US 20050131535 A1
An intraocular lens (30) having focusing capabilities permitting focusing movement of the lens (30) in response to normal ciliary body (24) movement incident to changes in the distance between the eye and an object under observation is provided. The lens (30) is designed for surgical implantation within the capsule (20) of an eye (10) and includes an optic (32) and an optic positioning element (33) which cooperate to form the lens (30). Accommodation is achieved by relying upon the thickening and thinning of the optic (32) as a result of the normal retracting and contracting of the ciliary body (24) in response to the distance of an object from the viewer.
1. In an accommodating intraocular lens for implantation within an eye, said lens comprising an optic having an initial thickness and an optic positioning element coupled with said optic, the improvement being that said optic initial thickness can be altered in response to a change in force on said optic.
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21. In an accommodating intraocular lens for implantation within an eye, said lens comprising:
a pair of optics immediately adjacent one another; and
an optic positioning element coupled with at least one of said optics.
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36. A method of providing accommodation to an eye comprising a ciliary body and whose natural lens has been removed, said method comprising the step of implanting an intraocular lens into the eye, said lens comprising an optic having an initial thickness which can be altered on response to movements of said ciliary body.
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1. Field of the Invention
The present invention relates to accommodating intraocular lenses which can be surgically implanted as a replacement for the natural crystalline lens in the eyes of cataract patients.
2. Description of the Prior Art
Cataracts occur when the crystalline lens of the eye becomes opaque. The cataracts may be in both eyes and, being a progressive condition, may cause fading vision and eventual blindness. Cataracts were once surgically removed along with the anterior wall of the capsule of the eye. The patient then wore eyeglasses or contact lenses which restored vision but did not permit accommodation and gave only limited depth perception.
The first implant of a replacement lens within the eye occurred in 1949 and attempted to locate the replacement lens in the posterior chamber of the eye behind the iris. Problems such as dislocation after implantation forced abandonment of this approach, and for some period thereafter intraocular lenses were implanted in the anterior chamber of the eye.
Others returned to the practice of inserting the lens in the area of the eye posterior to the iris, known as the posterior chamber. This is the area where the patient's natural crystalline lens is located. When the intraocular lens is located in this natural location, substantially normal vision may be restored to the patient and the problems of forward displacement of vitreous humor and retina detachment encountered in anterior chamber intraocular lenses are less likely to occur. Lenses implanted in the posterior chamber are disclosed in U.S. Pat. Nos. 3,718,870, 3,866,249, 3,913,148, 3,925,825, 4,014,049, 4,041,552, 4,053,953, and 4,285,072. None of these lenses has focusing capability.
Lenses capable of focusing offer the wearer the closest possible substitute to the crystalline lens. U.S. Pat. No. 4,254,509 to Tennant discloses a lens which moves in an anterior direction upon contraction of the ciliary body, and which is located anterior to the iris. Though providing focusing capabilities, it presents the same disadvantages as other anterior chamber lenses.
U.S. Pat. No. 4,409,691 to Levy is asserted to provide a focusable intraocular lens positioned within the capsule. This lens is located in the posterior area of the capsule and is biased toward the fovea or rear of the eye. The '691 lens is deficient because it requires the ciliary muscle to exert force through the zonules on the capsule in order to compress the haptics inward and drive the optic forward for near vision. However, the ciliary muscles do not exert any force during contraction because the zonules, being flexible filaments, exert only tension, not compression on the capsule. The natural elasticity of the lens causes the capsule to become more spherical upon contraction of the ciliary muscle. Thus, there is no inward force exerted on the capsule to compress the haptics of the Levy lens, and therefore accommodate for near vision.
U.S. Pat. No. 5,674,282 to Cumming is directed towards an accommodating intraocular lens for implanting within the capsule of an eye. The Cumming lens comprises a central optic and two plate haptics which extend radially outward from diametrically opposite sides of the optic and are movable anteriorly and posteriorly relative to the optic. However, the Cumming lens suffers from the same shortcomings as the Levy lens in that the haptics are biased anteriorly by pressure from the ciliary bodies. This will eventually lead to pressure necrosis of the ciliary body.
There is a need for an intraocular lens implant capable of focusing in a manner similar to the natural lens. This lens implant should be readily insertable into the capsule and should last for a substantial number of years without damaging any of the eye components.
The present invention fills this need by providing an intraocular lens with focusing capabilities which is safe for long-term use in an eye.
In more detail, the lens of the invention comprises an optic coupled to an optic positioning element. The optic positioning element is preferably balloon-shaped or preferably comprises an outwardly extending disc (optionally with thicker, radially extending “winged” portions separated by thin membranes). The optic is resilient and can be formed of a solid material (e.g., silicone) or can be gas-filled.
As a result of the size and shape of the inventive lens and the material of which the optic is formed, the focusing action of the natural lens is simulated. That is, the ciliary body of the eye continues to exert a muscular force radially outward from the center of the capsule through the zonular fibers so as to alter the thickness of the optic, resulting in a decrease in light convergence as is necessary for viewing objects distant from the viewer. When viewing an object close to the viewer, the ciliary body contracts, thus releasing the outward pull on the zonular fibers. This alters the thickness of the optic to result in an increase in light convergence as is necessary for viewing nearby objects.
The optic can be one of many shapes as described in more detail below. Furthermore, the optic can be formed of a solid, liquid, or gel refractive material, or the optic can be gas-filled (e.g., air) so long as the chosen materials are safe for use in the eye. The shape of the optic and the material of which the optic is formed are dependent upon one another. That is, the shape is chosen based upon the refractive index of the material used to form the optic, and this choice is made to result in an optic which will highly converge light upon contraction of the ciliary body. Thus, if the refractive index of the optic material is greater than about 1.33 (the refractive index of the fluids within the eye), then optic shapes such as meniscus, planoconvex, and biconvex would converge light. On the other hand, if the refractive index of the optic material is less than about 1.33, then optic shapes such as biconcave and planoconcave would converge light.
Referring now to the drawings, the present invention is in the form of an intraocular lens for surgical replacement of the human lens in the treatment of cataracts in the human eye.
Although not shown in the accompanying figures, the retina is composed of rods and cones which act as light receptors. The retina includes a fovea which is a rodless portion which provides for acute vision. The outside of the rearward or posterior portion of the eye 10 is known as the sclera. The sclera joins with, and forms a portion of, the covering for the optic nerve. Images received by the retina are transmitted through the optic nerve to the brain. The area between the retina and the capsule 20 is occupied by vitreous fluid. Finally, the eye 10 includes a ciliary muscle or body 24 having zonular fibers 26 (also referred to as zonules) which are attached to the capsule 20.
Ocular adjustments for sharp focusing of objects viewed at different distances is accomplished by the action of the ciliary body 24 on the capsule 20 and crystalline lens (which would be located at numeral 28 in the natural, unmodified eye) through the zonular fibers 26. The ciliary body 24 contracts, allowing the capsule 20 to return to a more spherical shape for viewing objects that are nearer the viewer. When the ciliary body 24 retracts and pulls on the zonular fibers 26 to make the capsule 20 more discoid, objects at a distance can be viewed in proper focus.
Preferably, the overall shape of lens 30 in its original resting, non-deformed shape generally conforms to the shape of capsule 20 when capsule 20 is focused to view an object near the viewer (
Intraocular lens 30 substitutes both locationally and functionally for the original, natural, crystalline lens (which would normally be at location 28). To insert the lens 30 into the capsule 20, an ophthalmic surgeon would remove the natural lens (and thus the cataracts) by conventional methods, leaving an opening 58 in the anterior wall 56 of the capsule 20. Lens 30 is then folded into a compact size for insertion into the capsule 20 through the opening 58. Once inserted, the capsule 20 is filled with fluids (e.g., saline solution) which enter the chamber 48 of the lens 30, causing the lens 30 to return to its original, non-deformed state as shown in
Implantation of the inventive lens 30 restores normal vision because, not only does the lens 30 replace the patient's occluded natural lens, but the normal responses of the ciliary body 24 cooperate with the lens 30 during focusing. In
Optic 32 is formed of a solid, liquid, or gel material (e.g., silicone) so it has a refractive index greater than that of the surrounding fluid in the eye (i.e., greater than 1.33). This refractive index, combined with the thinness of optic 32 as shown in
This increase in optic thickness combined with the fact that the refractive index of the optic 32 is greater than 1.33 (and preferably at least about 1.36, more preferably at least about 1.4, and even more preferably at least about 1.5) results in an increased convergence of light, thus enabling the eye to see objects near the viewer. The lens 30 thus follows the eye's natural physiology for focusing to provide a substitute means of optical accommodation.
While the anterior surface 34 and the posterior surface 36 of the lens 30 of
While lens 86 includes a meniscus-shaped optic 88 like that of the embodiment of
Although lens 86 has a gas-filled optic 88 rather than a solid optic, lens 86 still operates to provide accommodation in a somewhat similar manner as discussed above with respect to lens 30. In more detail and referring to
The lens 120 operates to provide accommodation in a manner similar to that described with respect to lens 86 of
Optic positioning element 144 comprises a skirt 146 which includes a plurality of radially extending elements 148. In the embodiment shown, elements 148 comprise respective openings 150. The respective sizes and shapes of openings 150 are not critical so long as they are capable of allowing fibrosis of the tissue. Furthermore, openings 150 can be omitted if desired.
Elements 148 are joined to one another by thin membranes 152. Alternately, optic positioning element 144 can simply include a circular or disc-shaped haptic having a substantially uniform thickness (i.e., rather than thicker radially extending elements 148 and thinner membranes 152) extending from the optic.
Elements 148 and membranes 152 are generally formed of the same material (e.g., silicones, acrylates) but with a difference in thicknesses, although the material can be different, and the selection of material is not critical so long as it is biologically safe and at least somewhat resilient. It will be appreciated that the respective thicknesses of elements 148 and membranes 152 can be adjusted as necessary by one of ordinary skill in the art. Ideally, the elements 148 will be of sufficient respective thicknesses to provide resistance to the force created on the outer edges 154 of the elements 148 by the contraction of the ciliary body. The respective thicknesses of the membranes 152 should be such that the flexibility of the overall skirt 146 is maintained while being resistant to tearing.
Lens 140 would operate to provide accommodation in a manner similar to that described with respect to lens 30 of
The lens 170 of
When the ciliary body (not shown) retracts or contracts as necessary (either pulling on the zonular fibers or releasing the pull on the zonular fibers), the fibrin (not shown) formed through openings 150 would result in a radially outward force on elements 176 (resulting in the thinning of optics 178, 180) or the release of that outward force (resulting in the thickening of optic 178, 180). Because optics 178, 180 are formed of materials (either the same or different) having respective refractive indices of greater than 1.33, thickening of optics 178, 180 would result in an increased convergence of light for near viewing, and thinning of optic 178, 180 would result in a decreased convergence of light for distance viewing.
Each of the foregoing embodiments can be used to obtain an accommodation improvement of at least about 1.5 diopters, preferably at least about 3.0 diopters, and more preferably from about 4-8 diopters. “Diopter” is defined as the reciprocal of the focal length in meters:
Importantly, this accommodation can be achieved with very little force being required by the eye. That is, the typical eye exerts anywhere from about 6-9 grams of force on an intraocular lens. However, the inventive optic can be designed to change shape sufficiently to produce the desired accommodation with as little as 1 gram of force. Thus, lenses according to the present invention provide a further advantage in that they can be designed to respond to a force over the entire range of from about 1 to about 9 grams.
For each of the foregoing embodiments illustrated in
Furthermore, the optics of each embodiment could be formed of a wide range of flexible, refractive materials so long as the necessary thickening or thinning thereof can be achieved. Suitable materials include gels, silicone, silicone blends, refractive liquids, elastomeric materials, rubbers, acrylates, gases such as air, and mixtures of the foregoing, so long as the material is flexible and resilient. The shape of the optic (e.g., meniscus, biconcave, biconvex) utilized will depend upon the refractive index of the material used to form the optic. That is, the combination of optic shape and optic material will need to be chosen so that the resulting lens will converge light when the ciliary body contracts for near viewing.
While the foregoing description shows certain types of optic positioning elements with certain optics (both optic shapes and optic materials), it will be appreciated that this is for illustration purposes only, and the optic positioning elements and optic types can be switched. For example, the combination optic 172 of
Although the invention has been described with reference to the preferred embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims. For example, while the foregoing method of inserting the lens into the capsule presumed that a portion of the anterior wall of the capsule would be removed with the natural lens, it will be appreciated that it may be possible to insert the lens through an incision in the anterior wall. Furthermore, while the foregoing description discloses that the inventive lenses could be utilized in cataract patients, the lenses may be used in any situation where the natural lens needs to be replaced. For example, the inventive lenses may be used to correct myopia, hyperopia, presbyopia, cataracts, or a combination thereof.
Finally, it will be appreciated that each of the foregoing lenses can be manufactured in either the accommodated or disaccommodated shape. That is, they can be manufactured in a default state of either an accommodated or disaccommodated shape, and the deformed state (i.e., the state caused by the forces within the eye during focusing) will be the other of the accommodated or disaccommodated shape.