Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Corneal implant
Reexamination Certificate
2000-01-10
2001-05-08
Nguyen, Dinh X. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Corneal implant
C623S006340, C623S006350
Reexamination Certificate
active
06228113
ABSTRACT:
This invention pertain to an optically transparent, intracorneal (intralamellar) onlay that corrects for astigmatism, either alone or in addition to one of various corrections for nearsightedness (myopia) or farsightedness (hyperopia).
In a normal eye, light rays are focused at a single place on the retina, the layer of light-sensitive tissue at the back of the eye. This focusing is accomplished by two structures: first, the cornea, the clear portion at the front of the eye; and second, the natural lens, located inside the eye behind the cornea. The cornea bends (or refracts) the incoming light rays toward a single focal point, providing nearly 80% of the focusing power of the eye. The lens further refines the refraction by directing the light rays onto a precise location on the retina. The retina receives the focused point of light and transmits a signal through the optic nerve to the brain.
Refractive errors, which include nearsightedness, farsightedness, and astigmatism, usually result from a defect in the shape of the cornea in relation to the length of the eye that causes the incoming light to be focused somewhere other than on the retina. In normal vision, the cornea is smooth and the curvature of the cornea is the same in all directions. In persons with nearsightedness or farsightedness (called spherical refractive errors), the curvature of the cornea is either too steep or too flat, respectively. This distortion of the cornea causes the light rays to reach a point of focus either in front or behind the retina, in both cases causing blurred vision.
Spherical refractive errors can be corrected with glasses or contact lenses, and by means of refractive surgery, including radial keratotomy, corneal transplantation, and laser surgery.
Another method for correcting refractive disorders caused by distortion of the cornea is corneal implantation. The cornea has five layers: the outer layer, the epithelium; Bowman's membrane; the multi-layered mid-region, the stroma; a strong membrane layer, Descetmet's membrane; and the inner layer, the endothelium. Corneal implants are usually placed within the multi-layered stroma.
One form of corneal implants to change the curvature of the cornea is a polymeric ring or ring segment (intrastromal corneal ring) or other inserts, placed in the periphery of the cornea (outside the visual field). See, e.g., U.S. Pat. Nos. 5,405,384; 5,733,334; 5,824,086; 5,876,439; and 5,888,243.
U.S. Pat. No. 4,298,004 describes injecting collagen or suitable material into the cornea to alter the radius of curvature.
An intracorneal lens has also been developed to correct for myopia with or without astigmatism. U.S. Pat. No. 5,123,921 describes a circular lens placed in the stroma by cutting a thin slice of tissue from the front of the cornea. The slice remained attached on one side, forming a flap. The flap was lifted, the lens placed on the exposed surface of the stroma, and the flap allowed to fall back over the lens. The refractive properties of the cornea changed because the front surface of the cornea took on the shape of the lens under the flap of tissue. The lens was made of a biocompatible material that allowed metabolites to diffuse easily, ensuring delivery of nutrients necessary for the health of the outer cornea. When correcting for astigmatism, the circular lens was made into a toric lens with different curvatures in different meridians.
U.S. Pat. No. 4,607,617 describes an intracorneal, circular lens made of a polysulfone material of high refractive index placed in the stroma of the cornea to correct refractive defects, which was said also to strengthen and shape the cornea to assist in treating astigmatism.
Astigmatism is another form of refractive error. The curvature of the cornea is warped in one direction. The eye is shaped more like a football than a basketball. This distortion bends incoming light rays in two directions, so that a single focal point is not attained. The multiple focal points result in distorted vision with images appearing indistinct and slanted. Depending on the orientation (or meridian) of the distortion, images are more in focus in one direction than in another. One person with astigmatism may not see vertical lines clearly, another may see fuzzy horizontal lines, and a third may not be able to focus diagonal lines properly. Because this type of refractive error is identified by the axis or meridian in which it is oriented, it may be called a “meridional” error.
Astigmatism can be corrected with glasses or contact lenses, designed to equalize the unequal curvatures of the light caused by the cornea. Because astigmatism is similar to having the spherical cornea bent so that there is a ridge running along one meridian, one approach to correcting astigmatism is to provide a compensating ridge in the orthogonal meridian. Historically, lenses have accomplished this by having different power curves to correct the distortion in different meridians. These lenses are called “toric lenses.” Because of the different powers, these lenses have a variable edge profile that is thinner in some places and thicker in others, and are difficult to make.
A variety of approaches to correcting spherical and meridional refractive errors by implanting lenses intraocularly, as contrasted to the intracorneal lens discussed above, have been proposed.
U.S. Pat. No. 4,277,852 describes an intraocular, glass lens that is placed in the eye in front of the natural lens to correct for astigmatism.
U.S. Pat. No. 4,435,856 describes an intraocular, bifocal implant with one lens fixed in the eye for distance and a second lens that can be selectively moved in and out of the optical axis to change the focal length.
U.S. Pat. No. 4,512,039 describes a toric, intraocular lens that corrects postoperative astigmatism by placement in the eye such that the vertical meridian is optically less powerful than the horizontal meridian.
U.S. Pat. No. 4,585,456 describes an intraocular lens that is inlayed on the intact natural lens and a means to maintain the lens position relative to the natural lens.
U.S. Pat. No. 4,769,035 describes an intraocular lens that is implanted on the natural lens to correct for nearsightedness and farsightedness. The circular lens has extensions to help maintain its position on the natural lens.
U.S. Pat. No. 4,816,031 describes an intraocular lens system that includes both a hard lens implant, a soft lens implant, and a microcircuit to change the focal point by varying the distance between the two lenses.
U.S. Pat. No. 5,133,747 describes the adhesion of an artificial, intraocular lens to the natural lens or to a previously implanted lens by adhesives or clips.
U.S. Pat. No. 5,171,266 describes a single intraocular lens that can be adjusted by a surrounding ring to change its power either regularly or more in one meridian than in another to provide astigmatic correction. The surrounding ring is adjusted by changing an external magnetic force.
To make a single lens that corrects for both spherical (nearsightedness and farsightedness) and meridional (astigmatism) visual problems is both mechanically difficult and expensive. Two different power curves are needed to correct astigmatism because the astigmatic cornea splits the light into separate focal points. Also, because of the different powers, the lenses have a variable edge profile, thinner in some parts and thicker in others. Correction of astigmatism in a given individual requires a customized lens to provide the correct spherical and meridional refraction. A large inventory of lenses is needed to encompass a set of combinations of spherical and meridional corrections that will adequately treat most patients. For example, to provide for spherical corrections from +5 diopters (D) to −5 D at 0.25 D intervals, 40 lenses are needed. To also include corrections for astigmatism up to −5 D at 0.25 D increments, a total of 800 lenses would be required.
I have discovered an intracorneal, rectangular onlay, that is a simple correction for astigmatism. This astigmatic on
Board of Supervisors of Louisiana State University and Agricultu
Davis Bonnie J.
Nguyen Dinh X.
Runnels John H.
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