Abstract:
An introocular lens (IOL) includes an optic; a haptic; a flexible membrane substantially encircling the optic and connected between the optic and the haptic, the flexible membrane having a flexibility greater than the optic and the haptic. The flexible membrane permits travel of the optic relative to the haptic to permit accommodation in the eye. The flexible membrane my also drive a curvature change in the optic as it travels during accommodation.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to an intraocular lens and, in particular, an intraocular lens with accommodating capability. 
     An intraocular lens (IOL) is a surgical device, which can be implanted into the eye to replace cloudy natural lens during cataract surgery. However, the artificial lens is different from the natural lens, which can change shape to facilitate accommodation of the eye. Therefore, almost every patient needs reading glasses for near work after cataract surgery. 
     IOLs are known with accommodating capabilities. Currently, a number of different approaches have been attempted for designing an accommodating IOL, such as forward movement of lens optic, curvature change of the lens optic, and change of refractive index of the lens optic. 
     SUMMARY OF INVENTION 
     In accordance with a broad aspect of the present invention there is provided an IOL comprising: an optic; a haptic; a flexible membrane substantially encircling the optic and connected between the optic and the haptic. The flexible membrane has a flexibility greater than the optic and greater than the haptic. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is front elevation of an intraocular lens. 
         FIG. 1B  is front elevation of another intraocular lens. 
         FIGS. 1C to 1E  are side elevations of the intraocular lens of  FIG. 1A  showing its positions during accommodation, wherein  FIG. 1C  is at rest and  FIGS. 1D and 1E  are undergoing accommodation by forward movement of the lens optic. 
         FIG. 2A  is front elevation of another intraocular lens. 
         FIG. 2B  is front elevation of another intraocular lens. 
         FIGS. 2C to 2E  are side elevations of the intraocular lens of  FIG. 2A  showing its positions during accommodation, wherein  FIG. 2C  is at rest,  FIG. 2D  is at a stage of accommodation and  FIG. 2E  is at a further stage of accommodation. 
         FIG. 3A  is front elevation of another intraocular lens. 
         FIGS. 3B to 3D  are side elevations of the intraocular lens of  FIG. 3A  showing its positions during accommodation, wherein  FIG. 3B  is at rest and  FIGS. 3C and 3D  are at progressive stages of accommodation. 
         FIGS. 4A and 4B  are front and side elevations, respectively, of lens optics useful in the present invention. 
         FIGS. 4C to 4F  are side elevations of further lens optics useful in the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, an IOL may provide accommodating capability by forward movement in the eye, varying the distance of the IOL or lens optic from the retina, and/or curvature change of the lens optic. To achieve these affects, the IOL may make use of the forces of zonule tension from ciliary muscle contractions. In addition, vitreous forces may act upon the IOL. Vitreous forces are also reliant, at least in part, on ciliary muscle contractions wherein such contractions result in posterior bulking within the eye, which decreases the volume of the vitreous cavity. Since the vitreous volume is fixed, the pressure on the contraction of the ciliary muscle cause vitreous movement wherein the peripheral vitreous is pushed back and the central vitreous moves oppositely and, therefore, forwardly. Consequently, the movement of the vitreous may push the lens optic forward in the eye. It appears that forward movement of the lens optic must be significant in order to adjust the lens power for example to provide near vision. However, minor curvature changes on the lens optic appear to change the lens power significantly. 
     An IOL providing accommodation by forward movement in the eye and/or curvature change of the lens optic is shown in  FIGS. 1A and 1C  to  1 E. In one embodiment, an IOL  10   a  includes a lens optic  12   a  and a haptic  14   a . As is known, lens optic  12   a  provides for the corrective refraction of light for focusing to the retina, while haptic  14   a  is a supporting structure for mounting the optic in the capsular bag. Haptic  14   a  includes mounting points  18   a , which engage against the capsular bag. 
     The lens optic is secured to the haptic through flexible, elastomeric membranes  16   a . Membranes  16   a  together at least substantially encircle optic  12   a . Each membrane has a flexibility greater than that of the surrounding materials. In particular, each membrane  16   a  has a flexibility greater than that of either lens optic  12   a  or haptic  14   a . Flexibility may be achieved by selection of materials or, as in the illustrated embodiment, by selection of the thickness of the membrane relative to the surrounding parts. For example, the membranes may be formed thinner and possibly much thinner than the haptic to render it more flexible than that part. While two membranes are shown, it is to be understood that one substantially circular membrane may be employed, if desired. Alternately, further membranes may be positioned such that they together encircle optic  12   a . For example, with reference to  FIG. 1B , an IOL is shown including four membranes  16   b  about optic  12   a.    
     The membranes are able to flex to permit movement of optic  12   a  relative to haptic  14   a , in response to the application of force to optic  12   a . The membranes, however, are resilient such that they are biased towards their original form as the application of force is diminished or discontinued. 
     Haptic  14   a  may be formed in various ways to mount the IOL in the posterior chamber or the anterior chamber of an eye and to support the membranes  16   a  and therethrough lens optic  12   a . While other haptic forms can be used as desired, in the illustrated embodiment, haptic  14   a  is a plate haptic including an upper half  20   a ′ and a lower half  20   a ″. The haptic includes a membrane support ring formed of segments  21 . In particular, each of the upper half and the lower half of the haptic includes a ring segment  21  that extends the haptic upwardly around the optic to support membranes  16   a . In the illustrated embodiment, ring segments  21  frame the membranes  16   a  to offer support for the membranes at their outer edges. Ring segments  21  may be formed as a part of the haptic or sepearately therefrom with a connection to the haptic. 
     Membranes  16   a  may be mounted at or close to the optic&#39;s largest diameter side edges  23  (see  FIG. 4 ) and each membrane extends along a section of the circumference about the optic such that membranes  16   a  together substantially encircle the optic. The membranes may be independent from each other, for example in one embodiment separated by slits or gaps  22 . In the illustrated embodiment, the IOL includes two membranes  16   a  about the optic, with each membrane being continuous between its ends and extending substantially about one half the optic circumference. The membranes are spaced apart at each of their ends to form gaps  22  therebetween. The gaps may, for example, be positioned on the sides of the IOL between the haptic mounting points  18   a.    
     Haptic  14   a  may also be discontinuous, for example by forming the upper half  20   a ′ separate from the lower half  20   a ″, for example, at a split or gap  24  adjacent to gaps  22  between membranes  16   a.    
     Gaps  22  and  24  reduce stiffness and resistance to bending for the IOL wherein only the optic provides stiffness between the upper half and the lower half of the haptic. As such, when the ciliary muscle contracts to change the zonule tension and increase the vitreous pressure, the IOL can easily bend between gaps  22  and  24 . Furthermore, where gaps  22 ,  24  are used that space the surrounding parts, the gaps can allow for greater range of motion to facilitate depth movement of the optic as the parts do not readily bear against each other. Gaps  22 ,  24  also permit dimensional expansion of the IOL wherein the diameter D r  of the IOL at rest ( FIG. 1C ) may be extended to diameter D e  wherein the IOL is expanded about gaps  22 ,  24  ( FIG. 1D ). The expansion to diameter D e  facilitates travel of optic  12   a  to thereby facilitate accommodation. 
     In an IOL having more than two membranes, as in  FIG. 1B , gaps  22   a ,  24   a  may be formed between each membrane  16   b  and between each ring segment  21   a . The ring segments  21   a  may be extended about the membranes  16   b  to support them on their outer edges. 
     The surface area of optic  12   a  and membranes  16   a  also act to trap vitreous fluid as it is moved within the eye by ciliary muscle contractions. The form of membranes  16   a  act to trap the fluid pressure and this creates a force, arrows F, that acts with the flexibility of membranes  16   a  to drive forward movement of the optic. 
     In operation, when the ciliary muscle contracts, vitreous pressure will increase and act on the posterior surface area of the lens optic and membranes  16   a  to push the lens optic forward as shown progressively from  FIG. 1C  where the IOL is at rest through the position of  FIG. 1D  to the position of  FIG. 1E . In addition, such movement of optic  12   a  and membranes  16   a  changes the pressure exerted at side edges  23  of the optic by the membranes. This causes the optic curvature to be changed. When the ciliary muscle relaxes, the vitreous pressure is released and the lens optic will return to its original form ( FIG. 1C ) and position because of material elasticity. A combination of forward movement and lens optic curvature change may provide the eye with significant accommodating power to focus on near objects. 
     The membranes can be formed at an angle to the optic to enhance their effect on optic curvature change when force is applied thereto. In one embodiment, the membranes together form a frustoconical surface formed at an angle α of 5 to 15 degrees or possibly 10 to 15 degrees from a plane defined through the optic side edges  23 . An increase in angle α increases the degree to which optic  12   a  can travel. Consequently, it may add more positive power for near vision. 
     The IOLs can be made from various materials, as would be appreciated by a skilled person. For example, the materials for the optic and possibly for other parts are clear and compatible for use in the body. The materials are selected and formed to be sufficiently stiff to retain the IOL form and position in the eye, but to be flexible to react to muscle contractions and vitreous fluid pressure. Where a foldable lens is useful, foldable materials such as silicone, acrylic, hydrogel, etc. may be used. One-piece construction may also be useful. In the illustrated embodiment a one-piece construction is used wherein the haptic, ring segments, membranes and optic are formed integral. 
     Lens optics useful in the present invention may vary, as desired. For example, a liquid form optic, as shown in  FIGS. 1A and 2A , or a solid form optic  12   d , as shown in  FIGS. 1B ,  2 B and  3 A can be selected for the lens optic. Some useful optic forms are shown in  FIG. 4 . For example, as shown in  FIGS. 4A and 4B , a liquid lens optic  12   a  may be used. Such a lens optic may include an outer capsule  26  forming an inner chamber  28  that may be filled with liquid material such as silicone or other liquid and clear materials. The lens capsule may be thinned centrally with an increasing peripheral thickness, as shown in  FIG. 4B . In other embodiments, a lens optic  12   b  may be used wherein the lens capsule  26   a  may be more uniformly thick ( FIG. 4C ), a lens optic  12   c  may be used wherein the lens capsule  26   b  can include one thicker side ( FIG. 4D ). Capsule design can be selected to control lens optic shape change and thereby curvature changes resulting from application of pressure. A liquid lens tends to have greater flexibility of a solid lens. Solid optics may include, for example, an optic  12   d  ( FIG. 4E ) including a form generally symmetrical about its edges  23  or an optic  12   e  ( FIG. 4F ) that is curved assymetrically on either side of its side edges  23 . If a solid optic is selected, soft and flexible materials may be used to construct the optic in order to facilitate curvature change. 
     It is to be understood that while a particular haptic form is shown, other haptic forms may be used as desired such as, for example, as shown in  FIGS. 2A to 2D , a frog leg form haptic  14   b , such as is disclosed in applicant&#39;s corresponding U.S. patent application Ser. No. 10/248,917 or a running leg form, also disclosed in the aforementioned patent application. In another embodiment, an alternate plate form, known as a pie shaped haptic  14   d  may be used such as is shown in  FIGS. 3A to 3D . In an IOL having a pie shaped haptic, membranes  16   b  are mounted along their outer edges to haptic  14   d . Gaps  22   b  may be provided between the membranes and gaps  25  may be formed in the haptic adjacent gaps  22   b  to provide the flex about gaps described hereinabove. Although not shown, a ring may be positioned or formed between membranes  16   b  and haptic  14   d , if desired, for additional support of the membranes. 
     It will be apparent that many other changes may be made to the illustrative embodiments, while falling within the scope of the invention and it is intended that all such changes be covered by the claims appended hereto.