Abstract:
A method of correcting refractive error in an eye, comprising the steps of marking at least one axis on the surface of the cornea. A portion of the cornea is then separated, forming a first anterior facing surface and a second posterior facing surface. An inlay having at least one axis indicated on the surface thereof is positioned between the first and second surfaces, and the at least one axis on the inlay is aligned with the at least one axis on the surface of the cornea. This results in precise positioning and orientation of the inlay and thus correction of astigmatic error in the cornea.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and apparatus for correcting the astigmatic refractive, error in the cornea of the eye. In particular, the cornea is modified by forming a flap in the cornea and exposing a portion of the cornea underlying the flap. The exposed portion is marked and an asymmetric inlay having a thin removable, transparent sheet with markings indicated thereon is positioned on the exposed portion of the cornea. The markings on the cornea and those on the sheet are aligned to ensure proper positioning of the asymmetric inlay.  
       BACKGROUND OF THE INVENTION  
       [0002]     A normal emetropic eye includes a cornea, a lens and a retina. The cornea and lens of a normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disorder known as ametropia, which is the inability of the lens and cornea to focus the far point correctly on the retina Typical types of ametropia are myopia, hypermetropia or hyperopia, and astigmatism.  
         [0003]     A myopic eye has either an axial length that is longer than that of a normal emetropic eye, or a cornea or lens having a refractive power stronger than that of the cornea and lens of an emetropic eye. This stronger refractive power causes the far point to be projected in front of the retina  
         [0004]     Conversely, a hypermetropic or hyperopic eye has an axial length shorter than that of a normal emetropic eye, or a lens or cornea having a refractive power less than that of a lens and cornea of an emetropic eye. This lesser refractive power causes the far point to be focused behind the retina.  
         [0005]     An eye suffering from astigmatism has a defect in the lens or shape of the cornea. Therefore, an astigmatic eye is incapable of sharply focusing images on the retina.  
         [0006]     Optical methods are known which involve the placement of lenses in front of the eye, for example, in the form of eyeglasses or contact lenses, to correct vision disorders. A common method of correcting myopia is to place a “minus” or concave lens in front of the eye to decrease the refractive power of the cornea and lens. In a similar manner, hypermetropic or hyperopic conditions can be corrected to a certain degree by placing a “plus” or convex lens in front of the eye to increase the refractive power of the cornea and lens. Lenses having other shapes can be used to correct astigmatism. The concave, convex or other shaped lenses are typically configured in the form of glasses or contact lenses.  
         [0007]     Although these optical methods can be used to correct vision in eyes suffering from low myopia, or in eyes suffering from hypermetropic, hyperopic or astigmatic conditions which are not very severe, these methods are ineffective in correcting vision in eyes suffering from severe forms of ametropia.  
         [0008]     However, surgical techniques exist for correcting these more severe forms of ametropia to a certain degree. For example, in a technique known as myopic keratomileusis, a microkeratome is used to cut away a portion of the front of the live cornea from the main section of the live cornea. The cut portion of the cornea is frozen and placed in a correlate where it is cut and reshaped. Altering the shape of the cut portion of the cornea changes the refractive power of this cut portion, which thus affects the location at which light entering the cut portion of the cornea is focused. The reshaped cut portion of the cornea is then thawed and reattached to the main portion of the live cornea. Hence, it is intended that the reshaped cornea will change the position at which the light entering the eye through the cut portion is focused, so that hopefully the light is focused directly on the retina, thus remedying the ametropic condition.  
         [0009]     The myopic keratomileusis technique is known to be effective in curing myopic conditions within a high range. However, the technique is impractical because it employs very complicated and time consuming freezing, cutting and thawing processes.  
         [0010]     Keratophakia is another known surgical technique for correcting severe ametropic conditions of the eye by altering the shape of the eye&#39;s cornea. In this technique an artificial, organic or synthetic lens is implanted inside the cornea to thereby alter the shape of the cornea and thus change its refractive power. Accordingly, as with the myopic keratomileusis technique, it is desirable that the shape of the cornea be altered to a degree that allows light entering the eye to be focused correctly on the retina.  
         [0011]     However, the conventional lenses and methods for type of correction are often impractical for correcting astigmatic error in the eye. Since an irregular shaped cornea or eye generally causes astigmatic error, to correct astigmatism an implanted lens must be a specific asymmetrical shape that would negate the irregularity. Often is difficult to properly position and maintain the lens in the correct orientation relative to the cornea, thereby making the procedure difficult and time consuming.  
         [0012]     Examples of known techniques for modifying corneal curvature, such as those discussed above, are described in U.S. Pat. No. 4,994,058 to Raven et al., U.S. Pat. No. 4,718,418 to L&#39;Esperance, U.S. Pat. No. 5,336,261 to Barrett et al., and a publication by Jose I. Barraquer, M.D. entitled “Keratomileusis and Keratophakia in the Surgical Correction of Aphakia”. The entire contents of each of these patents are incorporated herein by reference.  
         [0013]     Surgical techniques involving the use of ultraviolet and shorter wavelength lasers to modify the shape of the cornea also are known. For example, excimer lasers, such as those described in U.S. Pat. No. 4,840,175 to Peyman, which emit pulsed ultraviolet radiation, can be used to decompose or photoablate tissue in the live cornea so as to reshape the cornea.  
         [0014]     Specifically, a laser surgical technique known as laser in situ keratomileusis (LASIK) has been previously developed by the present inventor. In this technique, apportion of the front of a live cornea can be cut away in the form of a flap having a thickness of about 160 microns. This cut portion is removed from the live cornea to expose an inner surface of the cornea. A laser beam is then directed onto the exposed inner surface to abate a desired amount of the inner surface up to 150-180 microns deep. The cut portion is then reattached over the ablated portion of the cornea and assumes a shape conforming to that of the ablated portion.  
         [0015]     However, because only a certain amount of cornea can be ablated without the remaining cornea becoming unstable or experiencing outward bulging (eklasia), this technique is not especially effective in correcting very high myopia or large astigmatic error. That is, a typical live cornea is on average about 500 microns thick. The laser ablation technique requires that at least about 200 microns of the corneal stroma remain after the ablation is completed so that instability and outward bulging does not occur. Hence, this method typically cannot be effectively used to correct high myopia or large astigmatic error, because, in order to reshape the cornea to the degree necessary to alter its refractive power to sufficiently correct the focusing of the eye, too much of the cornea would need to be ablated.  
         [0016]     Other techniques exist for correcting astigmatic error using markings on a lens. However, these techniques generally only have a mark or multiple marks on a portion of the lens. This type of marking may indicate what direction the lens should be implanted in the cornea; however, they generally do not do not indicate where on the cornea they should be placed. For example, astigmatic correction is a relatively precise procedure and the lens must be placed both centrally on the cornea or at least in a predetermined position and oriented radially in the correct position, to negate the asymmetric shape of the cornea. The conventional procedures do not allow the proper alignment of the cornea surface and the lens implanted thereon. Therefore, existing procedures are inadequate to correct astigmatic error. Furthermore, many of these procedures have permanent markings on the lens, which may hinder the sight of the patient.  
         [0017]     Therefore, it is apparent that a need therefore exists for improved methods for further modifying the cornea to better correct ametropic conditions, and more specifically to correct astigmatic error.  
       SUMMARY OF THE INVENTION  
       [0018]     Accordingly, it is an object of the present invention to provide a method for adjusting the shape of a live cornea to correct high ametropic conditions.  
         [0019]     Another object of the invention is to provide a method for modifying the shape of a live cornea to correct astigmatic conditions.  
         [0020]     Yet another object of the present invention is to provide a method for adjusting the shape of a live cornea to correct astigmatic conditions by aligning the inlay with markings on the cornea.  
         [0021]     Still another object of the present invention is to provide an intracorneal inlay having removable alignment markings thereon.  
         [0022]     Still yet another object of the present invention is to provide an intracorneal inlay for correcting the refractive error in the eye having a removable, pliable sheet with markings thereon overlying at least a portion of the inlay to indicate the alignment of the inlay.  
         [0023]     Further still it is another object of the present invention to provide an inlay for correcting the refractive error in the eye that is positioned under a flap in the cornea and aligned with markings on an exposed surface of the cornea.  
         [0024]     The foregoing objects are basically attained by a method of correcting refractive error in the cornea of an eye, comprising the steps of marking at least one axis on the surface of the cornea, separating a portion of the cornea, forming a first anterior facing surface and a second posterior facing surface, positioning a inlay having at least one axis indicated on the surface thereof between the first and second surfaces, and aligning the at least one axis on the inlay with the at least one axis on the surface of the cornea.  
         [0025]     The foregoing objects are further attained by an inlay for correcting the refractive error in the cornea of the eye, comprising a first surface for placement onto an exposed surface of the cornea, a second surface opposite the first surface, and a removable sheet of material overlying the second surface, the sheet having markings thereon for accurately positioning the inlay on the exposed surface of the cornea  
         [0026]     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  
       [0027]     Referring to the drawings which form a part of this disclosure:  
         [0028]      FIG. 1  is an elevational front view of an eye with the cornea marked along the main optical axis;  
         [0029]      FIG. 2  is a plan top view of a marking device having 5 axes, according to the present invention;  
         [0030]      FIG. 3  is a side view in section of the marking device taken along lines  3 - 3  of  FIG. 2 .  
         [0031]      FIG. 4  is an elevational front view of the marking device of  FIG. 2  overlying the eye of  FIG. 1 ;  
         [0032]      FIG. 5  is an elevational front view of the eye of  FIG. 4  after markings were applied thereto by the marking device of  FIG. 3 ;  
         [0033]      FIG. 6  is an elevational front view of the eye of  FIG. 5  with a flap formed in the surface of the cornea;  
         [0034]      FIG. 7  is an elevational front view of the eye of  FIG. 6  with a device marking the main optical axis under the flap;  
         [0035]      FIG. 8  is an elevational front view of the eye of  FIG. 7  with the flap pivoted to expose a surface of the cornea and the marking device of  FIG. 3  adjacent thereto;  
         [0036]      FIG. 9  is an elevational front view of the eye of  FIG. 8  after markings are applied thereto by the marking device of  FIG. 3 ;  
         [0037]      FIG. 10  is plan top view of an inlay according to the present invention with a pliable material overlying the inlay;  
         [0038]      FIG. 11  is a side view in cross section taken along lines  11 - 11  of the inlay of  FIG. 10 ;  
         [0039]      FIG. 12  is a plan top view of a tool for holding the inlay adjacent a corneal surface and positioning it thereon;  
         [0040]      FIG. 13  is a side view on cross-section of the tool of  FIG. 12  taken along lines  13 - 13 ;  
         [0041]      FIG. 14  is a elevational front view of the eye of  FIG. 9  with the inlay of  FIG. 10  positioned on an exposed surface of the cornea using the tool of  FIG. 13 ;  
         [0042]      FIG. 15  is a side view in cross-section of the eye of  FIG. 14  taken along  
         [0043]      FIG. 16  is a elevational front view of the eye of  FIG. 15  with the flap repositioned, the inlay aligned and a pair of forceps removing the pliable material from the surface of the inlay;  
         [0044]      FIG. 17  is a side view in cross section of  FIG. 16 , taken along lines  17 - 17 ;  
         [0045]      FIG. 18  is a side view in section of the eye if  FIG. 17  after the pliable material has been removed;  
         [0046]      FIG. 19  is a plan top view of a ring shaped inlay suitable for the present procedure;  
         [0047]      FIG. 20  is a side cross sectional view of the inlay of  FIG. 19  taken along lines  20 - 20 ;  
         [0048]      FIG. 21  is a plan top view of a two-piece ring shaped inlay suitable for the present procedure; and  
         [0049]      FIG. 22  is a side cross sectional view of the inlay of  FIG. 21  taken along lines  22 - 22 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]     As shown in  FIGS. 1-17 , the refractive properties of the eye can be modified or altered by placing markings  26  and  28  on both the external or outer surface  14  of the cornea  12  of an eye  10  and an internal surface  16 , respectively. Surface  16  is generally exposed when a flap  18  is formed in the surface of the cornea. An inlay or implant  20  having a removable, pliable sheet  22  with markings  24  thereon is positioned on the exposed surface of the cornea, and the markings on the inlay are aligned with the markings  26  and  28 . Preferably, this procedure is used for astigmatic correction, but may be used with any type of correction to the vision of the eye.  
         [0051]     To begin, the refractive error in the eye is measured using wavefront technology, as is known to one of ordinary skill in the art. The refractive error measurements are used to determine the appropriate shape of lens or inlay  20  to best correct the error in the patient&#39;s cornea. Preferably, the inlay  20  is manufactured or shaped prior to the use of the wavefront technology and is stored in a sterilized manner until that specific inlay shape or size is needed. However, the information received during the measurements from the wavefront technology can be used to form the inlay using a cryolathe, or any other desired system or machine.  
         [0052]     As seen in  FIG. 1 , the main optical axis or visual axis  30  of the eye is marked with a dot  32  or any other type of marking, such as cross-hairs or an X. The exact position of visual axis  30  of the eye  10  is determined by asking the patient to focus on a small beam of light, as is known in the art, and the location on the corneal surface is marked, using a marker (such as ink). Preferably, the ink is any conventional ink that is water-soluble and will be washed away after several blinks of the eye or application of water or any other suitable liquid, thus allowing unhindered sight by the patient.  
         [0053]     A marking device  34 , as seen in  FIGS. 2 and 3 , can then be positioned adjacent the surface  12  of the cornea ( FIG. 4 ). Device  34  is preferably formed of metal or plastic and has a handle  36  and a substantially circular head  38 . Head  38  is formed of a substantially tubular or cylindrical portion  40  that extends from the handle  36  in a substantially circular manner, leaving an opening or area  42  within the tubular portion. Ten spokes  44  extend radially from a central portion  46  to the tubular portion  40  at equal intervals. In other words, the angle between each spoke  44  and the adjacent spoke is substantially equal to the angle between each other adjacent spoke. Spokes  44  define five separate axes or lines that extend from one portion of the tubular portion  40  to a side opposite or about 180 degrees therefrom. Each spoke is preferably substantially circular and in substantially the same plane as each other spoke. The spokes  44 , however, do not necessarily need to be circular and spaced equally apart from one another and can number any number desired, for example they can number from one to as many can be fit into the desired area  42 .  
         [0054]     Once the marking device  34  is positioned adjacent the external surface, the device  34  is centered using mark or dot  32 . Waterbased or removable ink (substantially similar to the ink used to mark the visual axis) is then used to mark the surface  14  of the cornea  12  along the spokes  44 . As seen in  FIG. 5 , this leaves, ten lines  26  extending radially from dot  32  or five axes extending in separate directions. The lines  26  are in substantially the same configuration as the marking device spokes  44 .  
         [0055]     Preferably, flap or portion  18  can be formed in the surface  14  of the cornea  12 , as seen in  FIG. 6 . The flap is formed in the stromal layer of the cornea, but does not necessarily need to be formed in the stromal layer and can be formed in any desired portion of the cornea. By forming the flap in the stromal layer, the cells of the cornea do not cause a gray to white response in the cornea, or protein detanurization The flap may be formed be any means desired, such as with a knife, microkeratome, or with a laser, such as a femtosecond laser or any other suitable laser.  
         [0056]     Preferably, an internal area of the cornea is separated into first and second substantially circular shaped internal surfaces  16  and  50 , respectively, as seen in  FIG. 8 , to form the circular shaped corneal flap  18 . First internal surface  16  faces in an anterior direction of cornea  12  and the second internal surface  50  faces in posterior direction of the cornea  12 . The flap  18  preferably has a uniform thickness of about 10-250 microns, and more preferably about 80-100 microns, but can be any suitable thickness. A portion  52  of flap  18  preferably remains attached to the cornea by an area at the periphery of the flap. However, the flap can be any suitable configuration, such as a flap attached to the cornea at a location other than at the periphery or a flap that is not attached to the cornea at all. Additionally, the flap may be shaped or sized as desired, and does not need to be circular.  
         [0057]     As seen in  FIG. 7 , a tool or device or spatula needle  54  is inserted under the flap  18 , in between surfaces  16  and  50  and marks the main optical or visual axis  30 . The mark  56  is preferably made on the first surface  16  and is lined up or positioned directly under or in about the same position as mark  32  on the external surface of the cornea.  
         [0058]     The flap is moved or pivoted about portion  52  using any device known in the art, such as a spatula or micro forceps or any other device, to expose the first and second corneal surfaces  16  and  50 , respectively. The flap preferably exposes a portion of the corneal surface that intersects the main optical axis  30  and allows uninhibited access thereto.  
         [0059]     Device  34  is positioned adjacent the exposed surface  16  and radial lines or axes  28  are made thereon using the removable ink, described above. Lines  28  are made in substantially the same positioning and placement as lines  26 . In other words, lines  28  underlie lines  26 , so that if flap  18  were replaced, lines  26  would overlie lines  28  and each overlying line would indicate substantially the same radian or axes. Lines  28  are formed in substantially the same manner as lines  26  and the description thereof applies to lines  28 .  
         [0060]     As seen in  FIGS. 10 and 11 , inlay or lens  20  is preferably a substantially circular intracorneal inlay. Additionally, inlay  20  is preferably any polymer or hydrogel having about 70% to about 95% water content, and more preferably of about 78% to about 80% water content; however, the water content can be any percentage desired. The inlay may be formed from synthetic or organic material or a combination thereof. For example, the inlay can be collagen combined with or without cells; a mixture of synthetic material and corneal stromal cells; silicone or silicone mixed with collagen; methylmetacrylate; any transparent material, such as polyprolidine, polyvinylpylidine, polyethylenoxyde, etc.; or any deformable polymer, which can change its shape with radiation after implantation.  
         [0061]     Furthermore, inlay  20  has a first side or surface  58  and a second side or surface  60 , and is preferably shaped with an asymmetrical cross-section, as seen specifically in  FIG. 11 , so that it can correct astigmatic error in the eye. Preferably, as stated above, inlay  20  may come in many configurations and not necessarily that shown in  FIG. 11 , to correct any different degrees and variations of astigmatic error. Furthermore, inlay  20  may be used to correct hyperopia, myopia or any other vision problems or a combination of these vision problems and astigmatism.  
         [0062]     Second surface  60  preferably is curved and pliable, so that it is able to conform to the first surface  16  of the cornea  12 . The implant is preferably substantially circular, having a diameter of between about 2-10 mm and can have a refractive index different than that of the cornea or the same as that of the cornea Preferably, the inlay has a refractive index of about 1.2 to 1.4, and more preferably of about 1.33. If the refractive index is the same as the cornea, the total refractive index of the cornea is altered after implantation of the inlay and repositioning of the flap. However, the inlay can be any size and/or configuration desired.  
         [0063]     Furthermore, as seen in  FIG. 11 , a pliable or bendable sheet or film of transparent material  62  is positioned to overlie and conform to surface  58 . Sheet  62  is preferably a synthetic material, such as any suitable polymer, and is substantially circular with markings or lines  24  thereon. Markings  24  have substantially the same positioning and placement as lines  26  and  28 , or are 10 lines that radially extend from a center to form five separate axes. The description of lines  26  and  28  applies to markings  24 . In other words, lines  24  are configured in such a manner that if the center of the markings  24  was placed on the marking  32  the lines can be adjusted or orientated so that markings  24  would overlie lines  28  and/or  26 , each line indicating substantially the same radian or axis. Furthermore the center  66  of the markings  24  is preferably in the center of the inlay or positioned in any predetermined portion of the inlay.  
         [0064]     This configuration of the lines and markings  28  and  24  allows the inlay to be placed on the exposed surface of the cornea directly over the visual axis  30  and oriented so that lines and markings  28  and  24  are precisely or substantially matched, as seen in  FIG. 14 . Furthermore, by placing the markings on the inlay and the cornea as described, an asymmetric astigmatic inlay can be correctly and accurately placed on the exposed surface of the cornea It is generally crucial to the sight of the patient&#39;s eye, especially during astigmatic correction, to have the inlay precisely oriented to correct the existing error. If the inlay is not both centered over the visual axis, or at least positioned in a predetermined position over the visual axis, and oriented properly with respect to radial position, the inlay will not correct the desired astigmatic error and may even increase the refractive error in the cornea Therefore, it can be seen that this inlay can be accurately positioned both radially and centrally on the eye to improve the vision of the eye.  
         [0065]     Preferably, inlay  20  is positioned adjacent the surface of the cornea, using tool or holding device  80 , in-between first and second corneal surfaces  16  and  50 . As seen in  FIGS. 12 and 13 , tool  80  is preferably a plastic tool having a handle  82  and a substantially circular head  84 ; however, tool  80  can be any material and shape desired that would allow the placement of inlay  20  on a corneal surface. Head  84  has an open center portion  86  defined by an L-shaped holding portion  88 , which is curved in a similar configuration as the surface of the cornea to facilitate positioning of the inlay; however, portion  88  can be straight or any other configuration desired. Portion  88  has a bottom wall  90  and a sidewall  92  that are sized and configured to hold inlay  20  therein ( FIGS. 14 and 15 ). Additionally, wall  90  has markings or lines  91  that are substantially similar and oriented to the lines or markings  24  on the inlay. These markings allow the inlay to be aligned with the tool  80  when positioning the inlay adjacent the cornea. Furthermore, the walls  86  and  88  have an opening  94  at one end, preferably opposite or 180-degrees away from the handle  92 . The opening allows the resilient head to separate and the inlay to be properly positioned in the exact or precise location desired on the exposed corneal surface, after it is aligned with the markings of the corneal surface, as described above.  
         [0066]     It is noted that the inlay can be positioned without the use of tool  80 , in any convention manner desired or any other manner, and does not necessarily need to be positioned on an internal surface of the cornea but may be placed or positioned on the external surface of the cornea.  
         [0067]     Once tool  80  is removed and the inlay properly positioned, the flap  18  is replaced so that it covers or lies over the sheet  62  in a relaxed state, as seen in  FIGS. 16 and 17 . In other words, inlay  20  or sheet  62  does not force flap  18  away from the internal surface  58  and therefore the refractive properties of the cornea are not altered due to a tension force being applied to the flap. Preferably, the flap  18 , the inlay  20 , the visual axis  30  and surface  16  are all precisely lined up using the above described markings and lines. If any markings are off, the inlay and/or the flap can be repositioned by using small forceps. The forceps can be extended underneath the flap  18  to move the inlay with respect to the visual axis either in a: rotational or a linear manner.  
         [0068]     As seen in  FIGS. 16 and 17 , forceps  68  are used in grasp the sheet  62  and move the sheet from the surface of the inlay, thus removing any markings on the inlay  20  that may hinder sight. Additionally, the markings on the eye would wash away after a short period of time due to the liquids developed naturally by the eye; however, if desired the ink my be washed of manually with the application of water or any other suitable liquid. Furthermore, it is noted that the sheet does not necessarily need to be removed and can remain on the inlay even after the procedure is completed. The ink on sheet  62  may be removable in the same manner as the ink to mark the cornea and would thus wash off after a short time period.  
         [0069]     Additionally, the markings may be placed directly on the inlay and do not necessarily need to be on a sheet. This type of marking would allow the same proper placement without the need to remove the sheet. As stated above, the ink forming the markings could be removable.  
         [0070]     It is noted that the markings do not necessarily need to be in the configuration described and can be any type of markings desired. For example, the markings can be radial dots that are positioned along the desired axes or radians or they can be concentric circles or a single circle or any other polygon desired or configuration of marks or dots desired that would allow the matching of the inlay, flap and surface of the cornea in the manner described above. Furthermore, the markings do not need to be removable and can be permanent, whether they are made with ink or actual alterations to the cornea and/or inlay, or the markings can be any combination of removable and/or permanent markings.  
         [0071]     As seen in  FIGS. 19 and 20 , the inlay can be a ring-shaped inlay  120  with first and second surfaces  158  and  160  lay  120  is formed from substantially similar materials and therefore would have substantially similar properties to those of inlay  20  and therefore, the description thereof applies to the material and properties of inlay  120 . As seen in  FIG. 19 , the inlay can have one portion that is larger than another portion, or in other words an asymmetric configuration that would correct astigmatic error as described above.  
         [0072]     Inlay  120  can be used for correction of myopia or astigmatism or both. As with the above-described inlay, inlay  120  has a sheet of pliable, transparent material  162  overlying surface  158 . However, sheet  162  is preferably ring-shaped and covers the ring-shaped portion of inlay  120 . Furthermore, as with sheet  62 , sheet  162  can be used to position and orientate inlay  120  relative to both the corneal flap  18  and the corneal surface  16  and the visual axis  30 , as described above. Sheet  162  can also be removed in a similar manner as to that described above for sheet  62 .  
         [0073]     As seen in  FIGS. 21 and 22 , inlay  220  can be a ring-shaped inlay similar to inlay  120  but with portion portions  220   a  and  220   b.  As seen specifically in  FIG. 22 , portion of the inlay  220   a  can be larger than portion  220   b  for correction of astigmatic error, as described above. Furthermore sheet  262  can overlie the inlay in a similar manner as sheet  162 . However, sheet  262  has two portions  262   a  and  262   b,  which overlie portions  220   a  and  220   b,  respectively. Inlay  220  is substantially similar to inlay  120  and inlay  20  and the descriptions thereof apply to inlay  220 .  
         [0074]     Additionally, the entire procedure for inlay  20  is applicable to both inlay  120  and inlay  220  and any description thereof is applicable to inlays  120  and  220 .  
         [0075]     While various advantageous 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.