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 . 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 . 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 . 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 . * 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 . 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 ] fig1 illustrates icl 10 having coating 16 that cover the entire surface of base lens 14 . as illustrated in fig2 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 . alternatively , as best seen in fig3 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 . as best seen in fig3 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 . 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 .
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 .