Abstract:
Intracomeal lenses having flow enhancement regions facilitate optimized nutrient transmission from posterior to anterior sides of lenses. Thinning, fenestration, and related structural emplacements permit, for example, hyperopic lenses to be crafted whereby nutrient transport is substantially enhanced in novel ways.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to intracorneal lenses. More particularly, the invention relates to an intracorneal lens formed with a flow enhancement portion for improving nutrient transport through the thickest portion of the lens.  
           [0002]    Various treatments are known for correcting corneal refractive errors. The use of lasers, for instance, to reshape the cornea by removing corneal tissue, has become increasingly popular in recent years. However, the removal of tissue can result in loss of the structural integrity of the cornea, and can also cause bulging. Furthermore, once corneal tissue has been removed, it can not easily be restored. Thus, laser vision correction is substantially irreversible.  
           [0003]    The need for a reversible treatment which does not adversely affect the structural integrity of the cornea has led to the use of intra-corneal implants, which do not require the removal of tissue. Instead, a single small incision is made in the cornea to make a flap or hinge, which is then folded back to expose the middle layer of corneal tissue known as the stromal bed. A corrective lens, typically formed of hydrogel material, is placed on the stromal layer. Then the flap is returned to its initial position and smoothed over the lens.  
           [0004]    Ideally, an intraocular lens should be made from a material having a relatively high index of refraction relative to the corneal stroma (i.e. greater than 1.45) and high permeability to water soluble nutrients, such as glucose, that are critical for maintaining optical health. Unfortunately, an ideal material having both these characteristics has yet to be found. Many high refractive index materials, such as polysulfone and PMMA, have been found to be insufficiently permeable, and could possibly cause nutritional stress leading to nebular opacification, anterior corneal necrosis, and other complications. On the other hand, many materials having higher permeability have lower refractive indices and less satisfactory optical qualities. Still other highly permeable materials require complex and expensive manufacturing processes.  
           [0005]    Attempts have been made in the past to improve nutrient transfer through corneal onlays or implants by providing a lens with one or more openings allowing nutrients to pass from the posterior side of the lens to the anterior side. U.S. Pat. No. 4,624,669 to Grendahl, for instance, discloses an intracorneal lens formed of polysulfone or PMMA, and having a plurality of pin holes or pores either positioned about the edge of the lens or randomly spaced about the entire surface area of the lens. U.S. Pat. No. 4,646,720 to Peyman et al. discloses an intracorneal lens having either a single, relatively large (up to about 64% of the total optical area of the lens) opening formed at the center of the lens or a plurality of randomly distributed smaller openings. U.S. Pat. No. 6,102,946 to Nigam discloses intracorneal lenses formed from microporous hydrogel material.  
           [0006]    Unfortunately, none of the prior art attempts discussed above have been entirely successful in providing an economically manufactured intracorneal lens in which both optical qualities and nutrient transfer are optimized.  
           [0007]    Therefore, it would be advantageous to develop an intraocular lens having a flow enhancement region which allows nutrients to pass from the posterior side of the lens to the anterior side without interfering with the optical qualities of the lens and without requiring complex or costly manufacturing processes.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the present invention, new intracorneal lenses have been designed with a flow enhancement region for allowing more effective transmission of nutrients from a posterior to an anterior side of a lens.  
           [0009]    In one broad aspect of the invention, the flow enhancement region comprises a thinned region in the thickest portion of the lens. The thinned region comprises a small surface area relative to the total optical area of the lens. In an especially preferred embodiment of the invention, the thinned region comprises from about 1% to about 5% of the total optical area of the lens. Preferably the thinned region comprises a gradual reduction in thickness to minimize such problems as glare, light scattering and reduction in optical image quality.  
           [0010]    In another broad aspect of the invention, the flow enhancement region comprises a fenestrated region in the thickest portion of the lens. The fenestrated region may consist of a single opening or a plurality of openings, and preferably comprises from about 1% to about 5% of the total optical area of the lens. Still more preferably, the walls of the opening or openings are angled to control the direction in which light is reflected.  
           [0011]    Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.  
           [0012]    Additional aspects, features, and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numbers. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a plan view of an intracorneal lens according to a preferred embodiment of the invention;  
         [0014]    [0014]FIG. 2 is a sectional view taken through line  2 - 2  of FIG. 1;  
         [0015]    [0015]FIG. 3 is a plan view of an intracorneal lens according to an alternate embodiment of the invention;  
         [0016]    [0016]FIG. 4 is a sectional view taken through line  4 - 4  of FIG. 3;  
         [0017]    [0017]FIG. 5 is a plan view of an intracorneal lens according to yet another alternate embodiment of the invention; and  
         [0018]    [0018]FIG. 6 is a sectional view taken through line  6 - 6  of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Referring now to the drawings, FIGS.  1 - 6  show various embodiments of an intracorneal lens  10  according to the present invention. Each of the illustrated intracorneal lenses is a hyperopic lens designed for the correction of far-sighted vision. As such, each intracorneal lens  10  includes an anterior surface  12  that is convex approaching the optical axis and a posterior surface  14  that is concave approaching the optical axis. In addition, each intracorneal lens  10  is thickest at its center and thinnest at its peripheral edge.  
         [0020]    In conventional hyperopic lenses, the increased thickness of the center results in reduced nutrient flow through the center of the lens, and a relatively large edge-to-center nutrient gradient. Edge-to-center nutrient gradients are not typically a concern in intracorneal lenses for the treatment of other types of vision problems such as myopia or astigmatism. Nonetheless, the teachings disclosed herein could easily be adapted to such lenses if needed. Accordingly, although these teachings are particularly beneficial in connection with hyperopic lenses, other types of lenses are included within the scope of the invention.  
         [0021]    Referring more specifically to FIGS. 1 and 2, the intracorneal lens  10 , comprises a lens body which may be formed of any optical material, preferably a hydrogel material, that is permeable or semi-permeable to water soluble nutrients such as glucose. The lens body includes a thinned central region  16  having a sufficiently small surface area relative to the total optical surface area to minimize light scattering. Both the thickness and the diameter of the thinned region depend on a variety of factors including the lens diameter, diopter power and water content of the lens material. Preferably, however, this diameter is selected such that the surface area of the thinned region  16  comprises about 1% to about 5% of the total optic area of the intracorneal lens  10 . For instance, in an intracorneal lens having a diameter of 5.0 mm, the thinned area  16  could be limited to the central 0.5 mm, which represents exactly 1% of the projected surface area of the intracorneal lens  10 .  
         [0022]    The thinned region  16  preferably comprises a gradual reduction in thickness approaching the center of the lens. This gradual reduction results in a reduction of light scattering and other visual symptoms relative to an abrupt reduction. In the illustrated embodiment, the thinned region  16  is created by forming an arcuate indentation  18  in the posterior surface  14  of the intracorneal lens.  
         [0023]    In a second embodiment of the invention, illustrated in FIGS. 3 and 4, a single opening or fenestration  20  is formed through the center of the intraocular lens  10 A. The diameter of the opening  20 , like the diameter of the thinned area in the previous embodiment, depends on factors such as the lens diameter, diopter power, and water content of the lens material but should comprise from about 1% to about 5% of the total optical area of the intraocular lens  10 A.  
         [0024]    The opening  20  preferably includes an angled sidewall  22  that slopes radially inwardly toward the center of the intraocular lens  10 A. The angle of the sidewall  22  can be selected to control the direction in which light is reflected, and thus to minimize glare, scattering and other undesirable optical effects.  
         [0025]    In the embodiment of FIGS. 5 and 6, the single opening is replaced by a plurality of smaller openings  24  clustered together in a fenestrated zone or region  26  at or near the thickest section, i.e. the center, of the intraocular lens  10 B. Once again, the total surface area of the fenestrated region preferably comprises from about 1% to about 5% of the total optical surface area. Furthermore, while the illustrated embodiment shows four circular openings that are generally equally spaced from the center, and provided at generally equal radial intervals from one another, the number, shape, and arrangement of the openings may be altered without departing from the principles of the invention.  
         [0026]    While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.