Patent Publication Number: US-9427311-B2

Title: Corneal inlay with nutrient transport structures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/233,802, filed Aug. 13, 2009, the entirety of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     This application relates generally to the field of corneal implants. For example, this application is directed to corneal inlays with an aperture to improve depth of focus (e.g. “masked” corneal inlays) and methods of making. 
     2. Description of the Related Art 
     The human eye functions to provide vision by transmitting and focusing light through a clear outer portion called the cornea, and further refining the focus of the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens. 
     The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In a normal, healthy eye, sharp images of distant objects are formed on the retina (emmetropia). In many eyes, images of distant objects are either formed in front of the retina because the eye is abnormally long or the cornea is abnormally steep (myopia), or formed in back of the retina because the eye is abnormally short or the cornea is abnormally flat (hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. 
     A normally functioning human eye is capable of selectively focusing on either near or far objects through a process known as accommodation. Accommodation is achieved by inducing deformation in a lens located inside the eye, which is referred to as the crystalline lens. Such deformation is induced by muscles called ciliary muscles. In most individuals, the ability to accommodate diminishes with age and these individuals cannot see up close without vision correction. If far vision also is deficient, such individuals are usually prescribed bifocal lenses. 
     SUMMARY 
     This application is directed to corneal inlays that are configured to position an aperture or opening within optical path of an eye. Such inlays can be useful for compensating for inadequate optical performance of an eye, which may be the result of age. Presbyopia is one well-known ailment that involves the degradation of accommodation that can be treated with aperture corneal inlays. Inlays with an opening may also be useful for treating aniridia. 
     An aperture corneal inlay can have many forms, such as including a light blocking (e.g., opaque) annulus surrounding an aperture. Such a device is sometimes referred to herein as a “mask.” In some embodiments, the small aperture can be a pin-hole aperture. Long-term acceptance of such inlays by patients can be enhanced by facilitating transmission of nutrients between tissues located anteriorly and posteriorly of the inlay. For example, the inlay can be made porous such that certain nutrients can readily pass therethrough. If the inlay is very thin, small perforations or holes can be formed through the annulus for this purpose. 
     In certain embodiments, a mask configured to be implanted in a cornea of a patient to increase the depth of focus of the patient is provided. The mask can include an anterior surface configured to reside adjacent a first corneal layer, a posterior surface configured to reside adjacent a second corneal layer, and an aperture configured to transmit along an optic axis light directed toward the aperture. The mask can further include a substantially opaque portion extending at least partially between the aperture and an outer periphery of the mask, and the opaque portion can include an inner region, an outer region, and a central region disposed between the inner and outer regions. A plurality of holes can extend between the anterior surface and the posterior surface, and the holes can be positioned at locations in the inner, outer and central regions. The central region can include a first porosity, the inner region can include a second porosity, the outer region can include a third porosity, and the first porosity can be greater than the second porosity or the third porosity. 
     In other embodiments, a mask can include an anterior surface configured to reside adjacent a first corneal layer, a posterior surface configured to reside adjacent a second corneal layer, and an aperture configured to transmit along an optic axis substantially all light directed toward the aperture. A substantially opaque portion can extend at least partially between the aperture and an outer periphery of the mask, and the opaque portion can include an inner region, an outer region, and a central region disposed between the inner and outer regions. The central region can include a first nutrient transport rate between the posterior and anterior surfaces, the inner region can include a second nutrient transport rate between the posterior and anterior surfaces, the outer region can include a third nutrient transport rate between the posterior and anterior surfaces, and the first nutrient transport rate can be greater than the second or third nutrient transport rates. 
     In a further embodiment, a method for improving the vision of a patient is provided. The method can include providing a mask that includes an anterior surface configured to reside adjacent a first corneal layer, a posterior surface configured to reside adjacent a second corneal layer, and an aperture configured to transmit light along an optic axis. The mask can further include a substantially opaque portion extending at least partially between the aperture and an outer periphery of the mask, and the opaque portion can include an inner region, an outer region, and a central region disposed between the inner and outer regions. A plurality of holes can extend between the anterior surface and the posterior surface, and the holes can be positioned at locations in the inner, outer and central regions. The central region can include a first porosity, the inner region can include a second porosity, the outer region can include a third porosity, and the first porosity can be greater than the second porosity or the third porosity. The method can further include inserting the mask into a cornea. 
     In certain embodiments, a corneal inlay is provided. The corneal inlay can include an anterior surface configured to reside adjacent a first corneal layer, a posterior surface configured to reside adjacent a second corneal layer, and an opening configured to transmit light therethrough. The corneal inlay can further include an outer zone adapted to substantially prevent transmission of light therethrough. The outer zone can have nutrient transport structures disposed therein, and the outer zone can be configured to provide enhanced nutrient flow at locations spaced away from the outer periphery compared to locations adjacent to the outer periphery. 
     The outer zone may comprise a first region and a second region at least partially disposed between the first region and the opening, and each of the first and second regions comprises nutrient transport structures disposed therein and one of the first and second regions is configured to have enhanced nutrient transport compared to the other of the first and second regions. The corneal inlay may also include a third region disposed between the region with enhanced nutrient transport and an outer or inner periphery of the corneal inlay. The region with enhanced nutrient transport may be configured to have greater nutrient transport than the third region. The corneal inlay can further include a first annular band disposed adjacent the opening and a second annular band disposed adjacent the outer periphery. The corneal inlay may also include one or more annular bands disposed adjacent the opening, adjacent an outer periphery of the corneal inlay, or both adjacent the opening and the outer periphery. The locations spaced away from the outer periphery can have higher porosity than locations adjacent to the outer periphery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of the human eye. 
         FIG. 2  is a cross-sectional side view of the human eye. 
         FIG. 3  is a cross-sectional side view of the human eye of a presbyopic patient wherein the light rays converge at a point behind the retina of the eye. 
         FIG. 4  is a cross-sectional side view of a presbyopic eye implanted with one embodiment of a mask wherein the light rays converge at a point on the retina. 
         FIG. 5  is a plan view of the human eye with a mask applied thereto. 
         FIG. 6  is a perspective view of one embodiment of a mask. 
         FIG. 7  is a frontal plan view of an embodiment of a mask with a hexagon-shaped pinhole like aperture. 
         FIG. 8  is a frontal plan view of an embodiment of a mask with an octagon-shaped pinhole like aperture. 
         FIG. 9  is a frontal plan view of an embodiment of a mask with an oval-shaped pinhole like aperture. 
         FIG. 10  is a frontal plan view of an embodiment of a mask with a pointed oval-shaped pinhole like aperture. 
         FIG. 11  is a frontal plan view of an embodiment of a mask with a star-shaped pinhole like aperture. 
         FIG. 12  is a frontal plan view of an embodiment of a mask with a teardrop-shaped pinhole like aperture spaced above the true center of the mask. 
         FIG. 13  is a frontal plan view of an embodiment of a mask with a teardrop-shaped pinhole like aperture centered within the mask. 
         FIG. 14  is a frontal plan view of an embodiment of a mask with a teardrop-shaped pinhole like aperture spaced below the true center of the mask. 
         FIG. 15  is a frontal plan view of an embodiment of a mask with a square-shaped pinhole like aperture. 
         FIG. 16  is a frontal plan view of an embodiment of a mask with a kidney-shaped oval pinhole like aperture. 
         FIG. 17  is a side view of an embodiment of a mask having varying thickness. 
         FIG. 18  is a side view of another embodiment of a mask having varying thickness. 
         FIG. 19  is a side view of an embodiment of a mask with a gel to provide opacity to the lens. 
         FIG. 20  is frontal plan view of an embodiment of a mask with a weave of polymeric fibers. 
         FIG. 21  is a side view of the mask of  FIG. 20 . 
         FIG. 22  is a frontal plan view of an embodiment of a mask having regions of varying opacity. 
         FIG. 23  is a side view of the mask of  FIG. 22 . 
         FIG. 24  is a frontal plan view of an embodiment of a mask that includes a centrally located pinhole like aperture and radially extending slots emanating from the center to the periphery of the mask. 
         FIG. 25  is a side view of the mask of  FIG. 24 . 
         FIG. 26  is a frontal plan view of an embodiment of a mask that includes a central pinhole like aperture, surrounded by a plurality of holes radially spaced from the pinhole like aperture and slots extending radially spaced from the holes and extending to the periphery of the mask. 
         FIG. 27  is a side view of the mask of  FIG. 26 . 
         FIG. 28  is a frontal plan view of an embodiment of a mask that includes a central pinhole like aperture, a region that includes a plurality of holes radially spaced from the aperture, and a region that includes rectangular slots spaced radially from the holes. 
         FIG. 29  is a side view of the mask of  FIG. 28 . 
         FIG. 30  is a frontal plan view of an embodiment of a mask that includes a non-circular pinhole like aperture, a first set of slots radially spaced from the aperture, and a region that includes a second set of slots extending to the periphery of the mask and radially spaced from the first set of slots. 
         FIG. 31  is a side view of the mask of  FIG. 30 . 
         FIG. 32  is a frontal plan view of an embodiment of a mask that includes a central pinhole like aperture and a plurality of holes radially spaced from the aperture. 
         FIG. 33  is a side view of the mask of  FIG. 32 . 
         FIG. 34  is an embodiment of a mask that includes two semi-circular mask portions. 
         FIG. 35  is an embodiment of a mask including two half-moon shaped portions. 
         FIG. 36  is an embodiment of a mask that includes a half-moon shaped region and a centrally-located pinhole like aperture. 
         FIG. 37  is an enlarged, diagrammatic view of an embodiment of a mask that includes particulate structure adapted for selectively controlling light transmission through the mask in a low light environment. 
         FIG. 38  is a view of the mask of  FIG. 37  in a bright light environment. 
         FIG. 39  is an embodiment of a mask that includes a barcode formed on the annular region of the mask. 
         FIG. 40  is another embodiment of a mask that includes connectors for securing the mask within the eye. 
         FIG. 41  is a plan view of an embodiment of a mask made of a spiraled fibrous strand. 
         FIG. 42  is a plan view of the mask of  FIG. 41  being removed from the eye. 
         FIG. 43  is a top view of another embodiment of a mask configured to increase depth of focus. 
         FIG. 43A  is an enlarged view of a portion of the view of  FIG. 43 . 
         FIG. 44A  is a cross-sectional view of the mask of  FIG. 43A  taken along the section plane  44 - 44 . 
         FIG. 44B  is a cross-sectional view similar to  FIG. 44A  of another embodiment of a mask. 
         FIG. 44C  is a cross-sectional view similar to  FIG. 44A  of another embodiment of a mask. 
         FIG. 45A  is a graphical representation of one arrangement of holes of a plurality of holes that may be formed on the mask of  FIG. 43 . 
         FIG. 45B  is a graphical representation of another arrangement of holes of a plurality of holes that may be formed on the mask of  FIG. 43 . 
         FIG. 45C  is a graphical representation of another arrangement of holes of a plurality of holes that may be formed on the mask of  FIG. 43 . 
         FIG. 46A  is an enlarged view similar to that of  FIG. 43A  showing a variation of a mask having non-uniform size. 
         FIG. 46B  is an enlarged view similar to that of  FIG. 43A  showing a variation of a mask having a non-uniform facet orientation. 
         FIG. 47  is a top view of another embodiment of a mask having a hole region and a peripheral region. 
         FIG. 48  is a flow chart illustrating one method of aligning a mask with an axis of the eye based on observation of an anatomical feature of the eye. 
         FIG. 49  is a flow chart illustrating one method of screening a patient for the use of a mask. 
         FIGS. 50A-50C  show a mask, similar to those described herein, inserted beneath an epithelium sheet of a cornea. 
         FIGS. 51A-51C  show a mask, similar to those described herein, inserted beneath a Bowman&#39;s membrane of a cornea. 
         FIG. 52  is a cross-sectional view of an eye illustrating a treatment of a patient wherein a flap is opened to place an implant and a location is marked for placement of the implant. 
         FIG. 52A  is a partial plan view of the eye of  FIG. 52  wherein an implant has been applied to a corneal flap and positioned with respect to a ring. 
         FIG. 53  is a cross-sectional view of an eye illustrating a treatment of a patient wherein a pocket is created to place an implant and a location is marked for placement of the implant. 
         FIG. 53A  is a partial plan view of the eye of  FIG. 53  wherein an implant has been positioned in a pocket and positioned with respect to a ring. 
         FIG. 54  is a flow chart illustrating one method for making a mask from a composition comprising a highly fluorinated polymer and an opacification agent. 
         FIG. 55  is a front view of an embodiment of a mask with a plurality of generally randomly distributed holes that have substantially equal size as described herein. 
         FIG. 56  is a front view of an embodiment of a mask with larger holes near the center of the annulus as described herein. 
         FIG. 57  is a front view of an embodiment of a mask with a hole region that has three sub-regions as described herein. 
         FIG. 58  is a plot of radial distance from the center of the aperture as a function of percentage of epithelial glucose depletion for the masks of  FIGS. 55 and 56 . 
     
    
    
     DETAILED DESCRIPTION 
     This application is directed to corneal inlays (e.g., masks) for improving the depth of focus of an eye of a patient and methods and apparatuses for making such corneal inlays. The masks generally employ pin-hole vision correction and have nutrient transport structures in some embodiments. The masks may be applied to the eye in any manner and in any location, e.g., as an implant in the cornea (sometimes referred to as a “corneal inlay”). The masks can also be embodied in or combined with lenses and applied in other regions of the eye, e.g., as or in combination with contact lenses or intraocular lenses. In some applications, discussed further below, the masks are formed of a stable material, e.g., one that can be implanted permanently. Corneal inlays with an opening may also be used to treat aniridia. 
     I. Overview of Depth of Focus Vision Correction 
     As discussed above, mask that has a pinhole aperture may be used to improve the depth of focus of a human eye. As discussed above, presbyopia is a problem of the human eye that commonly occurs in older human adults wherein the ability to focus becomes limited to inadequate range.  FIGS. 1-6  illustrate how presbyopia interferes with the normal function of the eye and how a mask with a pinhole aperture mitigates the problem. 
       FIG. 1  shows the human eye, and  FIG. 2  is a side view of the eye  10 . The eye  10  includes a cornea  12  and an intraocular lens  14  posterior to the cornea  12 . The cornea  12  is a first focusing element of the eye  10 . The intraocular lens  14  is a second focusing element of the eye  10 . The eye  10  also includes a retina  16 , which lines the interior of the rear surface of the eye  10 . The retina  16  includes the receptor cells which are primarily responsible for the sense of vision. The retina  16  includes a highly sensitive region, known as the macula, where signals are received and transmitted to the visual centers of the brain via the optic nerve  18 . The retina  16  also includes a point with particularly high sensitivity  20 , known as the fovea. As discussed in more detail in connection with  FIG. 8 , the fovea  20  is slightly offset from the axis of symmetry of the eye  10 . 
     The eye  10  also includes a ring of pigmented tissue known as the iris  22 . The iris  22  includes smooth muscle for controlling and regulating the size of an opening  24  in the iris  22 , which is known as the pupil. An entrance pupil  26  is seen as the image of the iris  22  viewed through the cornea  12  (See  FIG. 7 ). A central point of the entrance pupil  28  is illustrated in  FIG. 7  and will be discussed further below. 
     The eye  10  resides in an eye-socket in the skull and is able to rotate therein about a center of rotation  30 . 
       FIG. 3  shows the transmission of light through the eye  10  of a presbyotic patient. Due to either an aberration in the cornea  12  or the intraocular lens  14 , or loss of muscle control, light rays  32  entering the eye  10  and passing through the cornea  12  and the intraocular lens  14  are refracted in such a way that the light rays  32  do not converge at a single focal point on the retina  16 .  FIG. 3  illustrates that in a presbyotic patient, the light rays  32  often converge at a point behind the retina  16 . As a result, the patient experiences blurred vision. 
     Turning now to  FIG. 4 , there is shown the light transmission through the eye  10  to which a mask  34  has been applied. The mask  34  is shown implanted in the cornea  12  in  FIG. 4 . However, as discussed below, it will be understood that the mask  34  can be, in various modes of application, implanted in the cornea  12  (as shown), used as a contact lens placed over the cornea  12 , incorporated in the intraocular lens  14  (including the patient&#39;s original lens or an implanted lens), or otherwise positioned on or in the eye  10 . In the illustrated embodiment, the light rays  32  that pass through the mask  34 , the cornea  12 , and the lens  14  converge at a single focal point on the retina  16 . The light rays  32  that would not converge at the single point on retina  16  are blocked by the mask  34 . As discussed below, it is desirable to position the mask  34  on the eye  10  so that the light rays  32  that pass through the mask  34  converge at the fovea  20 . 
     Turning now to  FIG. 6 , there is shown one embodiment of the mask  34 . A variety of variations of the mask  34  are discussed hereinbelow. Section III discusses some materials that can be used to make the mask  34  and any of the variation thereof discussed hereinbelow. As seen, the mask  34  preferably includes an annular region  36  surrounding a pinhole opening or aperture  38  substantially centrally located on the mask  34 . The pinhole aperture  38  is generally located around a central axis  39 , referred to herein as the optical axis of the mask  34 . The pinhole aperture  38  preferably is in the shape of a circle. It has been reported that a circular aperture, such as the aperture  38  may, in some patients, produce a so-called “halo effect” where the patient perceives a shimmering image around the object being viewed. Accordingly, it may be desirable to provide an aperture  38  in a shape that diminishes, reduces, or completely eliminates the so-called “halo effect.” 
     II. Masks Employing Depth of Focus Correction 
       FIGS. 7-42  illustrate a variety of embodiments of masks that can improve the vision of a patient with presbyopia. The masks described in connection with  FIG. 7-42  are similar to the mask  34 , except as described differently below. Any of the masks discussed below, e.g., those shown in  FIGS. 7-42 , can be made of the materials discussed below in Section III. The mask  34  and any of the masks discussed below can include a locator structure, such as is discussed in U.S. Patent Publication No. 2006/0235428, filed Apr. 14, 2005 with the title “OCULAR INLAY WITH LOCATOR,” which is incorporated herein by reference in its entirety. The masks described in connection with  FIGS. 7-42  can be used and applied to the eye  10  of a patient in a similar fashion to the mask  34 . For example,  FIG. 7  shows an embodiment of a mask  34   a  that includes an aperture  38   a  formed in the shape of a hexagon.  FIG. 8  shows another embodiment of a mask  34   b  that includes an aperture  38   b  formed in the shape of an octagon.  FIG. 9  shows another embodiment of a mask  34   c  that includes an aperture  38   c  formed in the shape of an oval, while  FIG. 10  shows another embodiment of a mask  34   d  that includes an aperture  38   d  formed in the shape of a pointed oval.  FIG. 11  shows another embodiment of a mask  34   e  wherein the aperture  38   e  is formed in the shape of a star or starburst. 
       FIGS. 12-14  illustrate further embodiments that have tear-drop shaped apertures.  FIG. 12  shows a mask  34   f  that has a tear-drop shaped aperture  38   f  that is located above the true center of the mask  34   f .  FIG. 13  shows a mask  34   g  that has a tear-drop shaped aperture  38   g  that is substantially centered in the mask  34   g .  FIG. 14  shows a mask  34   h  that has a tear-drop shaped aperture  38   h  that is below the true center of the mask  34   h .  FIG. 12-14  illustrate that the position of aperture can be tailored, e.g., centered or off-center, to provide different effects. For example, an aperture that is located below the true center of a mask generally will allow more light to enter the eye because the upper portion of the aperture  34  will not be covered by the eyelid of the patient. Conversely, where the aperture is located above the true center of the mask, the aperture may be partially covered by the eyelid. Thus, the above-center aperture may permit less light to enter the eye. 
       FIG. 15  shows an embodiment of a mask  34   i  that includes an aperture  38   i  formed in the shape of a square.  FIG. 16  shows an embodiment of a mask  34   j  that has a kidney-shaped aperture  38   j . It will be appreciated that the apertures shown in  FIGS. 7-16  are merely exemplary of non-circular apertures. Other shapes and arrangements may also be provided and are within the scope of the present invention. 
     The mask  34  preferably has a constant thickness, as discussed below. However, in some embodiments, the thickness of the mask may vary between the inner periphery (near the aperture  38 ) and the outer periphery.  FIG. 17  shows a mask  34   k  that has a convex profile, i.e., that has a gradually decreasing thickness from the inner periphery to the outer periphery.  FIG. 18  shows a mask  34   l  that has a concave profile, i.e., that has a gradually increasing thickness from the inner periphery to the outer periphery. Other cross-sectional profiles are also possible. 
     The annular region  36  is at least partially and preferably completely opaque. The opacity of the annular region  36  prevents light from being transmitted through the mask  32  (as generally shown in  FIG. 4 ). Opacity of the annular region  36  may be achieved in any of several different ways. 
     For example, in one embodiment, the material used to make mask  34  may be naturally opaque. Alternatively, the material used to make the mask  34  may be substantially clear, but treated with a dye or other pigmentation agent to render region  36  substantially or completely opaque. In still another example, the surface of the mask  34  may be treated physically or chemically (such as by etching) to alter the refractive and transmissive properties of the mask  34  and make it less transmissive to light. 
     In still another alternative, the surface of the mask  34  may be treated with a particulate deposited thereon. For example, the surface of the mask  34  may be deposited with particulate of titanium, gold or carbon to provide opacity to the surface of the mask  34 . In another alternative, the particulate may be encapsulated within the interior of the mask  34 , as generally shown in  FIG. 19 . Finally, the mask  34  may be patterned to provide areas of varying light transmissivity, as generally shown in  FIGS. 24-33 , which are discussed in detail below. 
     Turning to  FIG. 20 , there is shown a mask  34   m  formed or made of a woven fabric, such as a mesh of polyester fibers. The mesh may be a cross-hatched mesh of fibers. The mask  34   m  includes an annular region  36   m  surrounding an aperture  38   m . The annular region  36   m  comprises a plurality of generally regularly positioned apertures  36   m  in the woven fabric allow some light to pass through the mask  34   m . The amount of light transmitted can be varied and controlled by, for example, moving the fibers closer together or farther apart, as desired. Fibers more densely distributed allow less light to pass through the annular region  36   m . Alternatively, the thickness of fibers can be varied to allow more or less light through the openings of the mesh. Making the fiber strands larger results in the openings being smaller. 
       FIG. 22  shows an embodiment of a mask  34   n  that includes an annular region  36   n  that has sub-regions with different opacities. The opacity of the annular region  36   n  may gradually and progressively increase or decrease, as desired.  FIG. 22  shows one embodiment where a first area  42  closest to an aperture  38   n  has an opacity of approximately 43%. In this embodiment, a second area  44 , which is outlying with respect to the first area  42 , has a greater opacity, such as 70%. In this embodiment, a third area  46 , which is outlying with respect to the second area  42 , has an opacity of between 85 to 100%. The graduated opacity of the type described above and shown in  FIG. 22  is achieved in one embodiment by, for example, providing different degrees of pigmentation to the areas  42 ,  44  and  46  of the mask  34   n . In another embodiment, light blocking materials of the type described above in variable degrees may be selectively deposited on the surface of a mask to achieve a graduated opacity. 
     In another embodiment, the mask may be formed from co-extruded rods made of material having different light transmissive properties. The co-extruded rod may then be sliced to provide disks for a plurality of masks, such as those described herein. 
       FIGS. 24-33  shows examples of masks that have been modified to provide regions of differing opacity. For example,  FIG. 24  shows a mask  34   o  that includes an aperture  38   o  and a plurality of cutouts  48  in the pattern of radial spokes extending from near the aperture  38   o  to an outer periphery  50  of the mask  34   o .  FIG. 24  shows that the cutouts  48  are much more densely distributed about a circumference of the mask near aperture  38   o  than are the cutouts  48  about a circumference of the mask near the outer periphery  50 . Accordingly, more light passes through the mask  34   o  nearer aperture  38   o  than near the periphery  50 . The change in light transmission through the mask  34   o  is gradual. 
       FIGS. 26-27  show another embodiment of a mask  34   p . The mask  34   p  includes an aperture  38   p  and a plurality of circular cutouts  49   p , and a plurality of cutouts  51   p . The circular cutouts  49   p  are located proximate the aperture  38   p . The cutouts  51   p  are located between the circular cutouts  49   p  and the periphery  50   p . The density of the circular cutouts  49   p  generally decreases from the near the aperture  38   p  toward the periphery  50   p . The periphery  50   p  of the mask  34   p  is scalloped by the presence of the cutouts  51 , which extend inward from the periphery  50   p , to allow some light to pass through the mask at the periphery  50   p.    
       FIGS. 28-29  shows another embodiment similar to that of  FIGS. 26-27  wherein a mask  34   q  includes a plurality of circular cutouts  49   q  and a plurality of cutouts  51   q . The cutouts  51   q  are disposed along the outside periphery  50   q  of the mask  34   q , but not so as to provide a scalloped periphery. 
       FIGS. 30 and 31  illustrate an embodiment of a mask  34   r  that includes an annular region  36   r  that is patterned and an aperture  38   r  that is non-circular. As shown in  FIG. 30 , the aperture  38   r  is in the shape of a starburst. Surrounding the aperture  38   r  is a series of cutouts  51   r  that are more densely spaced toward the aperture  38   r . The mask  34   r  includes an outer periphery  50   r  that is scalloped to provide additional light transmission at the outer periphery  50   r.    
       FIGS. 32 and 33  show another embodiment of a mask  34   s  that includes an annular region  36   s  and an aperture  38   s . The annular region  36   s  is located between an outer periphery  50   s  of the mask  34   s  and the aperture  38   s . The annular region  36   s  is patterned. In particular, a plurality of circular openings  56   s  is distributed over the annular region  36   s  of the mask  34   s . It will be appreciated that the density of the openings  56   s  is greater near the aperture  38   s  than near the periphery  50   s  of the mask  34   s . As with the examples described above, this results in a gradual increase in the opacity of the mask  34   s  from aperture  38   s  to periphery  50   s.    
       FIGS. 34-36  show further embodiments. In particular,  FIG. 34  shows a mask  34   t  that includes a first mask portion  58   t  and a second mask portion  60   t . The mask portions  58   t ,  60   t  are generally “C-shaped.” As shown in  FIG. 34 , the mask portions  58   t ,  60   t  are implanted or inserted such that the mask portions  58   t ,  60   t  define a pinhole or aperture  38   t.    
       FIG. 35  shows another embodiment wherein a mask  34   u  includes two mask portions  58   u ,  43   u . Each mask portion  58   u ,  43   u  is in the shape of a half-moon and is configured to be implanted or inserted in such a way that the two halves define a central gap or opening  45   u , which permits light to pass therethrough. Although opening  45   u  is not a circular pinhole, the mask portions  58   u ,  43   u  in combination with the eyelid (shown as dashed line  47 ) of the patient provide a comparable pinhole effect. 
       FIG. 36  shows another embodiment of a mask  34   v  that includes an aperture  38   v  and that is in the shape of a half-moon. As discussed in more detail below, the mask  34   v  may be implanted or inserted into a lower portion of the cornea  12  where, as described above, the combination of the mask  34   v  and the eyelid  45  provides the pinhole effect. 
     Other embodiments employ different ways of controlling the light transmissivity through a mask. For example, the mask may be a gel-filled disk, as shown in  FIG. 19 . The gel may be a hydrogel or collagen, or other suitable material that is biocompatible with the mask material and can be introduced into the interior of the mask. The gel within the mask may include particulate  53  suspended within the gel. Examples of suitable particulate are gold, titanium, and carbon particulate, which, as discussed above, may alternatively be deposited on the surface of the mask. 
     The material of the mask  34  may be any biocompatible polymeric material. Where a gel is used, the material is suitable for holding a gel. Examples of suitable materials for the mask  34  include the preferred polymethylmethacrylate or other suitable polymers, such as polycarbonates and the like. Of course, as indicated above, for non-gel-filled materials, a preferred material may be a fibrous material, such as a Dacron mesh. 
     The mask  34  may also be made to include a medicinal fluid or material, such as an antibiotic or other wound healing modulator that can be selectively released after application, insertion, or implantation of the mask  34  into the eye of the patient. Release of an antibiotic or other wound healing modulator after application, insertion, or implantation provides faster and/or improved healing of the incision. The mask  34  may also be coated with other desired drugs or antibiotics. For example, it is known that cholesterol deposits can build up on the eye. Accordingly, the mask  34  may be provided with a releasable cholesterol deterring drug. The drug may be coated on the surface of the mask  34  or, in an alternative embodiment, incorporated into the polymeric material (such as PMMA) from which the mask  34  is formed. 
       FIGS. 37 and 38  illustrate one embodiment where a mask  34   w  comprises a plurality of nanites  68 . “Nanites” are small particulate structures that have been adapted to selectively transmit or block light entering the eye of the patient. The particles may be of a very small size typical of the particles used in nanotechnology applications. The nanites  68  are suspended in the gel or otherwise inserted into the interior of the mask  34   w , as generally shown in  FIGS. 37 and 38 . The nanites  68  can be preprogrammed to respond to different light environments. 
     Thus, as shown in  FIG. 37 , in a high light environment, the nanites  68  turn and position themselves to substantially and selectively block some of the light from entering the eye. However, in a low light environment where it is desirable for more light to enter the eye, nanites may respond by turning or be otherwise positioned to allow more light to enter the eye, as shown in  FIG. 38 . 
     Nano-devices or nanites are crystalline structures grown in laboratories. The nanites may be treated such that they are receptive to different stimuli such as light. In accordance with one aspect of the present invention, the nanites can be imparted with energy where, in response to a low light and high light environments, they rotate in the manner described above and generally shown in  FIG. 38 . 
     Nanoscale devices and systems and their fabrication are described in Smith et al., “Nanofabrication,” Physics Today, February 1990, pp. 24-30 and in Craighead, “Nanoelectromechanical Systems,” Science, Nov. 24, 2000, Vol. 290, pp. 1502-1505, both of which are incorporated by reference herein in their entirety. Tailoring the properties of small-sized particles for optical applications is disclosed in Chen et al. “Diffractive Phase Elements Based on Two-Dimensional Artificial Dielectrics,” Optics Letters, Jan. 15, 1995, Vol. 20, No. 2, pp. 121-123, also incorporated by reference herein in its entirety. 
     Masks  34  made in accordance with the present invention may be further modified to include other properties.  FIG. 39  shows one embodiment of a mask  34   x  that includes a bar code  66  or other printed indicia. 
     The masks described herein may be incorporated into the eye of a patient in different ways. For example, as discussed in more detail below in connection with  FIG. 49 , the mask  34  may be provided as a contact lens placed on the surface of the eyeball  10 . Alternatively, the mask  34  may be incorporated in an artificial intraocular lens designed to replace the original lens  14  of the patient. Preferably, however, the mask  34  is provided as a corneal implant or inlay, where it is physically inserted between the layers of the cornea  12 . 
     When used as a corneal implant, layers of the cornea  12  are peeled away to allow insertion of the mask  34 . Typically, the optical surgeon (using a laser) cuts away and peels away a flap of the overlying corneal epithelium. The mask  34  is then inserted and the flap is placed back in its original position where, over time, it grows back and seals the eyeball. In some embodiments, the mask  34  is attached or fixed to the eye  10  by support strands  72  and  74  shown in  FIG. 40  and generally described in U.S. Pat. No. 4,976,732, incorporated by reference herein in its entirety. 
     In certain circumstances, to accommodate the mask  34 , the surgeon may be required to remove additional corneal tissue. Thus, in one embodiment, the surgeon may use a laser to peel away additional layers of the cornea  12  to provide a pocket that will accommodate the mask  34 . Application of the mask  34  to the cornea  12  of the eye  10  of a patient is described in greater detail in connection with  FIGS. 50A-51C . 
     Removal of the mask  34  may be achieved by simply making an additional incision in the cornea  12 , lifting the flap and removing the mask  34 . Alternatively, ablation techniques may be used to completely remove the mask  34 . 
       FIGS. 41 and 42  illustrate another embodiment, of a mask  34   y  that includes a coiled strand  80  of a fibrous or other material. Strand  80  is coiled over itself to form the mask  34   y , which may therefore be described as a spiral-like mask. This arrangement provides a pinhole or aperture  38   y  substantially in the center of the mask  34   y . The mask  34   y  can be removed by a technician or surgeon who grasps the strand  80  with tweezers  82  through an opening made in a flap of the corneal  12 .  FIG. 42  shows this removal technique. 
     Further mask details are disclosed in U.S. Pat. No. 4,976,732, issued Dec. 11, 1990 and in U.S. patent application Ser. No. 10/854,033, filed May 26, 2004, both of which are incorporated by reference herein in their entirety. 
     III. Preferred UV-Resistant Polymeric Mask Materials 
     Because the mask has a very high surface to volume ratio and is exposed to a great deal of sunlight following implantation, the mask preferably comprises a material which has good resistance to degradation, including from exposure to ultraviolet (UV) or other wavelengths of light. Polymers including a UV absorbing component, including those comprising UV absorbing additives or made with UV absorbing monomers (including co-monomers), may be used in forming masks as disclosed herein which are resistant to degradation by UV radiation. Examples of such polymers include, but are not limited to, those described in U.S. Pat. Nos. 4,985,559 and 4,528,311, the disclosures of which are hereby incorporated by reference in their entireties. In a preferred embodiment, the mask comprises a material which itself is resistant to degradation by UV radiation. In one embodiment, the mask comprises a polymeric material which is substantially reflective of or transparent to UV radiation. 
     Alternatively, the mask may include a component which imparts a degradation resistive effect, or may be provided with a coating, preferably at least on the anterior surface, which imparts degradation resistance. Such components may be included, for example, by blending one or more degradation resistant polymers with one or more other polymers. Such blends may also comprise additives which provide desirable properties, such as UV absorbing materials. In one embodiment, blends preferably comprise a total of about 1-20 wt. %, including about 1-10 wt. %, 5-15 wt. %, and 10-20 wt. % of one or more degradation resistant polymers. In another embodiment, blends preferably comprise a total of about 80-100 wt. %, including about 80-90 wt. %, 85-95 wt. %, and 90-100 wt. % of one or more degradation resistant polymers. In another embodiment, the blend has more equivalent proportions of materials, comprising a total of about 40-60 wt. %, including about 50-60 wt. %, and 40-50 wt. % of one or more degradation resistant polymers. Masks may also include blends of different types of degradation resistant polymers, including those blends comprising one or more generally UV transparent or reflective polymers with one or more polymers incorporating UV absorption additives or monomers. These blends include those having a total of about 1-20 wt. %, including about 1-10 wt. %, 5-15 wt. %, and 10-20 wt. % of one or more generally UV transparent polymers, a total of about 80-100 wt. %, including about 80-90 wt. %, 85-95 wt. %, and 90-100 wt. % of one or more generally UV transparent polymers, and a total of about 40-60 wt. %, including about 50-60 wt. %, and 40-50 wt. % of one or more generally UV transparent polymers. The polymer or polymer blend may be mixed with other materials as discussed below, including, but not limited to, opacification agents, polyanionic compounds and/or wound healing modulator compounds. When mixed with these other materials, the amount of polymer or polymer blend in the material which makes up the mask is preferably about 50%-99% by weight, including about 60%-90% by weight, about 65-85% by weight, about 70-80% by weight, and about 90-99% by weight. 
     Preferred degradation resistant polymers include halogenated polymers. Preferred halogenated polymers include fluorinated polymers, that is, polymers having at least one carbon-fluorine bond, including highly fluorinated polymers. The term “highly fluorinated” as it is used herein, is a broad term used in its ordinary sense, and includes polymers having at least one carbon-fluorine bond (C—F bond) where the number of C—F bonds equals or exceeds the number of carbon-hydrogen bonds (C—H bonds). Highly fluorinated materials also include perfluorinated or fully fluorinated materials, materials which include other halogen substituents such as chlorine, and materials which include oxygen- or nitrogen-containing functional groups. For polymeric materials, the number of bonds may be counted by referring to the monomer(s) or repeating units which form the polymer, and in the case of a copolymer, by the relative amounts of each monomer (on a molar basis). 
     Preferred highly fluorinated polymers include, but are not limited to, polytetrafluoroethylene (PFTE or Teflon®), polyvinylidene fluoride (PVDF or Kynar®), poly-1,1,2-trifluoroethylene, and perfluoroalkoxyethylene (PFA). Other highly fluorinated polymers include, but are not limited to, homopolymers and copolymers including one or more of the following monomer units: tetrafluoroethylene —(CF 2 —CF 2 )−; vinylidene fluoride —(CF 2 —CH 2 )—; 1,1,2-trifluoroethylene —(CF 2 —CHF)—; hexafluoropropene —(CF(CF 3 )—CF 2 )—; vinyl fluoride —(CH 2 —CHF)— (homopolymer is not “highly fluorinated”); oxygen-containing monomers such as —(O—CF 2 )—, —(O—CF 2 —CF 2 )—, —(O—CF(CF 3 )—CF 2 )—; chlorine-containing monomers such as —(CF 2 —CFCl)—. Other fluorinated polymers, such as fluorinated polyimide and fluorinated acrylates, having sufficient degrees of fluorination are also contemplated as highly fluorinated polymers for use in masks according to preferred embodiments. The homopolymers and copolymers described herein are available commercially and/or methods for their preparation from commercially available materials are widely published and known to those in the polymer arts. 
     Although highly fluorinated polymers are preferred, polymers having one or more carbon-fluorine bonds but not falling within the definition of “highly fluorinated” polymers as discussed above, may also be used. Such polymers include co-polymers formed from one or more of the monomers in the preceding paragraph with ethylene, vinyl fluoride or other monomer to form a polymeric material having a greater number of C—H bonds than C—F bonds. Other fluorinated polymers, such as fluorinated polyimide, may also be used. Other materials that could be used in some applications, alone or in combination with a fluorinated or a highly fluorinated polymer, are described in U.S. Pat. No. 4,985,559 and in U.S. Pat. No. 4,538,311, both of which are hereby incorporated by reference herein in their entirety. 
     The preceding definition of highly fluorinated is best illustrated by means of a few examples. One preferred UV-resistant polymeric material is polyvinylidene fluoride (PVDF), having a structure represented by the formula: —(CF 2 —CH 2 ) n —. Each repeating unit has two C—H bonds, and two C—F bonds. Because the number of C—F bonds equals or exceeds the number of C—H bonds, PVDF homopolymer is a “highly fluorinated” polymer. Another material is a tetrafluoroethylene/vinyl fluoride copolymer formed from these two monomers in a 2:1 molar ratio. Regardless of whether the copolymer formed is block, random or any other arrangement, from the 2:1 tetrafluoroethylene:vinyl fluoride composition one can presume a “repeating unit” comprising two tetrafluoroethylene units, each having four C—F bonds, and one vinyl fluoride unit having three C—H bonds and one C—F bond. The total bonds for two tetrafluoroethylenes and one vinyl fluoride are nine C—F bonds, and three C—H bonds. Because the number of C—F bonds equals or exceeds the number of C—H bonds, this copolymer is considered highly fluorinated. 
     Certain highly fluorinated polymers, such as PVDF, have one or more desirable characteristics, such as being relatively chemically inert and having a relatively high UV transparency as compared to their non-fluorinated or less highly fluorinated counterpart polymers. Although the applicant does not intend to be bound by theory, it is postulated that the electronegativity of fluorine may be responsible for many of the desirable properties of the materials having relatively large numbers of C—F bonds. 
     In preferred embodiments, at least a portion of the highly fluorinated polymer material forming the mask comprises an opacification agent which imparts a desired degree of opacity. In one embodiment, the opacification agent provides sufficient opacity to produce the depth of field improvements described herein, e.g., in combination with a transmissive aperture. In one embodiment, the opacification agent renders the material opaque. In another embodiment, the opacification agent prevents transmission of about 90 percent or more of incident light. In another embodiment, the opacification agent renders the material opaque. In another embodiment, the opacification agent prevents transmission of about 80 percent or more of incident light. Preferred opacification agents include, but are not limited to organic dyes and/or pigments, preferably black ones, such as azo dyes, hematoxylin black, and Sudan black; inorganic dyes and/or pigments, including metal oxides such as iron oxide black and ilminite, silicon carbide and carbon (e.g. carbon black, submicron powdered carbon). The foregoing materials may be used alone or in combination with one or more other materials. The opacification agent may be applied to one or more surfaces of the mask on all or some of the surface, or it may be mixed or combined with the polymeric material (e.g. blended during the polymer melt phase). Although any of the foregoing materials may be used, carbon has been found to be especially useful in that it does not fade over time as do many organic dyes, and that it also aids the UV stability of the material by absorbing UV radiation In one embodiments, carbon may be mixed with polyvinylidene fluoride (PVDF) or other polymer composition comprising highly fluorinated polymer such that the carbon comprises about 2% to about 20% by weight of the resulting composition, including about 10% to about 15% by weight, including about 12%, about 13%, and about 14% by weight of the resulting composition. 
     Some opacification agents, such pigments, which are added to blacken, darken or opacity portions of the mask may cause the mask to absorb incident radiation to a greater degree than mask material not including such agents. Because the matrix polymer that carries or includes the pigments may be subject to degradation from the absorbed radiation, it is preferred that the mask, which is thin and has a high surface area making it vulnerable to environmental degradation, be made of a material which is itself resistant to degradation such as from UV radiation, or that it be generally transparent to or non-absorbing of UV radiation. Use of a highly UV resistant and degradation resistant material, such as PVDF, which is highly transparent to UV radiation, allows for greater flexibility in choice of opacification agent because possible damage to the polymer caused by selection of a particular opacification agent is greatly reduced. 
     A number of variations of the foregoing embodiments of degradation resistant constructions are contemplated. In one variation, a mask is made almost exclusively of a material that is not subject to UV degradation. For example, the mask can be made of a metal, a highly fluorinated polymer, or another similar material. Construction of the mask with metal is discussed in more detail in U.S. application Ser. No. 11/000,562 filed Dec. 1, 2004 and entitled “Method of Making an Ocular Implant” and also in U.S. application Ser. No. 11/107,359 filed Apr. 14, 2005 with the title “Method of Making an Ocular Implant”, both of which are incorporated herein in their entirety by reference. As used in this context, “exclusively” is a broad term that allows for the presence of some non-functional materials (e.g., impurities) and for an opacification agent, as discussed above. In other embodiments, the mask can include a combination of materials. For example, in one variation, the mask is formed primarily of any implantable material and is coated with a UV resistant material. In another variation, the mask includes one or more UV degradation inhibitors and/or one or more UV degradation resistant polymers in sufficient concentration such that the mask under normal use conditions will maintain sufficient functionality in terms of degradation to remain medically effective for at least about 5 years, preferably at least about 10 years, and in certain implementations at least about 20 years. 
       FIG. 54  is a flow chart illustrating one method for making a mask from a composition comprising a highly fluorinated polymer and an opacification agent. At step  2000 , a liquid form of a polymer is created by dissolving polyvinylidene fluoride (PVDF) pellets into a solvent such as Dimethyl Acetamide (DMAC or DMA) using heat until the PVDF has completely dissolved. In one embodiment, the solution may be mixed for a minimum of 12 hours to ensure that the PVDF has completely dissolved. At step  2200 , the PVDF/DMAC solution is mixed with an opacification agent, such as carbon black, using a high speed shear mixer. In one embodiment, the carbon black comprises 13% by weight of the resulting composition while the PVDF comprises 87% by weight of the resulting composition. At step  2300 , the PVDF/carbon black solution is milled in a high speed mill, for example an Eiger high speed mill, to break up any large carbon agglomerates in the solution. The PVDF/carbon black solution may be run through the mill a second time to further break up any carbon agglomerates. At step  2400 , the resulting solution is applied to a silicone wafer to create a polymer film on the silicone disk. Here, approximately 55 g of the PVDF/carbon black solution is poured into a dispensing barrel for application on a silicone wafer. The silicone disk is placed on the spinner of a spin casting machine and the dispensing barrel is used to apply a bead of PVDF/carbon black solution to the silicone wafer in a circular pattern, leaving the center 1″ diameter of the disk empty. The spinner cycle is actuated to disperse the PVDF/carbon black solution over the disk, forming a uniform 10 micron thick film. The coated silicone disk is then placed on a hot-plate to evaporate the DMAC. At step  2500 , the coated silicon e wafer is placed under an Eximer laser. A laser cutting mask is mounted in the laser and the laser is actuated. Using the laser cutting mask, approximately 150 corneal mask patterns are laser machined into the PVDF/carbon black film. The corneal mask patterns are arranged such that the material extending approximately 5 mm from the edge of the silicon disk is not used. During the laser machining, the silicone disk may be bathed in Nitrogen gas in order to cool the surface. At step  2600 , the laser machined masks are removed from the silicone disk using a razor blade and placed into the bottom half of a convex Teflon forming mold. The top half of the Teflon forming mold is placed on top of the mask and the molds placed in an oven at about 160° C. At step  2700 , the molds are heated and baked to cure the masks. The molds are allowed to bake for approximately two hours at approximately 160° C. After two hours the oven temperature is reduced to about 30° C. and the masks are baked for approximately two hours or until the oven temperature has dropped to below around 40° C. 
     IV. Additives to Reduce Corneal Deposits and/or Promote Proper Healing 
     In some circumstances, corneal implants are associated with deposits on the cornea. Loading of one or more polyanionic compounds into the polymeric material of a corneal implant may reduce and/or substantially eliminate deposits on the cornea, possibly by attracting and/or retaining growth factors. 
     In a preferred embodiment the one or more polyanionic compounds include carbohydrates, proteins, natural proteoglycans, and/or the glycosaminoglycan moieties of proteoglycans, as well as derivatives (such as sulfated derivatives) and salts of compounds such as those in the aforementioned categories. Preferred polyanionic compounds include one or more of dermatan sulfate, chondroitin sulfate, keratan sulfate, heparan sulfate, heparin, dextran sulfate, hyaluronic acid, pentosan polysulfate, xanthan, carrageenan, fibronectin, laminin, chondronectin, vitronectin, poly L-lysine salts, and anionic, preferably sulfated, carbohydrates such as alginate may also be used, as well as salts and derivatives of the listed compounds. Examples of preferred anionic compounds and combinations of polyanionic compounds include keratan sulfate/chrondroitin sulfate-proteoglycan, dermatan sulfate proteoglycan, and dextran sulfate. 
     In one embodiment, a polyanionic compound comprises acidic sulfate moieties and the sulfur content is greater than about 5% by weight, preferably greater than about 10% by weight. In an even more preferred embodiment, the average molecular weight of a polyanionic compound is about 40,000 to 500,000 Daltons. 
     In a preferred embodiment, the total weight of the one or more polyanionic compounds in the loaded polymeric material is about 0.1% by weight to about 50% by weight, including about 5% by weight to about 20% by weight, about 12% by weight to about 17% by weight, about 0.5% by weight to about 4% by weight, and about 5% by weight to about 15% by weight. It should be noted that the percentages recited herein in relation to polyanionic compounds, opacification agents and wound healing modulator compounds are percent by weight with 100% being the total weight of the entire mask composition including all additives. 
     In one embodiment, the body of the mask is formed from a polymeric material having one or more polyanionic compounds loaded therein. Loading of a polyanionic compound is performed by mixing the polyanionic compound with the resin and any other additives of the polymeric material prior to molding or casting of the body of the mask. Although some of a polyanionic compound that is loaded into the polymeric material may be on the surface of the mask, loading is to be distinguished from coating in that a coated material would not have polyanionic material throughout the bulk of the mask. 
     The loaded polymeric material is preferably made by suspending or dissolving polymer, one or more polyanionic compounds and any other additives (such as wound healing modulators, as described below) in a solvent or solvent system, and then casting a film whereby the solvent or solvent system is removed such as by evaporation. Preferred casting methods include spin casting and other methods, including those known in the art, which can form a thin material of relatively even thickness. Although other methods of making thin substrates, such as extrusion, may be used, solvent casting is generally preferred because it does not need to be done at high temperatures that may cause degradation of some polyanionic compounds. The polymer, polyanionic compound, and/or other additives may be ground or milled, such as by ball milling, to reduce the particle size of the material prior to suspending, dissolving or melting as part of making the mask. 
     In methods using solvent casting, preferred solvents include those which are capable of dissolving the polymeric material, polyanionic compounds, and/or other additives. A suitable solvent or solvent system (i.e. combination of two or more solvents) may be chosen by one skilled in the art based upon known solubilities for a given polymeric material and/or routine experimentation based upon chemical principles. In solvent casting methods, the temperature of the solvent or solution should be no higher than the boiling point of the solvent or solvent system, and is preferably about 10° C. to about 70° C. During or after casting of the solution to form a film, the temperature may be elevated, including above the boiling point. 
     In one embodiment, a mask, such as an inlay, comprising PVDF, dextran sulfate, and carbon was made by spin casting. 100 grams of PVDC (about 71% by weight) in the form of pellets was dissolved in 400 grams of dimethylacetamide. 17 grams of carbon (about 12% by weight) and 24 grams of dextran sulfate (about 17% by weight) are ball milled to reduce particle size and then added to the PVDF/DMA solution. The percentages by weight are the percentages of the solids portion, that is the portion that is not the solvent. The solution was at room temperature (approximately 17° C. to about 25° C.). The solution was then spin cast to form a film. 
     In one embodiment, the device includes a wound healing modulator. When present, the wound healing modulator is on at least one surface or it may be loaded into the polymeric material. A wound healing modulator is defined as a compound that assists in proper healing of a wound, such as by increasing the rate of healing, decreasing inflammation, moderating or suppressing immune response, decreasing scarring, decreasing cell proliferation, reducing infection, encouraging transdifferentiation of keratocytes into cells that lay down collagen, and the like. Wound healing modulators include, without limitation, antibiotics, antineoplastics including antimitotics, antimetabolics and antibiotic types, anti-inflammatories, immunosupressants, and antifungals. Preferred compounds include, but are not limited to, fluorouracil, mitomycin C, paclitaxel, NSAIDs (e.g. ibuprofen, naproxen, flurbiprofen, carprofen, suprofen, ketoprofen), and cyclosporins. Other preferred compounds include proteoglycans, glycosaminoglycans, and salts and derivatives thereof, as well as other carbohydrates and/or proteins, including those disclosed above. 
     A wound healing modulator may be included in the mask by loading it into the polymeric material as discussed above with respect to the polyanionic compounds. It may also be included by binding it to one or more surfaces of the device. The “binding” of the wound healing modulator to the device may occur by phenomena that do not generally involve chemical bonds, including adsorption, hydrogen bonding, van der Waals forces, electrostatic attraction, ionic bonding, and the like, or it may occur by phenomena that do include chemical bonds. In a preferred embodiment, the total weight of the one or more wound healing modulator compounds in the loaded polymeric material is about 0.1% by weight to about 50% by weight, including about 5% by weight to about 20% by weight, about 12% by weight to about 17% by weight, about 0.5% by weight to about 4% by weight, and about 5% by weight to about 15% by weight. 
     In one embodiment, carbon, gold or other material on a surface of the mask acts as an adsorbent or otherwise participates in the binding of one or more wound healing modulators to the implant. The material on the surface of the mask that participates in binding the wound healing modulator may be part of the bulk material of the implant (distributed throughout the implant or which migrates to the surface during and/or following formation of the implant) and/or deposited on a surface of the mask, such as an opacification agent as described elsewhere infra. The implant is then exposed to one or more wound healing modulators, such as by dipping in a solution (including dispersions and emulsions) comprising at least one wound healing modulator, to allow wound healing modulator(s) to bind to the implant. The solvent used to assist in applying and binding the wound healing modulator to the implant is preferably biocompatible, does not leave a harmful residue, and/or does not cause dissolution or swelling of the polymeric material of the mask. If more than one wound healing modulator is used, binding may be performed by dipping in a single solution containing all desired wound healing modulators or by dipping the implant in two or more successive solutions, each of which contains one or more of the desired wound healing modulators. The process of binding wound healing modulator to the implant may be done at any time. In one embodiment, at least some of the wound healing modulator is bound to the implant as part of the manufacturing process. In another embodiment, a medical practitioner, such as an ophthalmologist, binds at least some of the wound healing modulator to the implant just prior to implantation. 
     In alternate embodiments, one or more wound healing modulators are bound to the implant using any suitable method for binding drugs or other useful compounds to implants and medical devices and/or using methods for making drug delivery devices which deliver a drug locally in the area of implantation or placement over a period of time. 
     V. Masks Configured to Reduce Visible Diffraction Patterns 
     Many of the foregoing masks can be used to improve the depth of focus of a patient. Various additional mask embodiments are discussed below. Some of the embodiments described below include nutrient transport structures that are configured to enhance or maintain nutrient flow between adjacent tissues by facilitating transport of nutrients across the mask. The nutrient transport structures of some of the embodiments described below are configured to at least substantially prevent nutrient depletion in adjacent tissues. The nutrient transport structures can decrease negative effects due to the presence of the mask in adjacent corneal layers when the mask is implanted in the cornea, increasing the longevity of the masks. The inventors have discovered that certain arrangements of nutrient transport structures generate diffraction patterns that interfere with the vision improving effect of the masks described herein. Accordingly, certain masks are described herein that include nutrient transport structures that do not generate diffraction patterns or otherwise interfere with the vision enhancing effects of the mask embodiments. 
       FIGS. 43-44  show one embodiment of a mask  100  configured to increase depth of focus of an eye of a patient suffering from presbyopia. The mask  100  is similar to the masks hereinbefore described, except as described differently below. The mask  100  can be made of the materials discussed herein, including those discussed in Section III. Also, the mask  100  can be formed by any suitable process, such as those discussed below in connection with  FIGS. 48 a -48 d    with variations of such processes. The mask  100  is configured to be applied to an eye of a patient, e.g., by being implanted in the cornea of the patient. The mask  100  may be implanted within the cornea in any suitable manner, such as those discussed above in connection with  FIGS. 50A-51C . 
     In one embodiment, the mask  100  includes a body  104  that has an anterior surface  108  and a posterior surface  112 . In one embodiment, the body  104  is capable of substantially maintaining natural nutrient flow between the first corneal layer and the second corneal layer. In one embodiment, the material is selected to maintain at least about ninety-six percent of the natural flow of at least one nutrient (e.g., glucose) between a first corneal layer (e.g., the layer  1210 ) and a second corneal layer (e.g., the layer  1220 ). The body  104  may be formed of any suitable material, including at least one of an open cell foam material, an expanded solid material, and a substantially opaque material. In one embodiment, the material used to form the body  104  has relatively high water content. 
     In one embodiment, the mask  100  includes and a nutrient transport structure  116 . The nutrient transport structure  116  may comprise a plurality of holes  120 . The holes  120  are shown on only a portion of the mask  100 , but the holes  120  preferably are located throughout the body  104  in one embodiment. In one embodiment, the holes  120  are arranged in a hex pattern, which is illustrated by a plurality of locations  120 ′ in  FIG. 45A . As discussed below, a plurality of locations may be defined and later used in the later formation of a plurality of holes  120  on the mask  100 . The mask  100  has an outer periphery  124  that defines an outer edge of the body  104 . In some embodiments, the mask  100  includes an aperture  128  at least partially surrounded by the outer periphery  124  and a non-transmissive portion  132  located between the outer periphery  124  and the aperture  128 . 
     Preferably the mask  100  is symmetrical, e.g., symmetrical about a mask axis  136 . In one embodiment, the outer periphery  124  of the mask  100  is circular. The masks in general have has a diameter within the range of from about 3 mm to about 8 mm, often within the range of from about 3.5 mm to about 6 mm, and less than about 6 mm in one embodiment. In another embodiment, the mask is circular and has a diameter in the range of 4 to 6 mm. In another embodiment, the mask  100  is circular and has a diameter of less than 4 mm. The outer periphery  124  has a diameter of about 3.8 mm in another embodiment. In some embodiments, masks that are asymmetrical or that are not symmetrical about a mask axis provide benefits, such as enabling a mask to be located or maintained in a selected position with respect to the anatomy of the eye. 
     The body  104  of the mask  100  may be configured to coupled with a particular anatomical region of the eye. The body  104  of the mask  100  may be configured to conform to the native anatomy of the region of the eye in which it is to be applied. For example, where the mask  100  is to be coupled with an ocular structure that has curvature, the body  104  may be provided with an amount of curvature along the mask axis  136  that corresponds to the anatomical curvature. For example, one environment in which the mask  100  may be deployed is within the cornea of the eye of a patient. The cornea has an amount of curvature that varies from person to person about a substantially constant mean value within an identifiable group, e.g., adults. When applying the mask  100  within the cornea, at least one of the anterior and posterior surfaces  108 ,  112  of the mask  100  may be provided with an amount of curvature corresponding to that of the layers of the cornea between which the mask  100  is applied. 
     In some embodiments, the mask  100  has a desired amount of optical power. Optical power may be provided by configuring the at least one of the anterior and posterior surfaces  108 ,  112  with curvature. In one embodiment, the anterior and posterior surfaces  108 ,  112  are provided with different amounts of curvature. In this embodiment, the mask  100  has varying thickness from the outer periphery  124  to the aperture  128 . 
     In one embodiment, one of the anterior surface  108  and the posterior surface  112  of the body  104  is substantially planar. In one planar embodiment, very little or no uniform curvature can be measured across the planar surface. In another embodiment, both of the anterior and posterior surfaces  108 ,  112  are substantially planar. In general, the thickness of the inlay may be within the range of from about 1 micron to about 40 micron, and often in the range of from about 5 micron to about 20 micron. In one embodiment, the body  104  of the mask  100  has a thickness  138  of between about 5 micron and about 10 micron. In one embodiment, the thickness  138  of the mask  100  is about 5 micron. In another embodiment, the thickness  138  of the mask  100  is about 8 micron. In another embodiment, the thickness  138  of the mask  100  is about 10 micron. 
     Thinner masks generally are more suitable for applications wherein the mask  100  is implanted at a relatively shallow location in (e.g., close to the anterior surface of) the cornea. In thinner masks, the body  104  may be sufficiently flexible such that it can take on the curvature of the structures with which it is coupled without negatively affecting the optical performance of the mask  100 . In one application, the mask  100  is configured to be implanted about 5 um beneath the anterior surface of the cornea. In another application, the mask  100  is configured to be implanted about 52 um beneath the anterior surface of the cornea. In another application, the mask  100  is configured to be implanted about 125 um beneath the anterior surface of the cornea. Further details regarding implanting the mask  100  in the cornea are discussed above in connection with  FIGS. 50A-51C . 
     A substantially planar mask has several advantages over a non-planar mask. For example, a substantially planar mask can be fabricated more easily than one that has to be formed to a particular curvature. In particular, the process steps involved in inducing curvature in the mask  100  can be eliminated. Also, a substantially planar mask may be more amenable to use on a wider distribution of the patient population (or among different sub-groups of a broader patient population) because the substantially planar mask uses the curvature of each patient&#39;s cornea to induce the appropriate amount of curvature in the body  104 . 
     In some embodiments, the mask  100  is configured specifically for the manner and location of coupling with the eye. In particular, the mask  100  may be larger if applied over the eye as a contact lens or may be smaller if applied within the eye posterior of the cornea, e.g., proximate a surface of the lens of the eye. As discussed above, the thickness  138  of the body  104  of the mask  100  may be varied based on where the mask  100  is implanted. For implantation at deeper levels within the cornea, a thicker mask may be advantageous. Thicker masks are advantageous in some applications. For example, they are generally easier to handle, and therefore are easier to fabricate and to implant. Thicker masks may benefit more from having a preformed curvature than thinner masks. A thicker mask could be configured to have little or no curvature prior to implantation if it is configured to conform to the curvature of the native anatomy when applied. 
     The aperture  128  is configured to transmit substantially all incident light along the mask axis  136 . The non-transmissive portion  132  surrounds at least a portion of the aperture  128  and substantially prevents transmission of incident light thereon. As discussed in connection with the above masks, the aperture  128  may be a through-hole in the body  104  or a substantially light transmissive (e.g., transparent) portion thereof. The aperture  128  of the mask  100  generally is defined within the outer periphery  124  of the mask  100 . The aperture  128  may take any of suitable configurations, such as those described above in connection with  FIGS. 6-42 . 
     In one embodiment, the aperture  128  is substantially circular and is substantially centered in the mask  100 . The size of the aperture  128  may be any size that is effective to increase the depth of focus of an eye of a patient suffering from presbyopia. For example, the aperture  128  can be circular, having a diameter of less than about 2.2 mm in one embodiment. In another embodiment, the diameter of the aperture is between about 1.8 mm and about 2.2 mm. In another embodiment, the aperture  128  is circular and has a diameter of about 1.8 mm or less. In another embodiment, the diameter of the aperture is about 1.6 mm. Most apertures will have a diameter within the range of from about 1.0 mm to about 2.5 mm, and often within the range of from about 1.3 mm to about 1.9 mm. 
     The non-transmissive portion  132  is configured to prevent transmission of radiant energy through the mask  100 . For example, in one embodiment, the non-transmissive portion  132  prevents transmission of substantially all of at least a portion of the spectrum of the incident radiant energy. In one embodiment, the non-transmissive portion  132  is configured to prevent transmission of substantially all visible light, e.g., radiant energy in the electromagnetic spectrum that is visible to the human eye. The non-transmissive portion  132  may substantially prevent transmission of radiant energy outside the range visible to humans in some embodiments. 
     As discussed above in connection with  FIG. 3 , preventing transmission of light through the non-transmissive portion  132  decreases the amount of light that reaches the retina and the fovea that would not converge at the retina and fovea to form a sharp image. As discussed above in connection with  FIG. 4 , the size of the aperture  128  is such that the light transmitted therethrough generally converges at the retina or fovea. Accordingly, a much sharper image is presented to the eye than would otherwise be the case without the mask  100 . 
     In one embodiment, the non-transmissive portion  132  prevents transmission of about 90 percent of incident light. In another embodiment, the non-transmissive portion  132  prevents transmission of about 92 percent of all incident light. The non-transmissive portion  132  of the mask  100  may be configured to be opaque to prevent the transmission of light. As used herein the term “opaque” is intended to be a broad term meaning capable of preventing the transmission of radiant energy, e.g., light energy, and also covers structures and arrangements that absorb or otherwise block all or less than all or at least a substantial portion of the light. In one embodiment, at least a portion of the body  104  is configured to be opaque to more than 99 percent of the light incident thereon. 
     As discussed above, the non-transmissive portion  132  may be configured to prevent transmission of light without absorbing the incident light. For example, the mask  100  could be made reflective or could be made to interact with the light in a more complex manner, as discussed in U.S. Pat. No. 6,551,424, issued Apr. 29, 2003, which is hereby incorporated by reference herein in its entirety. 
     As discussed above, the mask  100  also has a nutrient transport structure that in some embodiments comprises the plurality of holes  120 . The presence of the plurality of holes  120  (or other transport structure) may affect the transmission of light through the non-transmissive portion  132  by potentially allowing more light to pass through the mask  100 . In one embodiment, the non-transmissive portion  132  is configured to absorb about 99 percent or more of the incident light from passing through the mask  100  without holes  120  being present. The presence of the plurality of holes  120  allows more light to pass through the non-transmissive portion  132  such that only about 92 percent of the light incident on the non-transmissive portion  132  is prevented from passing through the non-transmissive portion  132 . The holes  120  may reduce the benefit of the aperture  128  on the depth of focus of the eye by allowing more light to pass through the non-transmissive portion to the retina. 
     Reduction in the depth of focus benefit of the aperture  128  due to the holes  120  is balanced by the nutrient transmission benefits of the holes  120 . In one embodiment, the transport structure  116  (e.g., the holes  120 ) is capable of substantially maintaining natural nutrient flow from a first corneal layer (i.e., one that is adjacent to the anterior surface  108  of the mask  100 ) to the second corneal layer (i.e., one that is adjacent to the posterior surface  112  of the mask  100 ). The plurality of holes  120  are configured to enable nutrients to pass through the mask  100  between the anterior surface  108  and the posterior surface  112 . As discussed above, the holes  120  of the mask  100  shown in  FIG. 43  may be located anywhere on the mask  100 . Other mask embodiments described herein below locate substantially all of the nutrient transport structure in one or more regions of a mask. 
     The holes  120  of  FIG. 43  extends at least partially between the anterior surface  108  and the posterior surface  112  of the mask  100 . In one embodiment, each of the holes  120  includes a hole entrance  140  and a hole exit  164 . The hole entrance  140  is located adjacent to the anterior surface  108  of the mask  100 . The hole exit  164  is located adjacent to the posterior surface  112  of the mask  100 . In one embodiment, each of the holes  120  extends the entire distance between the anterior surface  108  and the posterior surface  112  of the mask  100 . 
     The transport structure  116  is configured to maintain the transport of one or more nutrients across the mask  100 . The transport structure  116  of the mask  100  provides sufficient flow of one or more nutrients across the mask  100  to prevent depletion of nutrients at least at one of the first and second corneal layers (e.g., the layers  1210  and  1220 ). One nutrient of particular importance to the viability of the adjacent corneal layers is glucose. The transport structure  116  of the mask  100  provides sufficient flow of glucose across the mask  100  between the first and second corneal layers to prevent glucose depletion that would harm the adjacent corneal tissue. Thus, the mask  100  is capable of substantially maintaining nutrient flow (e.g., glucose flow) between adjacent corneal layers. In one embodiment, the nutrient transport structure  116  is configured to prevent depletion of more than about 4 percent of glucose (or other biological substance) in adjacent tissue of at least one of the first corneal layer and the second corneal layer. 
     The holes  120  may be configured to maintain the transport of nutrients across the mask  100 . In one embodiment, the holes  120  are formed with a diameter of about 0.015 mm or more. In another embodiment, the holes have a diameter of about 0.020 mm. In another embodiment, the holes have a diameter of about 0.025 mm. In another embodiment, the holes have a diameter of about 0.027 mm. In another embodiment, the holes  120  have a diameter in the range of about 0.020 mm to about 0.029 mm. The number of holes in the plurality of holes  120  is selected such that the sum of the surface areas of the hole entrances  140  of all the holes  100  comprises about 5 percent or more of surface area of the anterior surface  108  of the mask  100 . In another embodiment, the number of holes  120  is selected such that the sum of the surface areas of the hole exits  164  of all the holes  120  comprises about 5 percent or more of surface area of the posterior surface  112  of the mask  100 . In another embodiment, the number of holes  120  is selected such that the sum of the surface areas of the hole exits  164  of all the holes  120  comprises about 5 percent or more of surface area of the posterior surface  112  of the mask  112  and the sum of the surface areas of the hole entrances  140  of all the holes  120  comprises about 5 percent or more of surface area of the anterior surface  108  of the mask  100 . In another embodiment, the plurality of holes  120  may comprise about 1600 microperforations. 
     Each of the holes  120  may have a relatively constant cross-sectional area. In one embodiment, the cross-sectional shape of each of the holes  120  is substantially circular. Each of the holes  120  may comprise a cylinder extending between the anterior surface  108  and the posterior surface  112 . 
     The relative position of the holes  120  is of interest in some embodiments. As discussed above, the holes  120  of the mask  100  are hex-packed, e.g., arranged in a hex pattern. In particular, in this embodiment, each of the holes  120  is separated from the adjacent holes  120  by a substantially constant distance, sometimes referred to herein as a hole pitch. In one embodiment, the hole pitch is about 0.045 mm. 
     In a hex pattern, the angles between lines of symmetry are approximately 43 degrees. The spacing of holes along any line of holes is generally within the range of from about 30 microns to about 100 microns, and, in one embodiment, is approximately 43 microns. The hole diameter is generally within the range of from about 10 microns to about 100 microns, and in one embodiment, is approximately 20 microns. The hole spacing and diameter are related if you want to control the amount of light coming through. The light transmission is a function of the sum of hole areas as will be understood by those of skill in the art in view of the disclosure herein. 
     The embodiment of  FIG. 43  advantageously enables nutrients to flow from the first corneal layer to the second corneal layer. The inventors have discovered that negative visual effects can arise due to the presence of the transport structure  116 . For example, in some cases, a hex packed arrangement of the holes  120  can generate diffraction patterns visible to the patient. For example, patients might observe a plurality of spots, e.g., six spots, surrounding a central light with holes  120  having a hex patterned. 
     The inventors have discovered a variety of techniques that produce advantageous arrangements of a transport structure such that diffraction patterns and other deleterious visual effects do not substantially inhibit other visual benefits of a mask. In one embodiment, where diffraction effects would be observable, the nutrient transport structure is arranged to spread the diffracted light out uniformly across the image to eliminate observable spots. In another embodiment, the nutrient transport structure employs a pattern that substantially eliminates diffraction patterns or pushes the patterns to the periphery of the image. 
       FIG. 45B-45C  show two embodiments of patterns of holes  220  that may be applied to a mask that is otherwise substantially similar to the mask  100 . The holes  220  of the hole patterns of  FIGS. 45B-45C  are spaced from each other by a random hole spacing or hole pitch. In other embodiments discussed below, holes are spaced from each other by a non-uniform amount, e.g., not a random amount. In one embodiment, the holes  220  have a substantially uniform shape (cylindrical shafts having a substantially constant cross-sectional area).  FIG. 45C  illustrates a plurality of holes  220  separated by a random spacing, wherein the density of the holes is greater than that of  FIG. 45B . Generally, the higher the percentage of the mask body that has holes the more the mask will transport nutrients in a manner similar to the native tissue. One way to provide a higher percentage of hole area is to increase the density of the holes. Increased hole density can also permit smaller holes to achieve the same nutrient transport as is achieved by less dense, larger holes. 
       FIG. 46A  shows a portion of another mask  200   a  that is substantially similar to the mask  100 , except described differently below. The mask  200   a  can be made of the materials discussed herein, including those discussed in Section III. The mask  200   a  can be formed by any suitable process, such as those discussed below in connection with  FIGS. 48 a -48 d    and with variations of such processes. The mask  200   a  has a nutrient transport structure  216   a  that includes a plurality of holes  220   a . A substantial number of the holes  220   a  have a non-uniform size. The holes  220   a  may be uniform in cross-sectional shape. The cross-sectional shape of the holes  220   a  is substantially circular in one embodiment. The holes  220   a  may be circular in shape and have the same diameter from a hole entrance to a hole exit, but are otherwise non-uniform in at least one aspect, e.g., in size. It may be preferable to vary the size of a substantial number of the holes by a random amount. In another embodiment, the holes  220   a  are non-uniform (e.g., random) in size and are separated by a non-uniform (e.g., a random) spacing. 
       FIG. 46B  illustrates another embodiment of a mask  200   b  that is substantially similar to the mask  100 , except as described differently below. The mask  200   b  can be made of the materials discussed herein, including those discussed in Section III. Also, the mask  200   b  can be formed by any suitable process, such as those discussed below in connection with  FIGS. 48 a -48 d    and with variations of such processes. The mask  200   b  includes a body  204   b . The mask  200   b  has a transport structure  216   b  that includes a plurality of holes  220   b  with a non-uniform facet orientation. In particular, each of the holes  220   b  has a hole entrance that may be located at an anterior surface of the mask  200   b . A facet of the hole entrance is defined by a portion of the body  204   b  of the mask  200   b  surrounding the hole entrance. The facet is the shape of the hole entrance at the anterior surface. In one embodiment, most or all the facets have an elongate shape, e.g., an oblong shape, with a long axis and a short axis that is perpendicular to the long axis. The facets may be substantially uniform in shape. In one embodiment, the orientation of facets is not uniform. For example, a substantial number of the facets may have a non-uniform orientation. In one arrangement, a substantial number of the facets have a random orientation. In some embodiments, the facets are non-uniform (e.g., random) in shape and are non-uniform (e.g., random) in orientation. 
     Other embodiments may be provided that vary at least one aspect, including one or more of the foregoing aspects, of a plurality of holes to reduce the tendency of the holes to produce visible diffraction patterns or patterns that otherwise reduce the vision improvement that may be provided by a mask with an aperture, such as any of those described above. For example, in one embodiment, the hole size, shape, and orientation of at least a substantial number of the holes may be varied randomly or may be otherwise non-uniform. 
       FIG. 47  shows another embodiment of a mask  300  that is substantially similar to any of the masks hereinbefore described, except as described differently below. The mask  300  can be made of the materials discussed herein, including those discussed in Section III. Also, the mask  300  can be formed by any suitable process, such as those discussed below in connection with  FIGS. 48 a -48 d    and with variations of such processes. The mask  300  includes a body  304 . The body  304  has an outer peripheral region  305 , an inner peripheral region  306 , and a hole region  307 . The hole region  307  is located between the outer peripheral region  305  and the outer peripheral region  306 . The body  304  may also include an aperture region, where the aperture (discussed below) is not a through hole. The mask  300  also includes a nutrient transport structure  316 . In one embodiment, the nutrient transport structure includes a plurality of holes. At least a substantial portion of the holes (e.g., all of the holes) are located in the hole region  307 . As above, only a portion of the nutrient structure  316  is shown for simplicity. But it should be understood that the hole may be located through the hole region  307 . 
     The outer peripheral region  305  may extend from an outer periphery  324  of the mask  300  to a selected outer circumference  326  of the mask  300 . The selected outer circumference  325  of the mask  300  is located a selected radial distance from the outer periphery  324  of the mask  300 . In one embodiment, the selected outer circumference  325  of the mask  300  is located about 0.05 mm from the outer periphery  324  of the mask  300 . 
     The inner peripheral region  306  may extend from an inner location, e.g., an inner periphery  326  adjacent an aperture  328  of the mask  300  to a selected inner circumference  327  of the mask  300 . The selected inner circumference  327  of the mask  300  is located a selected radial distance from the inner periphery  326  of the mask  300 . In one embodiment, the selected inner circumference  327  of the mask  300  is located about 0.05 mm from the inner periphery  326 . 
     The mask  300  may be the product of a process that involves random selection of a plurality of locations and formation of holes on the mask  300  corresponding to the locations. As discussed further below, the method can also involve determining whether the selected locations satisfy one or more criteria. For example, one criterion prohibits all, at least a majority, or at least a substantial portion of the holes from being formed at locations that correspond to the inner or outer peripheral regions  305 ,  306 . Another criterion prohibits all, at least a majority, or at least a substantial portion of the holes from being formed too close to each other. For example, such a criterion could be used to assure that a wall thickness, e.g., the shortest distance between adjacent holes, is not less than a predetermined amount. In one embodiment, the wall thickness is prevented from being less than about 20 microns. 
     In a variation of the embodiment of  FIG. 47 , the outer peripheral region  305  is eliminated and the hole region  307  extends from the inner peripheral region  306  to an outer periphery  324 . In another variation of the embodiment of  FIG. 47 , the inner peripheral region  306  is eliminated and the hole region  307  extends from the outer peripheral region  305  to an inner periphery  326 . 
       FIG. 44B  shows a mask  400  that is similar to the mask  100  except as described differently below. The mask  400  can be made of the materials discussed herein, including those discussed in Section III. The mask  400  can be formed by any suitable process, such as those discussed below in connection with  FIGS. 48 a -48 d    and with variations of such processes. The mask  400  includes a body  404  that has an anterior surface  408  and a posterior surface  412 . The mask  400  also includes a nutrient transport structure  4316  that, in one embodiment, includes a plurality of holes  420 . The holes  420  are formed in the body  404  so that nutrient transport is provided but transmission of radiant energy (e.g., light) to the retinal locations adjacent the fovea through the holes  404  is substantially prevented. In particular, the holes  404  are formed such that when the eye with which the mask  1000  is coupled is directed at an object to be viewed, light conveying the image of that object that enters the holes  420  cannot exit the holes along a path ending near the fovea. 
     In one embodiment, each of the holes  420  has a hole entrance  460  and a hole exit  464 . Each of the holes  420  extends along a transport axis  466 . The transport axis  466  is formed to substantially prevent propagation of light from the anterior surface  408  to the posterior surface  412  through the holes  420 . In one embodiment, at least a substantial number of the holes  420  have a size to the transport axis  466  that is less than a thickness of the mask  400 . In another embodiment, at least a substantial number of the holes  420  have a longest dimension of a perimeter at least at one of the anterior or posterior surfaces  408 ,  412  (e.g., a facet) that is less than a thickness of the mask  400 . In some embodiments, the transport axis  466  is formed at an angle with respect to a mask axis  436  that substantially prevents propagation of light from the anterior surface  408  to the posterior surface  412  through the hole  420 . In another embodiment, the transport axis  466  of one or more holes  420  is formed at an angle with respect to the mask axis  436  that is large enough to prevent the projection of most of the hole entrance  460  from overlapping the hole exit  464 . 
     In one embodiment, the hole  420  is circular in cross-section and has a diameter between about 0.5 micron and about 8 micron and the transport axis  466  is between 5 and 85 degrees. The length of each of the holes  420  (e.g., the distance between the anterior surface  408  and the posterior surface  412 ) is between about 8 and about 92 micron. In another embodiment, the diameter of the holes  420  is about 5 micron and the transport angle is about 40 degrees or more. As the length of the holes  420  increases it may be desirable to include additional holes  420 . In some cases, additional holes  420  counteract the tendency of longer holes to reduce the amount of nutrient flow through the mask  400 . 
       FIG. 44C  shows another embodiment of a mask  500  similar to the mask  100 , except as described differently below. The mask  500  can be made of the materials discussed herein, including those discussed in Section III. The mask  500  can be formed by any suitable process, such as those discussed below in connection with  FIGS. 48 a -48 d    and with variations of such processes. The mask  500  includes a body  504  that has an anterior surface  508 , a first mask layer  510  adjacent the anterior surface  508 , a posterior surface  512 , a second mask layer  514  adjacent the posterior surface  512 , and a third mask layer  515  located between the first mask layer  510  and the second mask layer  514 . The mask  500  also includes a nutrient transport structure  516  that, in one embodiment, includes a plurality of holes  520 . The holes  520  are formed in the body  504  so that nutrient are transported across the mask, as discussed above, but transmission of radiant energy (e.g., light) to retinal locations adjacent the fovea through the holes  504  is substantially prevented. In particular, the holes  504  are formed such that when the eye with which the mask  500  is coupled is directed at an object to be viewed, light conveying the image of that object that enters the holes  520  cannot exit the holes along a path ending near the fovea. 
     In one embodiment, at least one of the holes  520  extends along a non-linear path that substantially prevents propagation of light from the anterior surface to the posterior surface through the at least one hole. In one embodiment, the mask  500  includes a first hole portion  520   a  that extends along a first transport axis  566   a , the second mask layer  514  includes a second hole portion  520   b  extending along a second transport axis  566   b , and the third mask layer  515  includes a third hole portion  520   c  extending along a third transport axis  566   c . The first, second, and third transport axes  566   a ,  566   b ,  566   c  preferably are not collinear. In one embodiment, the first and second transport axes  566   a ,  566   b  are parallel but are off-set by a first selected amount. In one embodiment, the second and third transport axes  566   b ,  566   c  are parallel but are off-set by a second selected amount. In the illustrated embodiment, each of the transport axes  566   a ,  566   b ,  566   c  are off-set by one-half of the width of the hole portions  520   a ,  520   b ,  520   c . Thus, the inner-most edge of the hole portion  520   a  is spaced from the axis  536  by a distance that is equal to or greater than the distance of the outer-most edge of the hole portion  520   b  from the axis  536 . This spacing substantially prevents light from passing through the holes  520  from the anterior surface  508  to the posterior surface  512 . 
     In one embodiment, the first and second amounts are selected to substantially prevent the transmission of light therethrough. The first and second amounts of off-set may be achieved in any suitable fashion. One technique for forming the hole portions  520   a ,  520   b ,  520   c  with the desired off-set is to provide a layered structure. As discussed above, the mask  500  may include the first layer  510 , the second layer  514 , and the third layer  515 .  FIG. 44C  shows that the mask  500  can be formed with three layers. In another embodiment, the mask  500  is formed of more than three layers. Providing more layers may advantageously further decrease the tendency of light to be transmitted through the holes  490  onto the retina. This has the benefit of reducing the likelihood that a patient will observe or otherwise perceive a patter that will detract from the vision benefits of the mask  500 . A further benefit is that less light will pass through the mask  500 , thereby enhancing the depth of focus increase due to the pin-hole sized aperture formed therein. 
     In any of the foregoing mask embodiments, the body of the mask may be formed of a material selected to provide adequate nutrient transport and to substantially prevent negative optic effects, such as diffraction, as discussed above. In various embodiments, the masks are formed of an open cell foam material. In another embodiment, the masks are formed of an expanded solid material. 
     As discussed above in connection with  FIGS. 45B and 45C , various random patterns of holes may advantageously be provided for nutrient transport. In some embodiment, it may be sufficient to provide regular patterns that are non-uniform in some aspect. Non-uniform aspects to the holes may be provided by any suitable technique. 
     In a first step of one technique, a plurality of locations  220 ′ is generated. The locations  220 ′ are a series of coordinates that may comprise a non-uniform pattern or a regular pattern. The locations  220 ′ may be randomly generated or may be related by a mathematical relationship (e.g., separated by a fixed spacing or by an amount that can be mathematically defined). In one embodiment, the locations are selected to be separated by a constant pitch or spacing and may be hex packed. 
     In a second step, a subset of the locations among the plurality of locations  220 ′ is modified to maintain a performance characteristic of the mask. The performance characteristic may be any performance characteristic of the mask. For example, the performance characteristic may relate to the structural integrity of the mask. Where the plurality of locations  220 ′ is selected at random, the process of modifying the subset of locations may make the resulting pattern of holes in the mask a “pseudo-random” pattern. 
     Where a hex packed pattern of locations (such as the locations  120 ′ of  FIG. 45A ) is selected in the first step, the subset of locations may be moved with respect to their initial positions as selected in the first step. In one embodiment, each of the locations in the subset of locations is moved by an amount equal to a fraction of the hole spacing. For example, each of the locations in the subset of locations may be moved by an amount equal to one-quarter of the hole spacing. Where the subset of locations is moved by a constant amount, the locations that are moved preferably are randomly or pseudo-randomly selected. In another embodiment, the subset of location is moved by a random or a pseudo-random amount. 
     In one technique, an outer peripheral region is defined that extends between the outer periphery of the mask and a selected radial distance of about 0.05 mm from the outer periphery. In another embodiment, an inner peripheral region is defined that extends between an aperture of the mask and a selected radial distance of about 0.05 mm from the aperture. In another embodiment, an outer peripheral region is defined that extends between the outer periphery of the mask and a selected radial distance and an inner peripheral region is defined that extends between the aperture of the mask and a selected radial distance from the aperture. In one technique, the subset of location is modified by excluding those locations that would correspond to holes formed in the inner peripheral region or the outer peripheral region. By excluding locations in at least one of the outer peripheral region and the inner peripheral region, the strength of the mask in these regions is increased. Several benefits are provided by stronger inner and outer peripheral regions. For example, the mask may be easier to handle during manufacturing or when being applied to a patient without causing damage to the mask. 
     In another embodiment, the subset of locations is modified by comparing the separation of the holes with minimum and or maximum limits. For example, it may be desirable to assure that no two locations are closer than a minimum value. In some embodiments this is important to assure that the wall thickness, which corresponds to the separation between adjacent holes, is no less than a minimum amount. As discussed above, the minimum value of separation is about 20 microns in one embodiment, thereby providing a wall thickness of no less than about 20 microns. 
     In another embodiment, the subset of locations is modified and/or the pattern of location is augmented to maintain an optical characteristic of the mask. For example, the optical characteristic may be opacity and the subset of locations may be modified to maintain the opacity of a non-transmissive portion of a mask. In another embodiment, the subset of locations may be modified by equalizing the density of holes in a first region of the body compared with the density of holes in a second region of the body. For example, the locations corresponding to the first and second regions of the non-transmissive portion of the mask may be identified. In one embodiment, the first region and the second region are arcuate regions (e.g., wedges) of substantially equal area. A first areal density of locations (e.g., locations per square inch) is calculated for the locations corresponding to the first region and a second areal density of locations is calculated for the locations corresponding to the second region. In one embodiment, at least one location is added to either the first or the second region based on the comparison of the first and second areal densities. In another embodiment, at least one location is removed based on the comparison of the first and second areal densities. 
     The subset of locations may be modified to maintain nutrient transport of the mask. In one embodiment, the subset of location is modified to maintain glucose transport. 
     In a third step, a hole is formed in a body of a mask at locations corresponding to the pattern of locations as modified, augmented, or modified and augmented. The holes are configured to substantially maintain natural nutrient flow from the first layer to the second layer without producing visible diffraction patterns. 
     VI. Methods of Applying Pinhole Aperture Devices 
     The various masks discussed herein can be used to improve the vision of a presbyopic patient as well as patient&#39;s with other vision problems. The masks discussed herein can be deployed in combination with a LASIK procedure, to eliminate the effects of abrasions, aberrations, and divots in the cornea. It is also believed that the masks disclosed herein can be used to treat patients suffering from macular degeneration, e.g., by directing light rays to unaffected portions of retina, thereby improving the vision of the patient. Whatever treatment is contemplated, more precise alignment of the central region of a mask that has a pin-hole aperture with the line of sight or visual axis of the patient is believed to provide greater clinical benefit to the patient. Other ocular devices that do not require a pin-hole aperture can also benefit from the alignment techniques discussed below. Also, various structures and techniques that can be used to remove an ocular devices are discussed below. 
     A. Alignment of the Pinhole Aperture with the Patient&#39;s Visual Axis 
     Alignment of the central region of the pinhole aperture  38 , in particular, the optical axis  39  of the mask  34  with the visual axis of the eye  10  may be achieved in a variety of ways. In one technique, an optical device employs input from the patient to locate the visual axis in connection with a procedure to implant the mask  34 . This technique is described in more detail in U.S. patent application Ser. No. 11/000,562, filed Dec. 1, 2004, the entire contents of which is hereby expressly incorporated by reference herein. 
     In other embodiments, systems and methods identify one or more visible ocular features that correlate to the line of sight. The one or more visible ocular feature(s) is observed while the mask is being applied to the eye. Alignment using a visible ocular feature enables the mask to perform adequately to increase depth of focus. In some applications, a treatment method enhances the correlation of the visible ocular feature and the line of sight to maintain or improve alignment of the mask axis and the line of sight. 
     Accurate alignment of the mask is believed to improve the clinical benefit of the mask. However, neither the optical axis of the mask nor the line of sight of the patient is generally visible during the surgical procedures contemplated for implanting masks. However, substantial alignment of the optical axis of the mask and the line of sight may be achieved by aligning a visible feature of the mask with a visible feature of the eye, e.g., a visible ocular feature. As used herein, the term “visible ocular feature” is a broad term that includes features viewable with a viewing aid, such as a surgical microscope or loupes, as well as those visible to the unaided eye. Various methods are discussed below that enhance the accuracy of the placement of the mask using a visible ocular feature. These methods generally involve treating the eye to increase the correlation between the location of the visible ocular feature and the line of sight or to increase the visibility of the ocular feature. 
       FIG. 48  is a flow chart illustrating one method of aligning a mask with an axis of the eye using a visible ocular feature. The method may include a step of identifying a visible ocular feature, a combination of visible ocular features, or a combination of a visible ocular feature and an optical effect that sufficiently correlate with the location of the line of sight of the eye. In one technique the entrance pupil or other visible ocular feature could be used alone to estimate the location of the line of sight. In another technique, the location of the line of sight can be estimated to be located between, e.g., half-way between, the center of the entrance pupil and the first Purkinje image. Other estimates can be based on a combination of two or more of the first Purkinje image, the second Purkinje image, the third Purkinje image, and the fourth Purkinje image. Other estimates can be based on one or more Purkinje image and one or more other anatomical features. In another technique, the location of the line of sight can be estimated as being located at the center of the pupil if the first Purkinje image is located close to the center of the entrance pupil. A single Purkinje image may provide an adequate estimate of the location of the line of sight if the Purkinje image is generated by a beam having a fixed or a know angle of incidence relative to a surface of the eye. The method may also include a step of identifying a visible feature of the mask to be aligned with a visible ocular feature, as discussed further below. 
     In a step  1000 , an eye is treated to affect or alter, preferably temporarily, a visible ocular feature. In some embodiments, the feature of the eye is altered to increase the correlation of the location of the ocular feature to the line of sight of the eye. In some cases, the treatment of step  1000  enhances the visibility of the ocular feature to the surgeon. The ocular feature may be any suitable feature, such as the pupil or any other feature that correlates or can be altered by a treatment to correlate with the line of sight of the patient. Some techniques involve the alignment of a feature of a mask with the pupil or a portion of the pupil. One technique for enhancing the visibility of the pupil or the correlation of the location of the pupil with the line of sight involves manipulating the size of the pupil, e.g., increasing or decreasing the pupil size. 
     In connection with the method of  FIG. 48 , any suitable criteria can be used to confirm alignment of an eye and a mask with a pin-hole aperture. For example, the mask can be considered aligned with the eye when any feature of the mask is aligned with any anatomical landmark on the eye so that an axis passing through the center of the pin-hole aperture is co-linear with or substantially co-linear with an optical axis of the eye, such as the line of sight and an axis passing through the center of the entrance pupil and the center of the eyeball. As used herein, “anatomical landmark” is a broad term that includes an visible ocular feature, such as the center of the entrance pupil, the intersection of the line of sight with a selected corneal layer, the inner periphery of the iris, the outer periphery of the iris, the inner periphery of the sclera, the boundary between the iris and the pupil, the boundary between the iris and the sclera, the location of the first Purkinje image, the location of the second Purkinje image, the location of the third Purkinje image, the location of the fourth Purkinje image, the relative position of any combination of Purkinje images, the combination of the location of a Purkinje image and any other anatomical landmark, and any combination of the foregoing or other anatomical feature. 
     The pupil size may be decreased by any suitable technique, including pharmacologic manipulation and light manipulation. One agent used in pharmacologic manipulation of pupil size is pilocarpine. Pilocarpine reduces the size of the pupil when applied to the eye. One technique for applying pilocarpine is to inject an effective amount into the eye. Other agents for reducing pupil size include: carbachol, demecarium, isoflurophate, physostigmine, aceclidine, and echothiophate. 
     Pilocarpine is known to shift the location of the pupil nasally in some cases. This can be problematic for some ocular procedures, e.g., those procedures directed at improving distance vision. The applicant has discovered, however, that such a shift does not significantly reduce the efficacy of the masks described herein. 
     While the alignment of the masks described herein with the line of sight is not significantly degraded by the use of pilocarpine, an optional step of correcting for the nasal shift of the pupil may be performed. 
     In one variation, the treatment of the step  1000  involves increasing pupil size. This technique may be more suitable where it is desired to align a visible mask feature near an outer periphery of the mask with the pupil. These techniques are discussed further below. 
     As discussed above, the treatment of the step  1000  can involve non-pharmacologic techniques for manipulating a visible ocular feature. One non-pharmacologic technique involves the use of light to cause the pupil size to change. For example, a bright light can be directed into the eye to cause the pupil to constrict. This approach may substantially avoid displacement of the pupil that has been observed in connection with some pharmacologic techniques. Light can also be used to increase pupil size. For example, the ambient light can be reduced to cause the pupil to dilate. A dilated pupil may provide some advantages in connection with aligning to a visible mask feature adjacent to an outer periphery of a mask, as discussed below. 
     In a step  1004 , a visible feature of a mask is aligned with the ocular feature identified in connection with step  1000 . As discussed above, the mask may have an inner periphery, an outer periphery, and a pin-hole aperture located within the inner periphery. The pin-hole aperture may be centered on a mask axis. Other advantageous mask features discussed above may be included in masks applied by the methods illustrated by  FIG. 48 . For example, such features may include nutrient transport structures configured to substantially eliminate diffraction patterns, structures configured to substantially prevent nutrient depletion in adjacent corneal tissue, and any other mask feature discussed above in connection with other masks. 
     One technique involves aligning at least a portion of the inner periphery of a mask with an anatomical landmark. For example, the inner periphery of the mask could be aligned with the inner periphery of the iris. This may be accomplished using unaided vision or a viewing aid, such as loupes or a surgical microscope. The mask could be aligned so that substantially the same spacing is provided between the inner periphery of the mask and the inner periphery of the iris. This technique could be facilitated by making the iris constrict, as discussed above. A viewing aid may be deployed to further assist in aligning the mask to the anatomical landmark. For example, a viewing aid could include a plurality of concentric markings that the surgeon can use to position the mask. Where the inner periphery of the iris is smaller than the inner periphery of the mask, a first concentric marking can be aligned with the inner periphery of the iris and the mask could be positioned so that a second concentric marking is aligned with the inner periphery of the mask. The second concentric marking would be farther from the common center than the first concentric marking in this example. 
     In another technique, the outer periphery of the mask could be aligned with an anatomical landmark, such as the inner periphery of the iris. This technique could be facilitated by dilating the pupil. This technique may be enhanced by the use of a viewing aid, which could include a plurality of concentric markings, as discussed above. In another technique, the outer periphery of the mask could be aligned with an anatomical landmark, such as the boundary between the iris and the sclera. This technique may be facilitated by the use of a viewing aid, such as a plurality of concentric markings. 
     In another technique, the mask can be aligned so that substantially the same spacing is provided between the inner periphery of the mask and the inner periphery of the iris. In this technique, the pupil preferably is constricted so that the diameter of the pupil is less than the diameter of the pin-hole aperture. 
     Alternatively, an artifact can be formed in the mask that gives a visual cue of proper alignment. For example, there could be one or more window portions formed in the mask through which the edge of the pupil could be observed. The window portions could be clear graduations or they could be at least partially opaque regions through which the pupil could be observed. In one technique, the surgeon moves the mask until the pupil can be seen in corresponding window portions on either side of the pin-hole aperture. The window portions enable a surgeon to align a visible ocular feature located beneath a non-transparent section of the mask with a feature of the mask. This arrangement enables alignment without a great amount of pupil constriction, e.g., where the pupil is not fully constricted to a size smaller than the diameter of the inner periphery. 
     Preferably the alignment of the ocular feature with one or more visible mask features causes the mask axis to be substantially aligned with the line of sight of the eye. “Substantial alignment” of the mask axis with the eye, e.g., with the line of sight of the eye (and similar terms, such as “substantially collinear”) can be said to have been achieved when a patient&#39;s vision is improved by the implantation of the mask. In some cases, substantial alignment can be said to have been achieved when the mask axis is within a circle centered on the line of sight and having a radius no more than 5 percent of the radius of the inner periphery of the mask. In some cases, substantial alignment can be said to have been achieved when the mask axis is within a circle centered on the line of sight and having a radius no more than 10 percent of the radius of the inner periphery of the mask. In some cases, substantial alignment can be said to have been achieved when the mask axis is within a circle centered on the line of sight and having a radius no more than 15 percent of the radius of the inner periphery of the mask. In some cases, substantial alignment can be said to have been achieved when the mask axis is within a circle centered on the line of sight and having a radius no more than 20 percent of the radius of the inner periphery of the mask. In some cases, substantial alignment can be said to have been achieved when the mask axis is within a circle centered on the line of sight and having a radius no more than 25 percent of the radius of the inner periphery of the mask. In some cases, substantial alignment can be said to have been achieved when the mask axis is within a circle centered on the line of sight and having a radius no more than 30 percent of the radius of the inner periphery of the mask. As discussed above, the alignment of the mask axis and the line of sight of the patient is believed to enhance the clinical benefit of the mask. 
     In a step  1008 , the mask is applied to the eye of the patient. Preferably the alignment of the optical axis of the mask and the line of sight of the patient is maintained while the mask is applied to the eye of the patient. In some cases, this alignment is maintained by maintaining the alignment of a mask feature, e.g., a visible mask feature, and a pupil feature, e.g., a visible pupil feature. For example, one technique maintains the alignment of at least one of the inner periphery and the outer periphery of the mask and the pupil while the mask is being applied to the eye of the patient. 
     As discussed above, a variety of techniques are available for applying a mask to the eye of a patient. Any suitable technique of applying a mask may be employed in connection with the method illustrated in  FIG. 48 . For example, as set forth above in connection with  FIGS. 50A-51C , various techniques may be employed to position the mask at different depths or between different layers within the cornea. In particular, in one technique, a corneal flap of suitable depth is hinged open. The depth of the flap is about the outermost 20% of the thickness of the cornea in one technique. In another technique, the depth of the flap is about the outermost 10% of the thickness of the cornea. In another technique, the depth of the flap is about the outermost 5% of the thickness of the cornea. In another technique, the depth of the flap is in the range of about the outermost 5% to about the outermost 10% of the thickness of the cornea. In another technique, the depth of the flap is in the range of about the outermost 5% to about the outermost 20% of the thickness of the cornea. Other depths and ranges are possible for other techniques. 
     Thereafter, in one technique, the mask is placed on a layer of the cornea such that at least one of the inner periphery and the outer periphery of the mask is at a selected position relative to the pupil. In variations on this technique, other features of the mask may be aligned with other ocular features. Thereafter, the hinged corneal flap is placed over the mask. 
     Additional techniques for applying a mask are discussed above in connection with  FIGS. 52A-53 . These methods may be modified for use in connection with alignment using visible features. These techniques enable the mask to be initially placed on the corneal layer that is lifted from the eye. The initial placement of the mask on the lifted corneal layer may be before or after alignment of a visible ocular feature with a visible mask feature. In some techniques, primary and secondary alignment steps are performed before and after the initial placement of the mask on the lifted corneal layer. 
     Many additional variations of the foregoing methods are also possible. The alignment methods involving alignment of visible features may be combined with any of the techniques discussed above in connection with optically locating the patient&#39;s line of sight. One technique involves removing an epithelial sheet and creating a depression in the Bowman&#39;s membrane or in the stroma. Also, the mask can be placed in a channel formed in the cornea, e.g., in or near the top layers of the stroma. Another useful technique for preparing the cornea involves the formation of a pocket within the cornea. These methods related to preparation of the cornea are described in greater detail above. 
     Some techniques may benefit from the placement of a temporary post-operative covering, such as a contact lens or other covering, over the flap until the flap has healed. In one technique, a covering is placed over the flap until an epithelial sheet adheres to the mask or grows over an exposed layer, such as the Bowman&#39;s membrane. 
     B. Methods of Applying a Mask 
     Having described method for locating the visual axis of the eye  10  or a visible ocular feature that indicates the location thereof, and for visually marking the visual axis, various methods for applying a mask to the eye will be discussed. 
       FIG. 49  shows one technique for screening a patient interested in increasing his or her depth of focus. The process begins at step  1100 , in which the patient is fitted with soft contact lenses, i.e., a soft contact lens is placed in each of the patient&#39;s eyes. If needed, the soft contact lenses may include vision correction. Next, at step  1110 , the visual axis of each of the patient&#39;s eyes is located as described above. At a step  1120 , a mask, such as any of those described above, is placed on the soft contact lenses such that the optical axis of the aperture of the mask is aligned with the visual axis of the eye. In this position, the mask will be located generally concentric with the patient&#39;s pupil. In addition, the curvature of the mask should parallel the curvature of the patient&#39;s cornea. The process continues at a step  1130 , in which the patient is fitted with a second set of soft contact lenses, i.e., a second soft contact lens is placed over the mask in each of the patient&#39;s eyes. The second contact lens holds the mask in a substantially constant position. Last, at step  1140 , the patient&#39;s vision is tested. During testing, it is advisable to check the positioning of the mask to ensure that the optical axis of the aperture of the mask is substantially collinear with the visual axis of the eye. Further details of testing are set forth in U.S. Pat. No. 6,551,424, issued Apr. 29, 2003, incorporated by reference herein in its entirety. 
     In accordance with a still further embodiment of the invention, a mask is surgically implanted into the eye of a patient interested in increasing his or her depth of focus. For example, a patient may suffer from presbyopia, as discussed above. The mask may be a mask as described herein, similar to those described in the prior art, or a mask combining one or more of these properties. Further, the mask may be configured to correct visual aberrations. To aid the surgeon surgically implanting a mask into a patient&#39;s eye, the mask may be pre-rolled or folded for ease of implantation. 
     The mask may be implanted in several locations. For example, the mask may be implanted underneath the cornea&#39;s epithelium sheet, beneath the cornea&#39;s Bowman membrane, in the top layer of the cornea&#39;s stroma, or in the cornea&#39;s stroma. When the mask is placed underneath the cornea&#39;s epithelium sheet, removal of the mask requires little more than removal of the cornea&#39;s epithelium sheet. 
       FIGS. 50 a  through 50 c    show a mask  1200  inserted underneath an epithelium sheet  1210 . In this embodiment, the surgeon first removes the epithelium sheet  1210 . For example, as shown in  FIG. 50 a   , the epithelium sheet  1210  may be rolled back. Then, as shown in  FIG. 50 b   , the surgeon creates a depression  1215  in a Bowman&#39;s membrane  420  corresponding to the visual axis of the eye. The visual axis of the eye may be located as described above and may be marked by use of the alignment apparatus  1200  or other similar apparatus. The depression  1215  should be of sufficient depth and width to both expose the top layer  1230  of the stroma  1240  and to accommodate the mask  1200 . The mask  1200  is then placed in the depression  1215 . Because the depression  1215  is located in a position to correspond to the visual axis of the patient&#39;s eye, the central axis of the pinhole aperture of the mask  1200  will be substantially collinear with the visual axis of the eye. This will provide the greatest improvement in vision possible with the mask  1200 . Last, the epithelium sheet  1210  is placed over the mask  1200 . Over time, as shown in  FIG. 50 c   , the epithelium sheet  1210  will grow and adhere to the top layer  1230  of the stroma  1240 , as well as the mask  1200  depending, of course, on the composition of the mask  1200 . As needed, a contact lens may be placed over the incised cornea to protect the mask. 
       FIGS. 51 a  through 51 c    show a mask  1300  inserted beneath a Bowman&#39;s membrane  1320  of an eye. In this embodiment, as shown in  FIG. 51 a   , the surgeon first hinges open the Bowman&#39;s membrane  1320 . Then, as shown in  FIG. 51 b   , the surgeon creates a depression  1315  in a top layer  1300  of a stroma  1340  corresponding to the visual axis of the eye. The visual axis of the eye may be located as described above and may be marked by any suitable technique, for example using a visible ocular feature or a technique employing patient input. The depression  1315  should be of sufficient depth and width to accommodate the mask  1300 . Then, the mask  1300  is placed in the depression  1315 . Because the depression  1315  is located in a position to correspond to the visual axis of the patient&#39;s eye, the central axis of the pinhole aperture of the mask  1300  will be substantially collinear with the visual axis of the eye. This will provide the greatest improvement in vision possible with the mask  1300 . Last, the Bowman&#39;s membrane  1320  is placed over the mask  1300 . Over time, as shown in  FIG. 51 c   , the epithelium sheet  1310  will grow over the incised area of the Bowman&#39;s membrane  1320 . As needed, a contact lens may be placed over the incised cornea to protect the mask. 
     In another embodiment, a mask of sufficient thinness, i.e., less than substantially 20 microns, may be placed underneath epithelium sheet  1210 . In another embodiment, a mask or an optic having a thickness less than about 20 microns may be placed beneath Bowman&#39;s membrane  1320  without creating a depression in the top layer of the stroma. 
     In an alternate method for surgically implanting a mask in the eye of a patient, the mask may be threaded into a channel created in the top layer of the stroma. In this method, a curved channeling tool creates a channel in the top layer of the stroma, the channel being in a plane parallel to the surface of the cornea. The channel is formed in a position corresponding to the visual axis of the eye. The channeling tool either pierces the surface of the cornea or, in the alternative, is inserted via a small superficial radial incision. In the alternative, a laser focusing an ablative beam may create the channel in the top layer of the stroma. In this embodiment, the mask may be a single segment with a break, or it may be two or more segments. In any event, the mask in this embodiment is positioned in the channel and is thereby located so that the central axis of the pinhole aperture formed by the mask is substantially collinear with the patient&#39;s visual axis to provide the greatest improvement in the patient&#39;s depth of focus. 
     In another alternate method for surgically implanting a mask in the eye of a patient, the mask may be injected into the top layer of the stroma. In this embodiment, an injection tool with a stop penetrates the surface of the cornea to the specified depth. For example, the injection tool may be a ring of needles capable of producing a mask with a single injection. In the alternative, a channel may first be created in the top layer of the stroma in a position corresponding to the visual axis of the patient. Then, the injector tool may inject the mask into the channel. In this embodiment, the mask may be a pigment, or it may be pieces of pigmented material suspended in a bio-compatible medium. The pigment material may be made of a polymer or, in the alternative, made of a suture material. In any event, the mask injected into the channel is thereby positioned so that the central axis of the pinhole aperture formed by the pigment material is substantially collinear with the visual axis of the patient. 
     In another method for surgically implanting a mask in the eye of a patient, the mask may be placed beneath the corneal flap created during keratectomy, when the outermost 20% of the cornea is hinged open. As with the implantation methods discussed above, a mask placed beneath the corneal flap created during keratectomy should be substantially aligned with the patient&#39;s visual axis, as discussed above, for greatest effect. 
     In another method for surgically implanting a mask in the eye of a patient, the mask may be aligned with the patient&#39;s visual axis and placed in a pocket created in the cornea&#39;s stroma. 
     Further details concerning alignment apparatuses are disclosed in U.S. application Ser. No. 10/854,032, filed May 26, 2004, incorporated by reference herein in its entirety. Further variations on techniques involving pharmacologic manipulation for alignment or other purposes are discussed in U.S. application Ser. No. 11/257,505, filed Oct. 24, 2005, which is hereby incorporated by reference herein in its entirety. 
     VII. Further Methods of Treating a Patient 
     As discussed above in, various techniques are particularly suited for treating a patient by applying masks such as those disclosed herein to an eye. For example, in some techniques, a visual cue in the form of a projected image for a surgeon is provided during a procedure for applying a mask. In addition, some techniques for treating a patient involve positioning an implant with the aid of a marked reference point. These methods are illustrated by  FIGS. 52-53B . 
     In one method, a patient is treated by placing an implant  1400  in a cornea  1404 . A corneal flap  1408  is lifted to expose a surface in the cornea  1404  (e.g., an intracorneal surface). Any suitable tool or technique may be used to lift the corneal flap  1408  to expose a surface in the cornea  1404 . For example, a blade (e.g., a microkeratome), a laser or an electrosurgical tool could be used to form a corneal flap. A reference point  1412  on the cornea  1404  is identified. The reference point  1412  thereafter is marked in one technique, as discussed further below. The implant  1400  is positioned on the intracorneal surface. In one embodiment, the flap  1408  is then closed to cover at least a portion of the implant  1400 . 
     The surface of the cornea that is exposed is a stromal surface in one technique. The stromal surface may be on the corneal flap  1408  or on an exposed surface from which the corneal flap  1408  is removed. 
     The reference point  1412  may be identified in any suitable manner. For example, the alignment devices and methods described above may be used to identify the reference point  1412 . In one technique, identifying the reference point  1412  involves illuminating a light spot (e.g., a spot of light formed by all or a discrete portion of radiant energy corresponding to visible light, e.g., red light). As discussed above, the identifying of a reference point may further include placing liquid (e.g., a fluorescein dye or other dye) on the intracorneal surface. Preferably, identifying the reference point  1412  involves alignment using any of the techniques described herein. 
     As discussed above, various techniques may be used to mark an identified reference point. In one technique the reference point is marked by applying a dye to the cornea or otherwise spreading a material with known reflective properties onto the cornea. As discussed above, the dye may be a substance that interacts with radiant energy to increase the visibility of a marking target or other visual cue. The reference point may be marked by a dye with any suitable tool. The tool is configured so that it bites into a corneal layer, e.g., an anterior layer of the epithelium, and delivers a thin ink line into the corneal layer in one embodiment. The tool may be made sharp to bite into the epithelium. In one application, the tool is configured to deliver the dye as discussed above upon being lightly pressed against the eye. This arrangement is advantageous in that it does not form a larger impression in the eye. In another technique, the reference point may be marked by making an impression (e.g., a physical depression) on a surface of the cornea with or without additional delivery of a dye. In another technique, the reference point may be marked by illuminating a light or other source of radiant energy, e.g., a marking target illuminator and projecting that light onto the cornea (e.g., by projecting a marking target). 
     Any of the foregoing techniques for marking a reference point may be combined with techniques that make a mark that indicates the location of an axis of the eye, e.g., the visual axis or line-of-sight of the eye. In one technique, a mark indicates the approximate intersection of the visual axis and a surface of the cornea. In another technique, a mark is made approximately radially symmetrically disposed about the intersection of the visual axis and a surface of the cornea. 
     As discussed above, some techniques involve making a mark on an intracorneal surface. The mark may be made by any suitable technique. In one technique a mark is made by pressing an implement against the instracorneal surface. The implement may form a depression that has a size and shape that facilitate placement of a mask. For example, in one form the implement is configured to form a circular ring (e.g., a thin line of dye, or a physical depression, or both) with a diameter that is slightly larger than the outer diameter of a mask to be implanted. The circular ring can be formed to have a diameter between about 4 mm and about 5 mm. The intracorneal surface is on the corneal flap  1408  in one technique. In another technique, the intracorneal surface is on an exposed surface of the cornea from which the flap was removed. This exposed surface is sometimes referred to as a tissue bed. 
     In another technique, the corneal flap  1408  is lifted and thereafter is laid on an adjacent surface  1416  of the cornea  1404 . In another technique, the corneal flap  1408  is laid on a removable support  1420 , such as a sponge. In one technique, the removable support has a surface  1424  that is configured to maintain the native curvature of the corneal flap  1408 . 
       FIG. 52  shows that the marked reference point  1412  is helpful in positioning an implant on an intracorneal surface. In particular, the marked reference point  1412  enables the implant to be positioned with respect to the visual axis of the eye. In the illustrated embodiment, the implant  1400  is positioned so that a centerline of the implant, indicated as M CL  extends through the marked reference point  1412 . 
       FIG. 52A  illustrates another technique wherein a reference  1412 ′ is a ring or other two dimensional mark. In such a case, the implant  1400  may be placed so that an outer edge of the implant and the ring correspond, e.g., such that the ring and the implant  1400  share the same or substantially the same center. Preferably, the ring and the implant  1400  are aligned so that the centerline of the implant M CL  is on the line of sight of the eye, as discussed above. The ring is shown in dashed lines because in the illustrated technique, it is formed on the anterior surface of the corneal flap  1408 . 
     In one technique, the corneal flap  1408  is closed by returning the corneal flap  1408  to the cornea  1404  with the implant  1400  on the corneal flap  1408 . In another technique, the corneal flap  1408  is closed by returning the corneal flap  1408  to the cornea  1404  over the implant  1400 , which previously was placed on the tissue bed (the exposed intracorneal surface). 
     When the intracorneal surface is a stromal surface, the implant  1400  is placed on the stromal surface. At least a portion of the implant  1400  is covered. In some techniques, the implant  1400  is covered by returning a flap with the implant  1400  thereon to the cornea  1404  to cover the stromal surface. In one technique, the stromal surface is exposed by lifting an epithelial layer to expose stroma. In another technique, the stromal surface is exposed by removing an epithelial layer to expose stroma. In some techniques, an additional step of replacing the epithelial layer to at least partially cover the implant  1400  is performed. 
     After the flap  1408  is closed to cover at least a portion of the implant  1400 , the implant  1400  may be repositioned to some extent in some applications. In one technique, pressure is applied to the implant  1400  to move the implant into alignment with the reference point  1412 . The pressure may be applied to the anterior surface of the cornea  1404  proximate an edge of the implant  1400  (e.g., directly above, above and outside a projection of the outer periphery of the implant  1400 , or above and inside a projection of the outer periphery of the implant  1400 ). This may cause the implant to move slightly away from the edge proximate which pressure is applied. In another technique, pressure is applied directly to the implant. The implant  1400  may be repositioned in this manner if the reference point  1412  was marked on the flap  1408  or if the reference point  1412  was marked on the tissue bed. Preferably, pushing is accomplished by inserting a thin tool under the flap or into the pocket and directly moving the inlay. 
       FIG. 53  shows that a patient may also be treated by a method that positions an implant  1500  in a cornea  1504 , e.g., in a corneal pocket  1508 . Any suitable tool or technique may be used to create or form the corneal pocket  1508 . For example, a blade (e.g., a microkeratome), a laser, or an electrosurgical tool could be used to create or form a pocket in the cornea  1504 . A reference point  1512  is identified on the cornea  1504 . The reference point may be identified by any suitable technique, such as those discussed herein. The reference point  1512  is marked by any suitable technique, such as those discussed herein. The corneal pocket  1508  is created to expose an intracorneal surface  1516 . The corneal pocket  1508  may be created at any suitable depth, for example at a depth within a range of from about 50 microns to about 300 microns from the anterior surface of the cornea  1504 . The implant  1500  is positioned on the intracorneal surface  1516 . The marked reference point  1512  is helpful in positioning the implant  1500  on the intracorneal surface  1516 . The marked reference point  1512  enables the implant  1500  to be positioned with respect to the visual axis of the eye, as discussed above. In the illustrated embodiment, the implant  1500  is positioned so that a centerline M CL  of the implant  1500  extends through or adjacent to the marked reference point  1512 . 
       FIG. 53A  illustrates another technique wherein a reference  1512 ′ is a ring or other two dimensional mark. In such case, the implant  1500  may be placed so that an outer edge of the implant and the ring correspond, e.g., such that the ring and the implant  1500  share the same or substantially the same center. Preferably, the ring and the implant  1500  are aligned so that the centerline of the implant M CL  is on the line of sight of the eye, as discussed above. The ring is shown in solid lines because in the illustrated embodiment, it is formed on the anterior surface of the cornea  1504  above the pocket  1508 . 
     After the implant  1500  is positioned in the pocket  1508 , the implant  1500  may be repositioned to some extent in some applications. In one technique, pressure is applied to the implant  1500  to move the implant into alignment with the reference point  1512 . The pressure may be applied to the anterior surface of the cornea  1504  proximate an edge of the implant  1500  (e.g., directly above, above and outside a projection of the outer periphery of the implant  1500 , or above and inside a projection of the outer periphery of the implant  1500 ). This may cause the implant  1500  to move slightly away from the edge at which pressure is applied. In another technique, pressure is applied directly to the implant  1500 . 
     VIII. Further Masks Configured to Reduce Visible Diffraction Patterns and Provide Nutrient Transport 
     Perforating a corneal inlay to provide nutrient transport can have the disadvantage that light also passes through the holes. Light transmission can reduce the opacity of the annulus to the point of degrading the optical performance of the inlay in some conditions. In dim light conditions for distance vision, increased light transmission through the annulus can increase the overall optical performance by increasing illumination of the retina. While this light may help with distance vision in dim conditions, it may decrease the quality of near vision. Therefore, it is desirable to limit the transmission of light while enhancing transmission of nutrients. 
     The inventors recognized that while nutrient transport through the cornea is largely in the posterior-anterior direction, nutrients also can flow laterally around edges of an inlay. Lateral flow of nutrients can be driven by a gradient of concentration, for example. Thus, even if an impermeable barrier is positioned in a small portion of the cornea, the tissue above the barrier benefits from lateral diffusion, and is not as nutrient-depleted as it would be without lateral diffusion. The closer a region of corneal tissue is to an edge of a nutrient barrier, the less at risk this tissue is to nutrient depletion. Accordingly, an inlay need not have as many perforations at locations near edges as may be at locations farther from edges. Conversely, depletion is at its greatest in the center of a nutrient barrier. Accordingly, there is an advantage to increasing porosity near the center of a nutrient barrier to compensate for the relatively lower lateral flow of nutrients in that central region. Thus, the inlay can be optimized to maintain the health of the cornea. 
     It is possible to design a hole pattern which transmits less light overall, but provides better nutrient transport where it is needed most by creating a gradient of porosity that increases toward a central region of a nutrient blocking structure of an inlay. For example, an arrangement can be provided in which a gradient of porosity is least at the edges and greatest in a central section of an annulus of an inlay. Increasing porosity can be accomplished in a number of ways. For example,  FIG. 55  illustrates an annular corneal inlay  3100  with holes  3102  providing porosity, the holes  3102  being generally randomly arranged, the holes  3102  having substantially the same diameter across the annulus. This pattern could be modified to have a greater number of holes toward a central region of the annulus in some embodiments. While the number of holes toward the central region can be increased, the generally random positioning of the holes is maintained in some embodiments to prevent the holes from producing visible diffraction patterns or other optical artifacts. 
     As described above in Section V above, other embodiments may be provided that vary at least one aspect of a plurality of holes to reduce the tendency of the holes to produce visible diffraction patterns or patterns that otherwise reduce the vision improvement that may be provided by a mask with an aperture or opening. For example, in one embodiment, the hole size, shape, and orientation of at least a substantial number of the holes may be varied randomly or may be otherwise non-uniform. The mask may also be characterized in that at least one of the hole size, shape, orientation, and spacing of a plurality of holes is varied to reduce the tendency of the holes to produce visible diffraction patterns. In certain embodiments, the tendency of the holes to produce visible diffraction patterns is reduced by having a plurality of the holes having a first hole size, shape, or spacing and at least another plurality of the holes with a second hole size, shape, or spacing different from the first hole size, shape, or spacing. In other embodiments, the mask is characterized in that at least one of the hole size, shape, orientation, and spacing of a substantial number of the plurality of holes is different than at least one of the hole size, shape, orientation, and spacing of at least another substantial number of the plurality of holes to reduce the tendency of the holes to produce visible diffraction patterns. In further embodiments, the holes are positioned at irregular locations. For example, the holes are positioned at irregular locations to minimize the generation of visible artifacts due to the transmission of light through the holes. 
       FIG. 56  illustrates an annular corneal inlay with holes providing porosity for nutrient transport, the holes being generally randomly arranged. The holes in the embodiment of  FIG. 56  are not substantially the same hole diameter across the annulus. Rather, the holes have different hole diameters in different regions of the mask. For example, as discussed in greater detail below, the holes have larger diameters in a central region of the inlay than near the inner and outer circumferences of the inlay to enhance porosity of the inlay toward the central region. Additional hole patterns and arrangements optimized for nutrient flow are discussed in U.S. Pat. No. 7,628,810, U.S. Patent Publication No. 2006-0113054, and U.S. Patent Publication No. 2006-0265058, the entirety of each of which is hereby incorporated by reference. 
     The mask illustrated in  FIG. 55  has an irregular hole pattern with holes that are substantially the same size. In one embodiment, the holes have a diameter of about 10 microns. The embodiment of the mask illustrated in  FIG. 56  has an irregular hole pattern. The mask includes an inner peripheral region neighboring (e.g., immediately adjacent to) the inner periphery of the mask, an outer peripheral region neighboring (e.g., immediately adjacent to) the outer periphery of the mask, and a plurality of annular bands between the inner periphery region and the outer periphery region. The bands can be modified such that there is a generally increasing porosity from at least one of the inner or outer periphery regions toward a central portion of the annulus. For example, in one arrangement, a fixed number of holes is located in each band, with the size of the holes being larger in bands closer to the center of the annulus than in bands that are farther from the center of the annulus. 
       FIG. 57  illustrates an embodiment of a mask  3000  that includes a body  3004  with an aperture or opening  3002 . The body  3004  includes a hole region  3010  between an outer periphery  3012  and an inner periphery  3014  of the body  3004 . The hole region  3010  includes a nutrient transport structure  3030 . Only a portion of the nutrient transport structure  3030  is shown for simplicity. The hole region  3010  can include two more sub-regions, and each sub-region includes a plurality of holes. Each sub-region can have at least one property that is different from at least one property of another sub-region. For example, properties of a sub-region can include average or mean hole size (radius, diameter, area, perimeter, etc.), number of holes per unit area (e.g., hole density), area of holes per unit area (e.g., percentage of sub-region area that includes holes), shape of the holes, spacing between holes, percentage of light transmission, percentage of nutrient depletion, nutrient transport rate (e.g., nutrient transport rate per unit area), or porosity.  FIG. 57  illustrates one embodiment with three sub-regions including an inner region  3020 , an outer region  3022 , and a central region  3024  between the inner region  3020  and the outer region  3022 . The inner region  3020  is located between the inner periphery  3014  and a selected first circumference  3026 , the outer region  3022  is located between the outer periphery  2012  and a selected second circumference  3028 , and the central region is located between the selected first circumference  3026  and the selected second circumference  3028 . Each of the sub-regions can have an area that is the same or different from an area of another sub-regions. For example, each sub-region may or may not be equally spaced radially from the center of the aperture. In certain embodiments, each sub-region is an annular band. 
     As discussed previously, the body  3004  may also include an inner peripheral region  3008  and/or an outer peripheral region  3006  that are substantially devoid of holes. The inner peripheral region  3008  can extend between the inner periphery  3014  and a selected inner circumference  3018 , and the outer peripheral region  3006  can extend between the outer periphery  3012  and a selected outer circumference  3016 . 
     Nutrient depletion can be greatest near the center of the annulus (e.g., about midway between the outer periphery  3012  and the inner periphery  3014 . Therefore, more hole area or porosity that allows nutrient transportion through the mask  3000  near the center of the annulus can decrease nutrient depletion caused by the mask  3000 . In certain embodiments, the central region  3024  has a greater ability to transport nutrients than the inner region  3020  and/or the outer region  3022 . For example, the central region  3024  has a central area and the plurality of holes in the central region  3024  may comprise a first percentage of the central area. Similarly, the inner region  3020  has an inner area and the plurality of holes in the inner region  3020  may comprise a second percentage of the inner area, and the outer region  3022  has an outer area and the plurality of holes in the outer region  3022  may comprise a third percentage of the outer area. The first percentage can be greater than the second percentage and/or the third percentage. In another example, the central region  3024  may include a first porosity, the inner region  3020  may include a second porosity, the outer region  3024  may include a third porosity, and the first porosity is greater than the second porosity and/or the third porosity. In other words, the central region  3024 , the inner region  3020 , and the outer region  3022  can include a nutrient transport property that improves nutrient transport through the mask  3000 . The central region  3024  can include a first nutrient transport property value, the inner region  3020  can include a second nutrient transport property value, the outer region  3022  can include a third nutrient transport property value, and the first nutrient transport property value can be greater than the second and/or third nutrient transport property value. The nutrient transport property can be, for example, porosity, hole percentage, hole size, number of holes per unit area, or nutrient transport rate. 
     The position of the sub-regions can have a variety of configurations. In certain embodiments, the central region is located at between about 10 to about 90 percent of the annular width of the mask from the inner periphery. In additional embodiments, the central region is located at between about 20 to about 60 percent, between about 30 and about 50 percent, or between about 30 and 40 percent of the annular width of the mask from the inner periphery. 
     The hole region  3010  may also include more than three regions (e.g., inner, outer, and central regions) that are described above. The hole region  3010  can include any number of regions from two to infinity. For example, the hole region  3010  can gradually change one or properties radially across the mask body  3004  and may not change in a step fashion. In one embodiment, the porosity increases and then decreases radially from the inner periphery to the outer periphery. For example, the porosity may be substantially zero at or near the inner periphery and gradually increase to a maximum porosity and then gradually decrease to be substantially zero at or near the outer periphery. 
     In one arrangement, as illustrated in  FIG. 56 , ten annular bands are disposed between the inner periphery region and the outer periphery region. The first band of the ten annular bands neighbors (e.g., is immediately adjacent to) the inner periphery region, the second band neighbors the first band, and so forth. The tenth band neighbors the outer periphery region. Each band includes 840 holes in one embodiment. The inner periphery region and outer periphery region can take any suitable form, but preferably include no holes. The radial width of the size of inner periphery region and outer periphery region can be any suitable width, for example optimized to maintain the mechanical integrity of the inlay or to provide for handling by a user. In one embodiment, the inner periphery region and outer periphery region are 50 about microns wide. In some embodiments, only one of the inner periphery region and outer periphery region is provided. In other words, one of the bands with holes can be located at the inner periphery or the outer periphery. 
     One embodiment is further described in Table I. Each of the bands has a band width, a percentage of light transmission through the band, and a hole diameter for the holes in the band, as illustrated in Table I. In the embodiment of Table I, the bands are configured to be of equal area, and thus have progressively smaller widths farther from the inner periphery of the inlay. However, annular bands can be provided with different areas between the inner periphery and the outer periphery in some embodiments. 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Properties of one embodiment of the inlay of FIG. 56. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Hole Diameter 
                   
                 Band Width 
               
               
                   
                 Band No. 
                 (microns) 
                 % Transmission 
                 (microns) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 5.45 
                 2.3 
                 146 
               
               
                   
                 2 
                 7.45 
                 4.3 
                 127 
               
               
                   
                 3 
                 9.45 
                 6.9 
                 114 
               
               
                   
                 4 
                 11.45 
                 10.2 
                 105 
               
               
                   
                 5 
                 10.45 
                 8.5 
                 97 
               
               
                   
                 6 
                 9.45 
                 6.9 
                 91 
               
               
                   
                 7 
                 8.45 
                 5.6 
                 86 
               
               
                   
                 8 
                 7.45 
                 4.3 
                 81 
               
               
                   
                 9 
                 6.45 
                 3.2 
                 78 
               
               
                   
                 10 
                 5.45 
                 2.3 
                 74 
               
               
                   
                   
               
            
           
         
       
     
     In some embodiments, the central portion of the light blocking portion of the inlay (e.g., a midline of the annulus) is farthest from a source of lateral nutrient flow. In such an embodiment, it may be desirable to locate the portion (e.g., the band) of greatest porosity at or around the central portion. In other embodiments, the peak porosity can be located between the mid-line of the annulus and the inner periphery. In some applications of a small aperture inlay, lateral flow emanating from the aperture at the inner periphery of the inlay and propagating outward through corneal tissue anterior and/or posterior of the annulus is expected to be less than lateral flow emanating from tissue radially outward of the outer periphery and propagating inward through corneal tissue anterior and/or posterior of the annulus. In one embodiment, the location of peak porosity is at about 40 percent or less of the annular width of the inlay from the inner periphery. Such an arrangement provides a higher percentage of total nutrient flow to tissue anterior and/or posterior of an inner portion of the annulus from the nutrient flow structure than is provided to similar tissue adjacent to an outer portion of the annulus. 
     In the embodiment of the inlay of  FIG. 56  described by Table I, the modeled average light transmission is about 5%. In the embodiment of the inlay of  FIG. 55 , the modeled average light transmission is about 6.75%. The inlays of  FIGS. 55 and 56  have an inner radius of 0.8 mm (e.g., an aperture with a diameter of 1.6 mm), and an outer radius of 1.9 mm (e.g., radial distance from the center of the aperture to the outer periphery of the inlay. 
       FIG. 58  illustrates a comparison of modeled glucose depletion in a cornea in which the inlays of  FIGS. 55 and 56  have been implanted as a function of radial distances from the center of the inlay or aperture.  FIG. 58  was obtained from a finite-element model of glucose transport in the human cornea. The inlays of  FIGS. 55 and 56  extend from the inner periphery at a radial distance of 0.8 mm to the outer periphery at a radial distance of 1.9 mm. The radial distance from the center of the aperture plotted in  FIG. 58  starts at 0 mm (e.g., center of the aperture) and goes to greater than 1.9 mm (e.g., greater than the outer periphery of the inlay). From  FIG. 58 , it is clear that increasing the porosity, in this case, by increasing the size of holes near the annulus midline, can reduce glucose depletion. In particular,  FIG. 58  shows that the embodiment of  FIG. 56  reduces depletion of glucose while at the same time decreasing the overall porosity or hole density from 6.75% to 5%. The reduced light transmission of the mask of  FIG. 56  compared to the mask of  FIG. 55  improves the visual acuity produced by the mask. Therefore, advantageously, the mask of  FIG. 56  has both improved nutrient transport and visual acuity compared to the mask of  FIG. 55 . 
     Various embodiments have been described above. Although the invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.