Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Intraocular lens
Reexamination Certificate
2000-09-07
2002-08-13
Dawson, Robert (Department: 1712)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Intraocular lens
C525S478000, C528S031000, C528S043000, C528S032000, C623S004100, C556S458000
Reexamination Certificate
active
06432137
ABSTRACT:
BACKGROUND OF THE INVENTION
The current invention relates to high refractive index, optically clear, silicone polymers, which are used, for example, to make intraocular lenses (IOL).
Optically clear materials, such as glass, polymethylmethacrylate and cured silicone materials, are used in intraocular lenses and are currently known in the art. In order to be useful for such lenses, the materials must have a number of suitable properties including optical clarity, appropriate mechanical properties, relatively low density, resistance to discoloration, and biological compatibility for long-term implantation as a medical device. The refractive power of a lens is a function of its optic shape and the refractive index of the material from which it is made. The higher the refractive index, the thinner a lens can be made for a specified power. Thus, refractive index is a very important property for materials used to make IOL's.
The flexibility of the materials is important to permit implanting intraocular lenses through small incisions for cataract surgery. Use of a flexible material permits folding or compression of the lens and/or supporting elements, such as haptics, during or prior to insertion, to reduce the size of the incision required. A smaller ocular incision reduces trauma and permits the use of sutureless incision techniques, thus reducing the potential for distorting the shape of the eye and inducing astigmatism.
Aphakic IOLs are used for replacement of the natural lens for treatment of cataracts. Phakic IOLs are used for the correction of myopia and hyperopia where the natural lens is not removed. Posterior chamber phakic lenses have been shown to improve best spectacle corrected visual acuity over external lenses. Most cataract IOLs are implanted in the space created by surgical removal of the diseased natural lens. Posterior chamber phakic IOLs require thinner and more flexible lens construction than the traditional aphakic, cataract IOLs to permit implantation between the iris and the natural lens (that is, in the posterior chamber of the eye) where a thick or stiff lens makes it difficult to avoid disrupting the normal functions of the eye, such as accommodation (focusing) of the natural lens, constriction and dilation of the iris, and the flow of the aqueous fluid (or humor) of the eye. Soft and flexible materials are especially important for phakic IOLs to allow the implant to move with the dynamics of the anatomy. A lens made from a material with high refractive index can be thinner and provide the same refractive power as a thicker lens made from a material having a low refractive index. Thinner lenses are inherently more flexible and are more easily folded or compressed for insertion through small incisions.
Such materials as silica have been used to reinforce optically clear silicones to increase tensile and tear strength. However, silica reinforcement also increases the stiffness of the material which may not be desirable for use in phakic IOLs. Also, reinforcing materials must have the same refractive index as the base material to achieve optical clarity. For example, if a 1.50 refractive index silicone is reinforced with silica which has a refractive index 1.46, the resulting material would scatter light and not be suitable for use as a lens. Thus, the use of reinforcing materials is difficult to execute in a lens, and it would be useful to be able to formulate reliably strong, optically clear silicone materials without using reinforcing agents.
The use of multiple IOLs (“piggybacked”) to achieve a specific optical power is a new technique used by surgeons where the specific required power is not available in a single lens or where a correction in power is required post-operatively. Addition of a lens to a sudophakic eye (where the natural lens has been removed and replaced with an IOL) is another application of the present invention since high refractive index, UV absorbency, and flexibility are important characteristics of such lenses.
Ultraviolet light (UV) absorbing materials are important for ocular prosthetics, such as IOLs, to avoid damage to tissues (such as the retina) from normal exposure to sunlight and other sources of UV light. Further, it is essential that such materials remain optically clear and avoid yellowing or other discoloration resulting from deposits or precipitates within the lens or on its surface. Methods for blocking UV light that are known in the art include the use of benzotriazole in the lens as an additive or as part of a copolymer.
There is, therefore, a need for an intraocular lens made from implantable materials with a high refractive index, that will absorb UV light, and provide adequate mechanical properties including a very high level of flexibility, while avoiding additives and agents that may be extractable or leachable or discolor the lens.
The current invention is useful in aphakic IOLs for the treatment of cataracts. However, the invention is particularly useful in phakic IOLs for refractive surgery. The development of phakic IOLs for the correction of myopia and hyperopia where the natural lens is not removed is described in U.S. Pat. No. 4,585,456, Blackmore, issued Apr. 29, 1986. The use of phakic IOLs has been shown to improve best spectacle corrected visual acuity (Dimitrity Dementiev M. D. and Alexander Hatsis, M. D.,
Symposium on Cataract, IOL and Refractive Surgery
, Session 3-B, Apr. 26-30 1997, Boston Mass., ASCRS, Fairfax, Va.). Posterior chamber phakic IOLs require thinner and more flexible lens construction than the traditional aphakic IOLs for the treatment of cataracts where the IOL is implanted in the space created by the surgical removal of the natural lens.
Optically clear silicone materials with a relatively high refractive index are known in the art. Such materials are typically formulated by the use of additives or co-monomers in the silicone polymer material; this generally results in undesirable trade-offs in the other properties of the material, such as strength, flexibility, elasticity or elongation.
Canadian Patent 1,273,144, Nishimura, published Aug. 21, 1990, discloses the inclusion of refractive index-modifying groups, such as phenyl groups, into hydride-containing siloxanes by reacting a portion of the hydride groups with carbon- carbon unsaturated bonds in the refractive index-modifying group. After this reaction, the unreacted hydride groups in the modified hydride-containing siloxane are reacted with a compound having at least two carbon-carbon unsaturated bonds to form a cross-linked polysiloxane. This system is somewhat difficult to control and may not be suited for mass production of silicone lenses because of potentially large batch-to-batch quality variations. For example, the refractive index-modifying groups must be sufficiently numerous and evenly distributed in the hydride-containing siloxane to provide for the desired refractive index without detrimentally affecting the other properties of the final polymer. At the same time, the unreacted hydride groups remaining in the siloxane must be sufficiently numerous and evenly distributed to provide for the desired cross-linking reaction. These factors can create a reaction control problem which may result in the final polymer not having the desired refractive index and /or not having one or more other desired physical properties.
U.S. Pat. No. 4,882,398, Mbah, issued Nov. 21, 1989, discloses optically-clear silicone compounds adaptable for use in windows, windshields and lenses. Although this patent does disclose certain aryl and aralkyl groups attached or bonded to a siloxane , there is no teaching or suggestion of the effect of such substitution on the refractive index of the final polymer. Also, the amount of these groups which is included should have little or no effect on the refractive index of the final polymer and would yield a low refractive index of about 1.41. This is consistent with the fact that for many of the disclosed uses (e.g., windows, windshields), refractive index is not a critical property.
Gas permeabl
Alexeeva Elena J.
Nanushyan Sergei R.
Valunin Igor
Dawson Robert
Frost Brown Todd LLC
Medennium, Inc.
Peng Kuo-Liang
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