Abstract:
An accommodating intraocular lens is provided having optical parameters that are altered in-situ, wherein an optic portion of the lens includes a lens piston that alters the shape of a lens element of the lens to alter the optical power of the lens, responsive to forces applied to a haptic portion to the lens by contraction of the ciliary muscles. Forces applied to the haptic portion are concentrated by the lens piston to provide a greater dynamic range, and may be further augmented by the use of haptic pistons disposed in the haptic portion of the lens.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/734,514, filed Dec. 12, 2003, now issued as U.S. Pat. No. 7,122,053, and claims the benefit of priority from U.S. provisional patent application Ser. No. 60/433,046, filed Dec. 12, 2002. 
    
    
     FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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&#39;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. 
     A cataract is any opacity of a patient&#39;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. 
     In treating a cataract, the surgeon removes the crystalline lens matrix from the lens capsule and replaces it with an intraocular lens (“IOL”) 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. 
     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. 
     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 “onion-like” layered structure, forces applied to the capsule by the ciliary muscles cause the lens to change shape. 
     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. This mechanism, called the “ciliary process” increases the diopter power of the lens. 
     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 known as “presbyopia”. Because the imaging distance is fixed, presbyopia typically entails the need for bi-focals to facilitate near and far vision. 
     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. 
     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 these 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. 
     U.S. Pat. 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. Pat. 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. Pat. No. 4,932,966 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 layers to provide accommodation. 
     Although fluid-actuated mechanisms such as described in the aforementioned patents have been investigated, accommodating lenses currently nearing commercialization, such as developed by Eyeonics, Inc. (formerly C&amp;C Vision, Inc.) of Aliso Viejo, Calif., rely on ciliary muscle contraction of the IOL haptics to move the optic towards or away from the retina to adjust the focus of the device. 
     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. 
     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. 
     It still further would be desirable to provide methods and apparatus that utilize pressure applied by the accommodating muscular action to obtain a volumetric mechanical advantage in deflecting 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 such volumetric mechanical advantage. 
     SUMMARY OF THE INVENTION 
     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. 
     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. 
     It is another object of the present invention to provide methods and apparatus that utilize pressure applied by the accommodating muscular action to obtain volumetric mechanical advantage in deflecting an optical surface of the IOL. 
     It is a further object of this invention to provide methods and apparatus for reversibly applying muscular pressure, through one or more actuators, to obtain a volumetric mechanical advantage in altering the optical parameters of one of more surfaces of the IOL. 
     These and other objects of the present invention are accomplished by providing an intraocular lens responsive to variations in capsule shape and/or forces exerted by the ciliary muscle to actuate one or more transducers. The transducers are coupled to a lens piston that deflects a surface of the lens, e.g., from a moderately convex to a highly convex shape. In accordance with the principles of the present invention, the lens piston provides a significant volumetric mechanical advantage in effecting deflection of an anterior or posterior surface of the lens, and greater dynamic range, compared to previously-known fluid-mediated accommodation systems. 
     In the context of the present invention, “volumetric mechanical advantage” means that a motion of the ciliary muscle, e.g., 100 microns, is amplified by the ratio of the transducer area over which force is applied to the area of the lens piston. It is expected that ratios of two or more may be achieved, but a ratio of one also is expected to be adequate for most patient populations. Operation of the lens piston may be enhanced using one or more haptic pistons that provide a further volumetric mechanical advantage compared to previously-known fluid-mediated accommodation systems. 
     In a preferred embodiment, the intraocular lens comprises an optic portion and a haptic (or non-optic) portion. The optic portion comprises a light transmissive substrate defining one or more fluid channels, one or more lens pistons coupled in fluid communication with the fluid channels, and anterior and posterior lens elements. One of the anterior and posterior lens elements includes a deflectable surface that is operatively coupled to the one or more lens pistons so that movement of the lens pistons causes the anterior or posterior lens to deflect. The other of the anterior or posterior lens elements may be coupled to the substrate or integrally formed therewith. 
     The haptic portion is disposed at the periphery of the optic portion and may comprise one or more arms that extend outward from the optic portion, each arm including a fluid channel coupled in fluid communication with the fluid channels in the optic portion. The haptic portion includes one or more transducers that engage the interior of the capsule and/or ciliary muscle, so that action of the ciliary process is communicated via the fluid channels to the one or more lens pistons. More preferably, the transducers further comprise a haptic piston including a force-concentrating element operatively coupled to a diaphragm. 
     In accordance with one aspect of the present invention, the transducer may be biased to maintain the lens piston in an accommodated state. For such embodiments, relaxation of the ciliary muscle causes the zonules to transition the capsule to an ellipsoidal shape. The capsule thereby applies compressive forces that deform the transducer, reduce fluid pressure in the lens piston, and cause the lens to transition to the unaccommodated state. Alternatively, the lens piston may not be pressurized when the transducer is in the undeformed state. In this latter case, the lens may be configured so that contraction of the ciliary muscle induces thickening near the capsular equator, which in turn compresses the transducer to pressurize the lens piston and transition the lens to the accommodated state. 
     The haptic pistons, lens piston(s) and fluid volumes may be manufactured so as to provide predetermined actuation forces appropriate for predetermined populations of patients, or alternatively may be tailored on a patient-by-patient basis, thereby enhancing the ability of the intraocular lens to adjust to different optical focusing powers and force magnifications. 
     In addition, the haptic portion may include one or more features, such as flanges, that apply a force on the capsular bag to maintain tension on the zonules. This arrangement enables the transducer to follow the equator of the capsule. 
     Methods of making and using the lens of the present invention also are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a sectional side view of a human eye; 
         FIGS. 2A and 2B  are, respectively, sectional side views of the lens and supporting structures of  FIG. 1  illustrating relaxed and contracted states of the ciliary muscles; 
         FIGS. 3A and 3B  are, respectively, an exploded perspective view and side sectional view, taken along line  3 B- 3 B of  FIG. 3A , of an exemplary intraocular lens of the present invention; 
         FIG. 4  is a perspective view of an alternative embodiment of lens pistons suitable for use in the intraocular lens of  FIG. 3 ; 
         FIGS. 5A and 5B  are, respectively, side sectional views of the haptic portion of the lens of  FIG. 3  in the accommodated and unaccommodated states; 
         FIGS. 6A-6C  are, respectively, a perspective view of the lens of  FIG. 3  disposed in a human eye and side sectional views of the lens in the accommodated and unaccommodated states; 
         FIGS. 7A-7C  are, respectively, a perspective view and side sectional views in the accommodated and unaccommodated states of an embodiment of the intraocular lens of the present invention that is directly actuated by ciliary muscle; 
         FIGS. 8A-8C  are, respectively, a perspective view and side sectional views in the accommodated and unaccommodated states of a further alternative embodiment of the intraocular lens of the present invention; 
         FIGS. 9A-9C  are, respectively, a perspective view and side sectional views in the accommodated and unaccommodated states of another alternative embodiment of the intraocular lens of the present invention; 
         FIGS. 10A-10C  are, respectively, a perspective view and side sectional views in the accommodated and unaccommodated states of a further embodiment of the intraocular lens of the present invention; 
         FIGS. 11A-11C  are, respectively, a perspective view and side sectional views in the accommodated and unaccommodated states of still another embodiment of the intraocular lens of the present invention; and 
         FIGS. 12A-12C  are, respectively, a perspective view and side sectional views in the accommodated and unaccommodated states of yet another embodiment of the intraocular lens of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the principles of the present invention, an intraocular lens is provided having a haptic portion and a light-transmissive optic portion. The optic portion contains one or more fluid-mediated pistons arranged to apply a deflecting force on an anterior or posterior element of the lens to provide accommodation of the lens. As used herein, the lens is fully “accommodated” when it assumes its most highly convex shape, and fully “unaccommodated” when it assumes its most flattened, ellipsoidal state. The lens of the present invention is capable of dynamically assuming any desired degree of accommodation between the fully accommodated state and fully unaccommodated state responsive to the ciliary process. 
     Forces applied to a transducer disposed in the haptic portion by the ciliary process are communicated to one or more lens pistons that control deflection of an anterior or posterior element of the lens, resulting in a larger dynamic range of accommodation than heretofore is believed to have been available. The lens piston and surrounding fluids all are index-matched to prevent the occurrence of optical aberrations throughout the range of motion of the lens piston. 
     In accordance with another aspect of the present invention, the transducer may include one or more haptic pistons that provide a volumetric mechanical advantage with respect to forces applied by the ciliary process to the lens piston. 
     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 , iris  12 , ciliary muscles  13 , ligament fibers or zonules  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 zonules  14  around its circumference to ciliary muscles  13 , which are in turn attached to the inner surface of eye  10 . Vitreous  18  is a thick, transparent substance that fills the center of eye  10 . 
     Isolated from the eye, the relaxed capsule and lens takes on a spherical shape. However, when suspended within the eye by zonules  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 and become thicker. This allows the lens and capsule to assume a more spherical shape, thus increasing the diopter power of the lens. 
     Accommodating lenses currently nearing commercialization, such as the Crystalens device under development by Eyeonics, Inc., Aliso Viejo, Calif., typically involve converting diametral movements of the ciliary muscle into forward and backward movement of an 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 capsule is very loose, and the zonules 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. 
     By contrast, according to one aspect of the present invention, an intraocular lens is designed to engage capsule  15  and to transition between the accommodated and unaccommodated states responsive to forces applied to capsule  15  by ciliary muscle  13  and zonules  14 , thereby more closely mimicking operation of the natural eye. Alternatively, the haptic portion may be disposed directly in contact with the ciliary muscle. 
     Referring to  FIGS. 3A and 3B , an exemplary embodiment of an intraocular lens constructed in accordance with the principles of the present invention is described. IOL  20  comprises optic portion  21  and haptic portion  22 . Optic portion  21  is constructed of light transmissive materials, while haptic portion  22  is disposed at the periphery of the optic portion and does not participate in focusing light on the retina of the eye. 
     Optic portion  21  comprises anterior lens element  23 , actuator layer  24  including lens piston  25 , substrate  26  and posterior lens element  27 , all made of light-transmissive materials, such as silicone or acrylic polymers or other biocompatible materials as are known in the art of intraocular lenses. Haptic portion  22  illustratively comprises arms  28  and  29  extending from substrate  26 , although other haptic configurations may be employed. Each of arms  28  and  29  terminates in transducer  30 . Transducers  30  preferably each comprise a haptic piston including force-concentrating fin  31 , diaphragm  32  and reservoir  33 . Reservoirs  33  are coupled in fluid communication with the interior of lens piston  25  via channels  34  that extend from the reservoirs to well  35  disposed beneath lens piston  25 . 
     In  FIG. 3B , transducers  30  are in an undeformed state in which force-concentrating fins  31  apply a maximum deflection to diaphragms  32 , thereby fully deflecting end wall  41  and driving anterior element  23  to the fully accommodated position. This corresponds to a fully-contracted state of the ciliary muscles, as described herein below. 
     Actuator layer  24  is disposed in recess  36  of substrate  26 , and preferably comprises a sturdy elastomeric material. Actuator layer  24  isolates the fluid in channels  34 , well  35  and the interior of lens piston  25  from the fluid disposed in the space  37  between anterior lens element  23  and actuator layer  24 . Fluids  38  and  39  disposed, respectively, within channels  34  and space  37 , preferably comprise silicone or acrylic oils and are selected to have refractive indices that match the materials of anterior lens element  23 , actuator layer  24  and substrate  26 . 
     In a preferred embodiment, lens piston  25  includes substantially nondeformable cylindrical side wall  40  coupled to expandable end wall  41 . End wall  41  is configured to deflect outward responsive to pressure applied within sidewall  40  by fluid movement from the haptic portion. End wall  41  contacts the interior surface of anterior lens element  23 , so that deflection of end wall  41  of the lens piston causes a corresponding deflection of anterior lens surface  23 . Such deflections cause the anterior lens element to assume a spherical shape with a shorter radius of curvature, thereby changing the diopter power of the lens. As will of course be understood, optic portion could instead be arranged so that the lens piston deflects posterior lens element  27 ; the arrangement depicted in  FIG. 3  is illustrative only. 
     The inner surface and thickness of anterior element  23  (relative to the optical axis of the lens) are selected so that the outer surface of anterior element  23  retains an optically corrective shape, e.g., spherical, throughout the entire range of motion of lens piston  25 , e.g., for accommodations 0-10 diopters. It should of course be understood that the inner surface and thickness of anterior element  23  may be selected to provide an aspherical outer surface, as required for a desired degree of optical correction. 
     As shown in  FIG. 3 , one preferred embodiment of actuator layer  24  includes a single lens piston  25  located at the center of optic portion  21 . Alternative embodiments of actuator layer  24 ′ may include an array of lens pistons  25 ′ spaced apart in a predetermined configuration on the anterior surface of the actuator layer, as depicted in  FIG. 4 , as may be required to impose a desired pattern of localized deflection on the anterior lens element. As will be apparent to one of skill in the art, an annular structure may be substituted for the individual lens pistons depicted in  FIG. 4 , and side walls  40  may be of any desired shape other than cylindrical. 
     Referring now to  FIGS. 5A and 5B , haptic pistons  42 , constructed in accordance with the principles of the present invention are described in greater detail. Haptic pistons comprise flexible and resilient transducers  30  that support force-concentrating fins  31  biased against diaphragms  32 . Each diaphragm  32  comprises an elastomeric cover for a corresponding reservoir  33  filled with fluid  38 . As described herein above, fluid  38  communicates through channels  34  into well  35  and the interior of lens piston  25 . Transducers  30  are constructed from a resilient, elastomeric material that changes shape responsive to forces applied by capsule  15  from the ciliary muscles  13  and zonules  14 . 
     In  FIG. 5A , haptic piston  42  is shown in an undeformed state (as in  FIG. 3B ), corresponding to the ciliary muscles being fully contracted. In this state, the apex of fin  31  bears against diaphragm  32  to develop the maximum force resulting from the bias of transducer  30 . Inward displacement of diaphragm  32  in turn displaces fluid through channels  34  (see  FIG. 3 ) to well  35 , resulting in expansion of end wall  41  of lens piston  25 . When transducer  30  is in the undeformed state, fin  31  displaces the maximum volume of fluid from the haptic portion to lens piston  25 , resulting in the maximum deflection of anterior element  23 , and thus the maximum degree of accommodation of the lens. This corresponds to the state in which the ciliary muscles are fully contracted, and zonules  14  and capsule  15  apply the least amount of compressive force to the anterior and posterior surfaces of transducer  30 . 
     When the ciliary muscles relax, however, the tension in the zonules increases, causing capsule  15  to assume an ellipsoidal shape (see  FIG. 2A ) and the lens to transition to its unaccommodated state. When the capsule becomes taut, it applies compressive forces F to the anterior and posterior surfaces of transducer  30 , causing the transducer to deform to the elliptical shape depicted in  FIG. 5B . Deformation of transducers  30  moves fins  31  away from diaphragms  32 , thereby unloading the diaphragms and reducing the fluid pressure applied to lens piston  25 . This in turn permits lens piston  25  to move to an undeflected state, reducing deflection of anterior lens element  23  and returning the lens to an unaccommodated state. 
     Referring now to  FIGS. 6A to 6C , IOL  20  is shown implanted into capsule  15  of human eye  10 . When so implanted, haptic arms  28  and  29  support the IOL within the capsule, while transducers  30  engage the interior of the capsule at locations adjacent to ciliary muscles  13 . In  FIG. 6B  the ciliary muscles are shown in a contracted state, in which the compressive forces applied by zonules  14  and capsule  15  to transducers  30  is lowest and transducers  30  assume the undeformed position. This also corresponds to transducers  30  applying the least tension to capsule  15  and zonules  14 . As discussed above, in the undeformed position, fins  30  are biased against diaphragms  32 , displacing fluid  38  from reservoirs  33  to the lens piston. In  FIG. 6C , the ciliary muscles are relaxed, and zonules  14  pull capsule  15  taut into an ellipsoidal shape. As noted above, in this state the capsule applies compressive forces to the lateral surfaces of transducers  30  that ensure that lens piston  25  is drawn to its fully retracted position. 
     In accordance with one aspect of the present invention, the volume of fluid in the accommodating lens may be selected so that the forces required to provide a useable range of accommodation are satisfactory for a preselected population of patients. Alternatively, the volume of fluid used in IOL  20  may be specified during manufacture for a given patient, or may be adjusted prior to implantation of the IOL on a patient-by-patient basis. In this manner, the forces developed by lens piston  25  and haptic pistons  42  may be tailored for a specific patient. In addition, the number, shape and placement of lens pistons  25 ′ on actuator layer  24 ′ may be selected, e.g., prescribed during manufacture, to optimize accommodation of the lens for a specific patient. 
     It may been noted that in the undeformed state, transducers  30  maintain the lens in the accommodated or high power state. Accordingly, any failure that allows the transducers to assume the undeformed state without any physiologic influence could result in a residual near-sighted condition. In accordance with another aspect of the present invention it would be advantageous to provide for a mechanism to relieve a small amount of quiescent pressure within the lens so that the lens piston assumes the unaccommodated, low power state. 
     To accomplish this result, a relief valve in the form of a sacrificial plug may de disposed on a channel that leads to an evacuated cavity. The plug may be constructed of material that remodels when activated by a laser to permit a reduction of the pressure in the lens piston, and thereby allowing the anterior lens element to assume the unaccommodated state. The plug preferably comprises a colored material that readily and preferentially absorbs laser light, for example, 1.06 micron wavelength radiation from a Nd:YAG laser. When irradiated, the plug experiences a phase change or otherwise deforms to permit a predetermined quantity of fluid in the channel  34  to enter the evacuated cavity. 
     Referring now to  FIGS. 7A to 7C , an alternative embodiment of the IOL of the present invention is described. IOL  50  comprises optic portion  51  and haptic portion  52 . Optic portion  51  comprises anterior lens element  53  and substrate  54  formed of light-transmissive materials. Substrate  54  includes lens piston  55  having expandable end wall  56 , and fluid channels  57  in fluid communication with the interior of lens piston  55 . Expandable end wall  56  contacts the inner surface of anterior lens element  53 , so that deflection of end wall  56  causes anterior lens element  53  to assume a more convex shape. The thickness profile of anterior lens element  53  is tailored to a desired degree of optical correction when deflected, as previously described. Channels  57  and space  58 , disposed between anterior lens element  53  and substrate  54 , are filled with fluid  59  having an index of refraction that is matched to the materials of anterior lens element  53  and substrate  54 . Substrate  54  may include integrally formed posterior lens element  60 . 
     Haptic portion  52  is disposed at the periphery of optic portion  51 , and includes transducers  61  that include force-concentrating fins  62  coupled to diaphragms  63 . Fluid channels  57  extend circumferentially along the edges of substrate  54  for an arc-length corresponding to the arc-length of haptic portions  52  to form edge recesses  64  that function as reservoirs. Transducer  61 , fin  62 , diaphragm  63  and edge recess  64  together form a haptic piston that adjusts the deflection of end wall  56  of lens piston  55  responsive to contraction and relaxation of the ciliary muscle, zonules and capsule. 
     As in the embodiment of  FIGS. 3-6 , transducers  61  are constructed so that, in the undeformed state, they bias force-concentrating fins  62  to cause the maximum inward displacement of diaphragms  63 . Because diaphragms  63  of the haptic pistons are coupled to fins  62 , compressive forces applied to the anterior and posterior faces of transducers  61  by the capsule during relaxation of the ciliary muscles urges the IOL to its unaccommodated state by deforming transducers  61  and withdrawing fluid from lens piston  55 . 
     As illustrated in  FIG. 7B , contraction of the ciliary muscles causes the zonules and capsule to relax, thereby reducing the compressive forces applied by the capsule to transducers  61 . This permits transducers  61  to return to an undeformed state in which fins  62  extend radially inward to displace diaphragms  63  into edge recesses  64 . This in turn displaces fluid  59  to the lens piston, causing end wall  56  to deflect anterior lens element  53  to the accommodated state. 
     Relaxation of the ciliary muscles causes the zonules and capsule to become taut, thereby compressing transducers  61  to deform to the position shown in  FIG. 7C . More specifically, the compressive forces applied by the zonules and capsule deform transducers  61  to an elongated shape. This in turn causes fins  62  and diaphragms  63  to deflect outward away from edge recesses  64 , and draw fluid from lens piston  55 , returning the lens to its unaccommodated state. 
     Referring to  FIGS. 8A-8C , another alternative embodiment of the intraocular lens of the present invention is described. IOL  70  includes optic portion  71  and haptic portion  72 . IOL  70  differs from the IOL  50  primarily in that haptic portion  72  is disposed around the entire optic portion, and in addition haptic portion  72  omits the use of haptic pistons, as in the preceding embodiments. 
     Optic portion  71  comprises anterior lens element  73  and substrate  74  formed of light-transmissive materials. Substrate  74  includes lens piston  75  having expandable end wall  76 , and fluid channels  77  in fluid communication with the interior of lens piston  75 . Expandable end wall  76  contacts the inner surface of anterior lens element  73 , so that deflection of end wall  76  causes anterior lens element  73  to assume a more convex shape, as in the preceding embodiments. The thickness profile of anterior lens element  73  is tailored to produce a desired degree of accommodation when deflected, as previously described. Channels  77  and space  78 , disposed between anterior lens element  73  and substrate  74 , are filled with fluid  79  having a matched index of refraction. Substrate  74  may define a posterior lens surface  80 , or may include a separate lens element. 
     Haptic portion  72  is disposed surrounding the periphery of optic portion  71 , and includes transducer  81 . Transducer  81  comprises diaphragm  82  including elastomeric ring  83  disposed along the midline of the diaphragm that biases the ring to the radially compressed state depicted in  FIGS. 8A and 8B . This state corresponds to the maximum deflection of lens piston  75 , and thus the state of maximum accommodation of lens  70 . Ring  83  also ensures that diaphragm  82  engages and applies tension to the capsule. Transducer  81  adjusts the deflection of end wall  76  of lens piston  75  responsive to contraction and relaxation of the ciliary muscle, zonules and capsule. 
     More specifically, contraction of the ciliary muscles causes the zonules and capsule to relax, thereby reducing the compressive forces applied by the capsule to transducer  81 . This permits the transducer to return to an undeformed state, in which ring  83  biases diaphragm  82  to displace fluid to lens piston  75 . This in turn causes end wall  76  to deflect anterior lens element  73  to the accommodated state. 
     Relaxation of the ciliary muscles causes the zonules and capsule to become taut, thereby applying compression to the anterior and posterior surfaces of transducer  81  to deform to the diaphragm to the position shown in  FIG. 8C . In particular, the compressive forces applied by the zonules and capsule deform transducer  81  to an elongated shape that reduces the pressure on fluid  59  and permits end wall  76  of lens piston  75  to transition to the undeflected state shown in  FIG. 8C . This in turn reduces deflection of anterior lens element  73  and returns the lens to its unaccommodated state. 
     Referring now to  FIGS. 9A-9C , a second family of embodiments of intraocular lenses is described. Unlike the preceding embodiments, in which action of the ciliary muscle is transmitted to the IOL via the zonules and capsule, in this embodiment action of the ciliary muscle directly against the transducer is communicated to the lens piston. As depicted in  FIG. 9A , IOL  90  may be implanted anterior to the capsule, and includes optic portion  91  and haptic portion  92 . 
     Optic portion  91  comprises anterior lens element  93  and substrate  94  formed of light-transmissive materials. Substrate  94  includes lens piston  95  having expandable end wall  96 , and fluid channels  97  in fluid communication with the interior of lens piston  95 . Expandable end wall  96  contacts the inner surface of anterior lens element  93 , so that deflection of end wall  96  causes anterior lens element  93  to assume a more convex shape. As in the preceding embodiments, the thickness profile of anterior lens element  93  may be tailored to produce a desired degree of accommodation when deflected. Channels  97  and space  98 , disposed between anterior lens element  93  and substrate  94 , are filled with fluid  99  having a matched index of refraction. Substrate  94  may define a posterior lens surface  100 , or may include a separate lens element. 
     The optical power provided by posterior lens surface  100  may be used to provide the base power of the device, and may be tailored for specific patient population. The profile of posterior lens surface  100  also may be chosen to provide optimal performance of the optical system in concert with the optical correction provided by anterior lens element  93  throughout its range of motion. 
     In addition or alternatively, any error of the refractive surface of anterior lens element  93 , for example 1 or 2 microns or less of wave error that the surface experiences throughout its range of motion, may be further reduced by adding a small compensating thickness to anterior lens element  93 , in exactly the reverse sense of the error, e.g., corresponding to the average error incurred at each point on anterior lens element  93  through its range of motion. 
     Haptic portion  92  includes a plurality of transducers  101 , each transducer comprising diaphragm  102 . Transducers  101  are designed to directly engage the ciliary muscle in the area of the sulcus, and comprise resilient, flexible diaphragms  102  that have an undeformed shape depicted in  FIG. 9C . The interiors of diaphragms  102  form reservoirs  103  communicate with channels  97 , and are filled with index-matched fluid  99 . 
     Contraction of the ciliary muscles applies a radially compressive force to the transducers that transitions the diaphragms to the shape depicted in  FIG. 9B . This causes fluid to be displaced from reservoirs  103  of transducers  101 , pressurizing the fluid in channels  99  and lens piston  95 . Responsive to this pressure increase, end wall  96  of the lens piston expands anteriorly, deflecting anterior lens element  93  and transitioning the lens to the accommodated state, as shown in  FIG. 9B . 
     When the ciliary muscle subsequently relaxes, the radially compressive forces applied by the muscles diminish, transducer  101  returns to an undeformed state of  FIG. 9C , and lens piston resumes its unexpandable position. This in turn reduces deflection of anterior lens element  93  and returns the lens to its unaccommodated state. 
     While the design of the haptic portion of the embodiment of  FIG. 9  is similar to those of previously-known fluid-mediated accommodating intraocular lenses, such as those described in the aforementioned patent to Christie, the presence of lens piston  95  is expected to provide significantly greater volumetric mechanical advantage and greater dynamic range than could be achieved with prior art designs. 
     Whereas previously-known designs distribute a pressure increase resulting from action of the ciliary muscle over the entire surface of the lens, the lens piston of the present invention amplifies motion of the ciliary muscle, e.g., 100 microns, by the ratio of the transducer area to the area of the lens piston. It is expected that ratios of 2 or more may be readily achieved, however, a ratio of one may be sufficient for many patient populations. Accordingly, the amount of fluid that must be displaced to optically correct axial displacement of the refractive surface of anterior lens element  23  is relatively small. 
     With respect to  FIGS. 10A-10C , a third family of embodiments of the intraocular lens of the present invention is described. Like the embodiments of  FIGS. 3-8 , IOL  110  is implanted within the capsule, includes haptic pistons, and is actuated by action of the ciliary muscles, zonules and capsule. However, as in the embodiment of  FIG. 9 , the lens is unaccommodated in its unstressed condition, and transitions to the accommodated state upon application of radially compressive forces. In particular, whereas the embodiments of  FIGS. 3-6  transition from the accommodated state to the unaccommodated state by virtue of lateral (anterior and posterior) compressive forces applied during the capsule during relaxation, the embodiment of  FIG. 10  transitions to the accommodated state upon thickening of the capsular equator during contraction of the ciliary muscles. 
     The structure of IOL  110  is similar to that of IOL  90  of  FIG. 9 , with like parts identified by like-primed numbers, except that transducers  101 ′ are surrounded by force concentrating elements  111 , and haptic portions  92 ′ further comprise flanges  112  that orient IOL  110  within the capsule and maintain tension on the zonules. 
     More specifically, IOL  110  includes optic portion  91 ′ and haptic portion  92 ′. Optic portion  91 ′ comprises anterior lens element  93 ′ and substrate  94 ′ formed of light-transmissive materials. Substrate  94 ′ includes lens piston  95 ′ having expandable end wall  96 ′, and fluid channels  97 ′ in fluid communication with the interior of lens piston  95 ′. Expandable end wall  96 ′ contacts the inner surface of anterior lens element  93 ′, so that deflection of end wall  96 ′ causes anterior lens element  93 ′ to assume a more convex shape. As in the preceding embodiments, the thickness profile of anterior lens element  93 ′ may be tailored to produce a desired degree of accommodation when deflected. Channels  97 ′ and space  98 ′, disposed between anterior lens element  93 ′ and substrate  94 ′, are filled with fluid  99 ′ having a matched index of refraction. Substrate  94 ′ defines posterior lens surface  100 ′. 
     Haptic portion  92 ′ includes transducers  101 ′, with each transducer having diaphragm  102 ′. Arcuate force-concentrating elements  111  are disposed radially outward of transducers  101 ′ and illustratively have fixed end  113  connected to haptic portion  92  and free end  114 . Elements  111  contact the equator of capsule  15  and flex radially inward or outward to follow thickening or thinning of the capsular equator responsive to contraction of the ciliary muscles. Elements  111 , diaphragms  102 ′, and reservoirs  103 ′ together form haptic pistons. Elements  111  and diaphragms  102 ′ have an undeformed shape depicted in  FIG. 10C . As in the preceding embodiments reservoirs  103 ′ communicate with channels  97 ′, and are filled with index-matched fluid  99 ′. As noted above, laterally-extending flanges  112  apply tension to the capsule to orient the IOL within the capsule and maintain tension on the zonules when the capsule changes shape responsive to action of the ciliary muscles. 
     As described herein above with respect to  FIG. 2 , contraction of the ciliary muscles causes the capsule to become more spherical and thicken along its equator. This thickening applies a radially compressive force to elements  111  of transducers  101 ′ that compresses diaphragms  102 ′ to the deformed shapes depicted in  FIGS. 10A and 10B . This causes fluid to be displaced from reservoirs  103 ′ of transducers  101 ′, pressurizing the fluid in channels  97 ′ and lens piston  95 ′. Responsive to this pressure increase, end wall  96 ′ of the lens piston expands anteriorly, deflecting anterior lens element  93 ′ and transitioning the lens to the accommodated state, as shown in  FIG. 10B . Frames  112  retain IOL  110  centered on the capsular equator as the capsule transitions to a more spherical shape. 
     When the ciliary muscle subsequently relaxes, the radially compressive forces applied by the muscles diminish, the capsule becomes more ellipsoidal, and the capsular equator thins. Frames  112  become compressed by the lateral forces applied by the capsule and zonules, and transducers  101 ′ follow the elongation of the capsule, with free ends  114  of elements  111  deflecting outward to the undeformed state depicted in  FIG. 10C . This in turn relieves compression of diaphragms  102 ′, so that fluid moves from channels  97 ′ back to reservoirs  103 ′, and lens piston  95 ′ resumes its unexpanded position. Consequently, anterior lens element  93 ′ returns to its undeflected state and lens  110  transitions to the unaccommodated state shown in  FIG. 10C . 
     Referring to  FIGS. 11A-11C , a further alternative embodiment of the intraocular lens of the present invention is described. IOL  120  is similar in construction to IOL  110 , and like components are designated by like double prime numbers. Thus, for example, while the anterior lens element of  FIG. 10A  is designated  93 ′, the anterior lens element of  FIG. 11A  is designated  93 ″. IOL  120  differs from IOL  110  of  FIG. 10  in that diaphragm  102 ′ is omitted, and reservoir  103 ″ is defined by an internal lumen of element  111 ″ that communicates with channel  97 ″ via opening  121 . In IOL  120 , element  111 ″ therefore defines transducer  101 ″. 
     As in IOL  110  of  FIG. 10 , IOL  120  is disposed within the capsule and transitions to the accommodated state upon thickening of the capsular equator during contraction of the ciliary muscles. Flanges  112 ″ that orient the IOL within the capsule and maintain tension on the zonules. 
     IOL  120  includes optic portion  91 ″ and haptic portion  92 ″. Optic portion  91 ″ comprises anterior lens element  93 ″ and substrate  94 ″ formed of light-transmissive materials. Substrate  94 ″ includes lens piston  95 ″ having expandable end wall  96 ″, and fluid channels  97 ″ in fluid communication with the interior of lens piston  95 ″. Expandable end wall  96 ″ contacts the inner surface of anterior lens element  93 ″, so that deflection of end wall  96 ″ causes anterior lens element  93 ″ to assume a more convex shape. As in the preceding embodiments, the thickness profile of anterior lens element  93 ″ may be tailored to produce a desired degree of accommodation when deflected. Channels  97 ″ and space  98 ″, disposed between anterior lens element  93 ″ and substrate  94 ″, are filled with index-matched fluid  99 ″. Substrate  94 ″ defines posterior lens surface  100 ″. 
     Haptic portion  92 ″ includes transducers  101 ″ in the form of arcuate elements  111 ″ having fixed end  113 ″ connected to haptic portion  92 ″ and free end  114 ″. Elements  111 ″ include internal lumens defining reservoirs  103 ″ that are in fluid communication with channels  97 ″ via openings  121 . Elements  111 ″ contact the equator of capsule  15  and flex radially inward or outward to follow thickening or thinning of the capsular equator responsive to contraction of the ciliary muscles. Elements  111 ″ have the undeformed shape depicted in  FIG. 11C . Reservoirs  103 ″ m , channels  97 ″ and lens piston  95 ″ are filled with index-matched fluid  99 ″. As noted above, laterally-extending flanges  112 ″ apply tension to the capsule to orient the IOL within the capsule and maintain tension on the zonules when the capsule changes shape responsive to action of the ciliary muscles. 
     As for IOL  110 , contraction of the ciliary muscles causes the capsule to become more spherical and thicken along its equator, thereby applying a radially compressive force to transducers  101 ″ that compresses elements  111 ″ to the deformed flatter (smaller volume) shapes depicted in  FIGS. 11A and 11B . This causes fluid to be displaced from reservoirs  103 ″ of transducers  101 ″, pressurizing the fluid in channels  97 ″ and lens piston  95 ″. Responsive to this pressure increase, end wall  96 ″ of the lens piston expands anteriorly, deflecting anterior lens element  93 ″ and transitioning the lens to the accommodated state, as shown in  FIG. 11B . Frames  112 ″ retain IOL  120  centered on the capsular equator as the capsule transitions to a more spherical shape. 
     When the ciliary muscle subsequently relaxes, the radially compressive forces applied by the muscles diminish, the capsule becomes more ellipsoidal, and the capsular equator thins. Frames  112 ″ become compressed by the lateral forces applied by the capsule and zonules, and transducers  101 ″ follow the elongation of the capsule, with free ends  114 ″ of elements  111 ″ deflecting outward to the undeformed rounder (larger volume) state depicted in  FIG. 11C . This in turn relieves compression of transducers  101 ″, so that fluid moves from channels  97 ″ back to reservoirs  103 ″, and lens piston  95 ″ resumes its unexpanded position. Consequently, anterior lens element  93 ″ returns to its undeflected state and lens  120  transitions to the unaccommodated state shown in  FIG. 11C . 
     In  FIGS. 12A-12C , still another embodiment of an intraocular lens constructed in accordance with the principles of the present invention is described. IOL  130  comprises optic portion  131  and haptic portion  132 . Optic portion  131  comprises anterior lens element  133  and substrate  134  formed of light-transmissive materials. Substrate  134  includes lens piston  135  having expandable end wall  136 , and fluid channels  137  in fluid communication with the interior of lens piston  135 . 
     Expandable end wall  136  contacts the inner surface of anterior lens element  133 , so that deflection of end wall  136  causes anterior lens element  133  to assume a more convex shape. The thickness profile of anterior lens element  133  is tailored to provide a desired degree of optical correction throughout its range of deflection. Channels  137  and space  138 , disposed between anterior lens element  133  and substrate  134 , are filled with fluid  139  having an index of refraction that is matched to the materials of anterior lens element  133  and substrate  134 . Substrate  134  includes posterior lens surface  140 . 
     Haptic portion  132  is disposed at the periphery of optic portion  131 , and includes transducers  141  having segments  142  slidably disposed in edge recesses  143 . Edge recesses  143  are defined by extensions  144  of fluid channels  137  that extend circumferentially along the edges of substrate  134  for an arc-length corresponding to the arc-length of haptic portions  132  and function as reservoirs. Segments  142  are coupled to diaphragms  145  so that force applied to the outer edges of segments  142  by the capsular equator causes the segments to be displaced radially inward. Laterally-extending flanges  146  apply tension to the capsule to orient IOL  130  within the capsule and maintain tension on the zonules. 
     Segment  142 , substrate extensions  144 , diaphragm  145  and edge recess  143  together form a haptic piston that transfers fluid to lens piston  135  responsive to contraction and relaxation of the ciliary muscle, zonules and capsule. Specifically, inward movement of segments  142  causes diaphragms  145  to displace inwardly into edge recesses  143 , thereby transferring fluid to lens piston  135 . As in the preceding embodiment, fluid entering lens piston  135  expands end wall  136 , thereby deflecting anterior lens element  133  to its accommodated shape, as shown in  FIGS. 12A and 12B . 
     In  FIG. 12C , when the ciliary muscles relax, the capsule elongates and applies laterally compressive forces to flanges  146 . As the capsule elongates, the forces applied to segments  142  decrease, allowing end wall  136  to return to its unexpanded state and permitting anterior lens element  133  to return to the unaccommodated state. 
     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.