Abstract:
An apparatus for forming a corneal flap includes a housing from which extend a shaft and a reciprocating member. An aplanating member is mounted at a distal end of the shaft to aplanate a region of the cornea. A cutting blade is mounted to the reciprocating member at a position selected to slice the aplanated region off the cornea.

Description:
FIELD OF INVENTION 
     This invention relates to ophthalmic surgery, and in particular, to surgery on the cornea. 
     BACKGROUND 
     The cornea of the eye plays a role in focusing light. By changing the shape of the cornea, it is possible to correct a patient&#39;s vision. Common surgical procedures for changing the shape of the cornea include temporarily removing the epithelium of the cornea to expose the underlying stroma, ablating selected portions of the stroma with a laser, and replacing the epithelium over the stroma. 
     In LASEK (“Laser assisted Sub Epithelial Keratomilieusis”) surgery, an incision along a circular arc on the cornea is made and the resulting flap is pulled back to expose the stroma of the cornea. The flap includes the epithelium and the Bowman&#39;s membrane separating the epithelium from the stroma. Unlike the flap that is made during LASIK (“Laser assisted In situ Keratomilieusis”), this flap does not include any portion of the stroma. Thus, when the flap is pulled back, it is the surface of the stroma, and not the interior of the stroma, that is exposed to the laser. This procedure thus results in a lower risk of complications. 
     In practice, because the epithelium is so thin, it is difficult to cut a flap without also cutting into the stroma. 
     SUMMARY 
     In one aspect, the invention includes an apparatus for forming a corneal flap. The apparatus includes a housing from which a shaft and a reciprocating member extend. At the distal end of the shaft is mounted an aplanating member for aplanating a region of the cornea. At the distal end of the reciprocating member is mounted a cutting blade for slicing an aplanated region of the cornea. 
     In some embodiments, the aplanating member is a roller, while in other embodiments, the aplanating member is a runner. 
     The cutting blade can be a wire, a knife, or any other structure configured to slice into the cornea. 
     In some embodiments, the aplanating member and the cutting blade are offset by an amount corresponding to a desired thickness of the flap. The aplanatihg member can be offset from the cutting member in either the proximal or distal direction. 
     Another aspect of the invention is an apparatus in which a forked end of a shaft defines a gap. An aplanating member, for aplanating a region of the cornea, extends across this gap. The apparatus also includes a reciprocating member having a distal tip formed into a bow. A cutting blade extends across this bow and is disposed to slice the aplanated region off the cornea. 
     In another aspect, the invention provides a method for forming a corneal flap by aplanating a region of the cornea and placing a reciprocating cutting blade on the aplanated region. The flap is then formed by translating the cutting blade across the aplanated region. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
    
    
     These and other features and advantages of the invention will be apparent from the following detailed description and the accompanying figures, in which: 
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 shows a surgical instrument incorporating the invention; 
     FIG. 2 shows the distal tip of the surgical instrument shown in FIG. 1; 
     FIG. 3 shows the surgical instrument slicing into the cornea; and 
     FIG. 4 shows an alternative embodiment of the surgical instrument. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a surgical instrument  10  for cutting a flap  11  in the cornea  12  includes a housing  13  that encloses a motor  14 . Also within the housing  13  is a power supply  16 , such as a battery, for providing power to the reciprocating motor  14 . A stationary shaft  18  extends distally from the housing  13  to a cutting tip  20  disposed at a distal end thereof. 
     At its distal end, the shaft  18  bifurcates into two prongs  22 A-B separated by a gap  24 . An aplanating member  26 , best seen in FIG.  2 . extends between the prongs  22 A-B and across the gap  24 . In the illustrated embodiment, the aplanating member  26  includes a roller  30  mounted to rotate about an axle  32  that extends across the gap  24 . The coupling between the roller  30  and the axle  32  has a coefficient of rolling friction that is low enough to enable it to roll as it is dragged across the cornea  12 . The aplanating member  26  can also be a stationary rod or runner having a cross section that includes a curved contact surface for sliding across the cornea  12 . The aplanating member  26  is preferably made from a biocompatible material having a low coefficient of sliding friction. 
     The cutting tip  20  includes a bow  28  mounted at the distal tip of a reciprocating member  33 . The motor  14  is coupled to the reciprocating member  33  so as to cause the bow  28  to move from side to side in a direction parallel or essentially parallel to the aplanating member  26 . In some embodiments, the motor  14  is coupled so as to cause the bow  28  to undergo orbital motion by moving along an elliptical path having a major axis parallel to the aplanating member  26 . 
     A cutting blade  35 , which can be a wire or a knife, extends across the opening of the bow  28  in a direction parallel to the aplanating member  26 . Referring to FIG. 3, the cutting blade  35  lies in a cutting plane that is vertically offset from a plane defined by the two prongs  22 A-B. The extent of this vertical offset  34  controls the thickness of the flap  11 . The cutting blade  35  is also horizontally offset from the aplanating member  26  either distally or proximally. The extent of this horizontal offset  36  is selected such that the surface of the cornea  12  that is exposed to the cutting blade  35  remains essentially flat even though it no longer lies under the aplanating member  26 . 
     As shown in FIG. 3, the aplanating member  26  is placed on the cornea  12  to flatten the cornea  12  in a region exposed to the reciprocating cutting blade  35 . The surgeon then translates the surgical instrument  10 . In the case in which the cutting blade  35  lies proximal to the roller  30 , the surgeon translates the surgical instrument  10  distally. Conversely, when the cutting blade  35  lies distal to the roller  30 , the surgeon translates the surgical instrument  10  proximally. In either case, the direction of motion is selected so that the cutting blade  35  slices into a portion of the cornea  12  that has recently been flattened, or aplanated, by the aplanating member  26 . 
     In another embodiment, shown in FIG. 4, an additional bow  38  is mounted onto or integrally formed with the reciprocating member  33  proximal to the cutting blade  35 . A lifting rod  40  extends across the additional bow  38  to support the flap that is sliced by the cutting blade  35 . Because the lifting rod  40  reciprocates with the reciprocating member  33 , the flap is unlikely to adhere to the lifting rod  40  during surgery. 
     Using a surgical instrument  10  as described herein, a surgeon can rapidly slice a flap  11  having a uniform and pre-defined thickness. By appropriately selecting the vertical offset  34  between the cutting blade  35  and the aplanating member  26 , the flap  11  can be sliced thinly enough to avoid exposing the stroma.