Patent Publication Number: US-9421089-B2

Title: Intraocular lens with post-implantation adjustment capabilities

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is a division of and claims the benefit of application U.S. Ser. No. 12/168,817 filed on Jul. 7, 2008, now abandoned, which is related to, and claims the benefit of U.S. Provisional 60/948,170 filed on Jul. 5, 2007, both of which are incorporated by reference herein and made a part of the present specification. 
    
    
     BACKGROUND 
     1. Field 
     The inventions relate to lenses and, more particularly, to intraocular lenses, the performance of which can be adjusted post-operatively or anytime after implantation in the eye. 
     2. Description of the Related Art 
     Cataract operations frequently involve the implantation of an artificial lens following cataract removal. Often, these lenses have a fixed focal length or, in the case of bifocal or multifocal lenses, can have several different fixed focal lengths. Known lenses can suffer from a variety of drawbacks. 
     SUMMARY 
     In some embodiments, a method of modifying an accommodating intraocular lens having an anterior optic, a posterior optic, and a support structure is provided. The method can involve modifying one or more portions of the intraocular lens after implantation (e.g., post-operatively or during a later sate of a procedure) in an eye. In one method, energy can be applied to at least a portion of the support structure to alter reaction forces between the support structure and at least one structure of the eye. In another method, energy can be applied to at least a portion of the anterior optic to alter the power of the optic, e.g., by altering the refractive index thereof. In another method, energy can be applied to at least a portion of the posterior optic to alter the power of the optic, e.g., by altering the refractive index thereof. In another method, energy can be applied to at least a portion of both of the anterior optic and the posterior optic to alter the power of both of the anterior optic and the posterior optic. In another method, energy can be applied to both the support structure and to at least a portion of at least one of the anterior optic and the posterior optic to alter the power of at least one of the optics. 
     In some embodiments, a method of modifying an accommodating intraocular lens having a first optic and a second optic after implantation in an eye comprises non-invasively applying energy to at least a portion of the first optic to adjust a refractive property of the first optic while leaving refractive properties of the second optic substantially unaffected. The method can also comprise, in some embodiments, non-invasively applying energy to at least a portion of the second optic to alter refractive properties of the second optic while leaving refractive properties of the first optic substantially unaffected. In some embodiments, a first energy source is applied to the first optic and a second energy source different from the first energy source is applied to the second optic. In some embodiments, the first optic comprises a first material responsive to the first energy source and the second optic comprises a second material responsive to the second energy source. 
     In some embodiments, a method of adjusting an intraocular lens having an anterior optic and a posterior optic after implantation in an eye comprises non-invasively applying energy to at least a portion of one of said anterior optic and said posterior optic while the lens is in the eye to alter a refractive property of said one of said optics while leaving refractive properties of a remaining one of said optics substantially unaffected. 
     In some embodiments, a method of modifying an accommodating intraocular lens comprising an anterior viewing element and a posterior viewing element comprises applying energy to one or more of the anterior and posterior viewing elements to change the index of refraction of the one or more viewing elements. In some embodiments, applying energy to one of the optics to change the index of refraction of the one optic leaves refractive properties of the remaining optic substantially unaffected. 
     In some embodiments, a method of modifying an accommodating intraocular lens comprising an anterior viewing element and a posterior viewing element comprises applying energy to one or more of the anterior and posterior viewing elements to change the shape (e.g., the curvature) of the one or more viewing elements. 
     In some embodiments, a method of modifying an accommodating intraocular lens comprising an anterior viewing element and a posterior viewing element comprises applying energy to one or more of the anterior and posterior viewing elements to change the power of the one or more viewing elements. 
     In some embodiments, a method of modifying an accommodating intraocular lens comprising an anterior portion having an anterior viewing element and an anterior biasing element and a posterior portion having a posterior viewing element and a posterior biasing element comprises applying energy to one or more of the anterior biasing element and the posterior biasing element to change the stiffness of the one or more biasing elements. 
     In some embodiments, a method of modifying an accommodating intraocular lens comprising an anterior portion having an anterior viewing element and an anterior biasing element and a posterior portion having a posterior viewing element and a posterior biasing element comprises applying energy to one or more of the anterior biasing element and the posterior biasing element to change the spring constant of the one or more biasing elements. 
     In some embodiments, a method of modifying an accommodating intraocular lens comprising an anterior portion having an anterior viewing element and an anterior biasing element and a posterior portion having a posterior viewing element and a posterior biasing element comprises applying energy to one or more of the anterior biasing element and the posterior biasing element to alter the separation of the anterior and posterior viewing elements, where the separation is that of the viewing elements when the viewing elements are in an unaccommodated state. 
     In some embodiments, an accommodating intraocular lens for implantation in an eye has an optical axis. The lens comprises an anterior portion which in turn comprises an anterior viewing element comprised of an optic having refractive power and an anterior biasing element comprising first and second anterior translation members extending from the anterior viewing element. The lens further comprises a posterior portion which in turn comprises a posterior viewing element in spaced relationship to the anterior viewing element and a posterior biasing element comprising first and second posterior translation members extending from the posterior viewing element. The anterior portion and posterior portion meet at first and second apices of the intraocular lens such that a plane perpendicular to the optical axis and passing through the apices is closer to one of said viewing elements than to the other of said viewing elements. The anterior portion and the posterior portion are responsive to force thereon to cause the separation between the viewing elements to change. 
     In some embodiments, an accommodating intraocular lens for implantation in an eye has an optical axis. The lens comprises an anterior portion, which in turn comprises an anterior viewing element comprised of an optic having refractive power, and an anterior biasing element comprising first and second anterior translation members extending from the anterior viewing element. The lens further comprises a posterior portion which in turn comprises a posterior viewing element in spaced relationship to the anterior viewing element, and a posterior biasing element comprising first and second posterior translation members extending from the posterior viewing element. The anterior portion and posterior portion meet at first and second apices of the intraocular lens. The anterior portion and the posterior portion are responsive to force thereon to cause the separation between the viewing elements to change. The first anterior translation member forms a first anterior biasing angle, as the lens is viewed from the side, with respect to a plane perpendicular to the optical axis and passing through the apices. The first posterior translation member forms a first posterior biasing angle, as the lens is viewed from the side, with respect to the plane. The first anterior biasing angle and the first posterior biasing angle are unequal. 
     In some embodiments, an accommodating intraocular lens comprises an anterior viewing element comprised of an optic having refractive power of less than 55 diopters and a posterior viewing element comprised of an optic having refractive power. The optics provide a combined power of 15-25 diopters and are mounted to move relative to each other along the optical axis in response to a contractile force by the ciliary muscle of the eye upon the capsular bag of the eye. The relative movement corresponds to change in the combined power of the optics of at least one diopter. Alternatively, the accommodating intraocular lens can further comprise a posterior viewing element comprised of an optic having a refractive power of zero to minus 25 diopters. 
     In some embodiments, an accommodating intraocular lens comprises an anterior portion which in turn comprises an anterior viewing element which has a periphery and is comprised of an optic having refractive power. The anterior portion further comprises an anterior biasing element comprising first and second anterior translation members extending from the anterior viewing element. The lens further comprises a posterior portion which in turn comprises a posterior viewing element having a periphery, the posterior viewing element being in spaced relationship to the anterior viewing element, and a posterior biasing element comprising first and second posterior translation members extending from the posterior viewing element. The first anterior translation member and the first posterior translation member meet at a first apex of the intraocular lens, and the second anterior translation member and the second posterior translation member meet at a second apex of the intraocular lens, such that force on the anterior portion and the posterior portion causes the separation between the viewing elements to change. Each of the translation members is attached to one of the viewing elements at at least one attachment location. All of the attachment locations are further away from the apices than the peripheries of the viewing elements are from the apices. 
     In some embodiments, an accommodating intraocular lens comprises an anterior portion comprised of a viewing element. The viewing element is comprised of an optic having refractive power. The lens further comprises a posterior portion comprised of a viewing element. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The lens further comprises a distending portion comprised of a distending member having a fixed end attached to the posterior portion and a free end sized and oriented to distend a portion of the lens capsule such that coupling of forces between the lens capsule and the intraocular lens is modified by the distending portion. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of an anterior viewing element and an anterior biasing element connected to the anterior viewing element. The anterior viewing element is comprised of an optic having refractive power. The lens further comprises a posterior portion comprised of a posterior viewing element and a posterior biasing element connected to the posterior viewing element. The lens has an optical axis which is adapted to be substantially coincident with the optical axis of the eye upon implantation of the lens. The anterior and posterior viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The biasing elements are joined at first and second apices which are spaced from the optical axis of the lens. The lens further comprises a distending member extending between the first and second apices. 
     In some embodiments, an accommodating intraocular lens comprises an anterior portion comprised of a viewing element. The viewing element is comprised of an optic having refractive power. The lens further comprises a posterior portion comprised of a viewing element. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The lens further comprises a retention portion comprised of a retention member having a fixed end attached to the anterior portion and a free end sized and oriented to contact a portion of the lens capsule such that extrusion of the implanted lens through the lens capsule opening is inhibited. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of a viewing element, the viewing element comprised of an optic having refractive power, and a posterior portion comprised of a viewing element. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The lens further comprises a distending portion comprised of a distending member attached to one of the portions, and oriented to distend the lens capsule such that the distance between a posterior side of the posterior viewing element and an anterior side of the anterior viewing element along the optical axis is less than 3 mm when the ciliary muscle is relaxed and the lens is in an unaccommodated state. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of a viewing element, the viewing element comprised of an optic having refractive power, and a posterior portion comprised of a viewing element. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The lens further comprises a distending portion comprised of a distending member attached to one of the portions, and oriented to distend the lens capsule. The distending causes the lens capsule to act on at least one of the posterior and anterior portions such that separation between the viewing elements is reduced when the ciliary muscle is relaxed and the lens is in an unaccommodated state. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of a viewing element, the viewing element comprised of an optic having refractive power, and a posterior portion comprised of a viewing element. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The lens further comprises a distending member attached to the posterior portion. The distending member is separate from the biasing members and reshapes the lens capsule such that force coupling between the ciliary muscle and the lens is modified to provide greater relative movement between the viewing elements when the lens moves between an unaccommodated state and an accommodated state in response to the ciliary muscle. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of an anterior viewing element and an anterior biasing element connected to the anterior viewing element, the anterior viewing element being comprised of an optic having refractive power. The lens further comprises a posterior portion comprised of a posterior viewing element and a posterior biasing element connected to the posterior viewing element. The lens has an optical axis which is adapted to be substantially coincident with the optical axis of the eye upon implantation of the lens. The anterior and posterior viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The biasing elements are joined at first and second apices which are spaced from the optical axis of the lens. The lens further comprises first and second distending members. Each of the members is attached to one of the anterior and posterior portions and extends away from the optical axis. The first member is disposed between the apices on one side of the intraocular lens and the second member is disposed between the apices on the opposite side of the intraocular lens. The distending members are oriented to distend portions of the lens capsule such that the viewing elements are relatively movable through a range of at least 1.0 mm in response to contraction of the ciliary muscle. 
     In some embodiments, an accommodating intraocular lens comprises an anterior portion which is in turn comprised of a viewing element. The anterior viewing element is comprised of an optic having a diameter of approximately 3 mm or less and a refractive power of less than 55 diopters. The lens further comprises a posterior portion comprised of a viewing element. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The lens further comprises a distending portion comprised of a distending member having a fixed end attached to the posterior portion and a free end sized and oriented to distend a portion of the lens capsule such that coupling of forces between the lens capsule and the intraocular lens is increased. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of a viewing element, the anterior viewing element being comprised of an optic having a refractive portion with a refractive power of less than 55 diopters. The lens further comprises a posterior portion comprised of a viewing element. The lens has an optical axis which is adapted to be substantially coincident with the optical axis of the eye upon implantation of the lens. The posterior viewing element comprises an optic arranged substantially coaxially with the anterior optic on the optical axis of the lens. The posterior optic has a larger diameter than the refractive portion of the anterior optic. The posterior optic comprises a peripheral portion having positive refractive power and extending radially away from the optical axis of the lens beyond the periphery of the refractive portion of the anterior optic, so that at least a portion of the light rays incident upon the posterior optic can bypass the refractive portion of the anterior optic. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion comprised of a viewing element, the anterior viewing element being comprised of an optic having a refractive power of less than 55 diopters. The lens further comprises a posterior portion comprised of a viewing element. The lens has an optical axis which is adapted to be substantially coincident with the optical axis of the eye upon implantation of the lens. The posterior viewing element comprises an optic arranged substantially coaxially with the anterior optic on the optical axis of the lens. The posterior optic has a larger diameter than the anterior optic. The posterior optic comprises a peripheral portion having positive refractive power and extending radially away from the optical axis of the lens beyond the periphery of the anterior optic, so that at least a portion of the light rays incident upon the posterior optic can bypass the anterior optic. 
     Some embodiments comprise an intraocular lens. The lens comprises an optic and a pair of elongate members extending from the optic. The members are comprised of a shape memory alloy. 
     In some embodiments, an accommodating intraocular lens for implantation in an eye has an optical axis and a lens capsule having a capsule opening for receiving the lens. The lens comprises a posterior portion comprised of a posterior viewing element, and an anterior portion comprised of an anterior viewing element. The anterior viewing element is comprised of an optic having refractive power. The viewing elements are mounted to move relative to each other along the optical axis in response to force generated by the ciliary muscle of the eye. The anterior portion is adapted to contact portions of the lens capsule while being spaced from the lens capsule in at least one location so as to provide a fluid flow channel that extends from a region between the viewing elements to a region outside the capsule. 
     Some embodiments comprise an accommodating intraocular lens. The lens comprises an anterior portion which in turn comprises an anterior viewing element having a periphery and comprised of an optic having refractive power, and an anterior biasing element comprising at least one anterior translation member attached to a first attachment area on the periphery of the anterior viewing element. The first attachment area has a thickness in a direction substantially perpendicular to the periphery and a width in a direction substantially parallel to the periphery. The ratio of the width to the thickness is equal to or greater than 3. 
     In certain embodiments, a method of manufacturing an intraocular lens having anterior and posterior viewing elements arranged along a common optical axis comprises defining an anterior viewing element mold space and a posterior viewing element mold space, arranging the anterior viewing element mold space and the posterior viewing element mold space along a mold axis substantially coincident with the optical axis of the lens, and molding the anterior viewing element in the anterior viewing element mold space while the anterior viewing element mold space and the posterior viewing element mold space are arranged substantially along the mold axis. 
     In certain embodiments, a method of preparing an accommodating intraocular lens having an optical axis for subsequent implantation comprises providing an intraocular lens having first and second viewing elements interconnected by plural members. At least a portion of the members are disposed from the optical axis by a distance greater than a periphery of at least one of the viewing elements. This distance is measured orthogonal to the optical axis. The method further comprises drawing the members inwardly toward the optical axis by relatively rotating the first and second viewing elements. In one variation of the method, the first and second viewing elements are relatively rotated about the optical axis. 
     In some embodiments, an accommodating intraocular lens comprises an anterior portion having an anterior viewing element, and a posterior portion having a posterior viewing element. The viewing elements are positioned to move relative to each other along an optical axis in response to action of the ciliary muscle of the eye. The anterior and posterior portions comprise a single piece of material. 
     In some embodiments, an accommodating intraocular lens comprises first and second optics. At least one of the optics has refractive power. The optics are mounted by an articulated frame to move relative to each other along an optical axis in response to action of a ciliary muscle. The frame is formed of a single piece of material. In one variation of the lens, at least one of the optics is formed of a material which is different from the material of the frame. 
     In some embodiments, an accommodating intraocular lens comprises an anterior portion having an anterior viewing element comprising an optic having refractive power. The lens further comprises a posterior portion having a posterior viewing element. The viewing elements are positioned to move relative to each other along an optical axis in response to action of the ciliary muscle of the eye. At least one of the anterior and posterior portions has at least one separation member with a contact surface. The at least one separation member is configured to prevent contact between the anterior viewing element and the posterior viewing element by inhibiting relative movement of the anterior and posterior portions toward each other beyond a minimum separation distance. The contact surface contacts an opposing surface of the intraocular lens over a contact area when the portions are at the minimum separation distance. At least one of the surfaces has an adhesive affinity for the other of the surfaces. The contact area is sufficiently small to prevent adhesion between the surfaces when the anterior portion and the posterior portion are separated by the minimum separation distance. In one variation of the lens, the contact surface and the opposing surface are comprised of the same material. 
     In some embodiments, an intraocular lens comprises first and second interconnected viewing elements mounted to move relative to each other along an optical axis in response to action of a ciliary muscle. At least one of the viewing elements includes an optic having refractive power. The lens is formed by the process of providing a first outer mold and a second outer mold, and an inner mold therebetween. The first outer mold and the inner mold define a first mold space, and the second outer mold and the inner mold define a second mold space. The process further comprises molding the viewing elements and the optic as a single piece by filling the first and second mold spaces with a material, such that the first viewing element is formed in the first mold space and the second viewing element is formed in the second mold space. The process further comprises removing the first and second outer molds from the lens while the inner mold remains between the viewing elements, and removing the inner mold from between the viewing elements while the viewing elements remain interconnected. 
     In some embodiments, a method of making an intraocular lens having first and second interconnected viewing elements wherein at least one of the viewing elements includes an optic having refractive power comprises providing a first outer mold and a second outer mold, and an inner mold therebetween. The first outer mold and the inner mold define a first mold space, and the second outer mold and the inner mold define a second mold space. The process further comprises molding the viewing elements and the optic as a single piece by filling the first and second mold spaces with a material, such that the first viewing element is formed in the first mold space and the second viewing element is formed in the second mold space. The process further comprises removing the first and second outer molds from the lens while the inner mold remains between the viewing elements, and removing the inner mold from between the viewing elements while the viewing elements remain interconnected. In one variation, providing the inner mold may comprise molding the inner mold. In another variation, the inner mold has a first inner mold face and a second inner mold face opposite the first inner mold face, and providing the inner mold comprises machining the inner mold, which in turn comprises machining the first inner mold face and the second inner mold face in a single piece of material. 
     In some embodiments, an accommodating intraocular lens comprises first and second optics. At least one of the optics has refractive power. The optics are mounted to move relative to each other along an optical axis in response to action of a ciliary muscle. The first optic is formed of a first polymer having a number of recurring units including first-polymer primary recurring units, and the second optic is formed of a second polymer having a number of recurring units including second-polymer primary recurring units. No more than about 10 mole percent of the recurring units of the first polymer are the same as the second-polymer primary recurring units and no more than about 10 mole percent of the recurring units of the second polymer are the same as the first-polymer primary recurring units. In one variation, the first optic may comprise an anterior optic, the second optic may comprise a posterior optic, the first polymer may comprise silicone, and the second polymer may comprise acrylic. In another variation, the first optic may comprise an anterior optic, the second optic may comprise a posterior optic, the first polymer may comprise high-refractive-index silicone, and the second polymer may comprise hydrophobic acrylic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus summarized the general nature of the disclosure, certain preferred embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which: 
         FIG. 1  is a sectional view of the human eye, with the lens in the unaccommodated state. 
         FIG. 2  is a sectional view of the human eye, with the lens in the accommodated state. 
         FIG. 3  is a perspective view of one embodiment of an intraocular lens system. 
         FIG. 4  is a side view of the lens system. 
         FIG. 5  is a rear perspective view of the lens system. 
         FIG. 6  is a front view of the lens system. 
         FIG. 7  is a rear view of the lens system. 
         FIG. 8  is a top view of the lens system. 
         FIG. 9  is a side sectional view of the lens system. 
         FIG. 10  is a top sectional view of the lens system. 
         FIG. 11  is a second perspective view of the lens system. 
         FIG. 12  is a third perspective view of the lens system. 
         FIG. 13  is a side view of the lens system in the unaccommodated state. 
         FIG. 14  is a side sectional view of the lens system in the unaccommodated state. 
         FIG. 15  is a top sectional view of the lens system in the unaccommodated state. 
         FIG. 16  is a sectional view of the human eye with the lens system implanted in the capsular bag and the lens system in the accommodated state. 
         FIG. 17  is a sectional view of the human eye with the lens system implanted in the capsular bag and the lens system in the unaccommodated state. 
         FIG. 17A  is a sectional view of an arm of the lens system. 
         FIG. 17B  is a sectional view of another embodiment of the arm of the lens system. 
         FIGS. 17C-17L  are sectional views of other embodiments of the arm of the lens system. 
         FIG. 17M  is a side sectional view of another embodiment of the lens system. 
         FIG. 17N  is a side sectional view of another embodiment of the lens system. 
         FIG. 18  is a side view of another embodiment of the lens system. 
         FIG. 19  is a side sectional view of another embodiment of the lens system. 
         FIG. 20  is a rear perspective view of another embodiment of the lens system. 
         FIG. 21  is a partial top sectional view of another embodiment of the lens system, implanted in the capsular bag. 
         FIG. 21A  is a front view of another embodiment of the lens system. 
         FIG. 21B  is a front view of another embodiment of the lens system. 
         FIG. 21C  is a front view of another embodiment of the lens system. 
         FIG. 22  is a partial side sectional view of another embodiment of the lens system, implanted in the capsular bag. 
         FIG. 22A  is a side view of a stop member system employed in one embodiment of the lens system. 
         FIG. 23  is a side view of a mold system for forming the lens system. 
         FIG. 24  is a side sectional view of the mold system. 
         FIG. 25  is a perspective view of a first mold portion. 
         FIG. 26  is a perspective view of a second mold portion. 
         FIG. 27  is a top view of the second mold portion. 
         FIG. 28  is a side sectional view of the second mold portion. 
         FIG. 29  is another side sectional view of the second mold portion. 
         FIG. 30  is a bottom view of a center mold portion. 
         FIG. 31  is a top view of the center mold portion. 
         FIG. 32  is a sectional view of the center mold portion. 
         FIG. 33  is another sectional view of the center mold portion. 
         FIG. 34  is a perspective view of the center mold portion. 
         FIG. 34A  is a partial cross sectional view of an apex of the lens system, showing a set of expansion grooves formed therein. 
         FIG. 35  is a schematic view of another embodiment of the lens system. 
         FIG. 36  is a schematic view of another embodiment of the lens system. 
         FIG. 37  is a perspective view of another embodiment of the lens system. 
         FIG. 38  is a top view of another embodiment of the lens system. 
         FIG. 38A  is a schematic view of another embodiment of the lens system, as implanted in the capsular bag. 
         FIG. 38B  is a schematic view of the embodiment of  FIG. 38A , in the accommodated state. 
         FIG. 38C  is a schematic view of biasers installed in the lens system. 
         FIG. 38D  is a schematic view of another type of biasers installed in the lens system. 
         FIG. 38E  is a perspective view of another embodiment of the lens system. 
         FIGS. 39A-39B  are a series of schematic views of an insertion technique for use in connection with the lens system 
         FIG. 40  is a schematic view of fluid-flow openings formed in the anterior aspect of the capsular bag. 
         FIG. 40A  is a front view of the lens system, illustrating one stage of a folding technique for use with the lens system. 
         FIG. 40B  is a front view of the lens system, illustrating another stage of the folding technique. 
         FIG. 40C  illustrates another stage of the folding technique. 
         FIG. 40D  illustrates another stage of the folding technique. 
         FIG. 40E  illustrates another stage of the folding technique. 
         FIG. 40F  illustrates another stage of the folding technique. 
         FIG. 40G  is a perspective view of a folding tool for use with the lens system. 
         FIG. 41  is a sectional view of an aspheric optic for use with the lens system. 
         FIG. 42  is a sectional view of an optic having a diffractive surface for use with the lens system. 
         FIG. 43  is a sectional view of a low-index optic for use with the lens system. 
         FIG. 44  is a side elevation view of another embodiment of the lens system with a number of separation members. 
         FIG. 45  is a front elevation view of the lens system of  FIG. 44 . 
         FIG. 46  is an overhead sectional view of the lens system of  FIG. 44 . 
         FIG. 47  is an overhead sectional view of the lens system of  FIG. 44 , with the viewing elements at a minimum separation distance. 
         FIG. 48  is a closeup view of the contact between a separation member and an opposing surface. 
         FIG. 49  is a side sectional view of an apparatus and method for manufacturing a center mold. 
         FIG. 50  is another side sectional view of the apparatus and method of  FIG. 49 . 
         FIG. 51  is another side sectional view of the apparatus and method of  FIG. 49 . 
         FIG. 52  is another side sectional view of the apparatus and method of  FIG. 49 . 
         FIG. 53  is another side sectional view of the apparatus and method of  FIG. 49 . 
         FIG. 54  is a side sectional view of the lens system in position on the center mold. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. The Human Eye and Accommodation 
       FIGS. 1 and 2  show the human eye  50  in section. Of particular relevance to the present disclosure are the cornea  52 , the iris  54  and the lens  56 , which is situated within the elastic, membranous capsular bag or lens capsule  58 . The capsular bag  58  is surrounded by and suspended within the ciliary muscle  60  by ligament-like structures called zonules  62 . 
     As light enters the eye  50 , the cornea  52  and the lens  56  cooperate to focus the incoming light and form an image on the retina  64  at the rear of the eye, thus facilitating vision. In the process known as accommodation, the shape of the lens  56  is altered (and its refractive properties thereby adjusted) to allow the eye  50  to focus on objects at varying distances. A typical healthy eye has sufficient accommodation to enable focused vision of objects ranging in distance from infinity (generally defined as over 20 feet from the eye) to very near (closer than 10 inches). 
     The lens  56  has a natural elasticity, and in its relaxed state assumes a shape that in cross-section resembles a football. Accommodation occurs when the ciliary muscle  60  moves the lens from its relaxed or “unaccommodated” state (shown in  FIG. 1 ) to a contracted or “accommodated” state (shown in  FIG. 2 ). Movement of the ciliary muscle  60  to the relaxed/unaccommodated state increases tension in the zonules  62  and capsular bag  58 , which in turn causes the lens  56  to take on a thinner (as measured along the optical axis) or taller shape as shown in  FIG. 1 . In contrast, when the ciliary muscle  60  is in the contracted/accommodated state, tension in the zonules  62  and capsular bag  58  is decreased and the lens  56  takes on the fatter or shorter shape shown in  FIG. 2 . When the ciliary muscles  60  contract and the capsular bag  58  and zonules  62  slacken, some degree of tension is maintained in the capsular bag  58  and zonules  62 . 
     II. The Lens System: Structure 
       FIGS. 3-17  depict one embodiment of an intraocular lens system  100  which is configured for implantation into the capsular bag  58  in place of the natural lens  56 , and is further configured to change the refractive properties of the eye in response to the eye&#39;s natural process of accommodation. With reference to  FIG. 3 , a set of axes is included to illustrate the sense of directional terminology which will be used herein to describe various features of the lens system  100 . The terms “anterior” and “posterior” refer to the depicted directions on the optical axis of the lens  100  shown in  FIG. 3 . When the lens  100  is implanted in an eye, the anterior direction extends toward the cornea and the posterior direction extends toward the retina, with the optical axis of the lens substantially coincident with the optical axis of the eye shown in  FIGS. 1 and 2 . The terms “left” and “right” refer to the directions shown on the lateral axis, which is orthogonal to the optical axis. In addition, the terms “upper” and “lower” refer to the directions depicted on the transverse axis which is orthogonal to both of the optical axis and the lateral axis. 
     This system of axes is depicted purely to facilitate description herein; thus, it is not intended to limit the possible orientations which the lens system  100  may assume during use. For example, the lens system  100  may rotate about, or may be displaced along, the optical axis during use without detracting from the performance of the lens. It is clear that, should the lens system  100  be so rotated about the optical axis, the transverse axis may no longer have an upper-lower orientation and the lateral axis may no longer have a left-right orientation, but the lens system  100  will continue to function as it would when oriented as depicted in  FIG. 3 . Accordingly, when the terms “upper,” “lower,” “left” or “right” are used in describing features of the lens system  100 , such use should not be understood to require the described feature to occupy the indicated position at any or all times during use of the lens system  100 . Similarly, such use should not be understood to require the lens system  100  to maintain the indicated orientation at any or all times during use. 
     As best seen in  FIG. 4 , the lens system  100  has an anterior portion  102  which is anterior or forward of the line A-A (which represents a plane substantially orthogonal to the optical axis and intersecting first and second apices  112 ,  116 ) and a posterior portion  104  which is posterior or rearward of the line A-A. The anterior portion  102  comprises an anterior viewing element  106  and an anterior biasing element  108 . The anterior biasing element  108  in turn comprises a first anterior translation member  110  which extends from the anterior viewing element  106  to the first apex  112  and a second anterior translation member  114  which extends from the anterior viewing element  106  to the second apex  116 . In the illustrated embodiment the first anterior translation member  110  comprises a right arm  110   a  and a left arm  110   b  (see  FIG. 3 ). In addition, the depicted second anterior translation member  114  comprises a right arm  114   a  and a left arm  114   b . However, in other embodiments either or both of the first and second anterior translation members  110 ,  114  may comprise a single arm or member, or more than two arms or members. 
     As best seen in  FIGS. 4, 5 and 7 , the posterior portion  104  includes a posterior viewing element  118  and a posterior biasing element  120 . The posterior biasing element  120  includes a first posterior translation member  122  extending from the posterior viewing element  118  to the first apex  112  and a second posterior translation member  124  extending from the posterior viewing element  118  to the second apex  116 . In the illustrated embodiment, the first posterior translation member comprises a right arm  122   a  and a left arm  122   b . Likewise, the depicted second posterior translation member  124  comprises a right arm  124   a  and a left arm  124   b . However, in other embodiments either or both of the first and second posterior translation members  122 ,  124  may comprise a single arm or member, or more than two arms or members. 
     In the embodiment shown in  FIG. 4 , the anterior biasing element  108  and the posterior biasing element are configured symmetrically with respect to the plane A-A as the lens system  100  is viewed from the side. As used herein to describe the biasing elements  108 ,  120 , “symmetric” or “symmetrically” means that, as the lens system  100  is viewed from the side, the first anterior translation member  110  and the first posterior translation member  122  extend from the first apex  112  at substantially equal first anterior and posterior biasing angles θ 1 , θ 2  with respect to the line A-A (which, again, represents the edge of a plane which is substantially orthogonal to the optical axis and intersects the first and second apices  112 ,  116 ) and/or that the second anterior translation member  114  and the second posterior translation member  124  extend from the second apex  116  at substantially equal second anterior and posterior biasing angles θ 3 , θ 4  with respect to the line A-A. Alternative or asymmetric configurations of the biasing elements are possible, as will be discussed in further detail below. It should be further noted that a symmetric configuration of the biasing elements  108 ,  120  does not dictate symmetric positioning of the viewing elements with respect to the line A-A; in the embodiment shown in  FIG. 4  the anterior viewing element  106  is closer to the line A-A than is the posterior viewing element. 
     Preferably, both the anterior viewing element  106  and the posterior viewing element  118  comprise an optic or lens having refractive power. (As used herein, the term “refractive” or “refractive power” shall include “diffractive” or “diffractive power”.) As discussed herein, in some embodiments, an intraocular lens such as the lens system  100  is configured to be modified post-operatively and in situ to change a performance characteristic of the system. For example, one or more of the viewing elements  106 ,  118  can be configured to be modifiable post-operatively to alter the power of the one or more viewing elements and/or the lens system, as discussed further below. In some embodiments, the support structures of the lens system  100  are configured to be modified post-operatively and in situ to change one or more performance characteristics of the support structures, such as the spring rate of the biasing members. The preferred power ranges for the optics are discussed in detail below. 
     In alternative embodiments one or both of the anterior and posterior viewing elements  106 ,  118  may comprise an optic with a surrounding or partially surrounding perimeter frame member or members, with some or all of the biasing elements/translation members attached to the frame member(s). As a further alternative, one of the viewing elements  106 ,  118  may comprise a perimeter frame with an open/empty central portion or void located on the optical axis (see  FIG. 20  and discussion below), or a perimeter frame member or members with a zero-power lens or transparent member therein. In still further variations, one of the viewing elements  106 ,  118  may comprise only a zero-power lens or transparent member. 
     In a presently preferred embodiment, a retention portion  126  is coupled to the anterior portion  102 , preferably at the anterior viewing element  106 . The retention portion  126  preferably includes a first retention member  128  and a second retention member  130 , although in alternative embodiments the retention portion  126  may be omitted altogether, or may comprise only one retention member or more than two retention members. The first retention member  128  is coupled to the anterior viewing element  106  at a fixed end  128   a  and also includes a free end  128   b  opposite the fixed end  128   a . Likewise, the second retention member  130  includes a fixed end  130   a  and a free end  130   b . The retention members  128 ,  130  are illustrated as being coupled to the anterior viewing element  106  at the upper and lower edges thereof; however, the retention members  128 ,  130  may alternatively be attached to the anterior viewing element  106  at other suitable edge locations. 
     In the preferred embodiment, the posterior portion  104  includes a distending portion  132 , preferably attached to the posterior viewing element  118 . The preferred distending portion  132  includes a first distending member  134  which in turn includes a fixed end  134   a , a free end  134   b  opposite the fixed end  134   a  and preferably also includes an opening  134   c  formed therein. The preferred distending portion  132  also comprises a second distending member  136  with a fixed end  136   a , a free end  136   b  and preferably an opening  136   c  formed therein. In alternative embodiments, the distending portion  132  may be omitted altogether, or may comprise a single distending member or more than two distending members. To optimize their effectiveness, the preferred location for the distending members  134 ,  136  is 90 degrees away (about the optical axis) from the apices  112 ,  116  on the posterior portion  104 . Where the biasing elements form more than two apices (or where two apices are not spaced 180 degrees apart about the optical axis), one or more distending members may be positioned angularly midway between the apices about the optical axis. Alternatively, the distending member(s) may occupy other suitable positions relative to the apices (besides the “angularly midway” positions disclosed above); as further alternatives, the distending member(s) may be located on the anterior portion  102  of the lens system  100 , or even on the apices themselves. The functions of the retention portion  126  and the distending portion  132  will be described in greater detail below. 
     III. The Lens System: Function/Optics 
     The anterior and posterior biasing elements  108 ,  120  function in a springlike manner to permit the anterior viewing element  106  and posterior viewing element  118  to move relative to each other generally along the optical axis. The biasing elements  108 ,  120  bias the viewing elements  106 ,  118  apart so that the elements  106 ,  108  separate to the accommodated position or accommodated state shown in  FIG. 4 . Thus, in the absence of any external forces, the viewing elements are at their maximum separation along the optical axis. The viewing elements  106 ,  118  of the lens system  100  may be moved toward each other, in response to a ciliary muscle force of up to 2 grams, to provide an unaccommodated position by applying appropriate forces upon the anterior and posterior portions  102 ,  104  and/or the apices  112 ,  116 . 
     When the lens system  100  is implanted in the capsular bag  58  ( FIGS. 16-17 ) the above described biasing forces cause the lens system  100  to expand along the optical axis so as to interact with both the posterior and anterior aspects of the capsular bag. Such interaction occurs throughout the entire range of motion of the ciliary muscle  60 . At one extreme the ciliary muscle is relaxed and the zonules  62  pull the capsular bag  58  radially so as to cause the bag to become more disk shaped. The anterior and posterior sides of the bag, in turn, apply force to the anterior and posterior portions  102 ,  104  of the lens system  100 , thereby forcing the viewing elements  106 ,  118  toward each other into the accommodated position. At the other extreme, the ciliary muscle contracts and the zonules  62  move inwardly to provide slack in the capsular bag  58  and allow the bag to become more football-shaped. The slack in the bag is taken up by the lens system due to the biasing-apart of the anterior and posterior viewing elements  106 ,  118 . As the radial tension in the bag is reduced, the viewing elements  106 ,  118  move away from each other into an accommodated position. Thus, the distance between the viewing elements  106 ,  118  depends on the degree of contraction or relaxation of the ciliary muscle  60 . As the distance between the anterior and posterior viewing elements  106 ,  118  is varied, the focal length of the lens system  100  changes accordingly. Thus, when the lens system  100  is implanted into the capsular bag (see  FIGS. 16-17 ) the lens system  100  operates in conjunction with the natural accommodation processes of the eye to move between the accommodated ( FIG. 16 ) and unaccommodated ( FIG. 17 ) states in the same manner as would a healthy “natural” lens. Preferably, the lens system  100  can move between the accommodated and unaccommodated states in less than about one second. 
     The entire lens system  100 , other than the optic(s), thus comprises an articulated frame whose functions include holding the optic(s) in position within the capsular bag and guiding and causing movement of the optic(s) between the accommodated and unaccommodated positions. 
     Advantageously, the entire lens system  100  may comprise a single piece of material, i.e. one that is formed without need to assemble two or more components by gluing, heat bonding, the use of fasteners or interlocking elements, etc. This characteristic increases the reliability of the lens system  100  by improving its resistance to material fatigue effects which can arise as the lens system experiences millions of accommodation cycles throughout its service life. It will be readily appreciated that the molding process and mold tooling discussed herein, lend themselves to the molding of lens systems  100  that comprise a single piece of material. However, any other suitable technique may be employed to manufacture single-piece lens systems. 
     In those embodiments where the optic(s) are installed into annular or other perimeter frame member(s) (see discussion below), the articulated frame may comprise a single piece of material, to obtain the performance advantages discussed above. It is believed that the assembly of the optic(s) to the articulated frame will not substantially detract from the achievement of these advantages. 
     The lens system  100  has sufficient dynamic range that the anterior and posterior viewing elements  106 ,  118  move about 0.5-4 mm, preferably about 1-3 mm, more preferably about 1-2 mm, and most preferably about 1.5 mm closer together when the lens system  100  moves from the accommodated state to the unaccommodated state. In other words the separation distance X (see  FIGS. 9-10, 14-15 ) between the anterior and posterior viewing elements  106 ,  118 , which distance may for present purposes be defined as the distance along the optical axis (or a parallel axis) between a point of axial intersection with the posterior face of the anterior viewing element  106  and a point of axial intersection with the anterior face of the posterior viewing element  118 , decreases by the amount(s) disclosed above upon movement of the lens system  100  to the unaccommodated state. Simultaneously, in the preferred mode the total system thickness Y decreases from about 3.0-4.0 mm in the accommodated state to about 1.5-2.5 mm in the unaccommodated state. 
     As may be best seen in  FIG. 6 , the first anterior translation member  110  connects to the anterior viewing element  106  via connection of the left and right arms  110   a ,  110   b  to first and second transition members  138 ,  140  at attachment locations  142 ,  144 . The second anterior translation member  114  connects to the anterior viewing element  106  via connection of left and right arms  114   a ,  114   b  to the first and second transition members  138 ,  140  at attachment locations  146 ,  148 . This is a presently preferred arrangement for the first and second anterior translation members  110 ,  114 ; alternatively, the first and second anterior translation members  110 ,  114  could be connected directly to the anterior viewing element  106 , as is the case with the connection of the first and second posterior translation members  122 ,  124  to the posterior viewing element  118 . 
     However the connection is established between the first and second anterior translation members  110 ,  114  and the anterior viewing element  106 , it is preferred that the attachment locations  142 ,  144  corresponding to the first anterior translation member  110  be farther away from the first apex  112  than is the closest edge or the periphery of the anterior viewing element  106 . This configuration increases the effective length of the first anterior translation member  110 /arms  110   a ,  110   b , in comparison to a direct or straight attachment between the apex  112  and the nearest/top edge of the anterior viewing element  106 . For the same reasons, it is preferred that the attachment locations  146 ,  148  associated with the second anterior translation member  114  be farther away from the second apex  116  than is the closest/bottom edge of the anterior viewing element  106 . 
     As best seen in  FIG. 7 , the first posterior translation member  122  is preferably connected directly to the posterior viewing element  118  via attachment of the left and right arms  122   a ,  122   b  to the element  118  at attachment points  150 ,  152 . Likewise, the second posterior translation member  124  is preferably directly connected to the posterior viewing element  118  via connection of the left and right arms  124   a ,  124   b  to the element  118  at attachment points  154 ,  156 , respectively. In alternative embodiments, the first and second posterior translation members  124 ,  122  can be connected to the posterior viewing element via intervening members as is done with the anterior viewing element  106 . No matter how these connections are made, it is preferred that the attachment locations  150 ,  152  be spaced further away from the first apex  112  than is the nearest edge or the periphery of the posterior viewing element  118 . Similarly, it is preferred that the attachment locations  154 ,  156  be spaced further away from the second apex  116  than is the closest edge of the posterior viewing element  118 . 
     By increasing the effective length of some or all of the translation members  110 ,  114 ,  122 ,  124  (and that of the arms  110   a ,  110   b ,  114   a ,  114   b ,  122   a ,  122   b ,  124   a ,  124   b  where such structure is employed), the preferred configuration of the attachment locations  142 ,  144 ,  146 ,  148 ,  150 ,  152 ,  154 ,  156  relative to the first and second apices  112 ,  116  enables the anterior and/or posterior viewing elements  106 ,  118  to move with respect to one another a greater distance along the optical axis, for a given angular displacement of the anterior and/or posterior translation members. This arrangement thus facilitates a more responsive spring system for the lens system  100  and minimizes material fatigue effects associated with prolonged exposure to repeated flexing. 
     In the illustrated embodiment, the attachment location  142  of the first anterior translation member  110  is spaced from the corresponding attachment location  146  of the second anterior translation member  114  along the periphery of the anterior viewing element, and the same relationship exists between the other pairs of attachment locations  144 ,  148 ;  150 ,  154 ; and  152 ,  156 . This arrangement advantageously broadens the support base for the anterior and posterior viewing elements  106 ,  118  and prevents them from twisting about an axis parallel to the lateral axis, as the viewing elements move between the accommodated and unaccommodated positions. 
     It is also preferred that the attachment locations  142 ,  144  of the first anterior translation member  110  be located equidistant from the first apex  112 , and that the right and left arms  110   a ,  110   b  of the member  110  be equal in length. Furthermore, the arrangement of the attachment locations  146 ,  148 , arms  114   a ,  114   b  and second apex preferably mirrors that recited above regarding the first anterior translation member  110 , while the apices  112 ,  116  are preferably equidistant from the optical axis and are situated 180 degrees apart. This configuration maintains the anterior viewing element  106  orthogonal to the optical axis as the viewing element  106  moves back and forth and the anterior viewing element flexes. 
     For the same reasons, a like combination of equidistance and equal length is preferred for the first and second posterior translation members  122 ,  124  and their constituent arms  122   a ,  122   b ,  124   a ,  124   b  and attachment points  150 ,  152 ,  154 ,  156 , with respect to the apices  112 ,  116 . However, as shown the arms  122   a ,  122   b ,  124   a ,  124   b  need not be equal in length to their counterparts  110   a ,  110   b ,  114   a ,  114   b  in the first and second anterior translation members  110 ,  114 . 
     Where any member or element connects to the periphery of the anterior or posterior viewing elements  106 ,  118 , the member defines a connection geometry or attachment area with a connection width W and a connection thickness T (see  FIG. 4  and the example illustrated therein, of the connection of the second posterior translation member  124  to the posterior viewing element  118 ). For purposes of clarity, the connection width is defined as being measured along a direction substantially parallel to the periphery of the viewing element in question, and the connection thickness is defined as measured along a direction substantially perpendicular to the periphery of the viewing element. (The periphery itself is deemed to be oriented generally perpendicular to the optical axis as shown in  FIG. 4 .) Preferably, no attachment area employed in the lens system  100  has a ratio of width to thickness less than 3. It has been found that such a geometry reduces distortion of the viewing element/optic due to localized forces. For the same reasons, it is also preferred that each of the translation members  110 ,  114 ,  122 ,  124  be connected to the periphery of the respective viewing elements at least two attachment areas, each having the preferred geometry discussed above. 
       FIGS. 17A and 17B  show two preferred cross-sectional configurations which may be used along some or all of the length of the translation members and/or arms  110   a ,  110   b ,  114   a ,  114   b ,  122   a ,  122   b ,  124   a ,  124   b . The shape is defined by a relatively broad and flat or slightly curved outer surface  182 . It is intended that when in use the outer surface faces away from the interior of the lens system and/or toward the capsular bag  58 . The remaining surfaces, proportions and dimensions making up the cross-sectional shape can vary widely but may advantageously be selected to facilitate manufacture of the lens system  100  via molding or casting techniques while minimizing stresses in the arms during use of the lens system. 
       FIGS. 17C-17L  depict a number of alternative cross-sectional configurations which are suitable for the translation members and/or arms  110   a ,  110   b ,  114   a ,  114   b ,  122   a ,  122   b ,  124   a ,  124   b . As shown, a wide variety of cross-sectional shapes may be used, but preferably any shape includes the relatively broad and flat or slightly curved outer surface  182 . 
     It is further contemplated that the dimensions, shapes, and/or proportions of the cross-sectional configuration of the translation members and/or arms  110   a ,  110   b ,  114   a ,  114   b ,  122   a ,  122   b ,  124   a ,  124   b  may vary along the length of the members/arms. This may be done in order to, for example, add strength to high-stress regions of the arms, fine-tune their spring characteristics, add rigidity or flexibility, etc. 
     As discussed above, each of the anterior viewing element  106  and the posterior viewing element  118  preferably comprises an optic having refractive power. In one preferred embodiment, the anterior viewing element  106  comprises a biconvex lens having positive refractive power and the posterior viewing element  118  comprises a convexo-concave lens having negative refractive power. The anterior viewing element  106  may comprise a lens having a positive power advantageously less than 55 diopters, preferably less than 40 diopters, more preferably less than 35 diopters, and most preferably less than 30 diopters. The posterior viewing element  118  may comprise a lens having a power which is advantageously between −25 and 0 diopters, and preferably between −25 and −15 diopters. In other embodiments, the posterior viewing element  118  comprises a lens having a power which is between −15 and 0 diopters, preferably between −13 and −2 diopters, and most preferably between −10 and −5 diopters. Advantageously, the total power of the optic(s) employed in the lens system  100  is about 5-35 diopters; preferably, the total power is about 10-30 diopters; most preferably, the total power is about 15-25 diopters. (As used herein, the term “diopter” refers to lens or system power as measured when the lens system  100  has been implanted in the human eye in the usual manner.) It should be noted that if materials having a high index of refraction (e.g., higher than that of silicone) are used, the optics may be made thinner which facilitates a wider range of motion for the optics. This in turn allows the use of lower-power optics than those specified above. In addition, higher-index materials allow the manufacture of a higher-power lens for a given lens thickness and thereby reduce the range of motion needed to achieve a given range of accommodation. 
     Some lens powers and radii of curvature presently preferred for use with an embodiment of the lens system  100  with optic(s) having a refractive index of about 1.432 are as follows: a +31 diopter, biconvex lens with an anterior radius of curvature of 5.944 mm and a posterior radius of curvature of 5.944 mm; a +28 diopter, biconvex lens with an anterior radius of curvature of 5.656 mm and a posterior radius of curvature of 7.788 mm; a +24 diopter, biconvex lens with an anterior radius of curvature of 6.961 mm and a posterior radius of curvature of 8.5 mm; a −10 diopter, biconcave lens with an anterior radius of curvature of 18.765 mm and a posterior radius of curvature of 18.765 mm; a −8 diopter, concavo-convex lens with an anterior radius of curvature of between 9 mm and 9.534 mm and a posterior radius of curvature of 40 mm; and a −5 diopter, concavo-convex lens with an anterior radius of curvature of between 9 mm and 9.534 mm and a posterior radius of curvature of 20 mm. In one embodiment, the anterior viewing element comprises the +31 diopter lens described above and the posterior viewing element comprises the −10 diopter lens described above. In another embodiment, the anterior viewing element comprises the +28 diopter lens described above and the posterior viewing element comprises the −8 diopter lens described above. In another embodiment, the anterior viewing element comprises the +24 diopter lens described above and the posterior viewing element comprises the −5 diopter lens described above. 
     The combinations of lens powers and radii of curvature specified herein advantageously minimize image magnification. However, other designs and radii of curvature provide modified magnification when desirable. 
     The lenses of the anterior viewing element  106  and the posterior viewing element  118  are relatively moveable as discussed above; advantageously, this movement is sufficient to produce an accommodation of at least one diopter, preferably at least two diopters and most preferably at least three diopters. In other words, the movement of the optics relative to each other and/or to the cornea is sufficient to create a difference between (i) the refractive power of the user&#39;s eye in the accommodated state and (ii) the refractive power of the user&#39;s eye in the unaccommodated state, having a magnitude expressed in diopters as specified above. Where the lens system  100  has a single optic, the movement of the optic relative to the cornea is sufficient to create a difference in focal power as specified above. 
     Advantageously, the lens system  100  in one embodiment can be customized for an individual patient&#39;s needs by shaping or adjusting only one of the four lens faces, and thereby altering the overall optical characteristics of the system  100 . This in turn facilitates easy manufacture and maintenance of an inventory of lens systems with lens powers which will fit a large population of patients, without necessitating complex adjustment procedures at the time of implantation. It is contemplated that all of the lens systems in the inventory have a standard combination of lens powers, and that a system is fitted to a particular patient by simply shaping only a designated “variable” lens face. This custom-shaping procedure can be performed to-order at a central manufacturing facility or laboratory, or by a physician consulting with an individual patient. In one embodiment, the anterior face of the anterior viewing element is the designated sole variable lens face. In another embodiment, the anterior face of the posterior viewing element is the only variable face. However, any of the lens faces is suitable for such designation. The result is minimal inventory burden with respect to lens power (all of the lens systems in stock have the same lens powers) without requiring complex adjustment for individual patients (only one of the four lens faces is adjusted in the fitting process). In another embodiment, any of the four faces of the two lens system can be customized after implantation, as discussed herein. 
     IV. The Lens System: Alternative Embodiments 
       FIG. 17M  depicts another embodiment of the lens system  100  in which the anterior viewing element  106  comprises an optic with a smaller diameter than the posterior viewing element  118 , which comprises an optic with a peripheral positive-lens portion  170  surrounding a central negative portion  172 . This arrangement enables the user of the lens system  100  to focus on objects at infinity, by allowing the (generally parallel) light rays incident upon the eye from an object at infinity to bypass the anterior viewing element  106 . The peripheral positive-lens portion  170  of the posterior viewing element  118  can then function alone in refracting the light rays, providing the user with focused vision at infinity (in addition to the range of visual distances facilitated by the anterior and posterior viewing elements acting in concert). In another embodiment, the anterior viewing element  106  comprises an optic having a diameter of approximately 3 millimeters or less. In yet another embodiment, the anterior viewing element  106  comprises an optic having a diameter of approximately 3 millimeters or less and a refractive power of less than 55 diopters, more preferably less than 30 diopters. In still another embodiment, the peripheral positive-lens portion  170  has a refractive power of about 20 diopters. 
       FIG. 17N  shows an alternative arrangement in which, the anterior viewing element  106  comprises an optic having a central portion  176  with refractive power, and a surrounding peripheral region  174  having a refractive power of substantially zero, wherein the central region  176  has a diameter smaller than the optic of the posterior viewing element  118 , and preferably has a diameter of less than about 3 millimeters. This embodiment also allows some incident light rays to pass the anterior viewing element (though the zero-power peripheral region  174 ) without refraction, allowing the peripheral positive-lens portion  170  posterior viewing element  118  to function alone as described above. 
       FIGS. 18 and 19  depict another embodiment  250  of the intraocular lens. It is contemplated that, except as noted below, this embodiment  250  is largely similar to the embodiment disclosed in  FIGS. 3-17 . The lens  250  features an anterior biasing element  108  and posterior biasing element  120  which are arranged asymmetrically as the lens system  100  is viewed from the side. As used herein to describe the biasing elements  108 ,  120 , “asymmetric” or “asymmetrically” means that, as the lens system  100  is viewed from the side, the first anterior translation member  110  and the first posterior translation member  122  extend from the first apex  112  at unequal first anterior and posterior biasing angles δ 1 , δ 2  with respect to the line B-B (which represents the edge of a plane which is substantially orthogonal to the optical axis and intersects the first and second apices  112 ,  116 ) and/or that the second anterior translation member  114  and the second posterior translation member  124  extend from the second apex  116  at substantially equal second anterior and posterior biasing angles δ 3 , δ 4  with respect to the line B-B. 
     In the embodiment shown in  FIGS. 18-19 , the first and second anterior biasing angles δ 1 , δ 3  are greater than the corresponding first and second posterior biasing angles δ 2 , δ 4 . This arrangement advantageously maintains the posterior viewing element  118  and apices  112 ,  116  in a substantially stationary position. Consequently, the moving mass of the lens system  250  is reduced, and the anterior viewing element  106  can move more quickly over a wider range along the optical axis under a given motive force. (Note that even where the posterior biasing element  120  and its constituent first and second posterior translation members  122 ,  124  are substantially immobile, they are nonetheless “biasing elements” and “translation members” as those terms are used herein.) In another embodiment, the anterior biasing element  108  and posterior biasing element  120  are arranged asymmetrically in the opposite direction, i.e. such that the first and second anterior biasing angles δ 1 , δ 3  are smaller than the corresponding first and second posterior biasing angles δ 2 , δ 4 . This arrangement also provides for a wider range of relative movement of the viewing elements, in comparison to a “symmetric” system. 
     It should be further noted that the viewing elements  106 ,  118  shown in  FIGS. 18-19  are asymmetrically positioned in that the posterior viewing element  118  is closer to the line B-B than is the anterior viewing element  106 . It has been found that this configuration yields desirable performance characteristics irrespective of the configuration of the biasing elements  108 ,  120 . In alternative embodiments, the viewing elements  106 ,  118  may be positioned symmetrically with respect to the line B-B, or they may be positioned asymmetrically with the anterior viewing element  106  closer to the line B-B than the posterior viewing element  118  (see  FIG. 4  wherein the line in question is denoted A-A). Furthermore, the symmetry or asymmetry of the biasing elements and viewing elements can be selected independently of each other. 
       FIG. 20  shows another embodiment  350  of an intraocular lens in which the posterior viewing element  118  comprises an annular frame member defining a void therein, while the anterior viewing element  106  comprises an optic having refractive power. Alternatively, the posterior viewing element  118  could comprise a zero power lens or a simple transparent member. Likewise, in another embodiment the anterior viewing element  106  could comprise an annular frame member with a void therein or a simple zero power lens or transparent member, with the posterior viewing element  118  comprising an optic having refractive power. As a further alternative, one or both of the anterior and posterior viewing elements  106 ,  118  may comprise an annular or other perimeter frame member which can receive a removable optic (or a “one-time install” optic) with an interference type fit and/or subsequent adhesive or welding connections. Such a configuration facilitates assembly and/or fine-tuning of the lens system during an implantation procedure, as will be discussed in further detail below. 
     V. The Lens System: Additional Features 
       FIG. 21  depicts the function of the distending portion  132  in greater detail. The lens system  100  is shown situated in the capsular bag  58  in the customary manner with the anterior viewing element  106  and posterior viewing element  118  arranged along the optical axis. The capsular bag  58  is shown with a generally circular anterior opening  66  which may often be cut into the capsular bag during installation of the lens system  100 . The first and second distending members  134 ,  136  of the distending portion  132  distend the capsular bag  58  so that intimate contact is created between the posterior face of the posterior viewing element and/or the posterior biasing element  120 . In addition, intimate contact is facilitated between the anterior face of the anterior viewing element  106  and/or anterior biasing element  108 . The distending members  134 ,  136  thus remove any slack from the capsular bag  58  and ensure optimum force coupling between the bag  58  and the lens system  100  as the bag  58  is alternately stretched and released by the action of the ciliary muscle. 
     Furthermore, the distending members  134 ,  136  reshape the capsular bag  58  into a taller, thinner configuration along its range of accommodation to provide a wider range of relative motion of the viewing elements  106 ,  118 . When the capsular bag  58  is in the unaccommodated state, the distending members  134 ,  136  force the capsular bag into a thinner configuration (as measured along the optical axis) in comparison to the unaccommodated configuration of the capsular bag  58  with the natural lens in place. Preferably, the distending members  134 ,  136  cause the capsular bag  58  to taken on a shape in the unaccommodated state which is about 1.0-2.0 mm thinner, more preferably about 1.5 mm thinner, along the optical axis than it is with the natural lens in place and in the unaccommodated state. 
     With such a thin “starting point” provided by the distending members  134 ,  136 , the viewing elements  106 ,  118  of the lens system can move a greater distance apart, and provide a greater range of accommodation, without causing undesirable contact between the lens system and the iris. Accordingly, by reshaping the bag as discussed above the distending members  134 ,  136  facilitate a range of relative motion of the anterior and posterior viewing elements  106 ,  118  of about 0.5-4 mm, preferably about 1-3 mm, more preferably about 1-2 mm, and most preferably about 1.5 mm. 
     The distending portion  132 /distending members  134 ,  136  are preferably separate from the anterior and posterior biasing elements  108 ,  120 ; the distending members  134 ,  136  thus preferably play no part in biasing the anterior and posterior viewing elements  106 ,  118  apart toward the accommodated position. This arrangement is advantageous because the apices  112 ,  116  of the biasing elements  108 ,  120  reach their point of minimum protrusion from the optical axis (and thus the biasing elements reach their minimum potential effectiveness for radially distending the capsular bag) when the lens system  100  is in the accommodated state (see  FIG. 16 ), which is precisely when the need is greatest for a taut capsular bag so as to provide immediate response to relaxation of the ciliary muscles. The preferred distending portion is “static” (as opposed to the “dynamic” biasing members  108 ,  120  which move while urging the viewing elements  106 ,  118  to the accommodated position or carrying the viewing elements to the unaccommodated position) in that its member(s) protrude a substantially constant distance from the optical axis throughout the range of motion of the viewing elements  106 ,  118 . Although some degree of flexing may be observed in the distending members  134 ,  136 , they are most effective when rigid. Furthermore, the thickness and/or cross-sectional profile of the distending members  134 / 136  may be varied over the length of the members as desired to provide a desired degree of rigidity thereto. 
     The distending portion  132 /distending members  132 ,  134  advantageously reshape the capsular bag  58  by stretching the bag  58  radially away from the optical axis and causing the bag  58  to take on a thinner, taller shape throughout the range of accommodation by the eye. This reshaping is believed to facilitate a broad (as specified above) range of relative motion for the viewing elements of the lens system  100 , with appropriate endpoints (derived from the total system thicknesses detailed above) to avoid the need for unacceptably thick optic(s) in the lens system. 
     If desired, the distending members  134 ,  136  may also function as haptics to stabilize and fixate the orientation of the lens system  100  within the capsular bag. The openings  134   c ,  136   c  of the preferred distending members  134 , 136  permit cellular ingrowth from the capsular bag upon positioning of the lens system  100  therein. Finally, other methodologies, such as a separate capsular tension ring or the use of adhesives to glue the capsular bag together in selected regions, may be used instead of or in addition to the distending portion  132 , to reduce “slack” in the capsular bag. 
     A tension ring can also act as a physical barrier to cell growth on the inner surface of the capsular bag, and thus can provide additional benefits in limiting posterior capsule opacification, by preventing cellular growth from advancing posteriorly on the inner surface of the bag. When implanted, the tension ring firmly contacts the inner surface of the bag and defines a circumferential barrier against cell growth on the inner surface from one side of the barrier to another. 
       FIG. 21A  shows an alternative configuration of the distending portion  132 , in which the distending members  134 ,  136  comprise first and second arcuate portions which connect at either end to the apices  112 ,  116  to form therewith an integral perimeter member. In this arrangement it is preferred that the distending members and apices form an oval with height I smaller than width J. 
       FIG. 21B  shows another alternative configuration of the distending portion  132 , in which arcuate rim portions  137  interconnect the apices  112 ,  116  and the free ends  134   b ,  136   b  of the distending members  134 ,  136 . Thus is formed an integral perimeter member with generally higher lateral rigidity than the arrangement depicted in  FIG. 21A . 
       FIG. 21C  shows another alternative configuration of the distending portion  132 , in which the distending members  134 ,  136  are integrally formed with the first and second posterior translation members  122 ,  124 . The distending members  134 ,  136  and translation members  122 ,  124  thus form common transition members  139  which connect to the periphery of the posterior viewing element  118 . 
       FIG. 22  shows the function of the retention portion  126  in greater detail. It is readily seen that the first and second retention members  128 ,  130  facilitate a broad contact base between the anterior portion of the lens system  100  and the anterior aspect of the capsular bag  58 . By appropriately spacing the first and second retention members  128 ,  130 , the members prevent extrusion of the anterior viewing element  106  through the anterior opening  66 . It is also readily seen that where contact occurs between the anterior aspect of the capsular bag  58  and one or both of the retention members  128 ,  130 , the retention members also participate in force coupling between the bag  58  and the lens system  100  as the bag is stretched and released by the action of the ciliary muscles. 
     As best seen in  FIGS. 21 and 22 , the anterior portion  102  of the lens system  100  forms a number of regions of contact with the capsular bag  58 , around the perimeter of the anterior viewing element  106 . In the illustrated embodiment, at least some of these regions of contact are located on the anteriormost portions of the anterior biasing element  108 , specifically at the transition members  138 ,  140 , and at the retention members  128 ,  130 . The transition members and the retention members define spaces therebetween at the edges of the anterior viewing element  106  to permit fluid to flow between the interior of the capsular bag  58  and the portions of the eye anterior of the bag  58 . In other words, the anterior portion of the lens system  100  includes at least one location which is spaced from and out of contact with the capsular bag  58  to provide a fluid flow channel extending from the region between the viewing elements  106 ,  118  to the exterior of the bag  58 . Otherwise, if the anterior portion  102  of the lens system  100  seals the anterior opening  66  of the bag  58 , the resulting prevention of fluid flow can cause the aqueous humor in the capsular bag to stagnate, leading to a clinically adverse event, and can inhibit the movement of the lens system  100  between the accommodated and unaccommodated states. 
     If desired, one or both of the retention members  128 ,  130  may have an opening  129  formed therein to permit fluid flow as discussed above. (See  FIG. 21A .) 
     The retention members  128 ,  130  and the transition members  138 ,  140  also prevent contact between the iris and the anterior viewing element  106 , by separating the anterior opening  66  from the anterior face of the viewing element  106 . In other words, the retention members  128 ,  130  and the transition members  138 ,  140  displace the anterior aspect of the capsular bag  58 , including the anterior opening  66 , anteriorly from the anterior viewing element  106 , and maintain this separation throughout the range of accommodation of the lens system. Thus, if contact occurs between the iris and the lens system-capsular bag assembly, no part of the lens system will touch the iris, only the capsular bag itself, in particular those portions of the bag  58  overlying the retention members  128 ,  130  and/or the transition members  138 ,  140 . The retention members  128 ,  130  and/or the transition members  138 ,  140  therefore maintain a separation between the iris and the lens system, which can be clinically adverse if the contacting portion(s) of the lens system are constructed from silicone. 
     As depicted in  FIG. 22A , one or more stop members or separation members  190  may be located where appropriate on the anterior and/or posterior biasing elements  108 ,  120  to limit the convergent motion of the anterior and posterior viewing elements  106 ,  118 , and preferably prevent contact therebetween. As the lens system  100  moves toward the unaccommodated position, the stop member(s) located on the anterior biasing element  108  come into contact with the posterior biasing element  120  (or with additional stop member(s) located on thereon), and any stop member(s) located on the posterior biasing element  120  come into contact with the anterior biasing element  108  (or with additional stop member(s) located thereon). The stop members  190  thus define a point or state of maximum convergence (in other words, the unaccommodated state) of the lens system  100 /viewing elements  106 ,  118 . Such definition advantageously assists in setting one extreme of the range of focal lengths which the lens system may take on (in those lens systems which include two or more viewing elements having refractive power) and/or one extreme of the range of motion of the lens system  100 . 
     The stop members  190  shown in  FIG. 22A  are located on the first and second anterior translation members  110 ,  114  of the anterior biasing element  108  and extend posteriorly therefrom. When the anterior and posterior viewing elements  106 ,  118  move together, one or more of the stop members  190  will contact the posterior translation member(s)  122 ,  124 , thereby preventing further convergent motion of the viewing elements  106 ,  118 . Of course, in other embodiments the stop member(s)  190  can be in any suitable location on the lens system  100 . 
       FIGS. 44-48  depict another embodiment of the lens system  100  having a number of stop members or separation members  190 . In this embodiment the stop members  190  include posts  190   a  and tabs  190   b , although it will be apparent that any number or combination of suitable shapes may be employed for the stop members  190 . Each of the stop members  190  has at least one contact surface  191 , one or more of which abuts an opposing surface of the lens system  100  when the anterior and posterior viewing elements  106 ,  118  converge to a minimum separation distance SD (see  FIG. 47 ). In the embodiment shown, one or more of the contact surfaces  191  of the posts  190   a  are configured to abut an opposing surface defined by a substantially flat anterior perimeter portion  193  of the posterior viewing element  118 , when the viewing elements  106 ,  118  are at the minimum separation distance SD. One or more of the contact surfaces  191  of the tabs  190   b  are configured to abut opposing surfaces defined by substantially flat anterior faces  195  of the distending members  134 ,  136 , only if the viewing elements  106 ,  118  are urged together beyond the minimum separation distance SD. This arrangement permits the tabs  190   b  to function as secondary stop members should the posts  190   a  fail to maintain separation of the viewing elements. 
     In other embodiments all of the contact surfaces  191  of the posts  190   a  and tabs  190   b  may be configured to contact their respective opposing surfaces when the viewing elements  106 ,  118  are at the minimum separation distance SD. In still further embodiments, the contact surfaces  191  of the tabs  190   b  may be configured to contact the opposing surfaces when the viewing elements  106 ,  118  are at the minimum separation distance SD and the contact surfaces  191  of the posts  190   a  configured to contact the opposing surfaces only if the viewing elements  106 ,  118  are urged together beyond the minimum separation distance SD. In one embodiment, the minimum separation distance SD is about 0.1-1.0 mm; in another embodiment the minimum separation distance SD is about 0.5 mm. 
     When one of the contact surfaces abuts one of the opposing surfaces, the two surfaces define a contact area CA (see  FIG. 48 , depicting an example of a contact area CA defined when the contact surface  191  of a post  190   a  contacts an opposing surface defined by the perimeter portion  193  of the posterior viewing element  118 ). Preferably, the contact surface and opposing surface are shaped to cooperatively minimize the size of the contact area, to prevent adhesion between the contact surface and the opposing surface, which is often a concern when one or both of these surfaces has an adhesive affinity for the other. In the embodiment shown, this non-adhesive characteristic is achieved by employing a substantially hemispherical contact surface  191  and a substantially flat opposing surface (perimeter portion  193 ). Of course, other configurations can be selected for the contact surface(s)  191 , including conical, frustoconical, hemicylindrical, pyramidal, or other rounded, tapered or pointed shapes. All of these configurations minimize the contact area CA while permitting the cross-sectional area CS of the stop member  190  (such as the post  190   a  depicted) to be made larger than the contact area CA, to impart sufficient strength to the stop member despite the relatively small contact area CA. Indeed, when constructing the contact surface(s)  191  any configuration may be employed which defines a contact area CA which is smaller than the cross-sectional area CS of the stop member  190 . As further alternatives, the contact surface(s)  191  may be substantially flat and the opposing surface(s) may have a shape which defines, upon contact with the opposing surface, a contact area CA which is smaller than the cross-sectional area CS of the stop member. Thus, the opposing surface(s) may have, for example, a hemispherical, conical, frustoconical, hemicylindrical, pyramidal, or other rounded, tapered or pointed shape. 
     Other design features of the stop members  190  can be selected to maximize their ability to prevent adhesion of the contact surface(s) to the corresponding opposing surface(s), or adhesion to each other of any part of the anterior and posterior portions  102 ,  104  of the lens system  100 . For example, the contact and opposing surfaces may be formed from dissimilar materials to reduce the effect of any self-adhesive materials employed in forming the lens system  100 . In addition the shape and/or material employed in constructing one or more of the stop members  190  can be selected to impart a spring-like quality to the stop member(s) in question, so that when the stop member is loaded in compression as the viewing elements are urged together at the minimum separation distance, the stop member tends to exert a resisting spring force, due to either bending or axial compression (or both) of the stop member, which in turn derive from the elasticity of the material(s) from which the stop member is constructed, or the shape of the stop member, or both. This springlike quality is particularly effective for inhibiting adhesion of areas of the anterior and posterior portions  102 ,  104  other than the contact surface(s) and opposing surface(s). 
     As used herein, the term “adhesion” refers to attachment to each other of (i) an area of the anterior portion  102  of the lens system  100  and (ii) a corresponding area of the posterior portion  104  (other than the apices  112 ,  116 ), wherein such attachment is sufficiently strong to prevent, other than momentarily, the anterior and posterior viewing elements  106 ,  118  from moving apart along the optical axis under the biasing force of the anterior and/or posterior biasing elements  108 ,  120 . If the areas in question are formed of different materials, adhesion may occur where at least one of the materials has an adhesive affinity for the other material. If the areas in question are formed of the same material, adhesion may occur where the material has an adhesive affinity for itself. 
     In the embodiment shown, four posts  190   a  are positioned near the perimeter of the anterior viewing element  106 , equally angularly spaced around the optical axis. In addition, two tabs  190   b  are located on either side of the anterior viewing element, midway between the apices  112 ,  116  of the lens system. Naturally, the number, type and/or position of the stop members  190  can be varied while preserving the advantageous function of maintaining separation between the anterior and posterior portions of the lens system. 
     The illustrated embodiment employs stop members  190  which extend posteriorly from the anterior portion  102  of the lens system  100 , so that the contact surfaces  191  are located on the posterior extremities of the stop members  190  and are configured to abut opposing surfaces formed on the posterior portion  104  of the lens system  100 . However, it will be appreciated that some or all of the stop members  190  may extend anteriorly from the posterior portion  104  of the lens system  100 , so that their contact surfaces  191  are located on the anterior extremities of the stop members  190  and are configured to abut opposing surfaces formed on the anterior portion  102  of the lens system  100 . 
     VI. Mold Tooling 
       FIGS. 23-34  depict a mold system  500  which is suitable for molding the lens system  100  depicted in  FIG. 3-17 . The mold system  500  generally comprises a first mold  502 , a second mold  504  and a center mold  506 . The center mold  506  is adapted to be positioned between the first mold  502  and the second mold  504  so as to define a mold space for injection molding or compression molding the lens system  100 . The mold system  500  may be formed from suitable metals, high-impact-resistant plastics or a combination thereof, and can be produced by conventional machining techniques such as lathing or milling, or by laser or electrical-discharge machining. The mold surfaces can be finished or modified by sand blasting, etching or other texturing techniques. 
     The first mold  502  includes a first mold cavity  508  with a first anterior mold face  510  surrounded by an annular trough  512  and a first perimeter mold face  514 . The first mold  502  also includes a projection  516  which facilitates easier mating with the second mold  504 . 
     The center mold  506  includes a first center mold cavity  518  which cooperates with the first mold cavity  508  to define a mold space for forming the anterior portion  102  of the lens system  100 . The first center mold cavity  518  includes a central anterior mold face  520  which, upon placement of the center mold  506  in the first mold cavity  508 , cooperates with the first anterior mold face  510  to define a mold space for the anterior viewing element  106 . In so doing, the first anterior mold face  510  defines the anterior face of the anterior viewing element  106  and the central anterior mold face  520  defines the posterior face of the anterior viewing element  106 . In fluid communication with the chamber formed by the first anterior mold face  510  and the central anterior mold face  520  are lateral channels  522 ,  524  (best seen in  FIG. 31 ) which form spaces for molding the first and second transition members  138 ,  140 , along with the arms  110   a ,  110   b  of the first anterior translation member  110  as well as the arms  114   a ,  114   b  of the second anterior translation member  114 . The first center mold cavity  518  also includes retention member cavities  526 ,  528  which define spaces for molding the first and second retention members  128 ,  130  to the anterior viewing element  106 . 
     The second mold  504  includes a second mold cavity  530  with a second posterior mold space  532 , a generally cylindrical transition  534  extending therefrom and connecting to a second perimeter mold face  536 . Lateral notches  538 ,  540  (best seen in  FIGS. 26 and 27 ) are formed in the second perimeter mold face  536 . The second mold  504  also includes an input channel  542  connected to an input channel opening  544  for introducing material into the mold system  500 . Also formed in the second mold  504  is an output channel  546  and an output channel opening  548 . A generally cylindrical rim  550  is included for mating with the projection  516  of the first mold  502 . 
     The center mold  506  includes a second center mold cavity  552  which cooperates with the second mold cavity  530  to define a mold space for the posterior portion  104  of the lens system  100 . The second center mold cavity  552  includes a central posterior mold face  554  which, upon placement of the center mold  506  in engagement with the second mold cavity  530 , cooperates with the second posterior mold face  532  and the transition  534  to define a chamber for forming the posterior viewing element  118 . In fluid communication with the chamber formed by the central posterior mold face  554  and the second posterior mold face  532  are lateral channels  556 ,  558 ,  560 ,  562  which provide a mold space for forming the arms  122   a ,  122   b  of the first posterior translation member  122  and the arms  124   a ,  124   b  of the second posterior translation member  124 . The second center mold cavity  552  includes lateral projections  564 ,  566  which coact with the notches  538 ,  540  formed in the second mold cavity  530 . The chambers formed therebetween are in fluid communication with the chamber defined by the central posterior mold face  554  and the second posterior mold face  532  to form the first and second distending members  134 ,  136  integrally with the posterior viewing element  118 . 
     The center mold  506  includes a first reduced-diameter portion  568  and a second reduced-diameter portion  570  each of which, upon assembly of the mold system  500 , defines a mold space for the apices  112 ,  116  of the lens system  100 . 
     In use, the mold system  500  is assembled with the center mold  506  positioned between the first mold  502  and the second mold  504 . Once placed in this configuration, the mold system  500  is held together under force by appropriate techniques, and lens material is introduced into the mold system  500  via the input channel  542 . The lens material then fills the space defined by the first mold  502 , second mold  504 , and the center mold  506  to take on the shape of the finished lens system  100 . 
     The mold system  500  is then disassembled, and in one embodiment the lens system  100  is left in position on the center mold  506  after removal of the first and second molds  502 ,  504 . This technique has been found to improve the effectiveness of any polishing/tumbling/deflashing procedures which may be performed (see further discussion below). Whether or not these or any other additional process steps are performed, the lens system  100  is preferably removed from the center mold  506  while maintaining the interconnection of the various components of the lens system  100 . 
     In another embodiment, the lens system  100  or a portion thereof is formed by a casting or liquid-casting procedure in which one of the first or second molds is first filled with a liquid and the center mold is placed then into engagement with the liquid-filled mold. The exposed face of the center mold is then filled with liquid and the other of the first and second molds is placed into engagement with the rest of the mold system. The liquid is allowed or caused to set/cure and a finished casting may then removed from the mold system. 
     The mold system  500  can advantageously be employed to produce a lens system  100  as a single, integral unit (in other words, as a single piece of material). Alternatively, various portions of the lens system  100  can be separately molded, casted, machined, etc. and subsequently assembled to create a finished lens system. Assembly can be performed as a part of centralized manufacturing operations; alternatively, a physician can perform some or all of the assembly before or during the implantation procedure, to select lens powers, biasing members, system sizes, etc. which are appropriate for a particular patient. 
     The center mold  506  is depicted as comprising an integral unit with first and second center mold cavities  518 ,  552 . Alternatively, the center mold  506  may have a modular configuration whereby the first and second mold cavities  518 ,  552  may be interchangeable to adapt the center mold  506  for manufacturing a lens system  100  according to a desired prescription or specification, or to otherwise change the power(s) of the lenses made with the mold. In this manner the manufacture of a wide variety of prescriptions may be facilitated by a set of mold cavities which can be assembled back-to-back or to opposing sides of a main mold structure. 
       FIGS. 49-53  depict one embodiment of a method for manufacturing the center mold  506 . First, a cylindrical blank  1500  formed from any material (such as Ultem) suitable for use in the mold tooling, is loaded into a holder  1502  as shown in  FIG. 49 . The holder  1502  has a main chamber  1504  which has an inner diameter substantially similar to that of the blank  1500 , a smaller-diameter secondary chamber  1506  rearward of the main chamber  1504 , and a passage  1508  located rearward of the secondary chamber  1506  and further defined by an annulus  1510 . The holder also includes two or more holder bores  1512  which facilitate attachment of the holder  1502  to a blocker (discussed in further detail below). The blank is “blocked” in the holder by filling the secondary chamber  1506  and passage  1508  with water-soluble wax  1514 . 
     Once the blank  1500  has been loaded and blocked into the holder  1502 , the holder  1502  is secured to a blocker  1516  by bolts or pins (not shown) which fit snugly into the holder bores  1512 . The holder bores  1512  align precisely with corresponding blocker bores  1517 , by virtue of a snug fit between the blocker bores  1517  and the bolts/pins. The blocker-holder assembly is then loaded into a conventional machine tool, such as a lathe and/or a mill, and one of the first and second center mold cavities  518 ,  552  (the second cavity  552  is depicted in  FIG. 51 ) is machined from the exposed face of the blank  1500  using conventional machining techniques. The holder  1502  and blank  1500 , with the second center mold cavity  552  formed thereon, are then removed from the blocker  1516  as shown in  FIG. 51 . 
     The main chamber  1504  is then filled with water-soluble wax  1520  forward of the second center mold cavity  552 , and the wax  1514  is removed from the secondary chamber  1506  and the passage  1508 . Next the holder  1502  is fixed to the blocker  1516  with the as-yet unmodified portion of the blank  1500  facing outward. Upon re-loading the holder-blocker assembly into the machine tool, a portion of the annulus  1510  is then cut away to facilitate tool access to the blank  1500 . A series of machining operations are then performed on the blank  1500  until the remaining mold cavity (the first center mold cavity  518  is depicted in  FIG. 53 ) has been formed. The completed center mold  506  may then be removed from the holder  1502 . 
     The machining technique depicted in  FIGS. 49-53  is advantageous in that it facilitates fabrication of the center mold  506  (with both the first and second center mold cavities  518 ,  552 ) from a single piece of material. While it is possible to machine the first and second center mold cavities  518 ,  552  from separate pieces of material which are subsequently glued together, such assembly creates a seam in the center mold which can retain contaminants and introduce those contaminants into the mold when forming the lens system  100 . In addition, the assembly of the center mold  506  from two halves introduces errors wherein the first and second center mold cavities  518 ,  552  may be angularly shifted with respect to each other about the optical axis, or wherein the mold cavities  518 ,  552  are non-concentric (i.e., shifted with respect to each other in a direction orthogonal to the optical axis). The method depicted in  FIGS. 49-53  eliminates these problems by retaining the blank  1500  in the holder  1502  throughout the fabrication process and by enforcing precise axial alignment, via forced alignment of the bores  1512  with the blocker bores  1517 , when machining of both mold cavities. 
     In another embodiment, the center mold  506  is formed by a molding process rather than by machining. The center mold  506  may be molded from any of the materials disclosed herein as suitable for forming the lens system  100  itself, including but not limited to silicone, acrylics, polymethylmethacrylate (PMMA), block copolymers of styrene-ethylene-butylene-styrene (C-FLEX) or other styrene-base copolymers, polyvinyl alcohol (PVA), polyurethanes, hydrogels or any other moldable polymers or monomers. 
     The lens system which is formed when employing the molded center mold  506  may itself be molded from the same material as the center mold  506 . For example, the center mold  506  may be molded from silicone, and then the lens system  100  may be molded from silicone by using the mold system  500  with the molded silicone center mold  506 . 
     The center mold  506  can be molded by any suitable conventional techniques. A polished, optical quality initial mold set can be used to make center molds which in turn will produce lens systems with optical quality surfaces on the posterior face of the anterior optic, and the anterior face of the posterior optic. Alternatively (or additionally), the molded center mold can be polished and/or tumbled to produce an optically-accurate center mold. 
     The molded center mold  506  offers several advantages over a machined center mold. First, it is quicker, cheaper and easier to produce the center mold in large quantities by molding instead of machining. This in turn facilitates leaving the lens system in position on the center mold (see  FIG. 54 ) while the lens system is tumbled, polished and/or deflashed, without incurring undue expense. The presence of the center mold between the optics increases the effectiveness of the tumbling/polishing/deflashing by increasing the hoop strength of the lens system, so that the energy of the impacting tumbling beads is not dissipated in macroscopic deformation of the lens system. Molding also permits softer materials to be employed in forming the center mold, and a softer center mold is more resistant to damage from deflashing tools and processes, resulting in fewer center molds lost to such process-related damage. 
     VII. Materials and Adjustability 
     Preferred materials for forming the lens system  100  include silicone, acrylics, polymethylmethacrylate (PMMA), block copolymers of styrene-ethylene-butylene-styrene (C-FLEX) or other styrene-base copolymers, polyvinyl alcohol (PVA), polyurethanes, hydrogels or any other suitable polymers or monomers. In addition, any portion of the lens system  100  other than the optic(s) may be formed from stainless steel or a shape-memory alloy such as nitinol or any iron-based shape-memory alloy. Metallic components may be coated with gold to increase biocompatibility. Where feasible, material of a lower Shore A hardness such as 15A may be used for the optic(s), and material of higher hardness such as 35A may be used for the balance of the lens system  100 . Finally, the optic(s) may be formed from a photosensitive silicone to facilitate post-implantation power adjustment as taught in U.S. patent application Ser. No. 09/416,044, filed Oct. 8, 1999, titled LENSES CAPABLE OF POST-FABRICATION POWER MODIFICATION, the entire contents of which are hereby incorporated by reference herein. 
     Methyl-methylacrylate monomers may also be blended with any of the non-metallic materials discussed above, to increase the lubricity of the resulting lens system (making the lens system easier to fold or roll for insertion, as discussed further below). The addition of methyl-methylacrylate monomers also increases the strength and transparency of the lens system. 
     The optics and/or the balance of the lens system  100  can also be formed from layers of differing materials. The layers may be arranged in a simple sandwich fashion, or concentrically. In addition, the layers may include a series of polymer layers, a mix of polymer and metallic layers, or a mix of polymer and monomer layers. In particular, a nitinol ribbon core with a surrounding silicone jacket may be used for any portion of the lens system  100  except for the optics; an acrylic-over-silicone laminate may be employed for the optics. A layered construction may be obtained by pressing/bonding two or more layers together, or deposition or coating processes may be employed. 
     Where desired, the anterior optic may be formed from a material different from that used to form the posterior optic. This may be done to take advantage of differences between the respective materials in refractive index, mechanical properties or resistance to posterior capsule opacification (“PCO”), or to achieve an appropriate balance of mechanical and optical properties. Additionally, the use of differing materials can increase resistance to intra-lenticular opacification (“ILO”). For example, the material forming the posterior optic may be selected for its resistance to PCO, and/or for its rigidity (so as to form a relatively rigid base for the biasing action of the biasing elements  108 ,  120 , thereby maximizing anterior displacement of the anterior biasing element). Thus, the posterior optic may be formed from acrylic; for example, a hydrophobic acrylic. The material forming the anterior optic may be selected for its high index of refraction, to keep to a minimum the size and weight of the anterior optic (and the lens system as a whole), thereby maximizing the range and speed of motion of the anterior optic in response to a given biasing force. To achieve these properties the anterior optic may be formed from silicone; for example, high-refractive-index silicones (generally, silicones with a refractive index greater than about 1.43, or silicones with a refractive index of about 1.46). 
     In other embodiments, the anterior optic may be formed from any suitable material (including those disclosed herein), and the posterior optic may be formed from any suitable material (including those disclosed herein) other than the material chosen to form the anterior optic. In one embodiment the anterior optic is formed from silicone and the posterior optic is formed from acrylic; in another embodiment the anterior optic is formed from acrylic and the posterior optic is formed from silicone. 
     The optics may be considered to be formed from different polymeric materials where no more than about 10 mole percent of recurring units of the polymer employed in the anterior optic are the same as the primary recurring units of the polymer employed in the posterior optic; and/or where no more than about 10 mole percent of recurring units of the polymer employed in the posterior optic are the same as the primary recurring units of the polymer employed in the anterior optic. In general, these conditions are desirable in order for the two materials to have sufficiently different material properties. As used herein, a “primary” recurring unit of a given polymer is the recurring unit which is present in such polymer in the greatest quantity by mole percentage. 
     In another embodiment, the optics may be considered to be formed from different polymeric materials where no more than about 10 mole percent of recurring units of the polymer employed in the anterior optic are of the same type as the primary recurring units of the polymer employed in the posterior optic; and/or where no more than about 10 mole percent of the recurring units of the polymer employed in the posterior optic are of the same type as the primary recurring units of the polymer employed in the anterior optic. As used herein, recurring units of the same “type” are in the same chemical family (i.e., having the same or similar functionality) or where the backbone of the polymers formed by such recurring units is essentially the same. 
     In one embodiment, portions of the lens system  100  other than the optic(s) are formed from a shape-memory alloy. This embodiment takes advantage of the exceptional mechanical properties of shape-memory alloys and provides fast, consistent, highly responsive movement of the optic(s) within the capsular bag while minimizing material fatigue in the lens system  100 . In one embodiment, one or both of the biasing elements  108 ,  120  are formed from a shape-memory alloy such as nitinol or any iron-based shape-memory alloy. Due to the flat stress-strain curve of nitinol, such biasing elements provide a highly consistent accommodation force over a wide range of displacement. Furthermore, biasing elements formed from a shape-memory alloy, especially nitinol, retain their spring properties when exposed to heat (as occurs upon implantation into a human eye) while polymeric biasing elements tend to lose their spring properties, thus detracting from the responsiveness of the lens system. For similar reasons, it is advantageous to use shape-memory alloys such as those discussed above in forming any portion of a conventional (non-accommodating) intraocular lens, other than the optic. 
     Where desired, various coatings are suitable for components of the lens system  100 . A heparin coating may be applied to appropriate locations on the lens system  100  to prevent inflammatory cell attachment (ICA) and/or posterior capsule opacification (PCO); naturally, possible locations for such a coating include the posterior biasing element  120  and the posterior face of the posterior viewing element  118 . Coatings can also be applied to the lens system  100  to improve biocompatibility; such coatings include “active” coatings like P-15 peptides or RGD peptides, and “passive” coatings such as heparin and other mucopolysaccharides, collagen, fibronectin and laminin. Other coatings, including hirudin, teflon, teflon-like coatings, PVDF, fluorinated polymers, and other coatings which are inert relative to the capsular bag may be employed to increase lubricity at locations (such as the optics and distending members) on the lens system which contact the bag, or Hema or silicone can be used to impart hydrophilic or hydrophobic properties to the lens system  100 . 
     It is also desirable subject the lens system  100  and/or the mold surfaces to a surface passivation process to improve biocompatibility. This may be done via conventional techniques such as chemical etching or plasma treatment. 
     Furthermore, appropriate surfaces (such as the outer edges/surfaces of the viewing elements, biasing elements, distending members, retention members, etc.) of the lens system  100  can be textured or roughened to improve adhesion to the capsular bag. This may be accomplished by using conventional procedures such as plasma treatment, etching, dipping, vapor deposition, mold surface modification, etc. As a further means of preventing ICA/PCO, a posteriorly-extending perimeter wall (not shown) may be added to the posterior viewing element  118  so as to surround the posterior face of the posterior optic. The wall firmly engages the posterior aspect of the capsular bag and acts as a physical barrier to the progress of cellular ingrowth occurring on the interior surface of the capsular bag. Finally, the relatively thick cross-section of the preferred anterior viewing element  118  (see  FIGS. 9, 10 ) ensures that it will firmly abut the posterior capsule with no localized flexing. Thus, with its relatively sharp rim, the posterior face of the preferred posterior viewing element  118  can itself serve as a barrier to cellular ingrowth and ICA/PCO. In order to achieve this effect, the posterior viewing element  118  is preferably made thicker than conventional intraocular lenses. As an alternative or supplement to a thick posterior viewing element, cell growth may be inhibited by forming a pronounced, posteriorly-extending perimeter rim on the posterior face of the posterior viewing element  118 . Upon implantation of the lens system  100 , the rim firmly abuts the inner surface of the capsular bag  58  and acts as a physical barrier to cell growth between the posterior face of the posterior viewing element  118  and the capsular bag  58 . 
     The selected material and lens configuration should be able to withstand secondary operations after molding/casting such as polishing, cleaning and sterilization processes involving the use of an autoclave, or ethylene oxide or radiation. After the mold is opened, the lens should undergo deflashing, polishing and cleaning operations, which typically involve a chemical or mechanical process, or a combination thereof. Suitable mechanical processes include tumbling, shaking and vibration; a tumbling process may involve the use of a barrel with varying grades of glass beads, fluids such as alcohol or water and polishing compounds such as aluminum oxides. Process rates are material dependent; for example, a tumbling process for silicone should utilize a 6″ diameter barrel moving at 30-100 RPM. It is contemplated that several different steps of polishing and cleaning may be employed before the final surface quality is achieved. 
     In one embodiment, the lens system  100  is held in a fixture to provide increased separation between, and improved process effect on, the anterior and posterior viewing elements during the deflashing/polishing/cleaning operations. In another embodiment, the lens system  100  is everted or turned “inside-out” so that the inner faces of the viewing elements are better exposed during a portion of the deflashing/polishing/cleaning.  FIG. 34A  shows a number of expansion grooves  192  which may be formed in the underside of the apices  112 ,  116  of the lens system  100  to facilitate eversion of the lens system  100  without damaging or tearing the apices or the anterior/posterior biasing elements  108 ,  120 . For the same reasons similar expansion grooves may be formed on the opposite sides (i.e., the outer surfaces) of the apices  112 ,  116  instead of or in addition to the location of grooves on the underside. 
     A curing process may also be desirable in manufacturing the lens system  100 . If the lens system is produced from silicone entirely at room temperature, the curing time can be as long as several days. If the mold is maintained at about 50 degrees C., the curing time is reduced to about 24 hours; if the mold is preheated to 100-200 degrees C. the curing time can be as short as about 3-15 minutes. Of course, the time-temperature combinations vary for other materials. 
     In certain embodiments, it can be desirable to alter one or more properties of a lens system  100  after the system  100  has been implanted in the eye  50  of a patient. For example, it can be desirable to correct for errors of ocular length and corneal curvature that may be made prior to implantation, improper positioning of the system  100  during implantation, and/or changes to the system  100  (e.g., movement of the system  100 ) that may occur after implantation as the patient heals. In some embodiments, some or all of the system  100  can be modified moments, hours, days, weeks, or years after the system  100  has been implanted. The adjustments or modifications can occur non-invasively, such as without cutting the eye  50  in order to access the lens system  100 , and/or can occur without physical manipulation of the system  100 . Advantageously, such adjustments can allow a patient to approach or achieve ideal vision (e.g., emmetropia) without glasses or other corrective lenses. In further advantageous embodiments, the system  100  permits accommodation, and can be adjusted to improve near and/or distant vision. In some situations, the lens system  100  can be modified post-operatively to improve near vision by inducing myopia in a patient. In some embodiments, the system  100  can be modified in multiple stages, and can permit adjustments as the patient ages. 
     In some embodiments, some or all of the system  100  can be modified after the system has been implanted in the eye and before the patient has been released. In some embodiments, some or all of the system can be modified after a period of healing has occurred. For example, some or all of the system  100  may be modified 1, 2, 4, 6, or 8 weeks or more after implantation. In some embodiments, some or all of the system  100  may be modified after it is has been determined that the eye&#39;s healing is substantially complete or that the patient&#39;s vision has substantially stabilized. 
     In certain embodiments, the shape and/or refractive properties of one or more of the viewing elements  106 ,  118  of the lens system  100  are altered in situ. In some embodiments, energy is applied to one or more of the elements  106 ,  118  to make the alterations without damaging surrounding ocular structures. Energy can also be applied to stabilize the material of which the elements  106 ,  118  are constructed, or to substantially prevent further changes to the molecular structure of the material, such as further polymerization due to exposure to normal light conditions or other forms of energy. For example, in some embodiments, the power of some or all of the refractive components of the lens system  100  can be changed (e.g., made more positive or more negative) by application of focused energy, and then “locked in” by application of additional energy to prevent further unwanted changes to the power of the system  100 . 
     In some embodiments, one or more of the viewing elements  106 ,  118  can comprise a composition capable of curing, undergoing stimulus-induced polymerization, or otherwise being induced to change properties in situ. Some suitable compositions are disclosed in U.S. Pat. No. 6,749,632, titled APPLICATION OF WAVEFRONT SENSOR TO LENSES CAPABLE OF POST-FABRICATION POWER MODIFICATION; U.S. Pat. No. 7,074,840, titled LIGHT ADJUSTABLE LENSES CAPABLE OF POST-FABRICATION POWER MODIFICATION VIA MULTI-PHOTON PROCESSES; U.S. Pat. No. 7,134,755, titled CUSTOMIZED LENSES; U.S. Pat. No. 6,917,416, titled LIGHT ADJUSTABLE ABERRATION CONJUGATOR; and U.S. Pat. No. 7,119,894, titled LIGHT ADJUSTABLE ABERRATION CONJUGATOR, the entire contents of each of which are hereby incorporated by reference herein and made a part of this specification. For example, in various embodiments, one or more of the viewing elements  106 ,  118  (and/or some or all of the remainder of the lens system  100 ) can comprise polyacrylates such as polyalkyl acrylates and polyhydroxyalkyl acrylates; polymethacrylates such as polymethyl methacrylate (“PMMA”), a polyhydroxyethyl methacrylate (“PHEMA”), and polyhydroxypropyl methacrylate (“HPMA”); polyvinyls such as polystyrene and polyvinylpyrrolidone (“NVP”); polysiloxanes such as polydimethylsiloxane; polyphosphazenes, and copolymers of thereof. Other suitable materials are disclosed in U.S. Pat. No. 4,260,725, titled HYDROPHILIC CONTACT LENS MADE FROM POLYSILOXANES WHICH ARE THERMALLY BONDED TO POLYMERIZABLE GROUPS AND WHICH CONTAIN HYDROPHILIC SIDECHAINS, and in the patents and references cited therein; the entire contents of each of the foregoing items are incorporated by reference herein and made a part of this specification. 
     In certain embodiments, polymerization is induced by application of delivery of energy, or energetic radiation, to the viewing elements  106 ,  118 . In some embodiments, the radiation comprises electromagnetic radiation having a single wavelength or a relatively small band of wavelengths, and may be provided by a laser or a light emitting diode. In other embodiments, the electromagnetic radiation comprises a band of wavelengths, and may include optical, ultraviolet, or infrared radiation. Other forms of radiation can also be used, including electron beam, microwave, radio frequency, or acoustic. Some suitable polymerization methods, including specific wavelengths and power levels that can be used, are disclosed in U.S. Pat. No. 7,105,110, titled DELIVERY SYSTEM FOR POST-OPERATIVE POWER ADJUSTMENT OF ADJUSTABLE LENS, the entire contents of which are hereby incorporated by reference herein and made a part of this specification. 
     In some embodiments, polymerization of the elements  106 ,  118  can alter the refractive properties (e.g., the index of refraction) of the elements  106 ,  118 . In further embodiments, polymerization of the elements  106 ,  118  can alter their shape (e.g., curvature). The refractive properties and/or shape of one or more of the elements  106 ,  118  thus can be modified to adjust the optical power of the elements  106 ,  118 . Also, the shape (e.g., curvature), index of refraction, refractive power, or other performance metric of any of the anterior or posterior surfaces of either of the anterior or posterior viewing elements  106 ,  118  can be modified to achieve the desired outcome. 
     In some embodiments, radiation is initially applied to only a portion of one or more of the elements  106 ,  118 . The radiation can be directed to or focused on a particular region of the elements  106 ,  118  and can polymerize the region to modify the refractive properties and/or shape thereof. In further embodiments, radiation is applied to the remaining portion(s) of the element or elements  106 ,  118  to polymerize, stabilize, or substantially prevent changes to the properties of the remaining portion(s). 
     In some instances, one or more of the elements  106 ,  118  may already comprise the desired optical properties prior to polymerization. For example, once a patient has healed from an implantation procedure, it may be determined that the system  100  provides proper focusing of incoming light over a full range of accommodation. Accordingly, in some embodiments, it may be desirable to cure or polymerize one or more of the elements  106 ,  118  substantially without changing the optical properties (e.g., the index of refraction or shape) of the elements. In certain of such embodiments, substantially all of one or more of the elements  106 ,  118 , or in further embodiments, substantially all of the system  100 , can be irradiated at about the same time (e.g., substantially simultaneously). 
     In some embodiments, only one of the elements  106 ,  118  is configured for alteration in situ, or one of the elements  106 ,  118  is substantially more alterable in situ than is the other of the elements. In some embodiments, only one of the elements  106 ,  118  is susceptible to polymerization under application of radiation, and the other of the elements  106 ,  118  is relatively unaffected by application of the radiation. For example, when both elements  106 ,  118  are formed from a unitary piece of material, one of the elements  106 ,  118  can be polymerized by an energy source during fabrication of the lens system  100  such that the polymerized lens would be relatively unaffected by any polymerizing radiation subsequently applied to the system  100 . In certain of such embodiments, the un-polymerized or adjustable lens is protected from the energy source during fabrication, such as, for example, by a removable energy-reflective or energy-absorbing shield, cover, or coating. 
     In other embodiments, the elements  106 ,  118  comprise different materials such that each of the elements  106 ,  118  is susceptible to polymerization by a different energy source. For example, in some embodiments, the anterior viewing element  106  can comprise a material configured to polymerize when exposed to a first band of UV radiation but not a second band of UV radiation, and the posterior viewing element  118  can comprise a material configured to polymerize when exposed to the second band of UV radiation but not the first band of UV radiation. Accordingly, in some embodiments, one of the elements  106 ,  118  can be selectively irradiated by an energy source substantially without polymerizing the other of the elements  118 . In further embodiments, the anterior viewing element  106  can be substantially transparent to the form of radiation capable of polymerizing the posterior viewing element  118 , which can facilitate polymerization of the posterior viewing element  118 . In still other embodiments, only one of the elements  106 ,  118  is susceptible to polymerization. 
     In some embodiments, the posterior viewing element  118  is alterable and the anterior viewing element  106  is not alterable, or is substantially less alterable. In certain of such embodiments, the anterior viewing element  106  can be polymerized or otherwise treated to at least partially shield the posterior viewing element  118  from polymerizing energy, such as UV rays. The anterior viewing element  106  thus can protect the posterior viewing element  118  from undesired polymerization prior to desired adjustment by a medical professional. The posterior viewing element  118  can later be altered by exposing the element to an energy source that the anterior viewing element  106  is transparent to, such as, for example, a different band of UV radiation or electromagnetic radiation outside the UV range. In other embodiments, the anterior viewing element  106  is alterable and the posterior viewing element  118  is not alterable, or is substantially less alterable. In some embodiments, an implanted system  100  having only one element  106 ,  118  susceptible to polymerization can be relatively easy to adjust because any polymerizing energy applied to the system  100  will affect only one of the elements  106 ,  118 . 
     In certain embodiments, both of the anterior and posterior viewing elements  106 ,  118  are alterable in situ. In some embodiments, both elements  106 ,  118  are adjusted at approximately the same time. For example, in some instances, it may be desirable to determine whether an implantation was successful near the time of the implantation. In various situations, a patient may be evaluated from about 1 to about 3 weeks after implantation, from about 2 to about 3 weeks after implantation, or after the eye has completely or substantially healed. In some instances, the system  100  may benefit from modifications at the time of a post-implantation examination. Accordingly, one or more of the elements  106 ,  118  can be modified, as described above, and both can be polymerized or stabilized to prevent further adjustments. In other instances, the system  100  may function as desired once the patient has healed, and the elements  106 ,  118  can be polymerized or stabilized to prevent subsequent undesirable adjustments. 
     In some embodiments, the elements  106 ,  118  can be adjusted at separate times. For example, if the system  100  functions as desired at a post-implantation examination, rather than polymerizing or stabilizing the elements  106 ,  118  at that time, one or more of the elements  106 ,  118  can instead be modified at one or more subsequent dates to account for vision changes as the patient ages. 
     In some instances, one of the elements  106 ,  118  can be adjusted during the post-implantation examination, and the other of the elements  106 ,  118  can be adjusted at a later time. In some embodiments, the first of the elements  106 ,  118  can adjusted to provide proper functioning of the system  100  near the time of the implantation, and the second of the elements  106 ,  118  is adjusted at a later time, which can be from about 1 to 6 months, from about 1 to 12 months, from about 1 to 2 years, from about 1 to 3 years, from about 1 to 5 years, or from about 1 to 10 years after implantation; or no less than about 6 months, no less than about 1 year, no less than about 2 years, or no less than about 5 years after implantation. Accordingly, in various embodiments, the lens system  100  can be adjusted at one or more dates to account for changes to the patient&#39;s vision as the patient ages. In some embodiments, the anterior viewing element  106  is adjusted prior to adjustment of the posterior viewing element  118 , which can help shield the posterior viewing element  118  from undesired radiation, as described above. 
     In some embodiments, the lens system  100  can be adjusted by curing, polymerizing, or otherwise altering one or more portions of the system  100  in addition to or instead of the viewing elements  106 ,  118 . For example, in some embodiments, one or more support components of the lens system  100 , such as the anterior biasing element  108 , the posterior biasing element  120 , the first apex  112 , and the second apex  116 , can comprise any of the materials described above, and further, can be adjusted by irradiation. 
     In certain embodiments, polymerization of one or more support components of the lens system  100  alters the stiffness, spring constant, and/or shape of the one or more support components. Accordingly, in some embodiments, polymerization can affect the manner in which the system  100  reacts to forces provided by the ciliary muscle  60 . For example, in some embodiments, polymerization of one or more of the support components stiffens the components such that the viewing elements  106 ,  118  are displaced relative to each other by a smaller amount when the ciliary muscle  60  applies force to the system  100 , as compared with the system  100  prior to polymerization. In some embodiments, polymerization affects the lens system&#39;s response time to changes in forces applied by the eye, e.g. by increasing or decreasing the length of time required for the lens to move from the unaccommodated state to the accommodated state and/or the time required for the lens to move from the accommodated state to the unaccommodated state. 
     In some embodiments, alteration of the shape of one or more of the support components can move the viewing elements  106 ,  118  closer together or further apart along the optical axis. Accordingly, in some embodiments, the power of the lens system  100  can be altered by polymerizing the support components, independent of any changes made to the properties of the viewing elements  106 ,  118 . In some embodiments, polymerization affects the lens system&#39;s range of motion, e.g. by affecting one or both of a separation distance between the anterior and posterior optic when the eye is in an unaccommodated state and a separation distance between the anterior and posterior optic when the eye is in an accommodated state. 
     In some embodiments, the support structures are cured during fabrication of the lens system  100 . In certain of such embodiments, one or more of the viewing elements  106 ,  118  are covered during fabrication in any suitable manner, such as those described above, and the remainder of the lens system  100  is exposed to an energy source. In some embodiments, the support structures are substantially unaffected by radiation that may subsequently be applied to the lens system  100  in situ, which can facilitate alteration of the properties of one or more of the viewing elements  106 ,  118 . 
     Any suitable portion of a lens system  100  may be pre-treated (e.g., polymerized) to substantially prevent subsequent alteration of that portion in situ. Similarly, any suitable portion of a lens system  100  may be alterable (e.g., un-polymerized) to allow for subsequent adjustment of the system  100  in situ. 
     VIII. Multiple-Piece and Other Embodiments 
       FIG. 35  is a schematic view of a two-piece embodiment  600  of the lens system. In this embodiment the anterior portion  102  and the posterior portion  104  are formed as separate pieces which are intended for separate insertion into the capsular bag and subsequent assembly therein. In one embodiment, each of the anterior and posterior portions  102 ,  104  is rolled or folded before insertion into the capsular bag. (The insertion procedure is discussed in further detail below.) The anterior portion  102  and posterior portion  104  are represented schematically as they may generally comprise any anterior-portion or posterior-portion structure disclosed herein; for example, they may simply comprise the lens system  100  shown in  FIGS. 3-17 , bisected along the line/plane A-A shown in  FIG. 4 . The anterior portion  102  and posterior portion  104  of the two-piece lens system  600  will include first and second abutments  602 ,  604  which are intended to be placed in abutting relation (thus forming the first and second apices of the lens system) during the assembly procedure. The first and second abutments  602 ,  604  may include engagement members (not shown), such as matching projections and recesses, to facilitate alignment and assembly of the anterior and posterior portions  102 ,  104 . 
     As a further alternative, the anterior and posterior portions  102 ,  104  of the lens system  600  may be hingedly connected at one of the abutments  602 ,  604  and unconnected at the other, to allow sequential (but nonetheless partially assembled) insertion of the portions  102 ,  104  into the capsular bag. The individual portions may be separately rolled or folded before insertion. The two portions  102 ,  104  are “swung” together and joined at the unconnected abutment to form the finished lens system after both portions have been inserted and allowed to unfold/unroll as needed. 
       FIG. 36  depicts schematically another embodiment  700  of a two-piece lens system. The lens system  700  is desirably similar to the lens system  600  shown in  FIG. 35 , except for the formation of relatively larger, curled abutments  702 ,  704  which are assembled to form the apices  112 ,  116  of the system  700 . 
       FIGS. 37 and 38  show a further embodiment  800  of the lens system, in which the anterior and posterior biasing elements  108 ,  120  comprise integral “band” like members forming, respectively, the first and second anterior translation members  110 ,  114  and the first and second posterior translation members  122 ,  124 . The biasing elements  108 ,  120  also form reduced-width portions  802 ,  804  which meet at the apices of the lens system  800  and provide regions of high flexibility to facilitate sufficient accommodative movement. The depicted distending portion  132  includes three pairs of distending members  134 ,  136  which have a curved configuration but nonetheless project generally away from the optical axis. 
       FIGS. 38A and 38B  depict another embodiment  900  of the lens system, as implanted in the capsular bag  58 . The embodiment shown in  FIGS. 38A and 38B  may be similar to any of the embodiments described above, except that the biasing elements  108 ,  120  are dimensioned so that the apices  112 ,  116  abut the zonules  62  and ciliary muscles  60  when in the unaccommodated state as seen in  FIG. 38A . In addition, the lens system  900  is configured such that it will remain in the unaccommodated state in the absence of external forces. Thus, when the ciliary muscles  60  contract, the muscles  60  push the apices  112 ,  116  closer together, causing the biasing elements  108 ,  120  to bow out and the viewing elements  106 ,  118  to separate and attain the accommodated state as shown in  FIG. 38B . When the ciliary muscles  60  relax and reduce/eliminate the force applied to the apices  112 ,  116  the biasing elements  108 ,  120  move the lens system  900  to the unaccommodated state depicted in  FIG. 38A . 
       FIGS. 38C and 38D  depict biasers  1000  which may be used bias the lens system  100  toward the accommodated or unaccommodated state, depending on the desired operating characteristics of the lens system. It is therefore contemplated that the biasers  1000  may be used with any of the embodiments of the lens system  100  disclosed herein. The bias provided by the biasers  1000  may be employed instead of, or in addition to, any bias generated by the biasing elements  108 ,  120 . In one embodiment (see  FIG. 38C ), the biasers  1000  may comprise U-shaped spring members having apices  1002  located adjacent the apices  112 ,  116  of the lens system  100 . In another embodiment (see  FIG. 38D ), the biasers  1000  may comprise any suitable longitudinal-compression springs which span the apices  112 ,  116  and interconnect the anterior and posterior biasing elements  108 ,  120 . By appropriately selecting the spring constants and dimensions of the biasers  1000  (in the case of U-shaped springs, the apex angle and arm length; in the case of longitudinal-compression springs, their overall length), the biasers  1000  can impart to the lens system  100  a bias toward the accommodated or unaccommodated state as desired. 
     The biasers  1000  may be formed from any of the materials disclosed herein as suitable for constructing the lens system  100  itself. The material(s) selected for the biasers  1000  may be the same as, or different from, the material(s) which are used to form the remainder of the particular lens system  100  to which the biasers  1000  are connected. The number of biasers  1000  used in a particular lens system  100  may be equal to or less than the number of apices formed by the biasing elements of the lens system  100 . 
       FIG. 38E  depicts a further embodiment of the lens system  100  in which the anterior translation members  110  and the posterior translation members  120  are paired in a number (in the example depicted, four) of separate positioners  1400  which are radially spaced, preferably equally radially spaced, about the optical axis. In the depicted embodiment, the anterior and posterior translation members  110 ,  120  connect directly to the periphery of the viewing elements  106 ,  118 ; however, in other embodiments any of the connection techniques disclosed herein may be employed. As shown, the anterior translation members  100  preferably extend anteriorly from the periphery of the anterior viewing element before bending and extending posteriorly toward the apex/apices  112 . As discussed above, this configuration is advantageous for promotion of fluid flow through an opening formed in the anterior aspect of the capsular bag  58 . It has been found that the lens configuration shown in  FIG. 38E  is well suited for the folding technique shown in  FIGS. 40A and 40B  below. In additional embodiments, the lens system  100  shown in  FIG. 38E  may incorporate any other suitable features of the other embodiments of the lens system  100  disclosed herein, such as but not limited to the distending members and/or retention members detailed above. 
     Any of the embodiments  100 ,  600 ,  700 ,  800 ,  900  of the lens system can include post-implantation adjustability, such as discussed above in Sections II and VII with respect to the lens system  100 . Accordingly, in some embodiments, any suitable portion of the any of the lens systems  100 ,  600 ,  700 ,  800 ,  900  can comprise a material capable of being adjusted in situ by application of energy thereto. 
     IX. Implantation Methods 
     Various techniques may be employed in implanting the various embodiments of the lens system in the eye of a patient. The physician can first access the anterior aspect of the capsular bag  58  via any appropriate technique. Next, the physician incises the anterior of the bag; this may involve making the circular opening  66  shown in  FIGS. 21 and 22 , or the physician may make a “dumbbell” shaped incision by forming two small circular incisions or openings and connecting them with a third, straight-line incision. The natural lens is then removed from the capsular bag via any of various known techniques, such as phacoemulsification, cryogenic and/or radiative methods. To inhibit further cell growth, it is desirable to remove or kill all remaining epithelial cells. This can be achieved via cryogenic and/or radiative techniques, antimetabolites, chemical and osmotic agents. It is also possible to administer agents such as P15 to limit cell growth by sequestering the cells. 
     In the next step, the physician implants the lens system into the capsular bag. Where the lens system comprises separate anterior and posterior portions, the physician first folds or rolls the posterior portion and places it in the capsular bag through the anterior opening. After allowing the posterior portion to unroll/unfold, the physician adjusts the positioning of the posterior portion until it is within satisfactory limits. Next the physician rolls/folds and implants the anterior portion in a similar manner, and aligns and assembles the anterior portion to the posterior portion as needed, by causing engagement of mating portions, etc. formed on the anterior and posterior portions. 
     Where the lens system comprises anterior and posterior portions which are partially assembled or partially integral (see discussion above in the section titled MULTIPLE-PIECE AND OTHER EMBODIMENTS), the physician employs appropriate implantation procedures, subsequently folding/rolling and inserting those portions of the lens system that are separately foldable/rollable. In one embodiment, the physician first rolls/folds one portion of the partially assembled lens system and then inserts that portion. The physician then rolls/folds another portion of the partially assembled lens system and the inserts that portion. This is repeated until the entire system is inside the capsular bag, whereupon the physician completes the assembly of the portions and aligns the lens system as needed. In another embodiment, the physician first rolls/folds all of the separately rollable/foldable portions of the partially assembled lens system and then inserts the rolled/folded system into the capsular bag. Once the lens system is in the capsular bag, the physician completes the assembly of the portions and aligns the lens system as needed. 
     It is contemplated that conventional intraocular lens folding devices, injectors, syringes and/or shooters can be used to insert any of the lens systems disclosed herein. A preferred folding/rolling technique is depicted in  FIGS. 39A-39B , where the lens system  100  is shown first in its normal condition (A). The anterior and posterior viewing elements  106 ,  118  are manipulated to place the lens system  100  in a low-profile condition (B), in which the viewing elements  106 ,  118  are out of axial alignment and are preferably situated so that no portion of the anterior viewing element  106  overlaps any portion of the posterior viewing element  118 , as viewed along the optical axis. In the low-profile position (B), the thickness of the lens system  100  is minimized because the viewing elements  106 ,  118  are not “stacked” on top of each other, but instead have a side-by-side configuration. From the low-profile condition (B) the viewing elements  106 ,  118  and/or other portions of the lens system  100  can be folded or rolled generally about the transverse axis, or an axis parallel thereto. Alternatively, the lens system could be folded or rolled about the lateral axis or an axis parallel thereto. Upon folding/rolling, the lens system  100  is placed in a standard insertion tool as discussed above and is inserted into the eye. 
     When the lens system  100  is in the low-profile condition (B), the system may be temporarily held in that condition by the use of dissolvable sutures, or a simple clip which is detachable or manufactured from a dissolvable material. The sutures or clip hold the lens system in the low-profile condition during insertion and for a desired time after insertion. By temporarily holding the lens system in the low-profile condition after insertion, the sutures or clip provide time for fibrin formation on the edges of the lens system which, after the lens system departs from the low-profile condition, may advantageously bind the lens system to the inner surface of the capsular bag. 
     The physician next performs any adjustment steps which are facilitated by the particular lens system being implanted. Where the lens system is configured to receive the optic(s) in “open” frame members, the physician first observes/measures/determines the post-implantation shape taken on by the capsular bag and lens system in the accommodated and/or unaccommodated states and select(s) the optics which will provide the proper lens-system performance in light of the observed shape characteristics and/or available information on the patient&#39;s optical disorder. The physician then installs the optic(s) in the respective frame member(s); the installation takes place either in the capsular bag itself or upon temporary removal of the needed portion(s) of the lens system from the bag. If any portion is removed, a final installation and assembly is then performed with the optic(s) in place in the frame member(s). 
     Where the optic(s) is/are formed from an appropriate photosensitive silicone as discussed above, the physician illuminates the optic(s) (either anterior or posterior or both) with an energy source such as a laser until they attain the needed physical dimensions or refractive index. The physician may perform an intervening step of observing/measuring/determining the post-implantation shape taken on by the capsular bag and lens system in the accommodated and/or unaccommodated states, before determining any needed changes in the physical dimensions or refractive index of the optic(s) in question. 
       FIG. 40  depicts a technique which may be employed during lens implantation to create a fluid flow path between the interior of the capsular bag  58  and the region of the eye anterior of the capsular bag  58 . The physician forms a number of fluid-flow openings  68  in the anterior aspect of the capsular bag  58 , at any desired location around the anterior opening  66 . The fluid-flow openings  68  ensure that the desired flow path exists, even if a seal is created between the anterior opening  66  and a viewing element of the lens system. 
     Where an accommodating lens system is implanted, the openings  68  create a fluid flow path from the region between the viewing elements of the implanted lens system, and the region of the eye anterior of the capsular bag  58 . However, the technique is equally useful for use with conventional (non-accommodating) intraocular lenses. 
       FIGS. 40A and 40B  illustrate another embodiment of a method of folding the lens system  100 . In this method the anterior viewing element  106  is rotated approximately 90 degrees about the optical axis with respect to the posterior viewing element  118 . This rotation may be accomplished by applying rotational force to the upper edge of the first transition member  138  and the lower edge of the second transition member  140  (or vice versa), as indicated by the dots and arrows in  FIG. 40A , while holding the posterior viewing element  118  stationary, preferably by gripping or clamping the distending members  134 ,  136 . Alternatively, rotational force may be applied in a similar manner to a right edge of one of the retention members  128 ,  130  and to a left edge of the other of the retention members while holding the posterior viewing element  118  stationary. As still further alternatives, the anterior viewing element  106  could be held stationary while rotational force is applied to the posterior viewing element  118 , at an upper edge of one of the distending members  134 ,  136  and at a lower edge of the other of the distending members; or both the anterior and posterior viewing elements  106 ,  118  could be rotated with respect to each other. 
     Preferably, the viewing elements  106 ,  118  are spread apart somewhat as the rotation is applied to the lens system so that the translation members and apices are drawn into the space between the viewing elements  106 ,  118  in response to the rotational force. Once the anterior viewing element  106  has been rotated approximately 90 degrees about the optical axis with respect to the posterior viewing element  118 , the lens system  100  takes on the configuration shown in  FIG. 40B , with the retention members  128 ,  130  generally radially aligned with the distending members  134 ,  136  and the translation members and apices disposed between the viewing elements  106 ,  118 . This configuration is advantageous for inserting the lens system  100  into the capsular bag  58  because it reduces the insertion profile of the lens system  100  while storing a large amount of potential energy in the translation members. From the folded configuration the translation members thus exert a high “rebound” force when the lens system has been inserted to the capsular bag  58 , causing the lens system to overcome any self-adhesion and spring back to the unfolded configuration shown in  FIG. 40A  without need for additional manipulation by the physician. 
     Once the lens system  100  is in the folded configuration shown in  FIG. 40B , it may be further folded and/or inserted into the capsular bag  58  by any suitable methods presently known in the art or hereafter developed. For example, as shown in  FIG. 40C  the folding method may further comprise inserting the folded lens system  100  between the prongs  1202 ,  1204  of a clip  1200 , preferably with the prongs  1202 ,  1204  oriented to extend along the transition members  138 ,  140 , or along the retention members  128 ,  130  and the distending members  134 ,  136 . 
       FIGS. 40D-40F  illustrate the use of jaws  1250 ,  1252  of a pliers or forceps to fold the lens system  100  as it is held in the clip  1200 . ( FIGS. 40D-40F  show an end view of the clip-lens system assembly with the jaws  1250 ,  1252  shown in section for clarity.) As shown in  FIGS. 40D and 40E , the edges of the jaws  1250 ,  1252  are urged against one of the anterior and posterior viewing elements  106 ,  118  while the jaws  1250 ,  1252  straddle the prong  1202  of the clip  1200 . The resulting three-point load on the lens system  1200  causes it to fold in half as shown in  FIG. 40E . As the lens system  100  approaches the folded configuration shown in  FIG. 40F , the jaws  1250 ,  1252  slide into a pincer orientation with respect to the lens system  100 , characterized by contact between the inner faces  1254 ,  1256  of the jaws  1250 ,  1252  and the anterior viewing element  106  or posterior viewing element  118 . With such a pincer orientation established, the forceps may be used to grip and compress the lens system with inward-directed pressure and the clip  1200  can be withdrawn, as shown in  FIG. 40F . With the lens system  100  thus folded, it can be inserted to the capsular bag  58  by any suitable method presently known in the art or hereafter developed. 
       FIG. 40G  depicts a folding tool  1300  which may be employed to fold the lens system  100  as discussed above in connection with  FIGS. 40A and 40B . The tool  1300  includes a base  1302  with brackets  1304  which hold the lens system  100  to the base  1302  by gripping the distending members  134 ,  136 . Formed within the base  1302  are arcuate guides  1306 . The tool further comprises a rotor  1308  which in turn comprises a horizontal rod  1310  and integrally formed vertical rods  1312 . The vertical rods  1312  engage the arcuate guides  1306 , both of which have a geometric center on the optical axis of the lens system  100 . The vertical rods  1312  and the arcuate guides  1306  thus coact to allow the horizontal rod to rotate at least 90 degrees about the optical axis of the lens system  100 . The horizontal rod  1310  is fixed with respect to the anterior viewing element  106  of the lens system  100  so as to prevent substantially no relative angular movement between the rod  1310  and the anterior viewing element  106  as the rod  1310  (and, in turn, the anterior viewing element  106 ) rotates about the optical axis of the lens system  100 . This fixed relationship may be established by adhesives and/or projections (not shown) which extend downward from the horizontal rod  1308  and bear against the upper edge of one of the transition members  138 ,  140  and against the lower edge of the other of the transition members as shown in  FIG. 40A . As an alternative or as a supplement to this arrangement, the projections may bear against the retention members  128 ,  130  in a similar manner as discussed above. 
     Thus, when the rotor  1308  is advanced through its range of angular motion about the optical axis of the lens system  100 , it forces the anterior viewing element  106  to rotate in concert therewith about the optical axis, folding the lens system as discussed above in connection with  FIGS. 40A and 40B . It is further contemplated that the folding tool  1300  may comprise the lower half of a package in which the lens system is stored and/or shipped to a customer, to minimize the labor involved in folding the lens system at the point of use. Preferably, the lens system is stored in the tool  1300  in the unfolded configuration, so as to avoid undesirable deformation of the lens system. 
     X. Thin Optic Configurations 
     In some circumstances it is advantageous to make one or more of the optics of the lens system relatively thin, in order to facilitate rolling or folding, or to reduce the overall size or mass of the lens system. Discussed below are various optic configurations which facilitate a thinner profile for the optic; any one of these configurations may be employed as well as any suitable combination of two or more of the disclosed configurations. 
     One suitable technique is to employ a material having a relatively high index of refraction to construct one or more of the optics. In one embodiment, the optic material has an index of refraction higher than that of silicone. In another embodiment, the material has an index of refraction higher than about 1.43. In further embodiments, the optic material has an index of refraction of about 1.46, 1.49 or 1.55. In still further embodiments, the optic material has an index of refraction of about 1.43 to 1.55. By employing a material with a relatively high index of refraction, the curvature of the optic can be reduced (in other words, the radius/radii of curvature can be increased) thereby reducing the thickness of the optic without loss of focal power. 
     A thinner optic can also be facilitated by forming one or more of the surfaces of one or more of the optics as an aspheric surface, while maintaining the focal power of the optic. As shown in  FIG. 41 , an aspheric, convex optic surface  1100  can be formed with the same radius of curvature (as a comparable-power spherical surface) at the vertex  1102  of the surface  1100  and a longer radius of curvature (with a common center point) at its periphery  1104 , creating a thinner optic without sacrificing focal power. This contrasts with a spherical optic surface  1106 , which is thicker at its vertex  1108  than is the aspheric surface  1102 . In one embodiment, the thickness of the optic is reduced by about 19% at the vertex relative to a comparable-power spherical optic. It is contemplated that thinner, aspheric concave optic surfaces may be used as well. A further advantage of an aspheric optic surface is that it provides better image quality with fewer aberrations, and facilitates a thinner optic, than a comparable spherical surface. 
       FIG. 42  depicts a further strategy for providing a thinner optic  1150 . The optic  1150  has a curved (spherical or aspheric) optic surface  1152  and a flat or planar (or otherwise less curved than a comparable refractive surface) diffractive optic surface  1154  in place of a second curved surface  1156 . The diffractive optic surface  1154  can comprise any suitable diffraction grating, including the grooved surface depicted or any other diffractive surface presently known or hereafter developed, including holographic optical elements. By appropriately configuring the diffractive surface  1154  as is well known in the art, the optic  1150  can be made thinner than one having both curved surfaces  1152 ,  1154 , while providing the same focal power. The use of the diffractive surface  1154  not only facilitates a thinner optic, but also reduces aberrations in the resulting image. 
     A further alternative for facilitating a thin, easy-to-fold optic is to employ, in place of a biconvex optic of refractive index greater than aqueous humor (i.e., greater than about 1.336), a biconcave optic of refractive index less than about 1.336, which is thinner at the optical axis than the biconvex optic. By constructing the biconcave optic of material having a refractive index less than about 1.336, the biconcave optic can be made to have the same effective focal power, when immersed in aqueous humor, as a given biconvex optic. 
     Still another alternative thin optic, shown in  FIG. 43 , is a biconcave optic  1160  of low refractive index (for example, about 1.40 or less or about 1.336 or less) which is clad with first and second cladding portions  1162 ,  1164  constructed of higher-index material (for example, about 1.43 or greater). Such an optic can be made to have the same effective focal power, when immersed in aqueous humor, as a thicker biconvex optic. 
     As a further alternative, one or more of the surfaces of the optics may be formed as a multifocal surface, with spherical and/or aspheric focal regions. A multifocal surface can be made with less curvature than a comparable-power single-focus surface and thus allows the optic to be made thinner. The additional foci provide added power which replaces or exceeds the power that is “lost” when the surface is reduced in curvature. In one embodiment, the multifocal optic is constructed as a concentric-ring, refractive optic. In another embodiment, the multifocal optic is implemented as a diffractive multifocal optic. 
     Although the inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.