Abstract:
A diffractive optical ICL made from two different hydrogel materials that are biologically acceptable for long term implantation in the cornea. The first material has a higher refractive index than the cornea and it is bound to the second material which has a refractive index similar to corneal tissue. The interface between the two materials consists of a microstructured diffractive surface. The adequate permeability of metabolites through both of the hydrogels of the diffractive ICL yields a safe implant for the cornea. Alternatively, the lens may be made of a single material and/or have an edge geometry that minimizes corneal irritation and allows the lens to sit within the corneal tissue smoothly and relatively flat.

Description:
[0001]    This application is a continuation-in-part application of U.S. patent application Ser. No. 08/908,230, filed Aug. 7, 1997, currently co-pending.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates generally to the field of optical intraocular lenses and, more particularly, to intracorneal lenses (“ICL”).  
           [0003]    The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing 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.  
           [0004]    The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In the normal, healthy eye, sharp images are formed on the retina (emmetropia). In many eyes, images are either formed in front of the retina because the eye is abnormally long (axial myopia), or formed in back of the retina because the eye is abnormally short (axial hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. In addition, due to age-related reduction in lens accommodation, the eye may become presbyopic resulting in the need for a bifocal or multifocal correction device.  
           [0005]    In the past, axial myopia, axial hyperopia and corneal astigmatism generally have been corrected by spectacles or contact lenses, but there are several refractive surgical procedures that have been investigated and used since 1949. Barraquer investigated a procedure called keratomileusis that reshaped the cornea using a microkeratome and a cryolathe. This procedure was never widely accepted by surgeons. Another procedure that has gained widespread acceptance is radial and/or transverse incisional keratotomy (RK or AK, respectively). Recently, the use of photablative lasers to reshape the surface of the cornea (photorefractive keratectomy or PRK) or for mid-stromal photoablation (Laser-Assisted In Situ Keratomileusis or LASIK) has been approved by regulatory authorities in the U.S. and other countries. All of these refractive surgical procedures cause an irreversible modification to the shape of the cornea in order to effect refractive changes, and if the correct refraction is not achieved by the first procedure, a second procedure or enhancement must be performed. Additionally, the long-term stability of the correction is variable because of the variability of the biological wound healing response between patients.  
           [0006]    Permanent intracorneal implants made from synthetic materials are also known for the correction of corneal refractive errors. For example, U.S. Pat. No. 5,123,921 (Werblin, et al.) discloses an intracorneal lens that is implanted intrastromally using a microkeratome. The lens itself has little refractive power, but changes the refractive power of the cornea by modifying the shape of the anterior surface of the cornea. The microkeratome used to implant this lens is complex and expensive and the lens requires a great deal of surgical skill to implant.  
           [0007]    There is a series of patents related to an intrastromal ring device used to induce refractive changes in the cornea (see U.S. Pat. Nos. 5,505,722, 5,466,260, 5,405,384, 5,323,788, 5,318,047, 5,312,424, 5,300,118, 5,188,125, 4,766,895, 4,671,276 and 4,452,235). The use of a ring-shaped device avoids implantation of the device within the central optical zone of the cornea, and is implanted in peripheral groove made by a special surgical instrument. The ring itself has no refractive power. Refractive changes are caused by the implanted ring changing the shape of the anterior surface of the cornea.  
           [0008]    A variation of the intrastromal ring is called Gel Injection Adjustable Keratoplasty (GIAK) and is described in U.S. Pat. Nos. 5,090,955 (Simon), 5,372,580 (Simon, et al.) and WIPO Publication No. WO 96/06584. Instead of a solid device, these publications disclose injecting a ring of biocompatible gel around the optic zone of the stroma to effect refractive changes to the cornea by changing the shape of the cornea.  
           [0009]    These prior art intracorneal devices all work by changing the shape of the cornea, and the devices themselves have little or no refractive properties. As a result, the preparation of the lamellar bed into which these devices are inserted is critical to the predictability of the refractive outcome, requiring very precise microkeratomes or other special surgical instruments and a great deal of surgical skill for success.  
           [0010]    Various intracorneal implants having a refractive power are also known. For example, U.S. Pat. No. 4,607,617 (Choyce) describes an implant made of polysulfone (refractive index 1.633). The high refractive index of polysulfone relative to stromal tissue (1.375) results in an implant that acts as an optical lens that effects a refractive change to the cornea without relying on a change in corneal shape. This lens was never clinically or commercially acceptable because the polysulfone material is too impermeable to glucose and other metabolites to maintain the corneal tissue anterior to the implant. Corneal ulcerations, opacifications and other complications were the clinical result.  
           [0011]    An implant that attempts to overcome the complications of polysulfone implants is described in U.S. Pat. No. 4,624,669 (Grendahl). This implant contains a plurality of microfenestrations that allows the flow of glucose and other metabolites through the lens. In animal studies, however, the microfenestrations were filled with keratocytes that created opacities, resulting in unacceptable light scattering and visual acuities. As a result, this implant was never commercially developed. In an attempt to limit damage to the anterior cornea and prevent keratocyte ingrowth, U.S. Pat. No. 5,628,794 (Lindstrom) discloses a limited diameter (2.5 mm) refractive multifocal implant for correction of presbyopia made from a rigid material having fenestrations, the implant and the fenestrations being coated with a hydrogel material. The inventors are not aware of clinical data for this lens. This limited diameter multifocal lens is not clinically acceptable for monofocal correction of myopia or hyperopia in most patients with normal pupil size under normal environmental light conditions.  
           [0012]    Previous attempts to correct presbyopic vision have generally been limited to spectacles or contact lenses. Recently, clinical investigations were initiated for a limited diameter (less than 2.5 mm), low water content (approximately 45%) monofocal hydrogel inlay that effectively created a multifocal cornea. These early clinical investigations; however, have not been encouraging due to compromised distance vision and unacceptable multifocal vision. These lenses are described in U.S. Pat. Nos. 5,196,026 and 5,336,261 (Barrett, et al.).  
           [0013]    Other lenses designed to overcome the complications of prior intracorneal lenses are described in WO 99/07309 (Patel, et al.) and EPO 0 420 549 (Stoy, et al.) and consist of a high water content hydrogel material that allows glucose and other metabolites to permeate through the lens and thus maintain the corneal tissue anterior to the implant.  
           [0014]    Despite these prior attempts to make a suitable corneal implant, a need continues to exist for a safe and biocompatible intracorneal lens.  
         BRIEF SUMMARY OF THE INVENTION  
         [0015]    The present invention improves upon the prior art by providing a diffractive optical ICL made from two different hydrogel materials that are biologically acceptable for long term implantation in the cornea. The first material has a higher refractive index than the cornea and it is bound to the second material which has a refractive index similar to corneal tissue. The interface between the two materials consists of a microstructured diffractive surface. The adequate permeability of metabolites through both of the hydrogels of the diffractive ICL yields a safe implant for the cornea. Alternatively, the lens may be made of a single material and/or have an edge geometry that minimizes corneal irritation and allows the lens to sit within the corneal tissue smoothly and relatively flat.  
           [0016]    Accordingly, one objective of the present invention is to provide a safe and biocompatible intracorneal lens.  
           [0017]    Another objective of the present invention is to provide a safe and biocompatible intracorneal lens with a high optical power.  
           [0018]    Still another objective of the present invention is to provide a safe and biocompatible intracorneal lens that does not rely on induced shape changes to the cornea to correct refractive errors of the eye.  
           [0019]    Still another objective of the present invention is to provide a safe and biocompatible intracorneal lens that contains a diffractive surface.  
           [0020]    Still another objective of the present invention is to provide a safe and biocompatible intracorneal lens that prevents unacceptable cellular ingrowth and deposits.  
           [0021]    These and other advantages and objectives of the present invention will become apparent from the detailed description and claims that follow.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0022]    [0022]FIG. 1 is a cross-section view of a first embodiment of the ICL of the present invention.  
         [0023]    [0023]FIG. 2 is a cross-section view of a second embodiment of the ICL of the present invention.  
         [0024]    [0024]FIG. 3 is a cross-section view of a third embodiment of the ICL of the present invention.  
         [0025]    [0025]FIG. 4 is an exploded cross-section view of the third embodiment of the ICL of the present invention taken at circle  4  in FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    ICL  10  of the present invention is designed to be implanted within a cornea and generally includes base lens  14  having a diffractive surface  18 , that is covered by coating  16 . Base lens  14  preferably has a diameter of at least  5  millimeters. Base lens  14  is preferably made from a material (“M 1 ”) which has a relatively high equilibrium water content at approximately body temperature, preferably 50% or greater, with a refractive index greater than corneal tissue and more preferably greater than 1.40. A high water content helps to ensure the flow of glucose and other metabolites through base lens  14 . A high refractive index material M 1  in combination with diffractive surface  18  allows ICL  10  to be made relatively thin but still have its own refractive power. While it is desirable for the material used to make base lens  14  to have as high of a water content and a refractive index as possible, increasing the water content of any high refractive index material will necessarily decrease the refractive index of that material because of the relatively low refractive index of water (1.336). In order to effect the desired refractive change to the cornea while maintaining an overall thin lens (less than 150 microns being preferred and 50 microns to 100 microns being most preferred) diffractive surface  18  is formed on base lens  14 . Diffractive surface  18  increases the power of ICL  10  without increasing the overall thickness of ICL  10 . The construction of diffractive surface  18  is well-known in the art and is described in U.S. Pat. No. 5,129,718 (Futhey, et al.), U.S. Pat. Nos. 5,076,684 and 5,116,111 (Simpson, et al.), U.S. Pat. Nos. 4,162,122, 4,210,391, 4,338,005, 4,340,283, 4,995,714, 4,995,715, 4,881,804, 4,881,805, 5,017,000, 5, 054, 905, 5,056,908, 5,120,120, 5,121,979, 5,121,980, 5,144,483, 5,117,306 (Cohen) and U.S. Pat. Nos. 4,637,697, 4,641,934 and 4,655,565 (Freeman), the entire contents of which are incorporated herein by reference. It will be understood by those skilled in the art that ICL  10  may be constructed to correct myopia, hyperopia, presbyopia and/or astigmatism by using diffractive monofocal or multifocal optics and superimposing or blending refractive optics when needed to correct astigmatism.  
         [0027]    Any of a variety of hydrogel materials having the correct physical properties may be used as M 1  to form base lens  14 . M 1  must have sufficient mechanical strength to allow for folding or rolling of ICL  10 ; M 1  must be photo stable; and M 1  preferably already has been shown safe in the contact lens and/or intraocular lens industry. Suitable monomers for M 1  include aryl methacrylates, arylalkyl (meth)acrylates, naphthyl (meth)acrylates, styrene, methylstyrene, N-vinylcarbazole, N,N dimethylacrylamides, 2-phenylethyl methacrylate, 3-phenylpropyl methacrylate, 4-phenylbutyl methacrylate, 2-phenoxyethyl methacrylate, 3-phenoxypropyl methacrylate, 4-phenoxybutyl methacrylate, beta naphthyl methacrylate, N-vinylcarbazole, N-vinyl-pyrrolidone, hydroxyethyl (meth)acrylates, polyethylene glycol (meth)acrylates, polyethylene oxide (meth)acrylates, 3-methoxy-2-hydroxypropyl-(meth)acrylate, (meth)acrylic acid and dihydroxyalkyl (meth)acrylates.  
         [0028]    One preferred formulation for M 1  is:  
         [0029]    N-vinyl-pyrrolidone—69%  
         [0030]    2-Phenylethyl methacrylate—29%  
         [0031]    allyl methacrylate (a crosslinker)—1%  
         [0032]    Lucirin TPO* (an initiator)—1%  
         [0033]    *diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide  
         [0034]    M 1  made according to this formulation has a refractive index of between 1.414 and 1.416, a water content of between 58% to 60% and a swell factor of 1.34.  
         [0035]    Coating  16  is used to cover diffractive surface  18  of base lens  14  and to provide a smooth surface so as to prevent any cellular ingrowth and resulting opacification along diffractive surface  18 . So as to reduce the overall thickness of ICL  10 , coating  16  preferably is less than 20 microns thick. The material used to make coating  16  (M 2 ) preferably has a refractive index close to that of the corneal tissue and an equilibrium water content at approximately body temperature of at least 65%. M 2  must be bondable to M 1  with similar swelling properties so as to not delaminate. M 2  should not distort or craze during rolling or folding of ICL  10 , and preferably should cure rapidly (e.g., in less than 3 minutes). M 2  must be photo stable and preferably already has been shown safe in the contact lens and/or intraocular lens industry.  
         [0036]    One preferred formulation for M 2  is:  
         [0037]    polyvinylpyrrolidone (MW-10K) (a plasticizer)—19%  
         [0038]    polyethylene glycol  200  (a plasticizer)—29%  
         [0039]    glyceryl methacrylate—49%  
         [0040]    ethyleneglycol dimethacrylate (a crosslinker)—0.5%  
         [0041]    Darocur  1173 * (an initiator)—2.5%  
         [0042]    *2-hydroxy-2-methyl-1-phenyl-propan-1-one M 2  made according to this formulation has a refractive index of 1.376, a water content of approximately 73% and a swell factor of 1.30.  
         [0043]    ICL  10  is made using molding techniques that are similar to those well-known in the contact lens and intraocular lens art. See, for example, U.S. Pat. No. 5,620,720 (Glick, et al.) the entire contents of which is incorporated herein by reference. A flexible bottom mold made from, for example, polypropylene, is filled with material M 1 . A first top mold made from, for example, polypropylene or fluoroethylene polypropylene (FEP), and containing the lens base curve and diffractive surface  18  is placed over the M 1  containing bottom mold. M 1  is cured, for example, under blue light (450 nm) at a flux of 14-15 mW/cm 2  for one hour. Alternatively, M 1  can be cured by replacing Lucirin TPO with 1% t-butylperoxy(2-ethyl-hexanoate) thermal initiator and thermal curing at 80° C. for 1 hour followed by a post-cure period of 1 hour at 100° C. The first top mold is removed and material M 2  is place on diffractive surface  18  of the newly formed base lens  14 . A second top mold, also made from polypropylene or FEP and having the same base curve as the first top mold but with no diffractive surface  18  is placed over the bottom mold. Pressure is applied to the top mold (approximately 100 lbs./in 2 ) and the mold assembly is exposed to ultraviolet light (366 nm) at a flux of 60-300 mW/cm 2  for three minutes. The second top mold is then removed and ICL  10  along with the bottom mold is placed in 65-75° C. heptane for several hours to extract the non-polymerized monomers. ICL  10  is removed from the bottom mold, allowed to air dry for several minutes and hydrated for at least two hours in hot, distilled water.  
         [0044]    [0044]FIG. 1 illustrates ICL  10  having coating  16  that cover the entire surface of base lens  14 . As illustrated in FIG. 2, ICL  10 ′ may alternatively have coating  16 ′ that is recessed into base lens  14 ′. Such a construction is easier to manufacture, with a more consistent lens edge, and helps prevent delamination of coating  16 ′ during lens insertion.  
         [0045]    Alternatively, as best seen in FIG. 3, ICL  110  of the present invention may be made entirely of M 1  material, having smooth anterior face  200  and posterior face  300  containing diffractive surface  318 .  
         [0046]    As best seen in FIGS. 3 and 4, ICL  10  or  110  may contain an outer peripheral edge  400  having curved posterior surface  301  and bicurved anterior surface  201 . Anterior surface  201  contains first portion  202  having a radius of curvature R 1  that intersects with second portion  203  having a radius of R 2 . Portion  202  preferably blends smoothly with the surrounding circular profile surface  200  and  203  at the points of intersection. Second portion  203  intersects with relatively straight portion  204  and is curved so as to smoothly blend portion  202  with portion  204 . Portion  204  has a length L and intersects with posterior surface  301 . R 1  preferably is between approximately 0.4 mm and 0.8 mm, with approximately 0.6 mm being most preferred. R 2  preferably is between approximately 0.01 mm and 0.05 mm, with approximately 0.02 being most preferred. L preferably is between approximately 0.005 mm and 0.03 mm, with approximately 0.01 mm being most preferred. The inventors have found that straight portion  204  thickens edge  400  and helps to prevent curling of edge  400 , which can cause corneal irritation and ulceration. First portion  202  and second portion  203  provide a smooth transition between anterior face  200  and straight portion  204 .  
         [0047]    This description is given for purposes of illustration and explanation. It will be apparent to those skilled in the relevant art that changes and modifications may be made to the invention described above without departing from its scope or spirit.