Abstract:
A method of corneal laser surgery is disclosed. A first periphery is defined at an anterior surface of the cornea. This first periphery bounds a first planar area. A second periphery is defined within stromal tissue of the cornea. This second periphery bounds a second planar area. The second planar area is sized differently than the first planar area. A layer of stromal tissue which is bounded by the second periphery is subsequently incised. Stromal tissue between substantial portions of the first periphery and the second periphery is also incised, such that at least some corneal tissue disposed between the first and second peripheries remains connected to corneal tissue outside of the first and second peripheries.

Description:
Priority is claimed as a continuation to U.S. Ser. No. 09/536,861, filed Mar. 27, 2000, now abandoned, which claims priority as a continuation-in-part to U.S. Pat. No. 6,110,166, issued on Aug. 29, 2000 from application Ser. No. 08/725,070, filed Oct. 2, 1996, which claims priority as a continuation-in-part to U.S. application Ser. No. 08/407,508, filed Mar. 20, 1995, now abandoned. The disclosures of each of the aforementioned priority documents is incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains generally to ophthalmic surgery which is useful for correcting vision deficiencies. More particularly, the present invention pertains to methods which surgically correct the vision of a patient by removing portions of the stroma to reshape the cornea. The present invention is particularly, but not exclusively useful as a method for correcting the vision of a patient by lifting a contoured corneal flap created by a laser beam to expose a bed of stromal tissue, photoaltering the exposed bed of stromal tissue in a predetermined manner and subsequently repositioning the flap. 
     BACKGROUND OF THE INVENTION 
     Vision impairments such as myopia (i.e. near-sightedness), hyperopia (i.e. far-sightedness) and astigmatism can be corrected using eyeglasses or contact lenses. Alternatively, the cornea of the eye can be reshaped surgically to provide the needed optical correction. For example, it is known that if part of the cornea is removed, the pressure exerted on the cornea by the aqueous humor in the anterior chamber of the eye will act to close the void created in the cornea, resulting in a reshaped cornea. By properly selecting the size, shape and location of a corneal void, the desired shape, and hence optical properties of the cornea can be obtained. 
     One procedure employed to reshape the cornea is to remove portions of the anterior portion of the cornea. For example, see U.S. Pat. No. 4,665,913 which issued to L&#39;Esperance for an invention entitled “Method for Ophthalmological Surgery,” and U.S. Pat. No. 4,669,466 which issued to L&#39;Esperance for an invention entitled “Method and Apparatus for Analysis and Correction of Abnormal Refractive Errors of the Eye.” Another procedure used to reshape the cornea removes and reshapes subsurface tissue such as stromal tissue. As an example of such a procedure, U.S. Pat. No. 4,907,586, which issued to Bille et al. for an invention entitled “Method for Reshaping the Eye,” discloses an intrastromal photoalteration technique for reshaping the cornea. Importantly for the purposes of the present invention, the above cited Bille patent discloses the use of a pulsed laser beam for photoalteration of intrastromal tissue. As disclosed by Bille, the pulsed laser beam penetrates corneal tissue and is focused at a point below the surface of the cornea to photoalter stromal tissue at the focal point. The ability to reach a subsurface location without necessarily providing a physical pathway allows for great flexibility in corneal reshapings and can reduce the total amount of tissue disruption required for a particular corneal reshaping. Further, as the prescribed corneal void shape becomes more complex and precise, the need to access subsurface tissue without a physical pathway becomes more important. 
     Recently developed so-called LASIK procedures incise the anterior portion of the cornea using a microkerotome to create a flap. It should be recognized that a microkeratome is a mechanical device that uses an automated blade to create a flap. Once created, the flap can be temporarily lifted for photoalteration of the exposed stroma. This procedure, like the procedure disclosed in Bille et al. &#39;586, has as its objective the removal of only stromal tissue with the consequent preservation of anterior corneal tissue. As discussed above, the LASIK procedure relies on a physically prepared pathway, and hence is limited to simple flap configurations. In contrast with the simple flap configurations which can be prepared using a microkerotome, the procedure of the present invention recognizes that a pulsed laser beam can be focused below the surface to create complex flap designs. 
     In light of the above, it is an object of the present invention to provide a method for corneal laser surgery that corrects the refractive characteristics of the cornea by removing only stromal tissue and minimizes the total amount of tissue undergoing photoalteration. Another object of the present invention is to provide a method for corneal laser surgery which creates a corneal flap having a complex peripheral edge such as a peripheral edge which can be repositioned in an interlocking relationship with undisturbed corneal tissue to hold the corneal flap in place during subsequent healing, or a peripheral edge that incorporates a tab to assist in lifting and repositioning the corneal flap. Still another object of the present invention is to provide a method for corneal laser surgery which creates a corneal flap that can be lifted to expose and then photoalter a bed of stromal tissue that has a complex shape, such as a convex, concave or irregularly shaped bed. Yet another object of the present invention is to provide a method for corneal laser surgery which is relatively easy to practice and comparatively cost effective. 
     SUMMARY OF THE PREFERRED EMBODIMENTS 
     In accordance with the present invention, a method for corneal laser surgery includes the step of first prescribing the size, shape and location of stromal tissue which needs to be removed in order to correct the vision deficiency of a patient. This volume of stromal tissue which is to be removed is generally in the form of a lentoid that is defined by an anterior surface and a posterior surface and may contain an annular surface. In general, the surfaces of the lentoid can be either plane, convex, concave or irregular. In the method of the present invention, a contoured corneal flap having an interior surface and a peripheral edge is created wherein the interior surface of the flap is shaped to conform to the anterior surface of the prescribed lentoid. 
     To create the contoured corneal flap, a pulsed laser beam is focused to a preselected start point within the stromal tissue. In accordance with preplanned procedures, the focal point will be located on the intended interior surface of the flap. The focal point is then moved within the stromal tissue to cut (photoalter) a layer of tissue having the desired contour of the interior surface of the flap (and hence the anterior surface of the prescribed lentoid). Next, the focal point is moved within the cornea to create a peripheral edge for the flap. In this case, the peripheral edge of the flap is a surface that extends from the perimeter of the interior surface of the flap to the anterior surface of the cornea. In the preferred embodiment of the present invention, the peripheral edge may incorporate features which allow the flap to interlock with the cornea when the flap is repositioned. Further, the peripheral edge of the flap may be formed with a tab to assist in lifting and repositioning the flap. Still further, the border of the anterior surface of the flap and the perimeter of the interior surface of the flap, both of which lie on the peripheral edge, are generally curvilinear, but are not closed curves. Rather, the flap is formed with a hinge of corneal tissue which allows for flap rotation about the hinge during lifting and repositioning of the flap relative to the cornea. 
     Once created, the contoured corneal flap can be lifted to expose a bed of intrastromal tissue. Next, an excimer laser can be used to photoalter the bed of intrastromal tissue in a predetermined manner, thus creating the posterior surface of the prescribed lentoid. Finally, the flap having a contoured inner surface that defines the anterior surface of the lentoid, can be repositioned over the newly created void and allowed to heal. The result is a reshaped cornea that effectively corrects a patient&#39;s vision deficiency. As envisioned for the present invention, lasers may be used for plasma mediated tissue ablation (generally superficial tissue) and for plasma mediated tissue disruption (generally internal bulk tissue). Accordingly, the term photoalteration will be used herein to indicate an operation wherein there may be either plasma mediated tissue ablation or plasma mediated tissue disruption. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a perspective view of a patient being treated with a pulsed/excimer laser in accordance with the method of the present invention; 
         FIG. 2  is a perspective view of an eye; 
         FIG. 3  is a cross sectional view of a portion of the cornea of the eye as seen along the line  3 - 3  in  FIG. 2  showing the anatomical layers of the cornea and a representative lentoid; 
         FIG. 4  is a plan view of the cornea after the incision of a flap; 
         FIG. 5A  is a cross-sectional view of a cornea as seen along the line  5 - 5  in  FIG. 4 , showing a flap incision for a flap having a concave interior surface; 
         FIG. 5B  is a cross-sectional view of a cornea as in  FIG. 5A , showing the cornea after the incision and lifting of a flap having a concave interior surface; 
         FIG. 5C  is a cross-sectional view of a cornea as in  FIG. 5B  showing the cornea prior to photoalteration of the exposed bed, and showing the posterior and annular surfaces of the lentoid in phantom. 
         FIG. 5D  is a cross-sectional view of a cornea as in  FIG. 5C  showing the cornea after photoalteration of the exposed bed of stromal tissue; 
         FIG. 5E  is a cross-sectional view of a cornea as in  FIG. 5D  showing the cornea after the removal of a lentoid of stromal tissue from the exposed bed of stromal tissue by photoalteration, and replacement of the flap; 
         FIG. 5F  is a cross-sectional view of a cornea as in  FIG. 5E  showing the reshaped cornea after removal of a lentoid of stromal tissue; 
         FIG. 6A  is a cross-sectional view of a cornea as in  FIG. 5A  showing the cornea after the incision of a flap having a convex interior surface; 
         FIG. 6B  is a cross-sectional view of a cornea as in  FIG. 6A  showing the cornea after the incision and lifting of a flap having a convex interior surface; 
         FIG. 7  is a plan view of a cornea after the incision of an oval flap; 
         FIG. 8  is a plan view of a cornea after the incision of an elongated flap; 
         FIG. 9  is a plan view of a cornea after the incision of a flap having a tab; 
         FIG. 10A  is a cross-sectional view of a cornea as seen along the line  10 - 10  in  FIG. 9 , showing a flap having an integral tab to assist in lifting and repositioning the flap; 
         FIG. 10B  is a cross-sectional view of a cornea as in  FIG. 10   a , showing the cornea after the incision and lifting of a flap having a tab; 
         FIG. 11  is a plan view of a cornea after the incision of a flap having an interlocking feature; and 
         FIG. 12  is a plan view of a cornea after the incision of a flap having a beveled peripheral edge with an acute angle between the peripheral edge and the interior surface of the flap. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIG. 1 , an apparatus  10  for alternately generating either a pulsed laser beam  12  or an excimer laser beam  13  is shown. As hereinafter disclosed in the specification and in  FIG. 1 , the combined numerals  12 / 13  will refer respectively to either the pulsed laser beam  12  or the excimer laser beam  13 . As contemplated for the present invention, the apparatus  10  will use both laser beams  12 / 13 . Specifically, a pulsed laser beam  12  will first be used to create a flap of corneal tissue and the excimer laser beam  13  will then be used to remove corneal tissue below the flap. It will be appreciated by the skilled artisan that in lieu of an excimer laser, a pulsed infrared laser beam or a visible pulsed laser beam may be used to remove corneal tissue below the flap. 
     In detail,  FIG. 1  shows the pulsed laser beam  12  being directed onto the eye  14  of a patient  16 . For purposes of the present invention, a pulsed laser beam  12  preferably has the physical characteristics similar to those of the pulsed laser beams generated by a laser system as disclosed and claimed in U.S. Pat. No. 4,764,930, which issued to Josef F. Bille et al. for an invention entitled “Multiwavelength Laser Source.” Furthermore, the present invention contemplates the use of a pulsed laser beam  12  which has pulses with durations as long as a few nanoseconds or as short as only a few femtoseconds. The pulsed laser beam  12  has a fluence of less than 100 joules per square centimeter. Also, as indicated above, the apparatus  10  will generate, a second type of laser beam; namely, an excimer laser beam  13 . 
       FIG. 2  shows the anatomical structure of the human eye  14  including the cornea  18 , the pupil  20 , the iris  22 , and the sclera  24 . In  FIG. 3  it can be seen that the cornea  18  includes five anatomically definable layers of tissue. Going in a direction from anterior to posterior in  FIG. 3 , the tissue layers of the cornea  18  are: the epithelium  26 , Bowman&#39;s membrane  28 , the stroma  30 , Decemet&#39;s membrane  32  and the endothelium  34 . Of these, the stroma  30  is of most importance for the present invention as it contains the only tissue which is to be removed for correction of the patient&#39;s vision. Also shown in  FIG. 3 , the anterior chamber  35  is a cavity filled with aqueous humor  37 . The pressure exerted by in the aqueous humor  37  maintains the shape of the cornea  18 . 
     As indicated above, it is known that the correction of myopic, hyperopic and astigmatic conditions can be accomplished by the removal of a predetermined volume of stromal tissue  30 . Further, the particular volume of stromal tissue  30  to be removed for the prescribed optical correction will depend on the amount and type of correction required and will generally be a lens shaped volume (a lentoid)  36 . An example of a lentoid volume  36  is shown in cross-section in  FIG. 3 . As shown, it is to also be appreciated that the lentoid volume  36  will be defined by an anterior surface  38 , a posterior surface  40  and may have a annular surface  39 . 
     In accordance with the methods of the present invention, access to the prescribed lentoid volume  36  is accomplished by using a pulsed laser beam  12  to create a contoured corneal flap  42 . By cross-referencing  FIGS. 4 ,  5 A and  5 B, it can be seen that the contoured flap  42  has an interior surface  44  and a peripheral edge  46 . A pulsed laser beam  12  is used to create the contoured flap  42  by focusing the pulsed laser beam  12  at a point within the stromal tissue  30  and moving the focal point of the pulsed laser beam  12  within the stromal tissue  30  to cut a subsurface layer  48 . Layer  48  is an interface between the interior surface  44  of flap  42  and the bed  50  of stromal tissue  30 , and as such, layer  48  has a shape conforming to the prescribed shape of the interior surface  44  of the flap  42 . 
     Next, the peripheral edge  46  for the flap  42  is created. To create the peripheral edge  46 , the pulsed laser beam  12  is focused at a point within the stromal tissue  30  and on the boundary  52  of the bed  50 . Then, the focal point of the pulsed laser beam  12  is moved within the stromal  30  to cut a layer  54 . Layer  54  extends from the boundary  52  of bed  50  to the anterior surface  56  of the cornea  18 . Layer  54  is an interface between the peripheral edge  46  of the flap  42  and the wall  58  that surrounds the bed  50 . The points where the peripheral edge  46  of the flap  42  intersects the anterior surface  56  of the cornea  18  is the anterior border  60 , and is shown in both  FIG. 4  and  FIG. 5B . Both the anterior border  60  and the boundary  52  of bed  50  may be curvilinear, but are not necessarily closed curves. Rather, in the preferred embodiment of the present invention, both the boundary  52 , and the anterior border  60  terminate within the stroma  30  to create a hinge  62  of stromal tissue  30  for flap  42 . Hinge  62  allows the flap  42  to be lifted while continuing to be attached to the remaining cornea  18 . 
     Once the flap  42  is created, the flap  42  can be lifted by rotating the flap  42  about the hinge  62  to expose the bed  50  of stromal tissue  30 . The contour of the exposed bed  50  as well as the contour of the interior surface  44  of the flap  42  will conform to the layer  48  cut into the stromal tissue  30  by the pulsed laser beam  12 . As shown in  FIGS. 5C and 5D , after the flap  42  has been lifted and the bed  50  of stromal tissue  30  is exposed, a pulsed laser beam  12  or an excimer laser beam  13  can be used to photoalter a portion or all of the bed  50  in a predetermined manner until the posterior bed surface  64  of stromal tissue  30  is reached. The shape of the posterior bed  64  can be selectively contoured using the laser beam  12 , 13  to conform to the prescribed shape of the posterior surface  40  of the prescribed lentoid  36 , as shown in  FIG. 5E . As indicated earlier, lasers may be used for plasma mediated tissue ablation (generally superficial tissue) and for plasma mediated tissue disruption (generally internal bulk tissue). Accordingly, the term photoalteration will be used herein to indicate an operation wherein there may be either plasma mediated tissue ablation or plasma mediated tissue disruption. 
     As further shown by cross-referencing  FIGS. 5D and 5E , after the photoalteration of the prescribed lentoid  36  volume by either an excimer laser beam  13  or a pulsed laser beam  12  is complete, the contoured flap  42  can be reengaged with the cornea  18  into a position covering the lentoid  36 . In particular, the flap  42  can be rotated about the hinge  62  until the peripheral edge  46  of the flap  42  is positioned into contact with a portion of the wall  58 . When the flap  42  is properly repositioned over the lentoid  36 , the anterior surface  56  of the cornea  18  will be smooth and continuous across the anterior border  60  from the flap  42  to the remaining portion of the cornea  18 . After repositioning, the flap  42  will heal in place, and this healing will result in a continuous tissue between the peripheral edge  46  of the flap  42  and a portion of the wall  58  of the cornea  18 . 
       FIG. 5E  shows the cornea  18  after the flap  42  has been repositioned, and shows an example of a lentoid  36  having an anterior surface  38 , an annular surface  39  and a posterior surface  40 . Further,  FIG. 5F  shows the reshaped cornea  18  which results after the methods of the present invention. As discussed above, after a prescribed lentoid  36  of stromal tissue  30  has been removed and the flap  42  repositioned over the lentoid  36 , the pressure exerted by the aqueous humor  37  in the anterior chamber  35  will cause the cornea  18  to close the lentoid  36  volume and hence reshape the cornea  18 . In particular, the pressure exerted by the aqueous humor  37  will push the posterior bed  64  into contact with the interior surface  44  of the repositioned flap  42 , where the two surfaces will subsequently heal together and become continuous stromal tissue  30 . By comparing  FIG. 5A  with  FIG. 5F , it can be seen that the curvature of the anterior surface  56  of the reshaped cornea  18  ( FIG. 5F ) differs from the curvature of the anterior surface  56  of the initial cornea  18  ( FIG. 5A ). 
     As can be expected, the lentoid  36  shape shown in  FIGS. 5A-5F  is only one of the many possible lentoid  36  shapes that can be prescribed and thereafter created by the methods of the present invention. In particular, the example lentoid  36  shape as shown in  FIGS. 5A-5F  has a convex anterior surface  38 , a concave posterior surface  40  and an annular surface  39  connecting the anterior  38  and posterior  40  surfaces. As shown, the contour of the convex anterior surface  38  does not necessarily have the same curvature as the anterior surface  56  of the cornea  18 . Rather, the points on the layer  48  cut by the pulsed laser beam  12  are located at variable distances from corresponding points on the anterior surface  56  of the cornea  18 . Although not required by the method of the present invention, the lentoid  36  may have anterior  38  and posterior  40  lentoid surfaces that have the same approximate curvature, such as the lentoid  36  shown in  FIGS. 5A-5F . When this type of lentoid  36  is prescribed, it can be conveniently created using an excimer laser  13  configured to photoalter the exposed bed  50  of stromal tissue  30  to a uniform depth. 
       FIGS. 6A and 6B  show an example of a flap  42  that can be cut using the methods of the present invention to create a prescribed lentoid  36  having a concave anterior surface  38 . As discussed above, the versatility of the pulsed laser beam  12 , alone or in combination with an excimer laser beam  13 , enables one skilled in the art to create a flap  42  in accordance with the present invention which will result in a lentoid  36  having a plane, concave, convex or irregularly shaped anterior surface  38 , and a plane, concave, convex or irregularly shaped posterior surface  40 . 
     Further, as shown in  FIG. 7 , using the methods of the present invention, an oval flap  68  can be created having an oval anterior border  70 . One benefit of the oval shape for flap  68  is that the oval shape allows for a bed  50  with a large exposed bed area. Similarly, as shown in  FIG. 8 , an elongated flap  72 , having an elongated anterior border  74  can be created with the methods of the present invention. An elongated flap  72  may also provide the benefit of exposing a bed  50  with a large exposed bed area. 
     Additionally, custom shaped flaps  76  can be created using the methods of the present invention. For example, as shown by cross-referencing FIGS.  9  and  10 A-B, a custom flap  76  having a tab  66  can be made. Referring to  FIG. 9 , the tab  66  may have a different curvature than the custom anterior border  78  of the flap  76 , and hence the tab  66  extends from the custom anterior border  78  to assist in lifting and repositioning the custom flap  76 . 
     In accordance with the methods of the present invention, an interlocking flap  80  as shown in  FIG. 11  can be created for the purposes of maintaining the flap  80  in place after repositioning to both facilitate healing and reduce any optical distortions that may occur if a repositioned flap  42  shifts before healing is completed. As shown in  FIG. 11 , the interlocking flap  80  contains an interlocking peripheral edge  82 . In one embodiment of the interlocking peripheral edge  82 , an annular ring  84  extends from the interlocking peripheral edge  82  for engagement with a corresponding recess  86  formed in the wall  88 . 
       FIG. 12  shows an alternative embodiment of an interlocking flap  90 , having a beveled peripheral edge  92  for interlocking of the flap  90  with the remaining cornea  18  after repositioning. In the embodiment shown in  FIG. 12 , the flap  90  is formed with the angle α between the beveled peripheral edge  92  and the interior surface  44  of the flap  90  as an acute angle. A flap  90  with a beveled peripheral edge  92  as shown in  FIG. 12  is further disclosed in co-pending and now-allowed application Ser. No. 08/725,070 entitled “Method for Corneal Laser Surgery,” which is incorporated herein by reference. 
     While the particular Method of Corneal Reshaping by Laser Incising a Contoured Corneal Flap as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of the construction or design herein shown other than as defined in the appended claims.