Abstract:
A surgical method of corneal reformation reduces the risk of trauma and shortens overall recovery while yielding improved visual acuity includes making a relatively shallow incision of no more than about 85 microns deep into the corneal epithelium, separating the corneal epithelial sheet from the underlying Bowman&#39;s Membrane using an epithelial separator or a specialized cannula, and lifting the epithelial sheet away from the ablation zone so that the Bowman&#39;s Membrane and underlying stromal bed can be reformed. Multiple surgical instruments include the optional use of vibration with an epithelial separator or cannula to separate an epithelial sheet from the cornea of no more than about 85 microns thick.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to methods for corneal reformation, specifically, to a method for corneal reformation that permits faster recovery with improved visual acuity and surgical instruments for performing such methods. 
   BACKGROUND OF THE INVENTION 
   The human eye includes a specialized structure referred to as the cornea. The cornea is a multi-layered structure, however, the three most superficial layers—the corneal epithelium, Bowman&#39;s Membrane, and the stromal bed—are the layers that are primarily implicated in corneal reformation surgery. The epithelium, which comprises the delicate covering of the human cornea and is only five or six cells thick, is the protective barrier against infection of the cornea. The cornea, being avascular, has unique immune requirements and an infection in this part of the eye is problematic since systemic antibiotics are relatively ineffective. Therefore, preservation of the epithelial integrity is critical in surgery as well as for general eye care. 
   The epithelium is adherent to the stromal surface along Bowman&#39;s Membrane which is a cell-free zone approximately 7 to 12 microns thick and defines the Basement Membrane. Bowman&#39;s Membrane is the most anterior structure of the stromal tissue which is the major lamellar structure of the corneal anatomy. In most surgeries of the cornea, efforts are made to prevent the tearing of the epithelium from Bowman&#39;s Membrane because such tearing causes pain, slow visual recovery, and predisposes to corneal infiltrates (precursors to infection). 
   Some corneal reformation techniques, such as LASIK, require the creation of a flap of corneal epithelium which may result in significant destruction of the stromal bed leading to trauma or even permanent damage to the eyes and compromise eyesight. PRK, on the other hand, removes the upper most layer(s) of corneal epithelium without danger to the underlying stromal bed but requires a long recovery period for the patient. 
   In LASIK, in order to create a useable flap, the flap must be relatively thick. A thick flap, however, requires corneal reformation by ablating underlying tissue that extends into the stromal bed of the cornea. Ablating this tissue has severe consequences. Unless sufficient tissue remains in the stromal bed, the cornea can destabilize resulting in keratoectasia. A patient&#39;s long recovery time after PRK surgery is disadvantageous for multiple reasons, such as lengthier vulnerability to infection, discomfort, and inability to return to daily routine quickly. 
   Accordingly, there is a need for a method of corneal reformation that reduces the risk of trauma and permanent damages to the eye while permitting quick recovery. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a method for reforming the cornea to alter visual acuity is presented whereby a shallow incision of less than about 85 microns is made into the corneal epithelium to create a sheet of epithelium. The sheet of epithelium is separated from the Bowman&#39;s Membrane using an epithelial separator or cannula and then is lifted from of the cornea to permit ablation of the underlying membrane followed by return of the epithelial sheet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and for further advantages thereof, reference is now made to the following Description of the Preferred Embodiments taken in conjunction with the accompanying Drawings in which: 
       FIG. 1   a  is a block diagram illustrating the present method; 
       FIGS. 1   b – 1   g  are pictorial representations illustrating steps of the present method; 
       FIG. 2  is a perspective view of a trephine used in practicing the present method; 
       FIG. 3  is a side elevational view of the trephine cutting band illustrated in  FIG. 2 ; 
       FIG. 4  is a bottom plan view of the trephine cutting band shown in  FIG. 3 ; 
       FIG. 5  is a sectional view taken generally along sectional lines  5 — 5  of  FIG. 3  of the trephine cutting band; 
       FIG. 6  is a perspective view of an embodiment of a surgical instrument used in the practice of the present method; 
       FIG. 7  is an enlarged side elevational view of the cannula shown in  FIG. 6 ; 
       FIG. 8  is sectional view taken generally along sectional lines  8 — 8  of  FIG. 7  of the cannula of the present invention; 
       FIG. 9  is a front elevation view taken generally at lines  9 — 9  of  FIG. 7  of the distal tip of the cannula of the present invention; 
       FIG. 10  is a side elevational view of another embodiment of a cannula used in the practice of the present method; 
       FIG. 11  is a sectional view taken generally along sectional lines  11 — 11  of  FIG. 10  of the cannula of the present invention; 
       FIG. 12  is a side elevational view of another embodiment of a cannula used in the practice of the present method; 
       FIG. 13  is a sectional view taken generally along sectional lines  13 — 13  of  FIG. 12  of the cannula of the present invention; 
       FIG. 14  is a perspective view of an embodiment of an epithelial separator used in the practice of the present method; 
       FIG. 15  is an enlarged side elevational view of the spatula-like portion of the epithelial separator shown in  FIG. 14 ; 
       FIG. 16  is a sectional view taken generally along sectional lines  16 — 16  of  FIG. 15  of the spatula-like portion of the epithelial separator of  FIG. 14 ; 
       FIG. 17  is a front elevational view taken generally along lines  17 — 17  of  FIG. 15  of the distal tip of the epithelial separator of the present invention shown in  FIG. 14 ; 
       FIG. 18  is a perspective view of a further embodiment of an epithelial separator used in the practice of the present method; 
       FIG. 19  is a side elevational view of the spatula-like portion of the epithelial separator shown in  FIG. 18 ; 
       FIG. 20  is a sectional view taken generally along sectional lines  20 — 20  of  FIG. 19  of the spatula-like portion of the epithelial separator shown in  FIG. 18 ; 
       FIG. 21  is a front elevational view taken generally along lines  21 — 21  of  FIG. 19  of the distal tip of the spatula-like portion of the epithelial separator of  FIG. 18 ; 
       FIG. 22  is a perspective view of a further embodiment of an epithelial separator used in the practice of the present method; 
       FIG. 23  is a side elevational view of the spatula-like portion of the epithelial separator of  FIG. 22 ; 
       FIG. 24  is a sectional view taken generally along sectional lines  24 — 24  of  FIG. 23  of the spatula-like portion of the separator shown in  FIG. 22 ; and 
       FIG. 25  is a front elevational front view taken generally along lines  25 — 25  of  FIG. 23  of the distal tip of the spatula-like portion of the epithelial separator of  FIG. 22 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present method for reforming the corneal surface of the mammalian eye has advantages of LASIK surgery while avoiding the disadvantages of PRK surgery. The present method is termed LASEK. Briefly, in practicing LASEK a gossamer thin sheet of no more than about 85 microns of the corneal epithelium is lifted from the corneal surface to permit corneal reformation of the underlying epithelium and is then replaced. The present method permits rapid recovery like LASIK. With the present method, the corneal bed is mostly maintained which prevents thickening or other indications of trauma. Another advantage of the present invention is that, unlike PRK, the eye is not treated with harsh chemicals that are used in PRK to remove the corneal epithelium and long recovery periods are avoided. Again, by reducing the cornea&#39;s exposure to irritants, damage to the cornea is avoided and recovery time is enhanced. 
   Referring to  FIGS. 1   a – 1   g , a block diagram of the present method is illustrated together with pictorial representations of steps of the present method. At step  10 , a full or partial thickness epithelial cut  12  is made in the epithelial layer  14  of cornea  16  of an eye. This incision  12  is no deeper than about 85 microns. The incision  12  forms a sheet  18  ( FIG. 1   f ) that can be lifted from the underlying Bowman&#39;s Membrane  20 . The area  22  of the cornea  16  and surrounding area that remains attached to the underlying corneal epithelium  14  is termed the “hinged region” as this region functionally serves as a hinge whereby the sheet  18  is maintained attached to the epithelium  14 . In a preferred embodiment of the invention, a curved, “C”-shaped, partial or full depth epithelial incision  12  is made to form an arc of between about 250 and 330 degrees. This incision  12  is preferably made using a guarded trephine, to be subsequently described with respect to  FIG. 2  which may be vibrated at step  24 . An example of a trephine is illustrated in  FIG. 2  for making an incision  12  of about 300 degrees. The incision  12  can alternatively be made by a variety of surgical tools such as a scalpel or knife. 
   In step  26 , an incision  28  using a scalpel or similar cutting instrument, preferably with a rounded blade, is made near the hinge  22  of the partial thickness epithelial cut  12 . This incision  28  is about 1 to about 2 millimeters long and is sufficiently deep to reach the corneal bed, stromal layer, or Bowman&#39;s Membrane  20  and is about 1 to about 2 millimeters long. A cutting instrument  30   a  for performing step  26  is illustrated in  FIG. 3   a . Cut  28  may be made using a fluid  38  expelled from the tip of instrument  30   a.    
   In step  32  of the present invention, the epithelial cells are stiffened by adding several drops of sodium chloride in a concentration ranging from about 3% to about 7% (such as Muro  128 ) for 10 seconds followed by rinsing with buffered saline solution. Stiffening of the epithelial cells makes them easier to handle. 
   After the incision  28  is made in step  26 , the epithelium layers remain firmly affixed to each other. To separate the corneal epithelium from the underlying epithelium an epithelial separator, such as instrument  30   b , is inserted under the layer  14  near its hinge region  22  at step  34  ( FIG. 1   c ). This insertion is done by entering the incision  28  made in step  26  and is preferably done by applying suction to the eye and using an epithelial separator  30   b  which may vibrate. Suction should last for no longer than about 45 seconds and, if necessary, should only be tried a second time after about 15 seconds has elapsed since the first attempt. Suction may not be necessary, however, when vibration is used at step  36 . Instead of using an epithelial separator, a cannula capable of ejecting media  38  may be used to enter the incision  28  created at step  26 . A more detailed description instruments  30   a–c  and manners of use are described in more detail below. An epithelial separator is contemplated to be no greater than about one-half millimeter in diameter which permits its entry under the epithelium without tearing what will become the sheet. The epithelial separator is inserted parallel to hinge  22  connecting the ends of the incision line or lines, whereby hinge  22  substantially marks the attachment boundary or hinge  22  of the sheet  18  after the epithelium  14  is lifted. 
   Once the epithelial separator  30   b  is inserted at or near the hinge region, the separator  30   b  is slid away from the hinge region  22  while being held substantially perpendicularly to the direction of movement and parallel to the uncut line at step  40  ( FIG. 1   d ). During step  40  the epithelial layers are teased apart by a gentle sawing, “window washing” motion. Alternatively, a cannula having an internal cavity and having one side having a plurality of apertures is contemplated whereby a medium such as gel, liquid, or gas (including air)  38 , hereinafter collectively referred to by the term “fluid”, can be used to tease the epithelial layers apart and to raise the epithelial layer. A more detailed description of this embodiment of the cannula will be also discussed below. 
   After the epithelial separator or cannula  30   b  is slid along under the corneal surface within the incision area created by cut  12  the epithelium layers are separated to form sheet  18  at step  42 . If the corneal area to be altered is relatively large, the sheet  18  may be bisected ( FIG. 1   e ) by making an incision  44  in the epithelium sheet to form two halves  18   a  and  18   b , or leafs, which may be more easily moved out of the ablation zone. Additional leafs may be created depending on the size of the corneal area to be altered. 
   At step  46 , the sheet  18  is lifted from the underlying surface to expose the Bowman&#39;s Membrane  20  or bare stoma in a re-treatment case and the corneal bed is ablated or altered by any of a variety of methods commonly known to one of ordinary skill in the art such as by excimer laser and refractive technology. 
   After ablating the corneal bed, as needed the sheet  18  is replaced over the underlying cornea at step  48  ( FIG. 1   g ) using an instrument  30   c  to refloat sheet  18  back into position. An instrument  30   c  is subsequently described with respect to  FIGS. 14–25 . 
   Several instruments are used in the practice of the present invention. To make the initial incision  12  (step  10 ,  FIG. 1   b ) a guarded trephine is preferable such as the one shown in  FIG. 2 . Guarded trephine generally identified by the numeral  50  includes a cutting member  52 , a shaft  54 , and a handle  56 . Cutting member  52  is shown in greater detail in  FIGS. 3–5 . Cutting member  52  includes a support band  58 , a cutting band  60 , cutting teeth  62 , spaced apart by gaps  64 , an outer surface  66 , an inner surface  68 , and an edge  70 . Cutting teeth  62  may protrude, for example, from cutting band  60  along the innermost about 90 microns leaving the remaining thickness of the outer surface  66  of cutting band  60  to form edge  70 . Cutting teeth  62  cut from about 250 to about 330 degrees along the circular cutting band  60  to form hinge region  22  ( FIG. 1   b ), or an uncut arc of the epithelium, of about 110 to about 30 degrees.  FIG. 4  illustrates trephine  50  for forming an uncut arc or hinge of about 60 degrees.  FIG. 5  is a cross-sectional view of cutting member  52  through the a gap  64  along sectional lines  5 — 5  in  FIG. 3 . Shown is inner surface  68 , bottom edge  70 , and beveled edge  72  of outer surface  66 . In a preferred embodiment, beveled edge  72  is angled towards inner surface  68  at about 30 degrees. Additionally, cutting band  60  may include a continuous cutting surface in which gaps  64  have been eliminated. 
   In a preferred embodiment of trephine  50 , cutting member  52  is connected to a vibration source  73 . Vibration source  73  may comprise, for example, a mechanical vibrator on an ultra sound vibration source. Vibration is in the range of 20 kHz to 200 kHz. As noted above, the incision made by trephine  50 , if approximately circular, and is about 250 to 330 degrees. Trephines for creating cuts of other dimensions are acceptable so long as the cut is partial to leave an area of attachment between the corneal epithelium its surrounding epithelium to form the hinge  22  ( FIG. 1   b ). 
   To accomplish steps  34  and  40  ( FIG. 1   a ), the separation of the corneal surface epithelium from the underlying cornea several embodiments of a cannula as described above may be used with the present method and are shown generally in  FIGS. 6–13 . The present cannula is hollow and is in fluid communication with a connector that can be received by a standard syringe which may contain a variety of fluid usable to separate the epithelial layers. One embodiment of a cannulas connected to a syringe, generally identified by the numeral  74 , or other pumping systems providing a fluid source is shown in  FIG. 6 . Syringe  74  includes a cannula  76 , a connector  78 , and a syringe body  80 , which further includes a plunger  82 . Cannula  76  includes a proximal end  84 , a distal section  86 , a distal tip  88 , a contact surface  90 , an upper surface  91 , and a plurality of apertures  92  as shown in  FIG. 7 . The length of the cannula  76  may range from about 10 millimeters to about 15 millimeters. Apertures  92  are disposed on one lateral surface, relative to contact surface  90  and upper surface  91  of distal section  86  of cannula  76 . Preferably, 15 to 25 apertures  92  are utilized for ejection of syringe media. Distal section  86  includes a channel  93  in fluid communication with apertures  92  and syringe body  80  for delivery of fluid to apertures  92 . The diameters of apertures  92  range from about 0.05 to about 0.10 millimeter and are spaced about 0.4 millimeter apart along the side of cannula  76 . The radius of curvature of cannula  76  is contemplated to range from about 8 millimeters to about 12 millimeters. Distal tip  88  is preferably tapered as shown in  FIG. 9  to allow cannula  76  to enter under the epithelium after an incision  28  is made as shown in  FIG. 1   c . During separation of the epithelial sheet, the syringe plunger  82  may be depressed to eject various media through the plurality of apertures  92  as mentioned above such as air, gel, liquid, to aid in the separation of the epithelial sheet. Distal tip  88  may also include an aperture as illustrated in  FIG. 1   b  for expelling media to create cut  28  in which case cannula  76  will have no apertures  92 . 
   Various embodiments of distal section  86  include multiple cross-sectional geometries; such as, for example, circular, trapezoidal, and oval as shown in  FIGS. 8–13 .  FIG. 8  illustrates a circular embodiment. 
   An embodiment of a trapezoidal geometry of the present cannula is shown in  FIGS. 10 and 11 . A trapezoidal cannula, generally identified by the numeral  94 , includes a proximal end  96 , a distal section  98 , a distal tip  100 , a contact surface  102 , an upper surface  104 , a plurality of apertures  106 , sides  108   a  and  108   b , and a channel  110 . The width of upper surface  104 , for example, in the range from about 0.5 millimeters to about 1.0 millimeters and the width of contact surface  102  to range from 0.75 millimeter to about 1.25 millimeter. The height of the trapezoid, i.e. the distance between contact surface  102  and upper surface  104  is to range from about 0.25 millimeters to about 0.5 millimeters. The length of the cannula  94  may range from about 10 millimeters to about 15 millimeters. The plurality of apertures  106  are disposed on one lateral surface, relative to contact surface  102 , of distal section  98  of cannula  94 . Preferably, 15 to 25 apertures  106  are utilized for ejection of syringe media. The diameter of apertures  106  ranges from about 0.05 to about 0.10 millimeter and are spaced about 0.4 millimeter apart along the side  108   a  of cannula  94 . The radius of curvature of cannula  94  is contemplated to range from about 8 millimeters to about 12 millimeters. Proximal end  84  is oriented with respect to distal section  86  to form a vertical angle that is in the range of about 40 degrees to about 60 degrees. 
   An embodiment of an oval geometry of the present cannula is shown in  FIGS. 12 and 13 . An oval cannula generally identified by the numeral  112  includes a proximal end  114 , a distal section  116 , a distal tip  118 , a contact surface  120 , an upper surface  122 , a plurality of apertures  124 , and a channel  126 . The short axis of the oval ranges in length from about 0.27 millimeters to about 0.5 millimeters and the long axis ranges in length from about 0.75 millimeters to about 1.25 millimeters. During use the short axis is perpendicular to the corneal surface. The length of oval cannula  112  ranges, for example, from about 10 millimeters to about 15 millimeters. The plurality of apertures  124  are disposed on one lateral surface, relative to contact surface  120 , of distal section  116  of cannula  112 . Preferably, 15 to 25 apertures  124  are utilized for ejection of syringe media. The diameter of apertures  124  ranges from about 0.05 to about 0.10 millimeter and are spaced about 0.4 millimeter apart along the side of cannula  112 . The radius of curvature of cannula  112 , for example, in the range from about 8 millimeters to about 12 millimeters. Proximal end  114  is oriented with respect to distal section  116  to form a vertical angle that is in the range of about 40 degrees to about 60 degrees. 
   To accomplish step  40  ( FIG. 1   a ), the separation of the corneal surface epithelium from the underlying epithelium, several embodiments of an epithelial separator as described above may be used with the present method, and are shown generally in  FIGS. 14–25 . An epithelial separator, generally identified by the numeral  128 , includes a slender spatula-like portion  130  connected to a handle  132  by a shaft  134 . Shaft  134  is oriented with respect to spatula-like portion  130  so that a vertical angle is formed that ranges from about 40 to about 60 degrees. 
   Spatula-like portion  130  includes a proximal end  136 , a distal section  138 , a distal tip  140 , a contact surface  142 , and an upper surface  144 . The height of the spatula-like portion  130  is no greater than about 0.5 millimeter and is preferably less than 0.4 millimeter. Various embodiments of distal section  138  include various cross-sectional geometries such as, for example, circular, triangular, and oval, as shown in  FIGS. 16–25 . A circular embodiment of spatula-like portion  130  is shown in  FIG. 16 . The circular embodiment of the spatula-like portion has a length between about 10 millimeters to about 15 millimeters and has a radius of curvature of about 8 millimeters to about 12 millimeters. Distal tip  106  is preferably tapered as shown in  FIG. 17  to form a leading edge that can enter under the incision into the epithelium in order to separate the epithelium from the corneal bed. Proximal end  136  is oriented with respect to distal section  138  to form a vertical angle that is in the range of about 40 degrees to about 60 degrees. 
   Another embodiment of a separator  128  is shown in  FIGS. 18–21 . A spatula-like portion  146  includes a proximal end  148 , a distal section  150 , a distal tip  152 , a contact surface  154 , and an upper surface  156 . Spatula-like portion  146  includes a triangular cross-sectional shape and is shown in  FIG. 20 , which is a section through sectional lines  20 — 20  of  FIG. 19 . Spatula-like portion  146  is triangular in cross-section having a height, generally, of no more than about 0.5 millimeter, and a base of about 1 millimeter, and with the base angles being acute and equal, each preferably less than about 30 degrees. The base, in reference to the triangular cross-section, lies substantially adjacent to the underlying cornea during separation of the epithelium from the corneal bed. The triangular embodiment of the spatula-like portion  146  has a length between about 10 millimeters to about 15 millimeters having a radius of curvature of about 10 millimeters to about 40 millimeters. Shown in  FIG. 21 , distal tip  152  of the triangular embodiment tapers to contact surface  154  to form leading edge  158 . The tip  152  of the spatula-like portion  146  is preferably angled having a chisel-like appearance so that the height of the spatula-like portion  146  tapers forward to the base to form leading edge  158  that has a narrower profile than the rearward section of the spatula. Such leading zone permits the spatula-like portion  146  to be inserted between the layers so that the rest of the spatula  146  can further separate the epithelial layers as the spatula-like portion  146  is moved further under the sheet of epithelium. Proximal end  148  is oriented with respect to distal section  150  to form a vertical angle that is in the range of about 40 degrees to about 60 degrees. 
   Another embodiment of a separator  128  is shown in  FIGS. 22–25 . A spatula-like portion  160  includes a proximal end  162 , a distal section  164 , a distal tip  166 , a contact surface  168 , and an upper surface  170 . Spatula-like portion  160  is shown in  FIG. 24 , which is a section through sectional lines  24 — 24  of  FIG. 23 . In the oval embodiment of spatula-like portion  160  the short-axis ranges in length from about 0.27 millimeters to about 0.5 millimeters and the long-axis ranges in length from about 0.75 millimeters to about 1.25 millimeters. The short axis is perpendicular to contact surface  168  and the long-axis is parallel to the contact surface  168 . As shown in  FIG. 25 , distal tip  166  tapers to form leading edge  172  so that the leading edge may enter into under the epithelium and be used to separate the epithelium from the underlying corneal bed. Proximal end  162  is oriented with respect to distal section  164  to form a vertical angle that is in the range of about 40 degrees to about 60 degrees. 
   Therefore, it can be seen that the present invention provides for a method and surgical instruments for creating and lifting a sheet of epithelium without killing the tissue or exposing the cornea and eye to dangerous toxins. 
   Whereas it is intended that the description of the present invention includes several embodiments for implementing the invention. Variations in the description likely to be conceived by those skilled in the art still fall within the breadth and scope of the disclosure of the present invention. It is also understood that additional applications of the present invention will be apparent to those skilled in the art upon a reading of the description and a consideration of the appended claims and drawings.