Abstract:
Infinite gradient refractive index ophthalmic devices and methods of making same. The method involves diffusing a monomer which polymerizes to a lower or higher corresponding opposite refractive index polymer into a lower or higher index polymer structure and polymerizing same to create the gradient structure. The resulting polymeric structure is used to manufacture ophthalmic devices, e.g., intraocular lenses.

Description:
FIELD OF THE INVENTION 
     The present invention relates to ophthalmic lenses in general and intraocular lenses (IOLs) in particular and to a method for making and using the same. More particularly, the present invention relates to mutlifocal IOLs with a certain level of accommodation designed for refractive correction in aphakic eyes where a diseased natural lens is surgically removed, such as in the case of cataracts. 
     BACKGROUND OF THE INVENTION 
     IOL implants have been used for many years in aphakic (i.e. absent lens) eyes as replacements for diseased natural crystalline lenses that have been surgically removed from the eyes. Many different IOL designs have been developed over past years and proven successful for use in aphakic eyes. Successful IOL designs to date primarily include an optic portion with supports therefore, called haptics, connected to and surrounding at least part of the optic portion. The haptic portions of an IOL are designed to support the optic portion of the IOL in the lens capsule, anterior chamber or posterior chamber of an eye. 
     Commercially successful IOLs have been made from a variety of biocompatible materials, ranging from more rigid materials such as polymethylmethacrylate (PMMA) to softer, more flexible materials capable of being folded or compressed such as silicones, certain acrylics, and hydrogels. Haptic portions of the IOLs have been formed separately from the optic portion and later connected thereto through processes such as heat, physical staking and/or chemical bonding. Haptics have also been formed as an integral part of the optic portion in what is commonly referred to as “single-piece” IOLs. 
     Softer, more flexible IOLs have gained in popularity in recent years due to their ability to be compressed, folded, rolled or otherwise deformed. Such softer IOLs may be deformed prior to insertion thereof through an incision in the cornea of an eye. Following insertion of the IOL in an eye, the IOL returns to its original pre-deformed shape due to the memory characteristics of the soft material. Softer, more flexible IOLs as just described may be implanted into an eye through an incision that is much smaller, i.e., 2.8 to 3.2 mm, than that necessary for more rigid IOLs, i.e., 4.8 to 6.0 mm. A larger incision is necessary for more rigid IOLs because the lens must be inserted through an incision in the cornea slightly larger than the diameter of the inflexible IOL optic portion. Accordingly, more rigid IOLs have become less popular in the market since larger incisions have been found to be associated with an increased incidence of postoperative complications, such as induced astigmatism. 
     After IOL implantation, both softer and more rigid IOLs are subject to compressive forces exerted on the outer edges thereof from natural brain-induced contraction and relaxation of the ciliary muscle and increases and decreases in vitreous pressure. Compressive forces of this kind are useful in a phakic eye for focusing the eye at various distances. Most commercially successful IOL designs for use in aphakic eyes have single focus optic portions that are fixed and focus the eye at only a certain fixed distance. Such single focus IOLs require the wearing of glasses to change the focus of the eye few bifocal IOLs have been introduced to the commercial market but suffer from the disadvantage that each bifocal image represents only about forty percent of the available light and the remaining twenty percent of the light is lost to scatter, which provides lessened visual acuity. 
     Because of the noted shortcomings of current IOL designs, there is a need for IOLs designed to provide multifocal visual imaging in aphakic eyes without the aid of eyeglasses. 
     Current multifocal IOLs are based on integrating a few optical zones within the IOL surface to create a limited number of focal points on the cornea, e.g. U.S. Pat. Nos. 6,695,880 and 6,089,711. Each focal point or zone offers corrected vision at a specific distance (near, intermediate, and far). Accommodating IOLs are designed to simulate the performance of the healthy natural lens when the focus shifts from far to near or vice versa by allowing the IOL to move within the eye. Neither type of lenses performs satisfactorily. 
     The present invention is based on the novel concept that making an IOL with a true infinite refractive index gradient (IRIG) would provide patients with improved near, far and intermediate vision. In fact, the human natural lens has a true IRIG that is responsible for accommodation, depth of field perception and contrast sensitivity. More importantly, the contribution of IRIG to the lens power of the natural lens decreases significantly with age at a rate of 0.286±0.067 diopter per year (ref). This change accounts almost entirely for the estimated overall loss of accommodation responsible for presbyopia and loss of contrast sensitivity. An IOL similar in IRIG to a healthy human natural lens would restore accommodation and adequate vision to cataract patients. 
     SUMMARY OF THE INVENTION 
     An ophthalmic device, e.g. a multifocal intraocular lens (IOL), made in accordance with the present invention is made from a polymeric material having a true IRIG. A true refractive index (RI) gradient is described as an RI, which decreases infinitesimally in one preferred direction (or increases infinitesimally), forming a continuum or gradient of infinite values from ophthalmic device edge to center (or center to edge). This embodiment of the invention mimics a healthy human natural lens, which provides normal accommodation for far, intermediate, and near vision with no distortion, loss of depth of field, or unwanted images such halos, bright spots or light scattering produced by discrete RI interfaces or changes between optical zones with a single RI. 
     In a further aspect, the present invention is a method for making IRIG ophthalmic devices. 
     In yet a further aspect, the present invention is IRIG intraocular lenses (IOLs) and methods for making same. 
     In yet another aspect, the present invention is a multifocal ophthalmic lens; 
     Accordingly, it is an object of the present invention to provide a multifocal intraocular lens with accommodation capabilities for use in aphakic eyes. 
     Another object of the present invention is to provide multifocal intraocular lenses for use in aphakic eyes, which minimize optical distortions, halos, and loss of depth of field. 
     Another object of the present invention is to provide multifocal intraocular lenses for use in aphakic eyes, which minimize existing optical aberrations. 
     Still another object of the present invention is to provide accommodating intraocular lenses capable of improving contrast sensitivity. 
     The method used to produce the lens of the present invention is as follows: 
     1. The first step involves producing the core material at the center of the IOL, which contains a higher RI copolymer. A rod measuring approximately 6 inches in length and 6 mm in diameter is produced by polymerizing a base polymer or base material having a RI between 1.30 and 1.7. The polymer rod is removed from the mold without allowing the polymerization to proceed to completion. 
     2. The second step involves placing the rod produced in step 1 in a center of a cylindrical mold measuring, for example, 6 inches (15.24 mm) in length and 10 mm in diameter. A solution of a lower refractive index monomer is allowed to diffuse or permeate into the base polymer to create a gradient RI and then polymerized around the 6 mm rod to create a monolithic polymer rod measuring 6 inches (15.24 mm) in length and about 10 mm in diameter and having a IRIG created by the fickian nature of the diffusion of the lower RI monomer into the higher RI polymer rod. 
     The polymer rod is machined into 17 mm×2 mm disks and IOLs were cut from the samples. This method creates IOLs with an IRIG suitable for multifocal accommodating lenses. It will be appreciated by one skilled in this art that the lens or optic part of many other types of ophthalmic devices could be prepared using the above-disclosed and below-illustrated process. All such devices are within the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the attached drawings in which like features are indicated by like numerals. 
         FIG. 1  is a schematic cross-sectional representation of a button, lens, ophthalmic device employing an IRIG polymer and illustrating the infinite gradient refractive index; 
         FIG. 2  illustrates a lens cut from an IRIG polymer button such as that shown in  FIG. 1 ; and 
         FIG. 3  shows refractive index of an IRIG polymer lens or ophthalmic device as a function of the distance from the center or line of focus of the device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Base Materials 
     Suitable lens-forming monomers for use in the present invention include carbazole and/or naphthyl moiety, carbazole, naphthalene, or a naphthyl group such as vinyl carbazole, vinyl naphthalene, lauryl methacrylate, stearyl methacrylate, methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, n-vinyl pyrolidone, styrene, eugenol (4-hydroxyvinylbenzene), .alpha.-methylstyrene. In addition, for high-refractive index foldable lens applications, suitable monomers include, but are not limited to: 2-ethylphenoxy methacrylate, 2-ethylphenoxy acrylate, 2-ethylthiophenyl methacrylate, 2-ethylthiophenylacrylate, 2-ethylaminophenyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-phenylethyl methacrylate, 3-phenylpropyl methacrylate, 4-phenylbutyl methacrylate, 4-methylphenyl methacrylate, 4-methylbenzyl methacrylate, 2-2-methylphenylethyl methacrylate, 2-3-methylphenylethyl methacrylate, 2-4-methylphenylethyl methacrylate, 2-(4-propylphenyl)ethyl methacrylate, 2-(4-(1-methylethyl)phenyl)ethyl methacrylate, 2-(4-methoxyphenyl)ethyl methacrylate, 2-(4-cyclohexylphenyl)ethyl methacrylate, 2-(2-chlorophenyl)ethyl methacrylate, 2-(3-chlorophenyl)ethyl methacrylate, 2-(4-chlorophenyl)ethyl methacrylate, 2-(4-bromophenyl)ethyl methacrylate, 2-(3-phenylphenyl)ethyl methacrylate, 2-(4-phenylphenyl)ethyl methacrylate), 2-(4-benzylphenyl)ethyl methacrylate, and the like, including the corresponding methacrylates and acrylates. N-vinyl pyrolidone, styrene, eugenol and .alpha.-methyl styrene may also be suitable for high-refractive index foldable lens applications. 
     A preferred lens-forming monomer mixture is the mixture of vinyl carbazole, lauryl methacrylate, and hydroxyethyl acrylate. 
     The copolymerizable cross-linking agent used in the lens-materials of this invention may be any terminally ethylenically unsaturated compound having more than one unsaturated group. Suitable cross-linking agents include, for example: ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, allyl methacrylate, 1,3-propanediol dimethacrylate, allyl methacrylate, 1,6-hexanediol dimethacrylate, 1,4-butanediol dimethacrylate, and the like. A preferred cross-linking agent is ethylene glycol dimethacrylate. 
     Suitable crosslinkers also include polymeric crosslinkers, such as, polyethylene glycol 1000 diacrylate, polyethylene glycol 1000 dimethacrylate, polyethylene glycol 600 dimethacrylate, polybutanediol 2000 dimethacrylate, polypropylene glycol 1000 diacrylate, polypropylene glycol 1000 dimethacrylate, polytetramethylene glycol 2000 dimethacrylate, and polytetramethylene glycol 2000 diacrylate. 
     An ultra-violet absorbing material can also be included in the polymeric lenses of this invention in order that the lenses may have an ultraviolet absorbance approximately equivalent to that of the natural lens of the eye. The ultraviolet absorbing material can be any compound which absorbs ultraviolet light, i.e., light having a wavelength shorter than about 400 nm, but does not absorb any substantial amount of visible light. The ultraviolet absorbing compound is incorporated into the monomer mixture and is entrapped in the polymer matrix when the monomer mixture is polymerized. Suitable ultraviolet absorbing compounds include vinyl anthracene, substituted benzophenones, such as 2-hydroxybenzophenone, and 2-(2-hydroxyphenyl)benzotriazoles. It is preferred to use an ultraviolet absorbing compound which is copolymerizable with the monomers and is thereby covalently bound to the polymer matrix. In this way possible leaching of the ultraviolet absorbing compound out of the lens and into the interior of the eye is minimized. Suitable copolymerizable ultraviolet absorbing compounds are the substituted 2-hydroxybenzophenones disclosed in U.S. Pat. No. 4,304,895 and the 2-hydroxy-5-acryloxyphenyl-2H-benzotriazoles disclosed in U.S. Pat. No. 4,528,311. The most preferred ultraviolet absorbing compound is 2-(3′-methallyl-2′-hydroxy-5′ methyl phenyl)benzotriazole and vinyl anthracene. 
     Ultraviolet and/or blue light absorbing chromophores may be added to the base polymer. Such chromophores can be any compound which absorbs violet/blue light, i.e., light having a wavelength between about 380 nm and 570 nm. Yellow and orange dyes, polymerizeable yellow and orange dyes, chromene, and any combination thereof. The preferred BLCB is a combination of vinyl anthracene and disperse orange 3 methacrylamide. 
     Lower RI Monomer 
     Monomers useful for this invention are those capable of forming a homopolymer with a glass transition temperature (Tg) equal or lower than 25° to allow for the production of a foldable lens. The primary requirement for selection of a lower RI monomer is that the RI of the corresponding homopolymer should be less than that of the base polymer and, of course, be capable of coupling to the base polymer, e.g., co-polymerizing therewith, to produce a material that does not elute of otherwise emit monomer or polymer constituents. Monomers useful for this invention include acrylate and methacrylate derivatives including: 
     
       
         
               
               
             
               
               
             
           
               
                   
               
               
                 Polymer 
                 Refractive Index 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Poly(pentadecafluorooctyl acrylate) 
                 1.3390 
               
               
                 Poly(tetrafluoro-3-(heptafluoropropoxy)propyl 
                 1.3460 
               
               
                 acrylate) 
               
               
                 Poly(tetrafluoro-3-(pentafluoroethoxy)propyl acrylate) 
                 1.3480 
               
               
                 Poly(undecafluorohexyl acrylate) 
                 1.3560 
               
               
                 Poly(nonafluoropentyl acrylate) 
                 1.3600 
               
               
                 Poly(tetrafluoro-3-(trifluoromethoxy)propyl acrylate) 
                 1.3600 
               
               
                 Poly(pentafluorovinyl propionate) 
                 1.3640 
               
               
                 Poly(heptafluorobutyl acrylate) 
                 1.3670 
               
               
                 Poly(trifluorovinyl acetate) 
                 1.3750 
               
               
                 Poly(octafluoropentyl acrylate) 
                 1.3800 
               
               
                 Poly(pentafluoropropyl acrylate) 
                 1.3850 
               
               
                 Poly(2-heptafluorobutoxy)ethyl acrylate) 
                 1.3900 
               
               
                 Poly(chlorotrifluoroethylene) 
                 1.3900 
               
               
                 Poly(2,2,3,4,4-hexafluorobutyl acrylate) 
                 1.3920 
               
               
                 Poly(trifluoroethyl acrylate) 
                 1.4070 
               
               
                 Poly(2-(1,1,2,2-tetrafluoroethoxy)ethyl acrylate) 
                 1.4120 
               
               
                 Poly(trifluoroisopropyl methacrylate) 
                 1.4177 
               
               
                 Poly(2,2,2-trifluoro-1-methylethyl methacrylate) 
                 1.4185 
               
               
                 Poly(2-trifluoroethoxyethyl acrylate) 
                 1.4190 
               
               
                 Poly(trifluoroethyl methacrylate) 
                 1.4370 
               
               
                 Poly(methyl octadecyl siloxane) 
                 1.4430 
               
               
                 Poly(methyl hexyl siloxane) 
                 1.4430 
               
               
                 Poly(methyl octyl siloxane) 
                 1.4450 
               
               
                 Poly(isobutyl methacrylate) 
                 1.4470 
               
               
                 Poly(vinyl isobutyl ether) 
                 1.4507 
               
               
                 Poly(methyl hexadecyl siloxane) 
                 1.4510 
               
               
                 Poly(vinyl ethyl ether) 
                 1.4540 
               
               
                 Poly(methyl tetradecyl siloxane 
                 1.4550 
               
               
                 Poly(vinyl n-butyl ether) 
                 1.4563 
               
               
                 Poly(3-hexoxypropylene oxide) 
                 1.4590 
               
               
                 Poly(ethylene glycol) 
                 1.4590 
               
               
                 Poly(vinyl n-pentyl ether) 
                 1.4590 
               
               
                 Poly(vinyl n-hexyl ether) 
                 1.4591 
               
               
                 Poly(4-fluoro-2-trifluoromethylstyrene) 
                 1.4600 
               
               
                 Poly(vinyl octyl ether) 
                 1.4613 
               
               
                 Poly(vinyl n-octyl acrylate) 
                 1.4613 
               
               
                 Poly(vinyl 2-ethylhexyl ether) 
                 1.4626 
               
               
                 Poly(vinyl n-decyl ether) 
                 1.4628 
               
               
                 Poly(2-methoxyethyl acrylate) 
                 1.4630 
               
               
                 Poly(acryloxypropyl methyl siloxane) 
                 1.4630 
               
               
                 Poly(4-methyl-1-pentene) 
                 1.4630 
               
               
                 Poly(3-methoxypropylene oxide 
                 1.4630 
               
               
                 Poly(t-butyl methacrylate) 
                 1.4638 
               
               
                 Poly(vinyl n-dodecyl ether) 
                 1.4640 
               
               
                 Poly(3-ethoxypropyl acrylate) 
                 1.4650 
               
               
                 Poly(vinyl propionate) 
                 1.4664 
               
               
                 Poly(vinyl acetate) 
                 1.4665 
               
               
                 Poly(vinyl propionate) 
                 1.4665 
               
               
                 Poly(vinyl methyl ether) 
                 1.4670 
               
               
                 Poly(ethyl acrylate) 
                 1.4685 
               
               
                 Poly(vinyl methyl ether) 
                 1.4700 
               
               
                 Poly(3-methoxypropyl acrylate) 
                 1.4710 
               
               
                 Poly(1-octadecene) 
                 1.4710 
               
               
                 Poly(2-ethoxyethyl acrylate) 
                 1.4710 
               
               
                 Poly(isopropyl acrylate) 
                 1.4728 
               
               
                 Poly(1-decene) 
                 1.4730 
               
               
                 Poly(lauryl methacrylate) 
                 1.4740 
               
               
                 Poly(vinyl sec-butyl ether)(isotactic) 
                 1.4740 
               
               
                 Poly(n-butyl acrylate) 
                 1.4740 
               
               
                 Poly(dodecyl methacrylate) 
                 1.4740 
               
               
                 Poly(ethylene succinate) 
                 1.4744 
               
               
                 Poly(tetradecyl methacrylate) 
                 1.4746 
               
               
                 Poly(hexadecyl methacrylate) 
                 1.4750 
               
               
                 Poly(2-fluoroethyl methacrylate) 
                 1.4768 
               
               
                 Poly(octyl methyl silane) 
                 1.4780 
               
               
                 Poly(methyl acrylate) 
                 1.4793 
               
               
                 Poly(dicyanopropyl siloxane) 
                 1.4800 
               
               
                 Poly(sec-butyl methacrylate) 
                 1.4800 
               
               
                 Poly(dimethylsiloxane-co-alpha-methylstyrene) 
                 1.4800 
               
               
                 Poly(n-hexyl methacrylate) 
                 1.4813 
               
               
                 Poly(n-butyl methacrylate) 
                 1.4830 
               
               
                 Poly(ethylidene dimethacrylate) 
                 1.4831 
               
               
                 Poly(2-ethoxyethyl methacrylate) 
                 1.4833 
               
               
                 Poly(n-propyl methacrylate) 
                 1.4840 
               
               
                 Poly(ethyl methacrylate) 
                 1.4850 
               
               
                 Poly(vinyl butyral) 
                 1.4850 
               
               
                 Poly(3,3,5-trimethylcyclohexyl methacrylate) 
                 1.4850 
               
               
                 Poly(2-nitro-2-methylpropyl methacrylate) 
                 1.4868 
               
               
                 Poly(1,1-diethylpropyl methacrylate) 
                 1.4889 
               
               
                 Poly(triethylcarbinyl methacrylate) 
                 1.4889 
               
               
                 Poly(methyl methacrylate) 
                 1.4893 
               
               
                 Poly(mercaptopropyl methyl siloxane) 
                 1.4900 
               
               
                 Poly(ethyl glycolate methacrylate) 
                 1.4903 
               
               
                 Poly(3-methylcyclohexyl methacrylate) 
                 1.4947 
               
               
                 Poly(cyclohexyl alpha-ethoxyacrylate) 
                 1.4969 
               
               
                 Poly(4-methylcyclohexyl methacrylate) 
                 1.4975 
               
               
                 Poly(decamethylene glycol dimethacrylate) 
                 1.4990 
               
               
                 Poly(2-bromo-4-trifluoromethyl styrene) 
                 1.5000 
               
               
                 Poly(ethyl alpha-chloroacrylate) 
                 1.5020 
               
               
                 Poly(2-methylcyclohexyl methacrylate) 
                 1.5028 
               
               
                 Poly(bornyl methacrylate) 
                 1.5059 
               
               
                 Poly(ethylene glycol dimethacrylate) 
                 1.5063 
               
               
                 Poly(cyclohexyl methacrylate) 
                 1.5065 
               
               
                 Poly(cyclohexanediol-1,4-dimethacrylate) 
                 1.5067 
               
               
                 Poly(tetrahydrofurfuryl methacrylate) 
                 1.5096 
               
               
                 Poly(1-methylcyclohexyl methacrylate) 
                 1.5111 
               
               
                 Poly(2-hydroxyethyl methacrylate) 
                 1.5119 
               
               
                 Poly(1-butene)(isotactic) 
                 1.5125 
               
               
                 Poly(vinyl methacrylate) 
                 1.5129 
               
               
                 Poly(vinyl chloroacetate) 
                 1.5130 
               
               
                 Poly(N-butyl methacrylamide) 
                 1.5135 
               
               
                 Poly(2-chloroethyl methacrylate) 
                 1.5170 
               
               
                 Poly(methyl alpha-chloroacrylate) 
                 1.5170 
               
               
                 Poly(2-diethylaminoethyl methacrylate) 
                 1.5174 
               
               
                 Poly(2-chlorocyclohexyl methacrylate) 
                 1.5179 
               
               
                 Poly(allyl methacrylate) 
                 1.5196 
               
               
                 Poly(methacrylonitrile) 
                 1.5200 
               
               
                 Poly(N-2-methoxyethyl)methacrylamide 
                 1.5246 
               
               
                 Poly(2,3-dimethylbutadiene){methyl rubber} 
                 1.5250 
               
               
                 Poly(2-chloro-1-(chloromethyl)ethyl methacrylate) 
                 1.5270 
               
               
                 Poly(1,3-dichloropropyl methacrylate) 
                 1.5270 
               
               
                 Poly(acrylic acid) 
                 1.5270 
               
               
                 Poly(N-vinyl pyrrolidone) 
                 1.5300 
               
               
                 Poly(methyl phenyl siloxane) 
                 1.5330 
               
               
                 Poly(2-chloroethyl alpha-chloroacrylate) 
                 1.5330 
               
               
                 Poly(2-aminoethyl methacrylate) 
                 1.5370 
               
               
                 Poly(furfuryl metacrylate) 
                 1.5381 
               
               
                 Poly(butylmercaptyl methacrylate) 
                 1.5390 
               
               
                 Poly(1-phenyl-n-amyl methacrylate) 
                 1.5396 
               
               
                 Poly(N-methyl methacrylamide) 
                 1.5398 
               
               
                 Poly(cyclohexyl alpha-bromoacrylate) 
                 1.5420 
               
               
                 Poly(sec-butyl alpha-bromoacrylate) 
                 1.5420 
               
               
                 Poly(2-bromoethyl methacrylate) 
                 1.5426 
               
               
                 Poly(ethylmercaptyl methacrylate) 
                 1.5470 
               
               
                 Poly(N-allyl methacrylamide) 
                 1.5476 
               
               
                 Poly(1-phenylethyl methacrylate) 
                 1.5487 
               
               
                 Poly(2-vinyltetrahydrofuran) 
                 1.5500 
               
               
                 Poly(vinylfuran) 
                 1.5500 
               
               
                 Poly(methyl m-chlorophenylethyl siloxane) 
                 1.5500 
               
               
                 Poly(p-methoxybenzyl methacrylate) 
                 1.5520 
               
               
                 Poly(isopropyl methacrylate) 
                 1.5520 
               
               
                 Poly(p-isopropyl styrene) 
                 1.5540 
               
               
                 Poly(isoprene), chlorinated 
                 1.5540 
               
               
                 Poly(1-phenylallyl methacrylate) 
                 1.5573 
               
               
                 Poly(p-cyclohexylphenyl methacrylate) 
                 1.5575 
               
               
                 Poly(2-phenylethyl methacrylate) 
                 1.5592 
               
               
                 Poly(methyl m-chlorophenyl siloxane) 
                 1.5600 
               
               
                 Poly{1-(o-chlorophenyl)ethyl methacrylate)} 
                 1.5624 
               
               
                 Poly(1-phenylcyclohexyl methacrylate) 
                 1.5645 
               
               
                 Poly(methyl alpha-bromoacrylate) 
                 1.5672 
               
               
                 Poly(benzyl methacrylate) 
                 1.5680 
               
               
                 Poly{2-(phenylsulfonyl)ethyl methacrylate} 
                 1.5682 
               
               
                 Poly(m-cresyl methacrylate) 
                 1.5683 
               
               
                 Poly(o-methoxyphenol methacrylate) 
                 1.5705 
               
               
                 Poly(phenyl methacrylate) 
                 1.5706 
               
               
                 Poly(o-cresyl methacrylate) 
                 1.5707 
               
               
                 Poly(2,3-dibromopropyl methacrylate) 
                 1.5739 
               
               
                 Poly(1,2-diphenylethyl methacrylate) 
                 1.5816 
               
               
                 Poly(o-chlorobenzyl methacrylate) 
                 1.5823 
               
               
                 Poly(m-nitrobenzyl methacrylate) 
                 1.5845 
               
               
                 Bisphenol-A polycarbonate 
                 1.5860 
               
               
                 Poly(4-methoxy-2-methylstyrene) 
                 1.5868 
               
               
                 Poly(o-methyl styrene) 
                 1.5874 
               
               
                 Polystyrene 
                 1.5894 
               
               
                 Poly(o-methoxy styrene) 
                 1.5932 
               
               
                 Poly(diphenylmethyl methacrylate) 
                 1.5933 
               
               
                 Poly(p-bromophenyl methacrylate) 
                 1.5964 
               
               
                 Poly(N-benzyl methacrylamide) 
                 1.5965 
               
               
                 Poly(p-methoxy styrene) 
                 1.5967 
               
               
                 Poly(4-methoxystyrene) 
                 1.5967 
               
               
                 Poly{1,1-cyclopentane bis(4-phenyl)carbonate} 
                 1.5993 
               
               
                 Poly(vinylidene chloride) 
                 1.6000 
               
               
                 Poly(o-chlorodiphenyl methyl methacrylate) 
                 1.6040 
               
               
                 Poly{2,2-propane bis[4-(2,6- 
                 1.6056 
               
               
                 dichlorophenyl)]carbonate} 
               
               
                 Poly(pentachlorophenyl methacrylate) 
                 1.6080 
               
               
                 Poly(2-chlorostyrene) 
                 1.6098 
               
               
                 Poly(alpha-methylstyrene) 
                 1.6100 
               
               
                 Poly(phenyl alpha-bromoacrylate) 
                 1.6120 
               
               
                 Poly{2,2-propane bis[4-(2,6- 
                 1.6147 
               
               
                 dibromophenyl)cabonate]} 
               
               
                 Poly(2,6-dichlorostyrene) 
                 1.6248 
               
               
                 Poly(beta-naphthyl methacrylate) 
                 1.6298 
               
               
                 Poly(alpha-naphthyl carbinyl methacrylate) 
                 1.6300 
               
               
                 Poly(phenyl methyl silane) 
                 1.6300 
               
               
                 Poly(alpha-naphthyl methacrylate) 
                 1.6410 
               
               
                 Poly(p-phenylene ether-sulphone) 
                 1.6500 
               
               
                 Poly{diphenylmethane bis(4-phenyl)carbonate} 
                 1.6539 
               
               
                 Poly(vinyl phenyl sulfide) 
                 1.6568 
               
               
                 Poly(2-vinylnapthalene) 
                 1.6818 
               
               
                 Poly(N-vinyl carbazole) 
                 1.6830 
               
               
                 Naphthalene-formaldehyde rubber 
                 1.6960 
               
               
                 Phenol-formaldehyde resin 
                 1.7000 
               
               
                   
               
             
          
         
       
     
       FIG. 1  illustrates, in section, a button, lens blank, or lens precursor ( 10 ) of the present invention. The shading  12  in  FIG. 1  shows the gradient refractive index. In  FIG. 1 , the more darkly shaded area represents that part of the lens precursor having a higher refractive index. Thus, for example, lower refractive index zones or portions are shown at  14 , while a higher refractive zone or portion is indicated at  16 . The center of the lens blank or button is indicated at  18 , while the gradient between the higher refractive index zone  16 , and the lower refractive index zone or segment  14  is shown by bracket  20 . 
       FIG. 2  shows schematically in section a lens  10 ′, manufactured from the button or lens precursor shown in  FIG. 1 . Lower refractive index zones or regions  14 ′ and a higher refractive index zone or region  16 ′ also is shown. The line of focus or center of lens  10 ′ is shown at  18 ′. The lens  10 ′ of  FIG. 2  would be manufactured from the lens precursor  10  of  FIG. 1  in accordance with processes well-known to one skilled in the art. Lens  10 ′ has, of course, anterior surface  24  and posterior surface  22 . In accordance with well-known manufacturing principles of optics, the radius of curvature of anterior surface  24  and posterior surface  22 , as well as the overall thickness of lens  10 ′ is adjusted to determine lens focal length, power, and other optical parameters. 
       FIG. 3  shows the approximate refractive index profile of an IRIG polymer lens of the present invention as a function of distance from the center of the lens or line of focus of lens  10 ′ in  FIG. 2 . 
     This invention will now be illustrated with reference to a number of examples. The examples are intended to be illustrative and not limiting. Thus, the attached claims should not be limited thereto. 
                                                                                                               TABLE 1               Base               RI at   RI at    RI at       Polymer   %   Second       center   3.0 mm   5.0 mm       Comp.   Conc.   Polymer   RI   of lens   from center   from center                                VC   30   100%   1.569   1.568   1.502   1.474       LM   37   LM       HEMA   30       EGDM   2.92       DYA   0.08       VC   30   100%   1.568   1.568   1.505   1.475       LM   37   LM       HEA   30       EGDM   2.92       DYA   0.08       VC   30   100%   1.563   1.554   1.498   1.469       EHA   37   EA       HEMA   30       EGDM   2.95       DYM   0.05       VC   30   100%   1.562   1.556   1.497   1.468       EHA   37   EA       HEA   30       EGDM   2.95       DYM   0.05       VN   30   100%   1.554   1.551   1.492   1.474       EHA   37   EA       HEMA   30       EGDM   2.95       DYM   0.05       VC   29   100%   1.551   1.550   1.482   1.474       EHA   37   EA       HEA   30       EGDM   2.98       DOA   0.02       VA   1.0            Preferred Formulations            VC   21.3   100%   1.539   1.537   1.481   1.474       HEA   28.0   LM       LM   46.7       EGDM   2.985       DOM   0.015       VA   0.7       MEB   0.3       VC   21.3   100%   1.536   1.535   1.481   1.474       HEA   28.0   LM       LM   46.7       EGDM   2.982       DOM   0.018       VA   0.7       MEB   0.3       VC   21.3   100%   1.535   1.535   1.481   1.474       HEA   28.0   LM       LM   46.7       EGDM   2.97       DOM   0.03       VA   0.7       MEB   0.3       VC   21.3   100%   1.537   1.536   1.483   1.474       HEA   28.0   LM       LM   46.7       EGDM   2.98       DOM   0.02       VA   0.7       MEB   0.3               VC: vinyl carbazole       VN: 2-vinyl naphthalene       EHA: 2-ethylhexylacrylate       LM: Lauryl methacrylate       HEMA; Hyroxyethylmethacrylate       HEA: Hydroxyethylacrylate       EA: Ethyl acrylate       EGDM: ethylene glycol dimethacrylate       VA: vinyl anthracene       MEB: 2-(2′-Methacryloxy-5′methylphenyl)benzotriazole       DYA: Disperse Yellow 7 Acrylate       DYM: Disperse Yellow 7 methacrylate       DOM: Disperse Orange 3 Methacrylamide            
General Preparation Steps for Polymers of Example 1-10
 
     STEP 1: The comonomers listed above in Table 1 were mixed in a glass flask using a magnetic stir bar for at least 30 minutes followed by sonication for the times indicated, and then stirring again for another 30 minutes. The combination of sonication and hydrophilic/hydrophobic repulsion forces allows the formation of nanoclusters. The size of the nanoclusters is theoretically controlled by the amount of energy provided during these steps. We found that sonicating for about 30 minutes at a power setting of 100% on a Branson 5510 provides optically clear materials with adequate optical and physical properties. AIBN was added at a concentration of 0.2%. The comonomer mixture with was placed in a Teflon tubular mold. The mold was placed in water bath at 70° C. for 2 hours. A soft polymer rod measuring 6 mm in diameter and 6 inches in length was removed from the mold and cooled to room temperature. 
     STEP 2: The rod produced in step 1 was suspended e.g., by one end in the center of a cylindrical mold measuring 6 inches (15.24 mm) in length and 10 mm in diameter. A solution of the second lower RI, monomer containing 0.2% AIBN was poured around the 6 mm rod produced in step 1 and kept at 40° C. for 48 hours in an oven to allow for diffusion to occur. The mold is transferred to a water bath at 70° C. for 12 hours and then to an oven at 100° C. for 24 hours. A final polymer rod measuring 6 inches (15.24 mm) in length and 10 mm in diameter and having a IRIG was produced. The polymer rod was machined into 17 mm×2 mm disks and IOLs were cut from the samples. The IOLS produced by this method are foldable and have good optical properties. 
     The refractive index was measured using a CLR 12-70 refractometer from Index Instrument. To asses the diffusion progression, RI was measured at three distances from the center of the IOL: 0 mm (center of the lens), 3.0 mm, and at 5.0 mm. 
     The results show that the RI decreases radially from the centre to the periphery of the lens in a manner similar to that of a young human lens. The fickian nature of diffusion of the lower refractive index monomer into the higher refractive index base material creates an IRIG. 
     It goes without saying that while the present invention has been described with reference to a lower RI monomer permeating or diffusing into a higher RI base material or base polymer, the reverse also is contemplated. In that variation a higher RI monomer would be diffused into a lower RI base material in accordance with the steps of the method of this invention. 
     Multifocal/Accommodating IOLs Made from IRIG Polymer 
     Current multifocal IOLs offer acceptable near and far vision but suffer from the following problems: 
     1. Poor intermediate vision 
     2. Loss of light hitting the retina 
     3. Visual artifacts such as halos, light scattering, and glare 
     4. No accommodation 
     These shortcomings are mainly caused by the limited number of refractive zones created on the surface of the lens. In contrast with the natural lens where refraction and accommodation is mainly afforded by a RI gradient throughout the bulk of the lens. The purpose of this invention is to create an IOL that simulates the gradient RI present in a young natural crystalline lens.
 
IRIG Multifocal/Accommodating IOL Preparation
 
     IOLs with a 6 mm diameter were cut from IRIG polymer rods prepared by the method described above. The refractive index at a distance r from the center of the lens may be evaluated by the following formula:
 
 n ( r )= n   0 ( r )∫−tan  h ( gr ) sech ( gr )
 
Where g is a gradient constant and n 0  is the refractive index at the center of the lens.
 
     Unlike “layered” GRI materials, the refractive index at any distance from the center follows a continuous progression evidenced by the integral function. 
     The lens power may be calculated from the index of refraction using the formula:
 
 P=− ( t/r )×( dn/dr )
 
Where t is the thickness of the lens and r is the radial distance.
 
     For example, a lens with a central power P 0  and a transition zone between r 1  and r 2  will have the following power function: 
     
       
         
           
             
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