Accommodating intraocular lens having peripherally actuated deflectable surface and method

Description of equivalent WO 2007047530 A2

0001ACCOMMODATING INTRAOCULAR LENS HAVING PERIPHERALLY ACTUATED DEFLECTABLE SURFACE AND METHOD

0002Field Of The Invention [0001] The present invention relates to intraocular lenses ("IOLs") having optical parameters that are changeable in-situ. More particularly, the invention has applications in IOLs for in-capsule implantation for cataract patients, wherein forces applied by the ciliary muscles in the eye induce movement of fluid media within the interior of the IOL, thereby altering an optical power of the lens to provide accommodation.

0003Background of the Invention [0002] Cataracts are a major cause of blindness in the world and the most prevalent ocular disease. Visual disability from cataracts accounts for more than 8 million physician office visits per year. When the disability from cataracts affects or alters an individual's activities of daily living, surgical lens removal with intraocular lens (IOL) implantation is the preferred method of treating the functional limitations. In the United States, about 2.5 million cataract surgical procedures are performed annually, making it the most common surgery for Americans over the age of 65. About 97 percent of cataract surgery patients receive intraocular lens implants, with the annual costs for cataract surgery and associated care in the United States being upwards of $4 billion. [0003] A cataract is any opacity of a patient's lens, whether it is a localized opacity or a diffuse general loss of transparency. To be clinically significant, however, the cataract must cause a significant reduction in visual acuity or a functional impairment. A cataract occurs as a result of aging or secondary to hereditary factors, trauma, inflammation, metabolic or nutritional disorders, or radiation. Age related cataract conditions are the most common.

0004[0004] In treating a cataract, the surgeon removes the crystalline lens matrix from the lens capsule and replaces it with an intraocular lens (^λλIOL") implant. The typical IOL provides a selected focal length that allows the patient to have fairly good distance vision. Since the lens can no longer accommodate, however, the patient typically needs glasses for reading. [0005] More specifically, the imaging properties of the human eye are facilitated by several optical interfaces. A healthy youthful human eye has a total power of approximately 59 diopters, with the anterior surface of the cornea (e.g. the exterior surface, including the tear layer) providing about 48 diopters of power, while the posterior surface provides about -4 diopters. The crystalline lens, which is situated posterior of the pupil in a transparent elastic capsule supported by the ciliary muscles, provides about 15 diopters of power, and also performs the critical function of focusing images upon the retina. This focusing ability, referred to as "accommodation, " enables imaging of objects at various distances.

0005[0006] The power of the lens in a youthful eye can be adjusted from 15 diopters to about 29 diopters by adjusting the shape of the lens from a moderately convex shape to a highly convex shape. The mechanism generally accepted to cause this adjustment is that ciliary muscles supporting the capsule (and the lens contained therein) , move between a relaxed state (corresponding to the moderately convex shape) to a contracted state (corresponding to the highly convex shape) . Because the lens itself is composed of viscous, gelatinous transparent fibers, arranged in an ^λΛonion-like" layered structure, forces applied to the capsule by the ciliary muscles cause the lens to change shape. [0007] Isolated from the eye, the relaxed capsule and lens take on a spherical shape. Within the eye, however, the capsule is connected around its circumference by approximately 70 tiny ligament fibers to the ciliary muscles, which in turn are attached to an inner surface of the eyeball. The ciliary muscles that support the lens and capsule therefore are believed to act in a sphincter muscular mode. Accordingly, when the ciliary muscles are relaxed, the capsule and lens are pulled about the circumference to a larger diameter, thereby flattening the lens, whereas when the ciliary muscles are contracted, the lens and capsule relax somewhat and assume a smaller diameter that approaches a more spherical shape, thereby increasing the diopter power of the lens . [0008] As noted above, the youthful eye has approximately 14 diopters of accommodation. As a person ages, the lens hardens and becomes less elastic, so that by about age 45-50, accommodation is reduced to about 2 diopters. At a later age the lens may be considered to be non-accommodating, a condition know as "presbyopia". Because the imaging distance is fixed, presbyopia typically entails the need for bi-focals to facilitate near and far vision. [0009] Apart from age-related loss of accommodation ability, such loss is innate to the placement of IOLs for the treatment of cataracts. IOLs are generally single element lenses made from a suitable polymer material, such as acrylics or silicones. After placement, accommodation is no longer possible, although this ability is typically already lost for persons receiving an IOL. There is significant need to provide for accommodation in IOL products so that IOL recipients will have accommodating ability. [0010] Although previously known workers in the field of accommodating IOLs have made some progress, the relative complexity of the methods and apparatus developed to date have prevented widespread commercialization of such devices. Previously known devices have proved too complex to be practical to construct or have achieved only limited success, due to the inability to provide accommodation of more than 1-2 diopters . [0011] U.S. Patent No. 5,443,506 to Garabet describes an accommodating fluid-filled lens wherein electrical potentials generated by contraction of the ciliary muscles cause changes in the index of refraction of fluid carried within a central optic portion. U.S. Patent No. 4,816,031 to Pfoff discloses an IOL with a hard PMMA lens separated by a single chamber from a flexible thin lens layer that uses microfluid pumps to vary a volume of fluid between the PMMA lens portion and the thin layer portion and provide accommodation. U.S. Patent No.

00064,932,966 to Christie et al . discloses an intraocular lens comprising a thin flexible layer sealed along its periphery to a support layer, wherein forces applied to fluid reservoirs in the haptics vary a volume of fluid between the plurality of layers to provide accommodation. [0012] Although fluid-actuated mechanisms such as described in the aforementioned patents have been investigated, commercially available accommodating lenses, such as developed by Eyeonics, Inc. of Aliso Viejo, California, rely on ciliary muscle contraction of the IOL haptics to vault the optic towards or away from the retina to adjust the focus of the device. [0013] One promising line of IOL apparatus and methods is disclosed in commonly assigned U.S. Patent Publication 2005/0119740 Al to Esch et al . There, apparatus and methods are described in which a patient's vision may be improved by implantation of an IOL having one or more pistons disposed at or near the center of a deformable surface of the IOL. Due to the potential for reflections to arise during movement of the piston near the optical axis of the IOL, it may be desirable to relocate the actuators to a peripheral portion of the IOL. [0014] In view of the foregoing, it would be desirable to provide apparatus and methods that restore appropriate optical focusing power action to the human eye.

0007[0015] It further would be desirable to provide methods and apparatus wherein a dynamic lens surface may be effectively manipulated by the ciliary muscular mechanisms within the eye.

0008[0016] It still further would be desirable to provide methods and apparatus that utilize pressure applied by the accommodating muscular action to deform an optical surface of the IOL. In particular, it would be desirable to provide an IOL in which muscular pressure may be applied through one or more actuators to obtain a mechanical advantage. [0017] It is yet further desirable to provide methods and apparatus that reduce the possibility of reflections within the IOL arising due to movement of mechanical actuators situated along or near the optical axis of the IOL.

0009Summary Of The Invention

0010[0018] In view of the foregoing, it is an object of the present invention to provide apparatus and methods that restore appropriate optical focusing power action to the human eye . [0019] It is a further object of this invention to provide methods and apparatus wherein a dynamic lens surface may be effectively manipulated by the ciliary muscular mechanisms within the eye.

0011[0020] It is another object of the present invention to provide methods and apparatus that utilize pressure applied by the accommodating muscular action to deform an optical surface of the IOL.

0012[0021] It is a further object of this invention to provide methods and apparatus for applying muscular pressure, through one or more actuators, to obtain a mechanical advantage in altering the optical parameters of one or more surfaces of the IOL. [0022] It is yet a further object of this invention to provide methods and apparatus that reduce the possibility of reflections within the IOL arising due to movement of mechanical actuators situated along or near the optical axis of the IOL.

0013[0023] These and other objects of the present invention are accomplished by providing a lens in which force exerted on a fluid reservoir by the movement of the ciliary muscles, zonules and capsule is applied to a dynamic optical surface.

0014[0024] In accordance with the principles of the invention, an IOL is provided having a dynamic lens surface that deflects in response to forces applied to one or more haptics. In a preferred embodiment, the deformable surface is anchored to a substrate near the optical axis of the IOL, and is deformed from an accommodated state to an unaccommodated state by deflection of the periphery of the deformable surface. In this manner, the IOL of the present invention reduces the possibility that light entering the IOL may be reflected due to movement of an actuator disposed at or near the optical axis of the IOL.

0015[0025] In accordance with another aspect of the present invention, a reservoir containing a fluid is disposed in a haptic portion of the IOL, so that compressive forces arising due to movement of the ciliary muscles are transmitted via the haptic portion and fluid to deform the dynamic surface, thereby varying the accommodation of the IOL. [0026] Methods of using the lens of the present invention also are provided.

0016Brief Description Of The Drawings [0027] Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which: [0028] FIG. 1 is a sectional side view of a human eye; [0029] FIGS. 2A and 2B are, respectively, detailed sectional side views of the lens and supporting structures of FIG. 1 illustrating relaxed and contracted states of the ciliary muscles; [0030] FIGS. 3A and 3B are, respectively, an exploded perspective and side sectional view taken along line SB- SB of an exemplary embodiment of an accommodating intraocular lens described in U.S. Patent Publication 2004/0169816 Al; [0031] FIGS. 4A-4C are schematic views of illustrating the use of fulcrum points to facilitate deflection of an optical surface as described in U.S. Patent Publication 2004/0169816 Al; [0032] FIGS. 5A-5D are, respectively, a perspective view, a top view, a cross-sectional perspective view taken along line 5C-5C, and an exploded perspective view of an embodiment of an accommodating intraocular lens of the present invention; and [0033] FIGS. 6A-6D are, respectively, a perspective view, a cross-sectional perspective view taken along line 6B-6B, an exploded perspective view, and a top transparent view of an alternative embodiment of an accommodating intraocular lens of the present invention.

0017Detailed Description Of The Invention [0034] The present invention is directed to an in-situ accommodating intraocular lens system. In accordance with the principles of the present invention, methods and apparatus are provided wherein a lens has an optic element comprising a deformable surface and an actuator that selectively deflects the deformable surface to change an optical power of the lens. In accordance with the principles of the present invention, a central portion of the deformable surface is anchored to a substrate and the lens transitions between the accommodated and unaccommodated positions by deflection of a peripheral region of the deformable surface. [0035] Referring to FIGS. 1 and 2, the structure and operation of a human eye are first described as context for the present invention. Eye 10 includes cornea 11 pupil 12, ciliary muscles 13, ligament fibers 14, capsule 15, lens 16 and retina 17. Natural lens 16 is composed of viscous, gelatinous transparent fibers, arranged in an "onion-like" layered structure, and is disposed in transparent elastic capsule 15. Capsule 15 is joined by ligament fibers 14 around its circumference to ciliary muscles 13, which are in turn attached to the inner surface of eye 10.

0018[0036] Isolated from the eye, the relaxed capsule and lens takes on a spherical shape. However, as described hereinabove, when suspended within the eye by ligament fibers 14, capsule 15 moves between a moderately convex shape (when the ciliary muscles are relaxed) to a highly convex shape (when the ciliary muscles are contracted) . As depicted in FIG. 2A, when ciliary muscles 13 relax, capsule 15 and lens 16 are pulled about the circumference, thereby flattening the lens. As depicted in FIG. 2B, when ciliary muscles 13 contract, capsule 15 and lens 16 relax somewhat, thus allowing the lens and capsule to assume a more spherical shape, and thus increasing the diopter power of the lens. [0037] As discussed hereinabove, commercially available accommodating lenses, such as the Crystalens device by Eyeonics, Inc., Aliso Viejo, California, typically involve converting diametral movements of the ciliary muscle into forward and backward movement of the optic portion of the IOL relative to the retina. This approach is thought to be required because, following extraction of a cataract-effected lens, the capsular bag is very loose, and the ligament fibers that couple the capsule to the ciliary muscles are no longer in tension. Devices such as the Crystalens thus do not employ the natural accommodation mechanisms described above, but instead rely directly on radially inward compressive forces applied by the ciliary muscle to the haptics of the IOL.

0019[0038] In accordance with principles of the present invention, compressive forces applied to the haptics of the IOL are employed to provide accommodation by deflecting a dynamic surface of the lens. This deflection causes a variation in the optical path of light passing through the lens, thus altering its optical parameters .

0020[0039] Referring now to FIGS. 3A and 3B, an embodiment of the accommodating IOL of U.S. Patent Publication No. 2004/0169816 Al is described. In that device, a flexible layer situated between two fluids of different indices of refraction is deflected to vary the accommodating power of the lens. IOL 20 comprises substrate 21, actuator element 22, flexible layer 23 and anterior element 24, assembled in a sandwiched configuration.

0021[0040] Substrate 21 preferably comprises a sturdy transparent polymer and includes posterior lens 25, haptics 26, lower chamber 27, reservoirs 28, passageways 29 and lower relief reservoirs 30. Lower chamber 27 communicates with reservoirs 28 disposed on the ends of haptics 26 via passageways 29. Lower chamber 27, reservoirs 28, passageways 29 and lower relief reservoirs 30 are filled with transparent fluid 31. The outwardly directed surfaces of haptics 26 comprise a resilient elastic material that permits force applied to those surfaces by the ciliary muscles to cause fluid to move from reservoirs 28 through passageways 29 into lower chamber 27.

0022[0041] Actuator element 22 comprises disk-shaped member 32 having a plurality of cells 33 extending upwardly from its upper surface. Each cell 33 illustratively comprises an annular sidewall 34 and top 35. The relative thicknesses of member 32 and sidewalls 34 and tops 35 are selected so that when pressurized fluid is introduced into lower chamber 27, tops 35 of cells 33 extend axially upward. Illustratively, cells 33 are arranged in a ring at a predetermined radius from the optical axis of lens 20, although more or fewer cells 33 may be employed, and their location selected to enhance deflection of layer 23, as described hereinbelow. [0042] Anterior element 24 preferably comprises a rigid transparent material, and includes anterior lens 36, and upper relief reservoirs 37. The interior surface of anterior element 24 is^' convex and forms upper chamber 38, which accommodates upward motion of flexible layer 23, as described hereinbelow. Upper relief reservoirs 37 are disposed in alignment with lower relief chambers 30 in substrate 21, outside the optical path of anterior lens 24. Upper chamber 38 communicates with upper relief reservoirs 37 via passageways 39, and is filled with transparent fluid 40. [0043] Flexible layer 23 is affixed around its circumference to substrate 21 and is disposed in contact with tops 35 of cells 33. Transparent fluid 41 is contained within space 42 between the upper surface of actuator element 22 and lower surface of layer 23. Lower relief reservoirs 30 communicate with space 42 via passageways 43 disposed in substrate 21. A portion of layer 23 divides upper relief reservoirs 37 from lower relief reservoirs 30, for purposes to be described hereinafter. Fluid 41 disposed in space 42, preferably has the same index of refraction as fluid 41 in lower chamber 27, and a different index of refraction than fluid 40 contained in upper chamber 38. [0044] When assembled as shown in FIG. 3B and implanted into the empty capsule of a cataract patient, compressive forces applied by the ciliary muscles cause fluid 31 to move from reservoirs 28 into lower chamber 27, thereby causing tops 35 of cells 33 to extend axially upward. Upward movement of tops 35 of cells 33 in turn causes layer 23 to deflect upward and displace fluid 40 in upper chamber 38. Fluid displaced from upper chamber 38 flows into upper relief reservoirs 37 via passageways 39. [0045] Simultaneously, because lower relief reservoirs 30 communicate with space 42, fluid 41 is drawn from lower relief reservoirs 30 as layer 23 is deflected upward by cells 33. Consequently, the portions of layer 23 that divide upper relief reservoirs 37 from lower relief reservoirs 30 serve as diaphragms that permit fluid to be simultaneously displaced into one reservoir and withdrawn from the other. This enables fluids 40 and 41 to pass freely in and out of the optical space in order to balance relative volumes of fluid, the total volume of fluids 40 and 41 remaining constant. [0046] Movement of layer 23, and the accompanying displacement of volumes of fluid 40 in upper chamber 38 with a corresponding volume of fluid 41 of a different index of fraction in space 42, changes the optical parameters of the lens, thereby moving the focus of the lens from near to far or vice-versa. Posterior lens 25, which in this case comprises a solid material, also provides additional optical power. Posterior lens 25 also may provide optical index dispersion so as to optimize aberration characteristics, including wave aberration of all order, or chromatic aberration. [0047] When the ciliary muscles relax, tops 35 of cells 33 contract, and layer 23 resiliently contracts to its original position. This in turn forces excess fluid 41 in space 42 back into lower relief reservoirs 30. In addition, as the pressure in upper chamber 38 is reduced, fluid 40 is drawn out of upper relief reservoirs 37 and into upper chamber 38.

0023[0048] In the embodiment of FIGS. 3, fluid 31 is forced into cell 33 by ciliary forces acting on the surface of reservoir 28, so that the actuator works in a direction parallel to the optical axis of the lens. As will be appreciated, actuator element 22 must be index matched to fluid 31, which moves with cells 33, as well as fluid 41 that surrounds cells 33 in space 42. Also in the embodiment of FIGS. 3, posterior lens 25 is formed from the same material as substrate 21. Alternatively, posterior lens 25 may comprise a different material than substrate 21, having a shape and optical parameters chosen to optimize the optical performance of the lens system. [0049] Relevant to the IOL of the present invention, cells 33 of the device depicted in FIGS. 3 act not only to deflect layer 23, but also serve as fulcrum contact points. This effect is described generally with respect to FIGS. 4A-4C, wherein the effect of the placement of the fulcrum contact points is described. Generally, fixation within the optical zone of surface 50 (corresponding to flexible layer 23 of the embodiment described hereinabove) , may be accomplished in several fashions depending on the effect and efficiency required of the fluid forces provided by the fluid being moved into the chamber or cell by the forces acting on the reservoirs in the IOL haptics. [0050] If it is desired that surface 50 assume a flatter configuration 50' that provides less optical focusing power (shown in dotted line in FIG. 4A) , then fixation at fulcrum point 51 would be desired. If, on the other hand, it is desired that surface 50 provide more power when the ciliary muscles contract (corresponding to highly convex configuration 50", shown in dotted line in FIG. 4B) , then fixation at fulcrum points 52 would be desirable.

0024[0051] As a further alternative, to obtain most efficient use of fluid power, e.g., to obtain maximal change in optical power for a given movement of surface 50 (corresponding to surface configuration 50''' in FIG. 4C) , some fixation at some intermediate fulcrum point 53 may be desired. Fulcrum point 53 also may be selected so as to minimize the change in the volumes of the total fluid within the optical zone, thereby obviating the need for relief reservoirs to absorb excess fluid volumes. In this latter case, deflection of the flexible layer causes sufficient redistribution of the fluids within the first and second chambers to alter the power of the lens. [0052] The foregoing discussion of fulcrum points may be advantageously employed not only in a two fluid system as described in U.S. Patent Publication No. 2004/0169816 Al, but also in a system such as described in commonly assigned U.S. Patent Publication No. 2005/0119740. In the accommodating IOL described in that application, one or more actuators disposed near the optical axis of a deformable lens element are employed to transition the lens between accommodated and unaccommodated states. [0053] In accordance with the principles of the present invention, the fulcrum concepts discussed above with respect to FIGS. 4A-4C are applied to a lens system similar to that of U.S. Patent Publication No.

00252005/0119740 Al to reduce the potential for reflections to arise from movement of the actuator disposed near the optical axis of the IOL. In particular, the actuators are moved to the periphery of the deformable lens element, while the center of the dynamic surface, along the optical axis of the IOL, is anchored to the lens substrate .

0026[0054] Referring now to FIGS. 5A-5D, a first embodiment of an IOL constructed in accordance with the principles of the present invention is described. IOL 60 is similar in design to the IOL of U.S. Patent Publication No. 2005/0119740 Al, except that in IOL 60 the actuators are disposed at the periphery of the anterior lens element. IOL 60 operates in the manner described for the dynamic surface of FIG. 4A, with its anterior lens element anchored to the lens substrate. Actuation of the actuators disposed at the periphery of the anterior lens element lift the edges of the lens element, thereby flattening the surface and reducing accommodation of the IOL. Conversely, lowering of the periphery of the anterior lens increases convexity and accommodation of IOL 60. [0055] As will be explained more fully below, IOL 60 assumes an accommodated position in its relaxed state, i.e., when no outside forces are acting on it. After implantation in a patient's eye, the IOL assumes the accommodated configuration when the ciliary muscles contract and the capsule relaxes. In contrast, when the ciliary muscles relax and the capsule is pulled taut, forces applied by the capsule to the haptic cause the IOL to transition to the unaccommodated state. [0056] IOL 60 comprises optic portion 61 and haptic portion 62. Optic portion 61 includes anterior lens element 63, substrate 64 and posterior lens surface 65. Haptic portion 62 illustratively comprises four deformable tubular members 66 mounted on extensions 67 projecting from substrate 64.. It should be understood that the invention may be practiced with more or less tubular members than shown in FIGS . 5. [0057] Substrate 64 preferably comprises a sturdy transparent polymer illustratively has posterior lens surface 65 integrally formed thereon. Anterior lens element 63 is coupled to the center of substrate 64 by anchor 68, while the periphery of the lens element is sealed to the edge of substrate 64 by sidewall 69. Anterior lens element 63 also includes a flexible circular partition 70 coupled to the substrate to define annular chamber 71. Space 72 defined by anterior lens element 63 and substrate 64 inward of partition 70 preferably is filled with fluid 73, such as a silicone oil, having a refractive index that matches the surrounding components of optic portion 61. [0058] Substrate 64 includes one or more relief reservoirs 74 disposed near the periphery of posterior lens surface 65 that communicate with space 72 via channels 75. Substrate 64 further includes peripheral passageway 76 that communicates with annular chamber 71 and the interior of tubular members 66 via passageways 77. The interior of tubular members 66, annular chamber 71, peripheral passageway 76 and passageways 77 all are filled with fluid 78 having an index of refraction matched to the surrounding components. Fluid 78 preferably, but need not be, the same as fluid 73 in space 72. [0059] Tubular members 66 include flexible fluid-tight endcaps 79 and are attached to extensions 67 of substrate 64 using a suitable biocompatible adhesive, thermal bonding, or other methods known in the art. Tubular member 66 preferably has a substantially circular cross- section in the relaxed state, i.e., when no forces are acting on it. The tubular members of haptic portion 62 are configured so that forces applied by the capsule to the anterior and posterior faces of the tubular members causes the tubular members to transition to an ellipsoidal shape, thereby inducing fluid 78 to flow through passageways 77 and into annular chamber 71 via peripheral passageway 76. When the lateral forces applied to the tubular member subside, for example, when the capsule becomes loose as a consequence of ciliary muscle contraction, tubular members 66 return to their unstressed shapes, causing fluid to flow from annular chamber 71 back to the interior of the tubular members. [0060] In accordance with the principles of the present invention, anchor 68 serves as the function of fulcrum point 51 of FIG. 4A, while annular chamber 71 serves as actuator. When fluid moves from the haptic portion 62 to annular chamber 71, the periphery of the anterior lens element lifts upwards, thereby flattening the lens surface and reducing the diopter power of the lens. To account for the increase in volume in space 72 resulting from lifting of the edges of anterior lens element 73, fluid 78 is drawn from flexible reservoirs 74 into space 72 via passageways 75. Likewise, when the lens moves to its accommodated state, fluid 78 moves through passageways 75 back to flexible reservoirs 74. [0061] In operation, when implanted in an eye, tubular members 66 of haptic portion 62 have a substantially circular shape when the ciliary muscles are contracted. This corresponds to the maximum volume of the interior of tubular members 66 and the minimum volume of fluid 73 in annular chamber 71. When the ciliary muscles relax, the capsule is pulled taut by the zonules and applies compressive forces to the anterior and posterior surfaces of tubular members 66. This causes the tubular members to deform to a non-circular cross-section, thereby squeezing fluid into annular chamber 71. Sidewall 69 and partition 70 expand responsive to the increased volume in annular chamber 71, thereby lifting the edge of anterior lens element 63. The increased volume of space 72 arising from this movement is made up by transfer of fluid 78 from flexible reservoirs 74 to space 72 via passageways 75. These actions result in IOL 60 assuming a less accommodated configuration.

0027[0062] When the ciliary muscles relax, tubular members 66 are no longer subjected to lateral compressive forces, and return to their unstressed geometry. This in turn reduces the volume of fluid in annular chamber 71, causing sidewall 69 and partition 70 to return to their undeformed shapes, thereby increasing the convexity of anterior lens element 63. Fluid 82 is likewise forced from space 72 between anterior lens element 63 and substrate 64, through passageway 75 and back into flexible reservoirs 74. IOL 60 thus returns to its accommodated configuration. [0063] IOL 60 may be manufactured as described above with predetermined volumes of fluids 73 and 78. Alternatively, tubular members 66 and/or flexible reservoirs may comprise a semi-permeable osmotic material and IOL manufactured to contain smaller amounts of fluids 73 and 78 than may be desired for operation of the IOL. In this alternative embodiment, IOL 60 may be implanted in a slightly collapsed state, thereby facilitating insertion. Subsequently, the osmotic gradient may cause water in the eye to permeate the tubular member and/or flexible reservoirs to increase the volume of fluids 73 and 78 to provide correction functioning of IOL 60. [0064] Referring now to FIGS. 6, an alternative embodiment of an IOL of the present invention is described. Like the embodiment of FIGS. 5, IOL 80 also has the center of the anterior lens element fixed to the substrate, so that the edges of the lens element lift to transition the IOL to the unaccommodated state. [0065] IOL 80 assumes an accommodated position when no outside forces are acting on it. After implantation in a patient's eye, the IOL assumes the accommodated configuration when the ciliary muscles contract. In contrast, when the ciliary muscles relax and the capsule is pulled taut by the zonules, the capsule applies forces to the haptic portion of the IOL, which in turn causes the IOL to transition to the unaccommodated state. [0066] IOL 80 comprises optic portion 81 and haptic portion 82. Optic portion 81 shapes and focuses light on the optic nerve while haptic portion 82 orients and supports the IOL with the capsule and actuates the accommodating mechanism of the IOL. As depicted in FIG. 6C, IOL 80 illustratively comprises anterior portion 83 affixed to posterior portion 84. [0067] Anterior portion 83 comprises a flexible optically transparent material that forms anterior lens element 85. Anterior lens element 85 includes anchor 86 that extends posteriorly from the center of the lens element 85. Lens element 85 is coupled around its edge 87 to haptic half 88 by flexible membrane 89. Spacers 90 also extend posteriorly from the interior surface of anterior portion 83. Posterior portion 84 comprises sturdy optically transparent polymer substrate 91, posterior lens surface 92 and posterior haptic half 93, peripheral step 94 and receptacle 95.

0028[0068] Anterior portion 83 is configured to attach to posterior portion 84 so that anchor 85 is fixedly received within receptacle 95, spacers 90 seat against peripheral step 94, and posterior haptic half 93 sealingly mates with anterior haptic half 88, as depicted in FIG. 6B. When so assembled, haptic halves 88 and 93 form chamber 96 that communicates with space 97 between anterior lens element 85 and substrate 92 through channels 98 disposed between spacers 90. The interior volume of the IOL, including chamber 96 and space 97, is filled with transparent fluid 99, which has an index of refraction selected to match the index of refraction of the surrounding components of IOL 80. Flexible membrane 89 allows edge 87 of anterior lens element 84 to move away from substrate 91 responsive to pressure variations in haptic portion 82.

0029[0069] In accordance with the present invention, haptic halves 88 and 93 of haptic portion 82 comprise a resilient elastic material that permits force applied to those surfaces to the haptic portion to deform. Preferably, when the ciliary muscles contract, the haptic portion is in an unstressed state and assumes a substantially circular cross-section. This corresponds to a maximum internal volume of chamber 96 and a minimum volume of space 97.

0030[0070] When the ciliary muscles relax, the zonules pull the capsule taut, thereby applying compressive forces to the anterior and posterior faces of the haptic portion which in turn cause fluid 99 to pass from chamber 96 through channels 98 and into space 97. Fluid entering space 97 causes edge 87 of anterior lens element 85 to lift in the anterior direction, thereby reducing the convexity of the anterior lens element and reducing the diopter power of the lens. The flexible nature of membrane 89 permits edge 87 to freely deflect when the volume of space 97 increases. [0071] The volume of fluid 99 preferably is selected so that when no external pressure is applied to IOL 80, fluid 99 fills the interior of the IOL and anterior lens element 85 has its most convex shape. Therefore, when pressure is applied to haptic portion 82, fluid 99 migrates beneath anterior lens element 85 to cause IOL 80 to transition to the unaccommodated state.

0031[0072] In addition, the anterior surface of substrate 91 preferably has a predetermined anterior profile, so that in the event of a loss of fluid 99 from the IOL, e.g., resulting in a failure of a seal, the IOL conforms to the anterior profile of the substrate and thus still provides the patient with a desired degree of correction. In a preferred embodiment, substrate 91 is symmetrical, such that peripheral step 94 has a uniform depth. In this case, anterior portion 81 may be attached to substrate 91 at any relative rotational angle. [0073] Anterior lens element 85 may have a constant thickness from the center to the outer edge, or a variable thickness. For example, the anterior lens element may be thinner near anchor 86 with an increasing thickness toward edge 87. Alternatively, the anterior lens element may be thicker near the anchor with a decreasing thickness toward edge 87. [0074] While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.