Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Intraocular lens
Reexamination Certificate
1999-10-13
2002-03-26
Nguyen, Dinh X. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Intraocular lens
C523S113000
Reexamination Certificate
active
06361561
ABSTRACT:
FIELD OF INVENTION
The present invention relates to an intraocular lens and to materials useful in maling intraocular lenses (IOLs), specifically, injectable IOLs and methods for their preparation. More particularly, the invention relates to high specific gravity silicone materials suitable for making accommodative IOLs, which can be injected into the capsular bag with greater convenience than previously suggested materials.
BACKGROUND OF THE INVENTION
The human eye is a highly evolved and complex sensory organ. It is composed of a cornea, or clear outer tissue which refracts light lays enroute to the pupil, an iris which controls the size of the pupil thus regulating the amount of light entering the eye, and a lens which focuses the incoming light Through the vitreous fluid to the retia. The retina converts the incoming light into electrical energy that is transmitted through the brain stem to the occipital cortex resulting in a visual image. In the perfect eye the light path from the cornea, through the lens and vitreous fluid to the retina is unobstructed. Any obstruction or loss in clarity within these structures causes scattering or absorption of light rays resulting in diminished visual acuity. For example, the cornea can become damaged resulting in oedema, scarring or abrasions, the lens is susceptible to oxidative damage, trauma and infection, and the vitreous can become cloudy due to hemorrhage or inflammation.
As the body ages, the effects of oxidative damage caused by environmental exposure and endogenous free radical production accumulate resulting in a loss of lens flexibility and denatured proteins that slowly coagulate reducing lens transparency. The natural flexibility of the lens is essential for focusing light onto the retina by a process referred to as accommodation. Accommodation allows the eye to automatically adjust the field of vision for objects at different distances. A common condition known as presbyopia results when the cumulative effects of oxidative damage diminish this flexibility reducing near vision acuity. Presbyopia usually begins to occur in adults during their mid-forties; mild forms are treated with glasses or contact lenses.
Lenticular cataract is a lens disorder resulting from the further development of coagulated protein and calcification. There are four common types of cataracts: senile cataracts associated with aging and oxidative stress, traumatic cataracts which develop after a foreign body enters the lens capsule or following intense exposure to ionizing radiation or infrared rays, complicated cataracts which are secondary to diseases such as diabetes mellitus or eye disorders such as detached retinas, glaucoma and retinitis pigmentosa, and toxic cataracts resulting from medicinal or chemical toxicity. Regardless of the cause, the disease results in impaired vision and may lead to blindness.
Treatment of severe lens disease requires the surgical removal of the lens involving phakoemulsification followed by irrigation and aspiratio. However, without a lens the eye is unable to focus the incoming light on the retina. Consequently, an artificial lens is used to restore vision. Three types of prosthetic lenses are available: cataract glasses, external contact lenses and IOLs. Cataract glasses have thick lenses, are uncomfortably heavy and cause vision artifacts such as central image magnification and side vision distortion. Contact lenses resolve many of the problems associated with glasses, but require frequent cleaning, are difficult to handle (especially for elderly patients with symptoms of arthritis), and are not suited for persons who have restricted tear production. Intaoclar lenses are used in the majority of cases to overcome the aforementioned difficulties associated with cataract glasses and contact lenses.
IOLs mentioned in the prior art literature usually belong to one the following categories: non-deformable, foldable, expansible hydrogels and injectable. The earliest IOLs coming into surgical practice are non-deformable implants having rigid structures composed of acrylates and methaacrylates. This type of lenses requires a large surgical incision in the capsular bag and is not accommodative. The large incision results in protracted recovery times and the likelihood of introducing astigmatis. In an effort to reduce recovery time and patient discomfort numerous small incision techniques and lenses have been developed.
Present IOLs designed for small incision implantation have elastomeric characteristics and are made of silicone materials. This type of lenses can be rolled or folded, inserted into the capsular sac then unfolded once inside. Occasionally, the folding of the lens before insertion results in permanent deformation adversely effecting the implant's optical qualities. Foldable lenses meet the requirement of reducing the large surgical incision non-deformable lenses required, but are not accommodative. Moreover, both non-deformable and foldable IOLs are susceptible to mechanical dislocation resulting in damage to the corneal endothelium.
It has further been suggested to use an elastomeric polymer that becomes pliable when heated to body temperature or slightly above in small incision IOL implantation. Once pliable, such a lens would be deformed along at least one axis reducing its size sufficient for easy insertion through a small incision. The lens is then cooled to retain the modified shape until re-heated. The cooled lens is inserted into the capsular sac and the natural body temperature warms the lens and it returns to its original shape. The primary drawback to the thermoplastic lens is the limited number of polymers that meet the exacting needs of this approach. Most polymers are composed of polymethylacrylate which have solid-liquid transition temperatures above 100° C. To reduce these transition temperatures modifications of the polymer substrate with the use of plasticizers is required which eventually may leach into the eye.
Dehydrated hydrogels have also been suggested for small incisions techniques. Hydrogel lenses are dehydrated before insertion and naturally rehydrated once inside the capsular sac. However, once fully rehydrated the polymer struggle is notoriously weak due to the large amount of water absorbed. The typical dehydrated hydrogel's diameter will expand from 3 mm to 6 mm resulting in a lens that contains about 85% water. At this water concentration the refractive index drops to approximately 1.36 which is unacceptable for an IOL. To achieve a refractive index equal or greater than that of the natural lens (>1.40) a significantly thicker lens is required; this is even further exacerbated when lens diameters exceed 6 mm.
To further develop IOLs and reduce surgical incisions to below 1.5 mm, techniques with injectable IOLs have been suggested, wherein the low viscosity lens material is directly injected into the empty capsular bag and cured in situ as a part of the surgical procedure. In this process the capsular bag is to be used as a mold to form the shape of the lens and thereby contribute control its refraction. There have been several attempts to develop materials suitable for use as injectable IOLs. For example, Gerace et al. describe a fast curing mixture of vinyl-containing polyorganosiloxane, organosilicone comprising hydride groups and a platinum group metal catalyst used to form an IOL in their U.S. Pat. Nos. 5,278,258, 5,391,590 ('590) and 5,411,553. The resulting polymers demonstrate a reduced tendency of discoloration compared to other platinum catalyzed siliconc polymers. The '590 patent also discloses a substantially non-functional polymer component of the mixture that has a viscosity at least 50 times greater than the functional polymers. The non-functional component is mixed with the functional components to adjust viscosity to a pre-determined specification. Kelman discloses an injectable collagen IOL in U.S. Pat. No. 5,476,515. This lens is clear, resistant to epithelialation and is capable of accommodation. It is made from a transparent collagen
Huo Peter P.
Liau Christine J. Y.
Norrby Sverker
Zhou Stephen Q.
Nguyen Dinh X.
Oppenheimer Wolff & Donnelly LLP
Pharmacia & Upjohn AB
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