupled to head portion  28  using a welded joint, but can be coupled thereto using in any conventional method, such as threads, friction or glue.  
      Head portion  28  is preferably formed from metal or any other suitable material and has an upper portion  30  and a lower portion  32 . Upper portion  30  is preferably substantially U-shaped with a first arm  34 , a second arm  36  and a base portion  38 . The handle is preferably coupled to the base portion  38 ; however, the handle can be coupled to any suitable portion of either the upper or lower portions.  
      As shown in  FIGS. 8, 10  and  11 , a groove  40  extends along the interior surface of first arm  34 , the interior surface of base portion  38  and the interior surface of the second arm  36 . In other words, the groove  40  extends along the interior surface of the upper portion  30  from of first end  44  of first arm  34  to the first end  46  of the second arm  36 . Preferably, transparent member  48  is sized and configured to frictionally fit within groove  40 . Transparent member  48  is preferably formed from plastic; however it can be formed from any transparent material desired, such as glass or any other suitable material. Transparent member  48  has an exposed side or surface  50  at the open end of the U-shaped area of upper portion  30 , or in other words, surface  50  extends from end  44  to end  46 . However, it is noted that it is not necessary to have a transparent member  48  positioned within groove  40 . The U-shaped area can have no material extending thereacross, and be completely open, if desired.  
      As shown in  FIGS. 8, 10  and  11 , arms  34  and  36  have grooves  52  and  54  extending along the exterior portion thereof. Grooves  52  and  54  preferably extend substantially along the length of a respective arm and are sized and configured to receive the reciprocating member.  
      Lower portion  32  is preferably unitary with upper portion and connected thereto by portion  56 , as shown in  FIG. 8 . Lower portion  32  preferably has an arcuate or rounded front or first end  58  and an arcuate or rounded second end  60 . Connecting first end  58  and second end  60  are substantially straight sides  62  and  64 . Sides  62  and  64  are preferably substantially parallel. First end  58  has a substantially arcuate area  65  removed therefrom. Centered in the middle of lower portion  32  is opening  66 . Opening  66  is preferably centered under and underlying transparent member  48 . Opening  66  is defined by surface  68 , which is adjacent sloped or angled surface  70 . Sloped surface  70  is adjacent another sloped surface  72 , which terminates at bottom surface  74 , which is a substantially flat, planar surface. Opening  66  is defined by these sloped surfaces to allow easy access of the cornea through the opening and, so that a portion of the surface of the cornea extends through the opening, as shown in  FIG. 3 .  
      As shown in  FIGS. 10 and 11 , lower portion  32  has an upper surface  76  that is substantially planar and positioned apart from the lower surface  35  of the upper portion  30 . Additionally, lower portion  32  has a recessed area  78 .  
      As shown in  FIGS. 6 and 12 - 16 , reciprocating member  20  preferably is formed from plastic (or other suitable material) and has a body or handle portion  80 , neck portion  82  and a head portion  84 . Handle portion  80  preferably is a cylindrical housing for an electric motor (not shown) and a battery source (not shown); however, handle portion  80  can merely be a gripping device with the motor and power source external thereto. Handle portion  80  also includes an on/off switch  86 , which turns on and off the electric motor. Neck portion  84  is preferably substantially cylindrical and connects the head portion  84  and the handle portion  80 , and preferably houses a shaft to connect the electric motor with the reciprocating head.  
      As shown in  FIGS. 12-16 , head portion  86  includes a cap  88 , a guard or attachment portion  90  and a reciprocating member  92 . Cap  88  is preferably formed of plastic and facilitates the connection of guard  90  and reciprocating member  92  to the neck and body of the reciprocating member  20 . Cap  88  has a recessed portion  94  that accommodates the end  96  of the shaft (not shown) and end  98  of reciprocating member  92 . Additionally, cap  88  has a front substantially flat surface  100  that receives screws or fasteners  102  and  104  that couple the guard  90  thereto.  
      Guard  90  is preferably formed of metal and has a substantially U-shaped portion  106 , as shown in  FIG. 16 . U-shaped portion  106  has a first arm  108 , a second arm  110  and a base portion  112 . First and second arms  108  and  110  are preferably substantially parallel and each extends at substantially 90° from the base portion  112 . Each arm  108  and  110  has an inner surface  114  and  116 , respectively, that is substantially smooth and straight. Additionally, the arms  108  and  110  have a thickness and are spaced from each other in such a manner that they can be inserted into the grooves  52  and  54  on the first and second arms of the positioning member, respectively.  
      Extending from the U-shaped portion  106  is connecting portion  118 . Connecting portion  118  has two openings or slots  120  and  122  to accommodate screws  102  and  104 , respectively, thereby coupling the guard  90  to the cap  88 .  
      As shown in  FIG. 12 , reciprocating member  92  is a metal wire frame and is substantially U-shaped or Y-shaped. Member  92  has a first arm  124 , a second arm  126 , a base portion  128  and a rear stem portion  130 . Base portion  128  is the portion of the reciprocating member where the first arm  124  meets or joins with the second arm  126 . Clamp member  132  couples reciprocating member  92  to the guard member  90 .  
      As shown in  FIGS. 12 and 15 , clamp member  132  is generally triangular and includes an upper clamp  134  and a lower clamp  136 . Upper clamp  134  overlies the reciprocating member  132  at approximately the base portion and has an opening therein that is adapted to receive a screw  138 . Lower clamp  136  is positioned between the reciprocating member  92  and the guard  90  and is substantially the same size and shape as the upper clamp, i.e., generally triangular. Lower clamp also has an opening therein to receive screw  138 .  
      Screw  138  extends through the openings in the upper and lower clamps and into the guard, as shown in  FIGS. 15 and 16 . Nut  140  couples to the screw  138  and is adapted to couple the reciprocating member  92  to the guard  90 . A bushing  142  is positioning around the screw  138  and is adapted to properly position the reciprocating member and reduce the friction to allow the reciprocating member to reciprocate freely.  
      As shown in  FIGS. 12 and 15 , rear stem portion  130  has a first wire portion  144  and a second wire portion  146  that are coupled together at the end  148  of the rear stem portion. As shown in  FIG. 12 , reciprocating drive  150  is coupled to end  96  of the drive shaft and extends between the first wire portion and the second wire portion. The drive  150  is preferably a cylindrical projection that extends upwardly from end  96 ; however, dive  150  can be any shape or configuration suitable to cause the reciprocating member to oscillate back and forth. Drive  150  preferably extends upwardly from the periphery of the drive shaft, preferably substantially parallel to the axis of the drive shaft. The end  96  of the drive shaft is adapted to rotate 360° about the axis of the drive shaft, and thereby rotate the drive  150  in a 360° circle about the axis of the drive shaft. This rotation causes the reciprocating member  92  to reciprocate about screw  138  when the drive  150  rotates.  
      First arm  124  is formed of a first wire portion  152  and a second wire portion  154  that couple or connect at first end  156 . Second arm  126  is formed of a third wire portion  158  and a fourth wire portion  160  and connect or couple at second end  162 . Reciprocating wire  24  extends across the mouth of the U-shaped portion of the reciprocating member  92 , i.e., wire  24  extends from first end  156  to second end  162 . As shown in  FIG. 15 , wire  24  extends though first arm  124  between first wire portion  152  and second wire portion  154  and through second arm  126  between third wire portion  158  and fourth wire portion  160 . Each end of wire  24  preferably is knotted and frictionally held between respective wire portions; however, wire  24  can be coupled to the arms of the reciprocating member in any suitable manner.  
      Reciprocating or cutting wire  24  is preferably substantially circular and formed from metal threads twined or twisted together. However, wire  24  can be any suitable material, such as single piece metal, surgical thread, TEFLON, DACRON, plastic, or any other material that would perform the desired cutting action. Additionally, the wire  24  does not necessarily need to be substantially circular and can be any suitable shape, such as substantially oval, substantially square, substantially rectangular, it can have a cutting edge or any other suitable shape. Furthermore, wire  24  has a diameter of preferably about 10 microns to about 500 microns and even more preferably about 50 microns to about 100 microns.  
      As noted above, preferably the wire  24  is reciprocated using an electric motor; however, the wire  24  can be reciprocated using an type of motor, electrical means, mechanical means or electro-mechanical means or any other means suitable, such as by hand. Additionally, wire  24  preferably oscillates back and forth at between a rate of about 50 vibrations per second to a rate of about 50,000 vibrations per second, and more preferably between about 8,000 vibrations per second to about 10,000 vibrations per second. Also, wire  24  oscillates back and forth at a rate between about 3 mm per second (when oscillating in the faster ranges) to 0.5 mm per second (when oscillating in the slower ranges); however, the wire  24  can oscillate at any suitable speed and distance. Furthermore, the wire can oscillate or reciprocate in any direction desirable and does not need to reciprocate from side to side. For example, the wire  24  can oscillate forward and backward or a combination of forward and backward and side to side. Preferably when oscillating forward and backward, wire  24  oscillates at a rate about 1 mm per second.  
     Preferable Operation  
      As shown in  FIGS. 1-3 , preferably positioning member  22  and reciprocating member  20  are coupled together by sliding the first and second arms  106 ,  108  of guard member  90  into the appropriate slots or grooves  52 ,  54  on the upper portion  30  of the positioning member  22 . Recessed area  78  preferably accommodates the head of screw  138 , and wire  24  is positioned between upper portion  30  and lower portion  32 . Preferably wire  24  is adjacent or even touching surface  76  of lower portion  32 , so that only a minimal amount of the surface of the cornea needs to extend through opening  66 . However, it is noted that the wire  24  can be positioned in any suitable position relative to the surface  76  and can also be positioned variably relative to surface  76  if desired. By positioning the wire relative thereto, the operator can more easily select the amount of cornea that extends through the opening  66  and the amount of epithelial layer that is separated.  
      Positioning member  22  is then positioned relative to the surface  14  of the cornea  16  of the eye  18 . Pressure can be applied to the positioning member  22  thereby allowing the appropriate amount of the corneal surface  14  to pass through opening  66  and allow a portion of the cornea  16  to extend through the opening  66  beyond surface  76 .  
      Reciprocating member can then be turned on, activating the reciprocating wire. The reciprocating wire is moved relative to the positioning member, as shown in  FIGS. 1-3 . The first and second arms  106 ,  108  slide out of grooves  52 ,  54 , respectively, as the reciprocating member  20  moves relative to the positioning member  22 , and the surface  14  of the cornea l 6 . This relative movement allows smooth and straight movement of the reciprocating wire  168  relative to the eye. As the reciprocating member  20  moves relative to the eye  18 , the reciprocating wire  168  cuts or shaves a portion of the epithelial layer away from the stromal layer.  
      Preferably the wire cuts or separates the epithelial layer and the Basal Laminer from the Bowman&#39;s membrane and stromal layer of the cornea. This separation is achieved by the cutting wire burrowing under the Basal Laminer and gently separating this layer from the stroma and the Bowman membrane. By inherent design the wire is sharp enough to cut through the surface of the cornea, but not into the stroma, and therefore, it is relatively easy to form the desired epithelial flap.  
      The wire separates the cornea  16  into a first layer  170  and a second layer  172 , forming flap  12 . The first layer faces in a posterior direction and the second layer faces in an anterior direction, relative to the eye. Preferably flap  12  remains coupled to the cornea by hinge  176 ; however, the flap can remain attached to the cornea in any suitable manner or can be removed completely from the cornea. To remove the flap completely, a device as described in copending application Ser. No. can be used. The contents of U.S. Pat. No. 6,551,307 and U.S. patent application Ser. No. 10/356,730, the entire contents of both of which are hereby incorporated by reference in their entirety.  
      Additionally, the flap  12  can remain attached to the cornea  16  by a portion that remains connected to the cornea at the main optical axis. Moving the reciprocating member  20  is a 360° arc about the main optical axis of the eye forms this type of flap. This arc can be achieved by hand or by having a positioning member that allows the reciprocating member  20  to be rotated thereabout.  
      While positioning member  22 , described herein, is preferable, it is possible to design any type of positioning member that would adequately position the wire  24  relative to the surface of the cornea. Any such positioning member can be fixed to the reciprocating member or can be a separate piece of equipment.  
     Embodiment of FIG.  17   
      Additionally, as shown in  FIG. 17 , the instrument  10 ′ includes a positioning member  22 ′ that can be coupled and/or affixed to the reciprocating member  20 ′ by a connecting member  191 . This instrument  10 ′ functions in a substantially similar manner as the instrument  10  in that the cornea extends through opening  66 ′ of the positioning member  22 ′ and is subsequently separated into first and second surfaces  170  and  172 , respectively, or more preferably into a flap  12 , as shown in  FIG. 4 .  
      However, the cutting wire  24 ′ preferably moves relative to the positioning member  22 ′ by movement of connecting portion  188 ′ which is coupled to a piston  190 , which is in turn connected to head portion  88 ′. Piston  190  is adapted to move the reciprocating member  92 ′ and thus the cutting wire  24 ′ in a back and forth motion as indicated by arrow  192 .  
      Any other description of instrument  10  is applicable to instrument  10 ′, as long as it is consistent with the specific description of  FIG. 17 , above. Additionally, any description of the reference numbers from the first embodiment of the present invention is applicable to the reference numbers used in  FIG. 17 .  
     Embodiment of FIG.  18   
      As shown in  FIG. 18 , a lens or blank  200  can be positioned overlying the surface of the cornea. Lens  200  allows the epithelial flap  12  to adhere thereto when the flap  12  is formed in the surface of the cornea. The flap can adhere to the lens using any suitable means such as a suctioning device or can adhere thereto merely by surface tension. Lens  200  can be any material suitable and is not necessarily transparent, let alone refractive. Lens  200  is merely a device that facilitates separation of the epithelial layer and Basal Laminer and can be any suitable material.  
      Flap  12  is formed using the lens  200  in the same manner as described above. Specifically, wire  24  separates the corneal surface into first and second corneal surfaces  170  and  172 , respectively, by cutting or separating the epithelial cells and the Basal Laminer from the stroma of the cornea. The combination of the Basal Laminer and epithelial layer allows the flap to remain intact. Additionally having it adhere to the surface of the contact further facilitates the keeping the structural integrity of the flap intact. The flap can remain attached to the cornea, as described above, i.e., either at the periphery or substantially surrounding the main optical axis, or the flap can be completely separated from the cornea to be repositioned at a later time.  
     Embodiment of FIGS.  19 - 21   
      As shown in  FIGS. 19-21 , cutting device  220  can be used to form a groove  222  in the surface of the cornea in the eye. Device  220  is preferably formed of metal or plastic; however, device  220  can be formed from any suitable material. The device  220  is preferably substantially cylindrical with a substantially flat, circular surface  224 . Extending substantially around the periphery  226  of the surface  224  is a cutting device or blade  228 .  
      Blade  228  extends preferably about 30 to about 130 microns in a direction substantially perpendicular to and away from planar surface  224 . Furthermore, blade  228  is arcuate and preferably extends about 350° around the periphery of the surface  224 ; however, it is noted that the blade can extend 360° around the periphery of the surface or less than 360°. For example the blade can extend in an arc of about 180° or less to about 360° or less, if desired. This design creates a gap  229  at the periphery  226  in the blade  228 .  
      Using device  220 , surface  224  is positioned adjacent the surface of the cornea so that the main optical axis  230  is in about the center of surface  224 . As sufficient force or pressure is applied to the to device  220  in a direction substantially parallel to the main optical axis, blade  228  cuts through the corneal surface and into the stromal layer, forming a groove  222 . However, since the blade has a gap  229 , the cornea groove  222  does not extend in a full circle or 360°, thus forming a connected or hinge portion  233 . The groove extends about an arc that is about the same as the blade, or in other words in an arc of about 350°. However, as with the blade  228 , the groove  222  can extend at any arc desired.  
      Once the groove  222  is formed the device  10 , described above, can be used to form a flap that has substantially the same configuration as the groove, where the hinge portion  233  allows the flap to remain attached to the cornea, forming a flap as described above in  FIG. 4 . However, the flap formed using device  220  will actually extend into and include a portion of the stroma at a depth of preferably about 30 microns to about 130 microns from the surface of the cornea; however, the flap can have any suitable thickness. For example, the flap can be less than 30 micros (for example, about 10 microns) or the flap can be greater than 130 microns, up to about 180 microns. The flap preferably has a substantially uniform thickness, since the device  10  described above generally cannot cut through the stromal layer and can only dissect in a direction substantially parallel to the surface of the cornea.  
      This procedure is preferable conventional methods for forming corneal flaps, since the flap formed by the present invention has a thickness of about 30 to about 130 microns. Due to limitations on the cutting blades, conventional flaps can only have a thickness of between about 130 microns to about 180 microns. This limitation on flap thickness limits the amount of cornea that can be ablated. Therefore, the maximum correction in an eye is about plus or minus 8-10 diopters. By forming a flap that is between about 30 microns to about 130 microns the change in refractive error can be up to about plus or minus 20 diopters.  
      Additionally, to facilitate the dissection of the stromal layer, the above-described cutting wire can have a serrated edge.  
      While preferred embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.