Patent Publication Number: US-2013231739-A1

Title: Small Diameter Corneal Inlays

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of pending application. Ser. No. 12/877,799, filed Sep. 8, 2010; which application is a continuation-in-part of application Ser. No. 11/554,544, filed Oct. 30, 2006, now U.S. Pat. No. 8,057,541, which claims the benefit of Provisional Appln. No. 60/776,458, filed Feb. 24, 2006; 
     Application Ser. No. 12/877,799, filed Sep. 8, 2010, is also a continuation-in-part of pending application Ser. No. 12/418,325, filed Apr. 3, 2009, which is a continuation-in-part of application Ser. No. 11/738,349, filed Apr. 20, 2007, now abandoned. 
     All of the aforementioned applications are incorporated by reference herein. 
    
    
     INCORPORATION BY REFERENCE 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Abnormalities in the human eye can lead to vision impairment. Some typical abnormalities include variations in the shape of the eye, which can lead to myopia (near-sightedness), hyperopia (far-sightedness) and astigmatism as well as variations in the tissue present throughout the eye, such as a reduction in the elasticity of the lens, which can lead to presbyopia. A variety of technologies have been developed to try and address these abnormalities, including corneal implants. 
     Corneal implants can correct vision impairment by altering the shape of the cornea. Corneal implants can be classified as an onlay or an inlay. An onlay is generally considered an implant that is placed over the cornea such that the outer layer of the cornea, e.g., the epithelium, can grow over and encompass the implant. An inlay is generally considered an implant that is implanted in the cornea beneath a portion of the corneal tissue by, for example, cutting a flap in the cornea and inserting the inlay beneath the flap. Because the cornea is the strongest refracting optical element in the human ocular system, altering the cornea&#39;s anterior surface is a particularly useful method for correcting vision impairments caused by refractive errors. Inlays are also useful for correcting other visual impairments including presbyopia. 
     SUMMARY OF THE INVENTION 
     The disclosure generally describes corneal inlays which are adapted to change the shape of the cornea to provide central near vision zone and a peripheral distance vision zone in the cornea. In general, the inlay is sized such that when positioned within the cornea, a central region of the cornea increases in curvature, thereby providing for near vision. A region peripheral to the central region provides for distance vision. 
     One aspect of the disclosure describes a corneal inlay comprising an inlay body having a diameter between about 1 mm and about 3 mm, wherein the body has an index of refraction that is substantially the same as a cornea. The inlay can have an index of refraction that is about 1.36 to about 1.39. 
     In some embodiments the diameter of the inlay is about 2 mm. 
     In some embodiments the inlay body has a central thickness that is about 20 microns to about 50 microns, and in some embodiments it is about 30 microns. 
     In some embodiments the inlay has a peripheral edge thickness between about 8 microns and about 15 microns, and in some embodiments is about 12 microns. 
     In some embodiments the inlay body has an anterior radius of curvature between about 7 mm and about 12 mm, and in some embodiments in about 10 mm. 
     In some embodiments the inlay body has a posterior radius of curvature between about 5 mm and about 10 mm, and in some embodiments is about 8.5 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a cross-sectional view of a conventional implantable lens. 
         FIG. 2A  is a perspective view depicting an example embodiment of an implantable lens. 
         FIG. 2B  is a top-down view depicting another example embodiment of the implantable lens. 
         FIGS. 2C-E  are cross-sectional views taken along line  1 - 1  of  FIG. 2B  depicting additional example embodiments of the implantable lens. 
         FIG. 3  is a cross-sectional view depicting an anterior portion of a human eye with an example embodiment of the lens implanted therein. 
         FIGS. 4-9  are cross-sectional views taken along line  1 - 1  of  FIG. 1B  depicting additional example embodiments of the implantable lens. 
         FIG. 10A  is a top-down view depicting another example embodiment of the implantable lens. 
         FIG. 10B  is a cross-sectional view taken along line  2 - 2  of  FIG. 10A  depicting another example embodiment of the implantable lens. 
         FIG. 11A  is a perspective view depicting another example embodiment of the implantable lens. 
         FIG. 11B  is a top-down view depicting another example embodiment of the implantable lens. 
         FIGS. 11C-D  are cross-sectional views taken along line  3 - 3  of  FIG. 11B  depicting additional example embodiments of the implantable lens. 
         FIGS. 12A-D  are block diagrams depicting an example method of manufacturing the implantable lens. 
         FIG. 13  is a cross-sectional view depicting another example embodiment of the implantable lens. 
         FIG. 14A  is a top-down view depicting another example embodiment of the implantable lens. 
         FIGS. 14B-C  are cross-sectional views taken along line  4 - 4  of  FIG. 14A  depicting additional example embodiments of the implantable lens. 
         FIG. 15  is a cross-sectional view of a cornea showing an intracorneal inlay implanted in the cornea according to an embodiment of the invention. 
         FIG. 16  is a diagram of an eye illustrating the use of a small diameter inlay to provide near vision according to an embodiment of the invention. 
         FIG. 17  is a cross-sectional view of a cornea showing an inlay implanted in the cornea and a change in the anterior corneal surface induced by the, inlay including a drape region according to an embodiment of the invention. 
         FIG. 18  illustrates various possible shapes for the drape region. 
         FIG. 19  is a cross-sectional view of a cornea showing a thickness profile for providing a desired refractive correction according to an embodiment of the invention. 
         FIG. 20  is a 3D topographic difference map showing the change in the anterior corneal surface induced by an inlay according to an embodiment of the invention. 
         FIG. 21  shows an average radial elevation profile induced by an inlay according to an embodiment of the invention. 
         FIG. 22  shows a contour map of the refractive change induced by an inlay according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Some corneal implants that are relatively flat around the outer edges, such as aspherical implants and shallow spherical implants to name a few, can suffer from edge lift. Edge lift occurs when the anterior surface of the implant around the outer edge tends to curve or lift back towards the apex.  FIG. 1  is a cross-sectional view of a conventional corneal implant  20  suffering from edge lift, which is exaggerated for the purposes of illustration. Here, the implant  20  has an outer edge  21 , an anterior surface  22 , an apex  23  and a posterior surface  24 . An ideal edge profile is indicated by dashed line  10 . In the ideal case, the most posterior point on the anterior surface  22  is located at the outer edge  21 . However, in a lens suffering from edge lift the most posterior point of the anterior surface  22  can be located at a position  24  closer to the apex  23  than the outer edge  21 . Edge lift can progress and build up over time and result in deteriorated optical performance and can also make the implantation procedure more difficult. 
     In some embodiments the inlays have modified edge regions that can reduce stimulation of adverse tissue reactions in proximity to the lens.  FIGS. 2A-E  depict various views of an example embodiment of implantable lens  100 .  FIG. 2A  is a perspective view depicting implantable lens  100 , where lens  100  has lens body  101 , anterior surface  102 , posterior surface  103  and outer edge surface  104 .  FIG. 2B  is a top-down view of lens  100  taken in direction  110 . Here it can be seen that lens body  101  has a generally circular outer profile  119  with central apex  105  representing the most anterior point of anterior surface  102 . Diameter  112  represents the overall diameter of lens body  101  and diameter  114  represents the diameter of corrective portion  122 , which is the portion of anterior surface  102  configured to provide correction for one or more specific visual impairments. 
       FIG. 2C  is a cross-sectional view of lens  100  taken along line  1 - 1  of  FIG. 2B . From this view it can be seen that anterior surface  102  is substantially spherical with radius of curvature  106  measured from vertex  108  located on central axis  118 , which intersects apex  105 . Likewise, posterior surface  103  also has its own radius of curvature  107  measured from vertex  109 . The corrective power of lens  100  is dependent upon these radii  106 - 107  and can be varied as desired by adjustment of either radii  106 - 107 . It can also be seen here that lens  100  is configured to correct for hyperopia, i.e., the relation of anterior surface  102  to posterior surface  103  gives lens body  101  a converging meniscus-like shape along line  1 - 1 . The thickness of lens body  101  along central axis  118  is referenced as center thickness  140 . 
       FIG. 2D  is an enlarged cross-sectional view of lens  100 , showing region  111  of  FIG. 2C  in greater detail. In  FIG. 2D , corrective portion  122  of anterior surface  102  is substantially spherical and anterior surface  102  also includes a beveled portion  124 . Here, beveled portion  124  is curved with a single radius of curvature and is referred to as bevel radius  124 . As used herein, “bevel” is defined to include flat surfaces, curved surfaces and surfaces of any other shape. Bevel radius  124  abuts spherical portion  122  at interface  123 . Adjacent to bevel radius  124  is outer edge surface  104 , the abutment between bevel radius  124  and outer edge surface  104  being referenced as interface  125 . Outer edge surface  104  includes first portion  126  and second portion  128 , which abut each other at interface  127 . Second edge surface portion  128  abuts posterior surface  103  at interface  129 . Here, first edge surface portion  126  is curved and is referred to as edge radius  126 . In this embodiment, edge thickness  130  is defined as the height of second edge surface portion  128  in the Z direction from the most posterior point of lens body  101  (interface  129  in this instance) to interface  127 . 
       FIG. 2E  is another cross-sectional view of region  111  depicting the example embodiment of  FIG. 2D  with edge radius slope angle  132 , which defines the slope of edge radius  126 . Edge radius slope angle  132  can be defined as the angle between axes  131  and  133 . Here, axis  131  is parallel to central axis  118  and intersects interface  125 , while axis  133  intersects interfaces  125  and  127 . Also depicted here is bevel radius slope angle  135 , which defines the slope of bevel radius  124 . Bevel radius slope angle  135  can be defined as the angle between axes  134  and  136 . Here, axis  134  is parallel to central axis  118  and intersects interface  123  and axis  136  intersects interfaces  123  and  125 . 
     As can be seen in  FIGS. 2D-E , edge radius  126  preferably slopes in the −Z direction to a greater degree than bevel radius  124 , so that edge radius  126  converges towards posterior surface  103  at a greater rate than bevel radius  124 . Stated in terms of slope angles, edge radius slope angle  132  is preferably smaller than bevel radius slope angle  135 . As a result, lens  100  is less susceptible to edge lift. Also, the gradual transition between spherical portion  122  and posterior surface  103  can reduce stimulation of adverse tissue reactions to lens  100 . 
     For instance,  FIG. 3  is a cross-sectional view depicting an anterior portion of human eye  200  including lens  202 , aqueous humor  203 , ciliary body  204 , iris  205  and cornea  206  with an example embodiment of lens  100  implanted therein. Here, lens  100  is shown implanted as a corneal inlay although, it should be noted that lens  100  can also be implanted as a corneal onlay in a position closer to the anterior surface of cornea  206 . The gradual transition in the edge region of lens  100  facilitates the acceptance of lens  100  by the surrounding corneal tissue  207 , more so than conventional lenses with an unbeveled sharp or steep transition between the anterior and posterior surfaces. As a result, lens  100  is less susceptible to undesirable conditions such as corneal haze and the like. In addition, during the implantation procedure, the modified edge region of lens  100  makes it easier to ascertain whether lens  100  is properly oriented or whether lens  100  is inverted. 
     In order to sustain the cornea  206  and prevent tissue necrosis, an adequate level of fluid and nutrient transfer should be maintained within cornea  206 . Accordingly, lens body  101  is preferably composed of a material with a permeability sufficient to allow fluid and nutrient transfer between corneal tissue  207  adjacent to anterior surface  102  and posterior surface  103 , in order to sustain the cornea over a desired period of time. For instance, in one example embodiment lens body  101  is composed of a microporous hydrogel material. Microporous hydrogels are described in further detail in U.S. Pat. No. 6,875,232 entitled “Corneal Implant and Method of Manufacture,” which is fully incorporated by reference herein. 
     TABLE 1 depicts example values for one embodiment of a 5.0 millimeter (mm) diameter lens  100  having a given diopter. These example values are for purposes of illustration only and in no way limit the implantable lens  100  to only these or similar values. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Diopter 
                 +2.25 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Lens diameter 112 (mm) 
                 5.00 
               
               
                   
                 Corrective diameter 114 (mm) 
                 4.90 
               
               
                   
                 Posterior radius 107 (mm) 
                 7.50 
               
               
                   
                 Center thickness 140 (mm) 
                 0.030 
               
               
                   
                 Bevel radius 124 (mm) 
                 5.500 
               
               
                   
                 Edge radius 126 (mm) 
                 0.025 
               
               
                   
                 Edge thickness 130 (mm) 
                 0.010 
               
               
                   
                 Edge slope angle 132 (degrees) 
                 50 
               
               
                   
                   
               
            
           
         
       
     
     The values of edge thickness  130 , edge radius  126 , edge slope angle  132  and bevel radius  124  are interdependent and based on the desired corrective values, the overall lens diameter  112 , the diameter of corrective portion  122 , and the shape of anterior surface  102  and posterior surface  103 . Preferably, a lens diameter  112  in the range of about 1-10 mm with a corrective portion diameter  114  of about 0.5 mm or greater will have an edge thickness less than or equal to about 0.015 mm, an edge radius  126  in the range of about 0.001-1 mm, an edge slope angle  132  between 0 and 90 degrees and a bevel radius  124  in the range of about 1-10 mm. These ranges are for illustrative purposes only and in no way limit the embodiments described herein. 
     It should be noted that the modified edge described herein can be used with any type, shape or configuration of implantable lens. For instance, lens  100  can be either a corneal inlay or onlay. Lens  100  can be configured to treat any visual impairment including, but not limited to, myopia, hyperopia, astigmatism, and presbyopia. Lens  100  can also be configured to treat any combination of visual impairments including, but not limited to, presbyopia with myopia or hyperopia and presbyopia with astigmatism. The overall outer profile  119  of lens  100  can be any shape, including, but not limited to, circular, elliptical, irregular, multi-sided, and shapes having an inner aperture. Outer edge surface  104  can configured with outcroppings such as fixation elements and the like. Also, lens body  101  can be fabricated from one or more different materials having any desired refractive index. Furthermore, as will be described in greater detail below, corrective portion  122  of anterior surface  102  can be substantially spherical with or without multiple focal zones, substantially aspherical with or without multiple aspherical surfaces, or any combination and the like. As used herein, the term substantially is intended to broaden the modified term. For instance, a substantially spherical surface does not have to be perfectly spherical, but can include non-spherical variations or errors and the like to a degree sufficient for implementation. 
       FIGS. 4-9  are cross-sectional views depicting additional example embodiments of lens  100  taken along line  1 - 1  in region  111  of  FIG. 1B . In the embodiment depicted in  FIG. 4 , corrective portion  122  of anterior surface  102  is substantially aspherical. The rate of curvature of aspherical surfaces typically decreases or increases as the surface progresses outwards towards outer edge surface  104 . In this embodiment, the rate of curvature of aspheric surface  122  decreases such that the surface is flatter near outer edge surface  104  than near apex  105  (not shown). Anterior surface  102  and posterior surface  103  diverge as the surfaces  102 - 103  progress radially outwards from apex  105  (not shown) towards interface  123 . From interface  123  to interface  125 , bevel radius  124  preferably converges towards posterior surface  103 . Likewise, from interface  125  to interface  127 , edge radius  126  also preferably converges towards posterior surface  103 . 
     Beveled portion  124  of anterior surface  102  can be flat or curved or any other desired shape. For instance, in  FIGS. 2C-E , beveled portion  124  is spherically curved, however, it should be noted that any type of curve can be used. In the embodiment depicted in  FIG. 5 , beveled portion  124  is flat. Likewise, first and second edge surface portions  126  and  128  can be flat or curved or any other desired shape. For instance, in  FIGS. 2C-E , edge radius  126  is substantially spherically curved and second edge surface portion  128  is curved at a variable rate. In the embodiment depicted in  FIG. 6 , first edge surface portion  126  is flat, while in the embodiment of  FIG. 7  second edge surface portion  128  is flat. Any combination of flat and curved surfaces can be implemented. For instance, in  FIG. 8 , beveled portion  124 , and first and second edge surface portions  126  and  128  are all flat. Also, edge surface  104  can be implemented in any desired manner. For instance, in  FIG. 9 , edge surface  104  is flat and oriented in only the Z direction. 
       FIG. 10A  is a top-down view depicting another example embodiment of lens  100  having a ring-like shape. Here, lens  100  includes inner aperture  302  and inner edge surface  304 .  FIG. 10B  is a cross-sectional view of the embodiment of lens  100  depicted in  FIG. 10A  taken along line  2 - 2 . Here, it can be seen that anterior surface  102  also includes inner beveled portion  306  located between corrective portion  122  and inner edge surface  304 . Like outer edge surface  104 , inner edge surface  304  includes first portion  308  and second portion  310 , which, in this embodiment, are both curved. Beveled portion  306  abuts corrective portion  122  at interface  305  and first portion  308  abuts beveled portion  306  at interface  307 . Second portion  310  abuts first portion  308  at interface  309  and abuts posterior surface  103  at interface  311 . It should be noted that edge surface  304  and beveled portion  306 , like edge surface  104  and beveled portion  124  described above, can be shaped or configured in any manner desired. Lenses  100  of the type depicted in  FIGS. 10A-B  are described in more detail in U.S. application Ser. No. 11/032,913, entitled “Myopic Corneal Ring with Central Accommodating Portion” and filed Jan. 11, 2005, which is fully incorporated by reference herein. 
     As mentioned above, lens  100  with the modified edge region as described herein can also be implemented as a multifocal lens.  FIG. 11A  is a perspective view depicting an example embodiment of implantable lens  100  configured to provide multifocal correction. Here, lens  100  includes two corrective regions  402  and  404  each having a different refractive index. The different refractive indices in each region allow for correction of visual impairments over different distance ranges. For instance, the refractive indices of regions  402  and  404  can be predetermined such that region  402  provides refractive correction over relatively near distances while region  404  provides correction over relatively far distances or vice-versa. Any combination and number of two or more corrective regions can be used. Likewise, any refractive index can be used including refractive indices that are substantially similar to cornea  206  (about 1.36-1.39) and refractive indices that are greater than or less than that of cornea  206 . 
       FIG. 11B  is a top down view depicting this embodiment of lens  100  taken along direction  410 . In this embodiment, lens  100  has apex  105 , a generally circular outer edge profile  409  and regions  402  and  404  have diameters  406  and  408 , respectively. The transition between regions  402  and  404  is referenced as interface  403 . Here, regions  402  and  403  are arranged as generally concentric circular regions. It should be noted that regions  402  and  403  can be arranged in any desired manner such as eccentric, hemispherical, irregular and the like. Also, any number of two or more regions can be implemented with any number or none of those regions being integrally coupled together. 
       FIG. 11C  is a cross-sectional view depicting the embodiment of  FIG. 11B  taken over line  3 - 3 . Here, corrective portion  122  of anterior surface  102  is substantially spherical having one radius of curvature  106  and posterior surface  103  is also substantially spherical having one radius of curvature  107 . Adjustment of these radii  106 - 107  along with the selection of the appropriate refractive index for regions  402 - 404  can provide the proper diopter values for each zone to treat a given individual.  FIG. 11D  is an enlarged cross-sectional view of this embodiment lens  100 , showing region  411  of  FIG. 11C  in greater detail. In this embodiment, similar to the embodiment depicted in  FIG. 2D , lens  100  includes bevel radius  124 , edge radius  126  and curved second edge surface portion  128 . 
     To provide different refractive indices, in one example embodiment regions  402  and  404  are fabricated from different materials integrally coupled together at interface  403 . For instance, each region  402  and  404  can be fabricated from different microporous hydrogel materials. In one example embodiment, lens  100  is fabricated by first forming a solid polymeric cylindrical core  502 , such as that depicted in  FIG. 12A , which corresponds to region  402  and has approximately the same diameter as diameter  406  of region  402 . This core can then be surrounded by a monomeric solution  503  in a manner similar to that depicted in  FIG. 12B . Polymeric core  502  is preferably at least slightly soluble in monomeric solution  503 . Monomeric solution  503  can then be polymerized to form outer polymeric cylindrical region  504  surrounding inner core  502  as depicted in  FIG. 12C . Outer region  504  preferably corresponds to region  404  and has approximately the same diameter or a slightly larger diameter than diameter  408  of region  404 . Inner core  502  and outer region  504  together form lens core  506 , from which one or more lens can be fabricated, such as, for instance, by separating core  506  into disc-shaped buttons  508  as depicted in  FIG. 12D . Each individual button can be machined or cut into the desired shape and further processed (e.g., softened, hydrated, etc.) to form an individual lens body  101 . 
     As mentioned above, polymeric core  502  is preferably at least slightly soluble in monomeric solution  503 . This is so that solution  503  can dissolve the outer surface of core  502  and become interdispersed and mixed with the dissolved portion of core  502 . Once solution  503  is polymerized and solidified, an interface region  505  between cores  502  and  504  can be formed where the different polymers in cores  502  and  504  together form an interpenetrating network. This interface region corresponds to interface region  430  in  FIG. 13  below and integrally couples regions  402  and  404  together. 
       FIG. 13  is a cross-sectional view of an example embodiment of lens  100  having interface region  430 . By integrally coupling regions  402  and  404  together, interface region significantly reduces the risk that regions  402  and  404  will separate, such as can be the case when an adhesive is used to join regions  402  and  404 . Furthermore, interface region  430  can have a refractive index or range of refractive indices between the refractive indices of regions  402  and  404 . As a result, interface region  430  can act as an optical transition between regions  402  and  404  and add a third multifocal region to lens  100 . This can eliminate an immediate or sharp transition between the refractive indices of regions  402  and  404  that could result in visual artifacts such as halo or glare. 
     The width  420  of interface region  430  can be varied as desired. For instance, to generate a wider interface region  430 , monomeric solution  504  can be left in contact with inner core  502  for a longer period of time before polymerization, or, the solubility of inner polymeric core  502  in monomeric solution  504  can be increased. Generally, the wider interface region  430  becomes, the more noticeable region  430  to the subject as a multifocal region. 
     It should be noted that lens  100  can be fabricated in any manner and is not limited to the example described with respect to  FIGS. 12A-D . Other polymerization methods known in the art including, but not limited to, dip coating, spinning, casting, and the polymerization of pre-polymers, can be used in the formation of regions  402  and  404 . 
     In another example embodiment, each region  402  and  404  is configured with varying levels of permeability. For instance, region  402  can have a level of permeability to fluid and nutrients that is sufficient to substantially sustain cornea  206 , while region  404  can have a permeability to either fluid or fluid and nutrients that is relatively less than region  402 , including being entirely impermeable to fluid and nutrients. This allows for the use of more types of materials having a wider range of refractive indices and/or structural characteristics. 
     In order to allow enough fluid/nutrient transfer to sustain cornea  206 , the size of any impermeable region is preferably minimized. For instance, any circular central region, similar to the embodiment of region  402  described with respect to  FIG. 11B , that is impermeable to fluid and nutrients is preferably less than about 3 mm in diameter (diameter  406 ) or about 7.1 square mm. However, it should be noted that lens  100  is not limited to any one total impermeable surface area, the size and surface area of any impermeable region being dependent on the shape of the region and the relative level of permeability of any accompanying regions. For instance, an example embodiment of lens  100  having many concentric regions arranged in a bullseye fashion where the regions alternate between permeable and impermeable could allow for a total surface area of impermeable regions that is greater than 7.1 square mm. 
       FIG. 14A  is a top-down view depicting another example embodiment of multifocal lens  100  where corrective portion  122  of anterior surface  102  includes surfaces  602  and  604  having different rates of curvature. Surfaces  602  and  604  have diameters  610  and  612 , respectively.  FIG. 14B  is a cross-sectional view of another example embodiment of lens  100  taken along line  4 - 4  of  FIG. 14A . Here, surfaces  602  and  604  are each substantially spherical but have different radii of curvature  605  and  606 , respectively. The abutment between surface  602  and  604  is referenced as interface  603 . Each surface  602  and  604  can be configured with a different diopter value to correct for separate distances ranges (e.g., near-far, far-near, etc.). TABLE 2 depicts example values for three embodiments of a 5.0 millimeter (mm) diameter lens  100  having multiple spherical surfaces  602  and  604  similar to that depicted in  FIG. 14B . Each of the three embodiments provides for a different degree of correction for relatively far distances (sphere) and relatively near distances (add). These corrective values are shown in the format “sphere diopter/add diopter.” All of these example values are for purposes of illustration only and in no way limit the implantable lens  100  to only these or similar values. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Parameter 
                 0.00/1.75 
                 0.00/2.00 
                 0.00/2.25 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Lens diameter 112 (mm) 
                 5.00 
                 5.00 
                 5.00 
               
               
                 Posterior radius 107 (mm) 
                 7.50 
                 7.50 
                 7.50 
               
               
                 Center thickness 140 (mm) 
                 0.020 
                 0.021 
                 0.022 
               
               
                 Bevel radius 124 (mm) 
                 4.770 
                 4.770 
                 4.770 
               
               
                 Edge radius 126 (mm) 
                 0.025 
                 0.050 
                 0.050 
               
               
                 Edge thickness 130 (mm) 
                 0.010 
                 0.010 
                 0.010 
               
               
                 Edge slope angle 132 (degrees) 
                 45 
                 45 
                 45 
               
            
           
           
               
            
               
                 Spherical Surface 602 
               
            
           
           
               
               
               
               
            
               
                 Diameter 610 (mm) 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Radius 605 (mm) 
                 7.252 
                 7.217 
                 7.182 
               
            
           
           
               
            
               
                 Spherical Surface 604 
               
            
           
           
               
               
               
               
            
               
                 Diameter 612 (mm) 
                 4.90 
                 4.90 
                 4.90 
               
               
                 Radius 606 (mm) 
                 7.505 
                 7.505 
                 7.505 
               
               
                   
               
            
           
         
       
     
       FIG. 14C  is a cross-sectional view of another example embodiment of lens  100  taken along line  4 - 4  of  FIG. 14A . Here, surfaces  602  and  604  are each substantially aspherical. Surfaces  602  and  604  each have a radius  614  and  616 , respectively, measured along central axis  118 . Radius  616  is measured along central axis  118  from vertex  622  to an imaginary position of surface  604  corresponding to the point where surface  604  would intersect central axis  118  if surface  604  were to extend all the way to central axis  118  as indicated by dashed line  620 . 
     Because aspherical surfaces are inherently multifocal, the inclusion of multiple aspherical surfaces provides an added dimension of multifocality to lens  100 . For instance, surface  602  can have any asphericity (Q) and can provide a range of diopter values varying at any rate from apex  105  to interface  603  and can be configured to provide for correction over relatively near distances, while surface  604  can have a range of diopter values varying at any rate from interface  603  to interface  123  and can be configured to provide correction over relatively far distances. One of skill in the art will readily recognize that each surface  602  and  604  can have any range of diopter values and provide for correction over any distance. 
     TABLE 3 depicts example values for one embodiment of a 5.0 millimeter (mm) diameter lens  100  having multiple aspherical surfaces  602  and  604  similar to that depicted in  FIG. 14C . Each of the three embodiments provides for a different degree of correction for relatively far distances and relatively near distances. All of these example values are for purposes of illustration only and in no way limit the implantable lens  100  to only these or similar values. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Parameter 
                 0.00/1.75 D 
                 0.00/2.00 D 
                 0.00/2.25 D 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Lens diameter 112 (mm) 
                 5.00 
                 5.00 
                 5.00 
               
               
                 Posterior radius 107 (mm) 
                 7.50 
                 7.50 
                 7.50 
               
               
                 Center thickness 140 (mm) 
                 0.020 
                 0.021 
                 0.022 
               
               
                 Bevel radius 124 (mm) 
                 4.770 
                 4.770 
                 4.770 
               
               
                 Edge radius 126 (mm) 
                 0.025 
                 0.025 
                 0.025 
               
               
                 Edge thickness 130 (mm) 
                 0.010 
                 0.010 
                 0.010 
               
               
                 Edge slope angle 132 
                 45 
                 45 
                 45 
               
               
                 (degrees) 
               
            
           
           
               
            
               
                 Aspherical Surface 602 
               
            
           
           
               
               
               
               
            
               
                 Diameter 610 (mm) 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Radius 614 (mm) 
                 7.217 
                 7.182 
                 7.148 
               
               
                 Asphericity (Q) 
                 −1.015 
                 −1.001 
                 −0.987 
               
            
           
           
               
            
               
                 Aspherical Surface 604 
               
            
           
           
               
               
               
               
            
               
                 Diameter 612 (mm) 
                 4.90 
                 4.90 
                 4.90 
               
               
                 Radius 616 (mm) 
                 7.452 
                 7.452 
                 7.452 
               
               
                 Asphericity (Q) 
                 −0.225 
                 −0.225 
                 −0.225 
               
               
                   
               
            
           
         
       
     
     Although not depicted in  FIGS. 14A-C , lens  100  can have one or more transition surfaces at interface  603  that provide for a smoother transition between surfaces  602  and  604 , as sharp transitions can stimulate adverse tissue reactions. Edge surface  104  and beveled portion  124  are also not depicted in  FIGS. 14A-C , but it can be included as desired. Also, it should be noted that lens  100  can have any number of multifocal surfaces or refractive regions as desired. The multifocal surfaces  602  and  604 , substantially spherical or substantially aspherical, can also be arranged in any manner desired including, but not limited to, eccentric, hemispherical, irregular and the like. 
       FIG. 15  shows an example of an intracorneal inlay  31  implanted in a cornea  30 . The inlay  31  may have a meniscus shape with an anterior surface  32  and a posterior surface  33 . The inlay  31  is preferably implanted in the cornea at a depth of 50% or less of the cornea (approximately 250 microns or less), and is placed on the stromal bed  35  of the cornea created by a micro keratome. The inlay  31  may be implanted in the cornea  30  by cutting a flap  34  into the cornea, lifting the flap  34  to expose the cornea&#39;s interior, placing the inlay  31  on the exposed area of the cornea&#39;s interior, and repositioning the flap  34  over the inlay  31 . The flap  34  may be cut using a laser, e.g., a femtosecond laser, a mechanical keratome or manually by an ophthalmic surgeon. When the flap  34  is cut into the cornea, a small section of corneal tissue is left intact to create a hinge for the flap  34  so that the flap  34  can be repositioned accurately over the inlay  33 . After the flap  34  is repositioned over the inlay, the cornea heals around the flap  34  and seals the flap  34  back to the un-cut peripheral portion of the anterior corneal surface. Alternatively, a pocket or well having side walls or barrier structures may be cut into the cornea, and the inlay inserted between the side walls or barrier structures through a small opening or “port” in the cornea. 
     The inlay  31  changes the refractive power of the cornea by altering the shape of the anterior corneal surface. In  FIG. 15 , the pre-operative anterior corneal surface is represented by dashed line  36  and the post-operative anterior corneal surface induced by the underlying inlay  31  is represented by solid line  37 . 
     The inlay may have properties similar to those of the cornea (e.g., index of refraction around 1.376, water content of 78%, etc.), and may be made of hydrogel or other clear bio-compatible material. To increase the optical power of the inlay, the inlay may be made of a material with a higher index of refraction than the cornea, e.g., &gt;1.376. Materials that can be used for the inlay include, but are not limited to, Lidofilcon A, Poly-HEMA, poly sulfone, silicone hydrogel, and the like. The index of refraction may be in the range of 1.33 to 1.55. 
     This section discusses the use of small intracorneal inlays having diameters that are small in comparison with the pupil for correcting presbyopia. In the preferred embodiment, a small inlay (e.g., 1 to 2 mm in diameter) is implanted centrally in the cornea to induce an “effect” zone on the anterior corneal surface that is smaller than the optical zone of the cornea for providing near vision. Here, “effect” zone is the area of the anterior corneal surface affected by the inlay. The implanted inlay increases the curvature of the anterior corneal surface within the “effect” zone, thereby increasing the diopter power of the cornea within the “effect” zone. Distance vision is provided by the region of the cornea peripheral to the “effect” zone. 
     Presbyopia is characterized by a decrease in the ability of the eye to increase its power to focus on nearby objects due to a loss of elasticity in the crystalline lens with age. Typically, a person suffering from Presbyopia requires reading glasses to provide near vision. 
       FIG. 16  shows an example of how a small inlay can provide near vision to a subject&#39;s eye while retaining some distance vision according to an embodiment of the invention. The eye  38  comprises the cornea  39 , the pupil  40 , the crystalline lens  41  and the retina  42 . In this example, the small inlay (not shown) is implanted centrally in the cornea to create a small diameter “effect” zone  43 . The small inlay has a smaller diameter than the pupil  40  so that the resulting “effect” zone  43  has a smaller diameter than the optical zone of the cornea. The “effect” zone  43  provides near vision by increasing the curvature of the anterior corneal surface, and therefore the diopter power within the “effect” zone  43 . The region  44  of the cornea peripheral to the “effect” zone provides distance vision. 
     To increase the diopter power within the “effect” zone  43 , the small inlay has a higher curvature than the pre-implant anterior corneal surface to increase the curvature of the anterior corneal surface within the “effect” zone  43 . The inlay may further increase the diopter power within the “effect” zone  43  by having an index of refraction that is higher than the index of refraction of the cornea (n comea =1.376). Thus, the increase in the diopter power within the “effect” zone  43  may be due to the change in the anterior corneal surface induced by the inlay or a combination of the change in the anterior cornea surface and the index of refraction of the inlay. For early presbyopes (e.g., about 45 to 55 years of age), at least 1 diopter is typically required for near vision. For complete presbyopes (e.g., about 60 years of age or older), between 2 and 3 diopters of additional power is required. 
     An advantage of the small intracorneal inlay is that when concentrating on nearby objects  45 , the pupil naturally becomes smaller (e.g., near point miosis) making the inlay effect even more effective. Further increases in the inlay effect can be achieved by simply increasing the illumination of a nearby object (e.g., turning up a reading light). 
     Because the inlay is smaller than the diameter of the pupil  40 , light rays  47  from distant objects  46  by-pass the inlay and refract using the region of the cornea peripheral to the “effect” zone to create an image of the distant objects on the retina  42 , as shown in  FIG. 16 . This is particularly true with larger pupils. At night, when distance vision is most important, the pupil naturally becomes larger, thereby reducing the inlay effect and maximizing distance vision. 
     A subject&#39;s natural distance vision is in focus only if the subject is emmetropic (i.e., does not require glasses for distance vision). Many subjects are ammetropic, requiring either myopic or hyperopic refractive correction. Especially for myopes, distance vision correction can be provided by myopic Laser in Situ Keratomileusis (LASIK), Laser Epithelial Keratomileusis (LASEK), Photorefractive Keratectomy (PRK) or other similar corneal refractive procedures. After the distance corrective procedure is completed, the small inlay can be implanted in the cornea to provide near vision. Since LASIK requires the creation of a flap, the inlay may be inserted concurrently with the LASIK procedure. The inlay may also be inserted into the cornea after the LASIK procedure since the flap can be re-opened. Therefore, the small inlay may be used in conjunction with other refractive procedures, such as LASIK for correcting myopia or hyperopia. 
     A method for designing a small inlay to provide near vision will now be described.  FIG. 17  shows a small inlay  49  implanted in the cornea  48  and the change in the shape of the anterior corneal surface  53  induced by the inlay  49 . In  FIG. 17 , the pre-implant anterior corneal surface is represented by dashed line  52  and the post-implant anterior corneal surface induced by the inlay  49  is represented by solid line  53 . The inlay  49  does not substantially affect the shape of the anterior corneal surface in the region of the cornea peripheral to the “effect” zone so that distance vision is undisturbed in the peripheral  54 . In the case where a distance corrective procedure is performed prior to implantation of the inlay, the pre-implant anterior corneal surface  52  is the anterior corneal surface after the distance corrective procedure but before implantation of the inlay. 
     The inlay  49  has a finite edge thickness  55 . The edge thickness  55  can not be made zero due to the finite material properties of the inlay. The finite edge thickness  55  of the inlay produces a draping effect, as described further below. To minimize the draping effect, the edge thickness  55  of the inlay  49  can be made as small as possible, e.g., less than about 20 microns. In addition to a finite edge thickness  55 , the inlay may have a tapered region (not shown) that tapers downward from the anterior surface  50  of the inlay to the edge  55  of the inlay. The tapered region may be 10-30 microns in length. 
     In  FIG. 17 , the portion of the anterior corneal surface directly above the inlay is altered by the physical shape of the inlay  49 . Because of the finite edge thickness  55  of the inlay  49 , the anterior corneal surface does not immediately return to its pre-implant shape for a diameter larger than the physical inlay  49 . Eventually, the anterior corneal surface returns to the pre-implant corneal surface  52 . Therefore, the draping effect produces a drape region  56  that extends the shape change of the anterior corneal surface induced by the inlay  49 . 
       FIG. 18  illustrates a variety of possible draping shapes  58 .  FIG. 18  shows the radius (d I /2) of an inlay region  59  and the total radius (d Z /2) of the shape change due to the draping effect. The possible draping shapes  58  are shown in dashed lines, and may depend on factors such as the edge thickness, the local mechanical properties of the flap material, the diameter of the inlay (dI), the mechanical properties of the inlay material, and other geometric factors. The precise shape of the drape can be approximated by invitro or invivo clinical experiments and/or by complex mechanical modeling using techniques such as finite element analysis. 
     It is useful to define the optical zone diameter (dz) corresponding to the size of the anterior corneal surface affected by the inlay  49 , as shown in  FIG. 17 . For purposes of the design method, it is sufficient to assume that the relationship between the optical zone and the inlay diameter, given the other variables, can be determined by the methods outlined above. 
     A method for designing a small inlay to provide near vision according to an embodiment will now be given. 
     (1) The first step is to determine the maximum optical zone (dz) that is an acceptable tradeoff between the near vision improvement and the loss of distance vision. Considerations include the pupil size of the specific subject or a group of characteristic subjects (e.g., subjects within a particular age range) while reading nearby objects and the pupil size for distance viewing, especially at night. In an exemplary application, the inlay is placed in one eye to provide near vision and distance correction by other means is performed on the fellow eye. In this example, both eyes contribute to distance vision, with the non-inlay eye providing the sharpest distance vision. The eye with the inlay provides near vision. 
     (2) Given the empirically derived or theoretically derived relationship between the optical zone (dz) and the inlay diameter (dI), approximate the inlay diameter that achieves the optical zone. 
     (3) Design the inlay using the method outlined in detail below. This method is similar to the design methods described in U.S. application Ser. No. 11/293,644, titled “Design of Intracorneal Inlays,” filed on Dec. 1, 2005, the entirety of which is incorporated herein by reference. 
     (4) Finally, use optical ray-trace methods to assess the image quality of distance and near images with the inlay using the entire corneal surface (i.e., the corneal surface within the inlay diameter (dI), between the inlay diameter and the optical zone (dz), and the peripheral to the optical zone). Make small adjustments to the inlay design to optimize the distance and near image quality based on the inlay design method outlined below and the predicted drape shape given by the methods described above. 
     The design method of step three will now be given. 
       FIGS. 17 and 18  show two regions affected by the inlay design: a “central region”  57  defined by the inlay diameter (dI), and a “drape region”  56  falling between the inlay diameter and the optical zone (dz). The design method described below is used to design inlays to produce desired shapes of the anterior corneal surface in the central region to correct presbyopia. This design method assumes that the inlay material has the same index of refraction as the cornea. 
     A first step in the design of an inlay in the central region is determining a thickness profile that the inlay must induce on the anterior corneal surface to produce a desired anterior corneal curvature. The desired ADD power needed to provide near focus dictates the desired anterior corneal curvature in the central region ( FIG. 18 ). 
     A first step in determining the thickness profile of the inlay is to determine an anterior radius of curvature, r′ a , that provides the desired refractive change, ΔRx=Rxdist−ADD, where ADD is the desired ADD power prescribed for near vision and Rxdist is the distance refraction prior to inlay implant. Rxdist is approximately zero diopters for emmetropic individuals, or is equal to the achieved or targeted post-operative distance refraction after a surgical procedure to correct the distance ammetropia. The equivalent change in the cornea&#39;s refractive power, ΔK equiv , at the anterior surface is given by: 
     
       
         
           
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     
                       K 
                       equiv 
                     
                   
                   = 
                   
                     
                       1 
                       
                         
                           1 
                           / 
                           Rxdist 
                         
                         - 
                         V 
                       
                     
                     - 
                     
                       1 
                       
                         
                           1 
                           / 
                           ADD 
                         
                         - 
                         V 
                       
                     
                   
                 
               
               
                 
                   Equaiton 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
     where V is a spectacle vertex distance, e.g., 0.012 meters, from a spectacle to the cornea&#39;s anterior surface. The spectacle vertex distance, V, takes into account that measurements of the cornea&#39;s refractive power are typically taken with a spectacle located a distance from the cornea&#39;s anterior surface, and translates these power measurements to the equivalent power at cornea&#39;s anterior surface. 
     The pre-implant refractive power at the anterior corneal surface may be approximated by Kavg-Kpost, where Kavg is the average corneal refractive power within approximately the optical zone created by the inlay and Kpost is a posterior corneal refractive power. The desired radius of curvature, r′ a , of the anterior surface may be given by: 
     
       
         
           
             
               
                 
                   
                     r 
                     a 
                     ′ 
                   
                   = 
                   
                     
                       ( 
                       
                         1.376 
                         - 
                         1 
                       
                       ) 
                     
                     
                       ( 
                       
                         Kavg 
                         - 
                         Kpost 
                         + 
                         
                           Δ 
                            
                           
                               
                           
                            
                           
                             K 
                             equiv 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
     For purposes of design and analysis, Kpost may be approximated as −6 diopters. The pre-implant radius of curvature, r preimplant , may be approximated by: 
         r   preimplant =(1.376−1)/( K avg− K post)   Equation 3
 
     The two radii of curvature need not originate from the same origin. 
       FIG. 19  shows a cross-sectional view of a thickness profile  60  specified by a difference between the desired anterior corneal surface  62  and the pre-implant anterior corneal surface  61 . In  FIG. 19 , arrows  63  pointing from the pre-implant anterior surface  61  to the desired anterior surface  62  represent the axial thickness, L(r), of the thickness profile  60  at different positions along an r axis that is substantially perpendicular to an optical z axis. The double arrow  64  represents a center thickness, L c , of the thickness profile. In this embodiment, the thickness profile  60  is rotationally symmetric about the z axis. Thus, the entire thickness profile may be defined by rotating the cross-sectional view shown in  FIG. 19  about the z axis. 
     The thickness L(r) of the thickness profile may be given by: 
     
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                         ( 
                         r 
                         ) 
                       
                     
                     = 
                     
                       
                         L 
                         c 
                       
                       + 
                       
                         
                           Z 
                           preimplant 
                         
                          
                         
                           ( 
                           
                             r 
                             ; 
                             
                               r 
                               preimplant 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         
                           Z 
                           anew 
                         
                          
                         
                           ( 
                           
                             r 
                             ; 
                             
                               r 
                               a 
                               ′ 
                             
                           
                           ) 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   and 
                    
                   
                     
 
                   
                    
                   
                     
                       L 
                       c 
                     
                     = 
                     
                       
                         
                           Z 
                           anew 
                         
                          
                         
                           ( 
                           
                             
                               d 
                               1 
                             
                             2 
                           
                           ) 
                         
                       
                       - 
                       
                         
                           Z 
                           preimplant 
                         
                          
                         
                           ( 
                           
                             
                               d 
                               1 
                             
                             2 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
     where L c  is the center thickness of the thickness profile, Z implant (r) is the pre-operative anterior corneal surface as a function of r, Z anew (r) is the desired anterior corneal surface as a function of r, and d I  is the diameter of the inlay. In the example above, the anterior surfaces Z anew  and Z preimplant  were assumed to be spherical. This need not be the case. The anterior surfaces may also be aspheric. More generally, the desired anterior surface Z anew  may be a function of desired ADD and also more complex design parameters, e.g., an aspheric surface for higher-order aberration correction. Also, the pre-implant anterior surface Z preimplant  is generally aspheric. For designs requiring aspheric surfaces, the surface function Z(r) may be given by the general aspheric form: 
     
       
         
           
             
               
                 
                   
                     Z 
                      
                     
                       ( 
                       r 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           r 
                           2 
                         
                         / 
                         
                           r 
                           c 
                         
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   k 
                                 
                                 ) 
                               
                                
                               
                                 
                                   ( 
                                   
                                     r 
                                     / 
                                     
                                       r 
                                       c 
                                     
                                   
                                   ) 
                                 
                                 2 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         a 
                         4 
                       
                        
                       
                         r 
                         4 
                       
                     
                     + 
                     
                       
                         a 
                         6 
                       
                        
                       
                         r 
                         6 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   5 
                 
               
             
           
         
       
     
     where: r c  is the radius of curvature 
     k is a conic constant 
     a 4  and a 6  are higher order aspheric constants 
     For a spherical surface, k=0, a 4 =0, and a 6 =0. The human cornea may be approximated by k=−0.16, a 4 =0 and a 6 =0. The radius of curvature, r c , may be specified by the ADD power for correction of presbyopia, and the other parameters may specify corrections for higher-order aberrations. 
     The above expressions for the thickness profile are intended to be exemplary only. Other mathematical expressions or parameters may be used to describe similar or other thickness profiles. Therefore, the invention is not limited to particular mathematical expressions or parameters for describing the thickness profile. 
     After the required thickness profile L(r) is determined, the inlay is dimensioned to have substantially the same thickness profile. The profiles should have the same thickness to within about one micron, which would cause a diopter difference of about one eight of a diopter if the center thickness differs by one micron. An eighth of a diopter is half the accuracy with which ophthalmic refractive errors are manually recorded. Next, the thickness profile of the inlay is increased by the finite edge thickness (h edge ) by the manufacturing process. This finite edge thickness is one factor inducing the drape as illustrated in  FIG. 18 . When implanted in the cornea, the thickness profile of the inlay is substantially transferred to the anterior corneal surface through the intervening flap, thereby producing the desired post-implant anterior corneal surface in the central region. The draping effect causes the change in the anterior corneal surface thickness to extend beyond the central region. This draping effect can be minimized, e.g., by reducing the finite edge thickness of the inlay as much as possible. 
     The design method above assumed that the index of refractive of the inlay is the same as the cornea, in which case changes in refractive power of the cornea is due solely to the change in the anterior corneal surface induced by the inlay. An inlay with intrinsic power (e.g., a higher index of refraction than the cornea) may also be used, in which changes in the refractive power is provided by a combination of the physical inlay shape and the intrinsic power (i.e., index of refraction) of the inlay. Design methods for inlays with intrinsic power are described in application Ser. No. 11/381,056, titled “Design of Inlays with Intrinsic Diopter Power,” filed on May 1, 2006, the entirety of which is incorporated herein by reference. 
     For some applications, it is desirable for an inlay to induce an effective optical zone on the anterior corneal surface that is much larger than the inlay diameter. The increase in the effective optical zone allows the inlay to produce a much larger clinical effect on the patient&#39;s vision than the actual inlay diameter. In one example, a 1.5 mm-2 mm range diameter inlay has an increased effective optical zone of 4 mm-5 mm, in which the optical effect of the inlay is 2× to 3× greater than its diameter. The increased effective optical zone can also be achieved with inlay diameters outside the above range. For example, the diameter of the inlay may go down to 1 mm or less for some designs, while achieving the desired optical effect. 
     The increase in the effective optical zone (i.e., “effect” zone) of the inlay can be achieved by increasing the draping effect of the inlay. Increasing the draping effect extends the drape region, and therefore the effective optical zone (i.e., the area of the anterior corneal surface affected by the inlay). The draping effect may be increased, e.g., by increasing the finite edge thickness of the inlay so that the anterior corneal surface returns to its pre-implant surface at a larger radius. 
     Small diameter inlays inducing effective optical zones much larger than the inlay diameter may be used to correct hyperopia. For example, an inlay with a diameter of 2 mm can provide increased diopter power over an effective optical zone having a diameter of 4 mm. The curvature of the anterior corneal surface in the drape region is greater than the pre-implant anterior corneal surface. Therefore, the draping effect extends the area of the anterior corneal surface where the curvature is increased, thereby extending the effective optical zone of the inlay and providing increased diopter power over a wider diameter than the inlay diameter. This increase in the effective optical zone allows for the correction of hyperopia using smaller diameter inlays. 
     An inlay with increased effective optical zone may also be used to correct various vision impairments including presbyopia, hyperopia, myopia, and higher order aberrations. In the case of presbyopia, a sufficient “effect” zone may be achieved with an even smaller diameter inlay. For example, a 1 mm diameter inlay may be used to produce a 2 mm diameter “effect” zone. 
     Clinical data will now be presented in which the effective optical zone induced by an inlay is larger than the inlay diameter. In general, topographic instruments can be used to measure the change in the anterior surface elevation induced by an inlay, calculate the change in the anterior surface curvature and deduce the change in the diopter power.  FIG. 20  shows an example of a 3D topographic difference map showing the change in the anterior corneal surface for a subject (subject  1 ) between a preoperative examination and a one week postoperative examination. In this example, an intracorneal inlay was implanted in subject  1  having a diameter of 2 mm, a center thickness of approximately 36 microns, and an edge thickness of approximately 30 microns. The inlay was placed under a corneal flap created using a laser keratome (by Intralase, Inc.) at a depth of approximately 110 microns. A Scheimpflug topographer (“Pentacam” by Oculus, Inc.) was used to measure the surfaces. From  FIG. 20 , it is clear that the implanted inlay steepened the anterior corneal surface. 
       FIG. 21  shows the average radial elevation profile calculated from data in  FIG. 20 . Average radial profiles for two additional subjects (subjects  2  and  3 ) who received the same inlay design are also shown. Note that the central anterior surface elevation change was less than the center thickness of the inlay. This reflects biomechanical interactions between the inlay material, stromal bed on which it rests and the overlying keratometric flap. However, in all cases the inlay increased the anterior surface elevation beyond the physical diameter of the inlay.  FIG. 21  suggests that the effective optical zone induced by the inlay was approximately twice the inlay diameter for this particular design. Inlays with different diameters, center thicknesses and thickness profiles may have different “effect” zone sizes. 
       FIG. 22  shows a contour map of the refractive change induced by the intracorneal inlay. This is calculated from the elevation differences by calculating the sagittal curvature map and converting to diopter power using: 
       Diopter power=( n   c −1)/sagittal curvature
 
     where n c  is the index of refraction of the cornea. Again, the effective optical zone of the inlay was greater than the diameter of the inlay. 
     In some embodiments the inlay has a diameter between about 1 mm and about 3 mm, and in some particular embodiments the inlay is about 2 mm in diameter. In some embodiments the inlay central thickness (from anterior to posterior surfaces) is about 20 microns to about 40 microns, while in some particular embodiments the inlay central thickness is about 30 microns, and in some more particular embodiment the central thickness is about 32 microns. In some embodiments the inlay has an edge thickness of about 3 microns to about 16 microns, and in some particular embodiments the edge thickness is about 12 microns. In some embodiments the anterior surface radius of curvature is about 7 mm to about 13 mm, and in some particular embodiments the anterior surface radius of curvature is about 10 mm. In some embodiments the posterior surface radius of curvature is about 5 mm to about 12 mm, and in some particular embodiments the posterior surface radius of curvature is about 8.5 mm. 
     In one particular embodiment the inlay has a diameter of about 2 mm, the central thickness is about is about 32 microns, the edge thickness is about 12 microns, the anterior surface radius of curvature is about 10 mm, and the posterior surface radius of curvature is about 8.5 mm. 
     Exemplary embodiments have been shown and described herein. It will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from that which is described herein.