Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Corneal implant
Reexamination Certificate
1995-06-06
2001-04-10
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Corneal implant
C623S005160
Reexamination Certificate
active
06214044
ABSTRACT:
FIELD OF THE INVENTION
This invention is a hybrid intrastromal corneal ring (“ICR”) comprising at least one outer layer of a physiologically compatible polymer having a low modulus of elasticity, which polymer may be hydratable and may be hydrophilic. The inner portion of the ICR may be hollow or may contain one or more physiologically compatible polymers.
BACKGROUND OF THE INVENTION
Anomalies in the overall shape of the eye can cause visual disorders. Hyperopia (“farsightedness”) occurs when the front-to-back distance in the eyeball is too short. In such a case, parallel rays originating greater than 20 feet from the eye focus behind the retina. In contrast, when the front-to-back distance of eyeball is too long, myopia (“nearsightedness”) occurs and the focus of parallel rays entering the eye occurs in front of the retina. Astigmatism is a condition which occurs when the parallel rays of light do not focus to a single point within the eye, but rather have a variable focus due to the fact that the cornea is aspherical and refracts light in a different meridian at different distances. Some degree of astigmatism is normal, but where it is pronounced, the astigmatism must be corrected.
Hyperopia, myopia, and astigmatism are usually corrected by glasses or contact lenses. Surgical methods for the correction of such disorders are known. Such methods include radial keratotomy (see, e.g., U.S. Pat. Nos. 4,815,463 and 4,688,570) and laser corneal ablation (see, e.g., U.S. Pat. No. 4,941,093).
Another method for correcting those disorders is through the implantation of polymeric rings in the eye's corneal stroma to change the curvature of the cornea. Previous work involving the implantation of polymethylmethacrylate (PMMA) rings, allograft corneal tissue, and hydrogels is well documented. One of the ring devices involves a split ring design which is inserted into a channel previously dissected in the stromal layer of the cornea. A minimally invasive incision is used both for producing the channel and for implanting the implant.
The use of instastromal corneal rings made completely of certain hard, hydrophobic polymers is known. For instance, in the article “Intrastromal Implantation Eines Justierbaren Kunststofforings Zur Hornhautrefraktionsanderung”, Hartmann et al., Kongress der Deutschen Gesellschaft fur Intraokularingen Implantation, delivered by h. Fryler et al., Spring-Verlag, Wien, pages 465-475, the use of intrastromal ring implants of rings of silicone, polymethylmethacrylate (“PMMA”), and fluorocarbons TEFLON®, a PTFE available from DuPont. Other disclosures of the use of PMMA in such intrastromal rings is found in U.S. Pat. No. 4,452,235 to Reynolds; U.S. Pat. No. 4,671,276 to Reynolds; U.S. Pat. No. 4,766,895 to Reynolds; and U.S. Pat. No. 4,961,744 to Kilmer et al. These documents do not suggest the use of multiple-layers of differing materials in the intrastromal corneal ring.
The use of soft polymers as intrastromal inserts is not widely known. For instance, U.S. Pat. No. 5,090,955 to Simon, suggests an ICR which is made by introducing a settable polymer into an intrastromal channel which has been previously made and allowing the polymer to set. This procedure does not allow the surgeon to specify the size of the resulting ring nor is it a process which allows control of the flowing polymer within the eye.
Temirov et al, “Refractive circular tunnel keroplasty in the correction of high myopia”, Vestnik Oftalmologii 1991: 3-21-31, suggests the use of collagen thread as intrastromal corneal rings material.
They specifically do not suggest the use of soft or hydrophilic polymers insertable into the cornea as intrastromal corneal rings.
SUMMARY OF THE INVENTION
This invention is a hybrid intrastromal corneal ring comprising at least one outer layer of a soft, low modulus, often hydrophilic, physiologically compatible polymer.
The portion of the ICR inside that outer layer may be hollow and adapted to be fillable with a biologic agent, drug or other liquid, emulsified, or time-release eye treatment material. The inner portion may comprise variously a core of a high modulus, physiologically compatible polymer or a further composite of a low modulus polymer or a high modulus polymer core or a high modulus polymer or a low modulus polymer core. The inner portion may comprise a polymeric material which is polymerized in situ after introduction into a hollow center layer.
The term “high modulus polymer” is meant to include physiologically compatible polymers such as PMMA; TEFLON; certain longer chain silicones; polycarbonate; and polyolefins such as polyethylene, polypropylene, polybutylene, their mixtures or other polyolefin interpolymers. The term “low modulus polymer” is meant to include physiologically compatible polymers and hydrogels, such as polyhydroxyethyl methacrylate (“polyHEMA”) or polyvinylpyrrolidone (“PVP”) or elastomeric materials and biologic polymers such as crosslinked dextran, hyaluronic acid, and heparin or the like. The low modulus hydratable polymers, in any case, may be of the type which is sufficiently cross-linked such that they do not swell upon contact with water (and subsequent hydration) or of the type which swells when hydrated. Additionally, the class of low modulus polymers is meant to include elastomeric polymers, e.g., latex rubber, colloids of polyester and polyether, polyurethanes, lower molecular weight silicones, isoprene, and the like, which are stable and physiologically compatible. Finally, the low modulus polymer may be a reinforced hydrogel such as an interpenetrating network of polymerized vinyl pyrrolidone and methyl methacrylate.
Our intrastromal corneal rings may be implanted into the stroma using a number of known techniques. If hydratable polymers are used, they may be hydrated before or after introduction into the intrastromal passageway created by the surgical device used to introduce these devices into the eye. If the outer layer is hydrated before insertion into the eye, the final size of the ring is set before that insertion. If the hydratable polymers are allowed to hydrate within the corneal space, the device (if appropriate polymers are chosen) will swell within the eye to its final size. If prehydrated, the outer layer often provides a measure of lubricity to the ICR, allowing it to be inserted with greater ease. Other of the noted low modulus polymers may also provide such lubricity.
This invention allows for adjustment of intrastromal corneal rings thickness and diameter and provides a softer interface between a harder polymer core and corneal tissue.
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Temirov et al., “Refractive circular tunnel keroplasty in the correction of high myopia”Vestnki Oftalmologii(1991) 3:23-31.
Simón et al., “Refractive remodelling of the cornea by intrastromal
KeraVision Inc.
KeraVision, Inc.
Macey Harry J.
Willse David H.
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