prior art anterior chamber lenses have generally been made from polymethyl methacrylate ( pmma ), which is a relatively hard thermoplastic . prior to the present invention , a certain amount of rigidity was believed necessary to maintain stability of the implant in the anterior chamber . see also u . s . pat . no . 6 , 228 , 115 ( hoffmann , et al . ), the entire contents of which being incorporated herein by reference , wherein a stiffening element is added to the haptic to achieve the desirable stability of the lens . the inventors of the present invention have discovered that the compressive forces of pmma anterior chamber lenses is far in excess of what is required for stability . recent advances in biocompatible materials makes it possible to construct anterior chamber lenses from soft materials such as silicones , hydrogels and soft acrylics . with these softer materials , there is some question as to the stability of the implant in the anterior chamber . the inventors of the present invention have discovered that lenses made from soft material are stable when certain compressive forces and contact areas are used . for example , the commercially available bausch & amp ; lomb nuvita model ma 20 exhibits a force response of approximately 2 . 7 mn at 1 mm of compression when measured according to the industry standard compression test , iso / dis 11979 - 3 . the iol illustrated in fig1 - 3 exhibits a force response of less than approximately 0 . 35 mn at 1 mm of compression when made from a soft acrylic material , which is similar to the commercially available alcon model sa30el posterior chamber lens . the broad haptic contact areas found on posterior chamber iols such as the alcon model sa30el are not suitable for implantation in the anterior chamber because such designs can cause translational movement of the haptic contact points relative to the anterior chamber tissue , resulting in chronic irritation and the formation of synechia . the formation of calluses around the haptics may also cause late - onset glaucoma . accordingly , the inventors have discovered that an iol having haptics that contact the anterior chamber angle at only four locations , and with a ratio of haptic spread to optic diameter of less than 1 . 5 , and preferably around 1 . 3 provides sufficient stability without excessive angle contact . as seen in fig1 - 3 , iol 10 meets the design requirement of the present invention . iol 10 is preferably made in a single piece entirely from a soft acrylic , such as those described in u . s . pat . nos . 5 , 290 , 892 , 5 , 403 , 901 , 5433746 , 5 , 674 , 960 and 5 , 861 , 031 ( namdaran , et al .) and 5 , 693 , 095 ( freeman , et al . ), the entire contents of which being incorporated herein by reference . such a material allows iol 10 to be rolled or folded so as to fit through a 3 . 5 mm or less surgical incision and implanted in the anterior chamber of an eye . iol 10 generally contains two opposing pairs of footplates 12 joined to optic 14 by haptics 16 and stems 18 . optic 14 may have any suitable diameter , but is preferably between 5 . 0 mm and 6 . 0 mm . footplates 12 are separated by haptic 16 by a distance s , that is preferably less than 1 . 5 times the diameter of optic 14 , and most preferably around 1 . 3 times the diameter of optic 14 . footplates 12 and haptics 16 preferably are between 0 . 20 and 0 . 30 mm thick , which provides sufficient compressive force , while minimizing axial vaulting of lens 10 to less than 1 . 5 mm and preferably less than 1 . 0 mm when footplates 12 and haptics 16 are compressed 1 mm . as discussed above , the compressive force of haptics 16 and footplates 12 needs to be sufficient for the stability of iol 10 , but not large enough to cause irritation or pupil ovaling . preferably , iol 10 exhibits a force response of approximately less than 0 . 35 mn , and more preferably , approximately less than 0 . 30 mn , when footplates 12 and haptics 16 are compressed 1 mm according to industry standard test iso / dis 11979 - 3 . 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 .
an anterior chamber phakic lens made from a foldable , highly biocompatible material that has a very low haptic compression force and low axial displacement , yet is stable in the anterior chamber .