Surgery – Instruments – Light application
Reexamination Certificate
1994-02-08
2002-01-29
Shay, David M. (Department: 3739)
Surgery
Instruments
Light application
C606S003000, C606S010000, C606S013000, C606S027000
Reexamination Certificate
active
06342053
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a coupler apparatus for use in combination with a noninvasive ophthalmological method for reshaping the anterior surface of the cornea in order to achieve emmetropia (i.e., normal vision characterized by the absence of ocular refractive error; the emmetropic eye focuses parallel rays of light onto the retina to produce a clear image). The method of the invention uses light energy to induce thermal changes to the collagen in the stromal portion of the cornea in order to physically reorganize the stromal collagen to produce the desired reshaping of the cornea. The method is described in commonly-assigned, copending U.S. patent application Ser. No. 556,886 filed Jul. 23, 1990 which is hereby incorporated by reference as if fully set forth herein.
The apparatus of this invention is referred to as a coupler based on its utility, which is to couple a heat and light energy source to the cornea surface. It is made of a material which is substantially transparent to the light energy used to reshape the cornea. In this fashion the coupler acts as a heat sink. The coupler conducts heat from the anterior portion of the cornea during the heating of the stroma. The coupler has a corneal engaging surface so that the coupler is positioned on the anterior surface of the cornea. This corneal engaging surface has a radius of curvature which approximates the desired emmetropic shape of the cornea following the heating of the stroma and rearrangement of the collagen.
Today there are over 100 million people in the United States alone who wear eyeglasses or contact lenses to correct ocular refractive errors. The most common ocular refractive errors include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. In myopia, the refractive power of the eye is excessive meaning that parallel rays of light are focused in front of the retina producing a blurred image. Myopic vision can be modified, reduced or corrected by adding a spherical concave lens of the correct spherical curvature in front of the eye or by flattening the cornea axisymmetrically around the visual axis to reduce its refractive power.
In hyperopia (also termed hypermetropia), the refractive power of the eye is deficient meaning that parallel rays of light are focused behind the retina producing a blurred image. Hyperopic vision can be modified, reduced or corrected by adding a spherical convex lens of the correct spherical curvature in front of the eye or by steepening the cornea axisymmetrically around the visual axis to increase its refractive power.
In astigmatism, the refractive power of the eye is unequal in all meridians meaning that parallel rays of light are focused differently along different meridians producing a blurred image. Astigmatic vision can be modified, reduced or corrected by adding a non-spherical lens of the correct cylindrical curvatures along various meridians in front of the eye or by flattening and/or steepening the cornea with the correct cylindrical curvatures to compensate for refractive errors along various meridians.
Current widely used devices or methods for correcting ocular refractive errors include eyeglasses, contact lenses and refractive surgery such as radial keratotomy. Eyeglasses and contact lenses may be inconvenient, difficult to wear or impediments in daily activities.
Refractive surgery procedures offer an alternative to eyeglasses and contact lenses but these procedures may be difficult to control in order to achieve accurate refractive corrections. Radial keratotomy is a refractive surgical procedure designed to correct myopia. This technique involves making a series of deep, radial incisions in the cornea with a pattern that resembles the spokes of a bicycle wheel. The incisions themselves do not cross the center of the cornea, the central optic zone. The series of symmetrical cuts flatten the cornea.
Significant percentages of patients who have been subjected to radial keratotomy experience overcorrection, undercorrection or induced astigmatism. Radial keratotomy patients may also suffer from side effects and postoperative complications such as fluctuating refraction, glare, reduced night vision, photophobia, endothelial cell loss, and corneal infection. Another postoperative complication of radial keratotomy is permanent weakening of the cornea due to the fact that the technique requires deep incisions that heal quite slowly. Trauma to the eyes may result in the rupture of the incisions leading to catastrophic loss of the cornea in some cases.
Another method of refractive surgery is laser keratomileusis (i.e., carving the cornea by application of laser energy) also termed laser refractive keratectomy or photorefractive keratectomy. This method of refractive surgery is currently being used in clinical trials in man to correct refractive errors. This technique employs the use of a laser that emits ultraviolet light, typically an argon fluoride excimer laser that operates at a wavelength of 193 nanometers. The laser light causes a breakdown of intramolecular bonds resulting in ablation of tissue by photodecomposition. The shape of the cornea is changed by selectively ablating material in the cornea thus “carving” the anterior corneal surface into a new shape. U.S. Pat. No. 4,665,913 discloses one technique of photorefractive keratectomy.
As is the case for other forms of refractive surgery, photorefractive keratectomy may lead to inadequate refractive corrections and to undesirable side effects. Particularly troublesome is the postoperative complication associated with corneal wound repair, a process that tends to “fill in” the ablated cornea volume with a combination of epithelial and stromal tissues. This process in the human cornea is sometimes referred to as a wound-healing response. There are also concerns about the potential phototoxic effect of ultraviolet light generated by corneal tissue fluorescence and the potential toxic effect of molecular ablation products present in the photoablation plume.
Another method of refractive surgery is intrastromal photorefractive keratoplasty. In this technique a laser beam is focussed inside the corneal stromal tissue to modify tissue either by photoablation or by a change in the tissue's viscoelastic properties. U.S. Pat. No. 4,907,586 discloses one such method for optical laser surgery. It is not clear when the supporting work for this patent was performed. The wavelengths of the laser beams to be used are specified to be 526 nanometers, 1.053 microns, or 2.94 microns. Some of these wavelengths (526 nanometers and 1.053 microns) are transmitted, at least in part, through the cornea possibly causing damage to the retina. If laser induced optical breakdown (i.e., laser induced plasma formation) is used to increase the absorption of these wavelengths, the hot plasma will reradiate light with a broad wavelength distribution that includes phototoxic light in the ultraviolet spectral region. The final wavelength (2.94 microns) specified in U.S. Pat. No. 4,907,586 is absorbed completely in the anterior portion (particularly, the epithelium) of the cornea [G. L. Valderrama, et al.,
SPTE Proceedings
, Vol. 1064, 135-145 (1989)] so that it cannot produce intrastromal tissue modification. The alleged intrastromal photorefractive keratoplasty method is unworkable at some wavelengths and undesirable at other wavelengths because there may be severe damage caused to ocular structures.
Thermokeratoplasty is another method that has been used to reshape the cornea. This is done by the application of heat to the cornea. Corneal stromal collagen shrinks when heated to a temperature of 55° to 58° C., without the destruction of the tissue. The stroma is the central, thickest layer of the cornea and consists mainly of collagen fibers. If the pattern of shrinkage is properly selected the resulting change in the stress field and mechanical properties caused by the shrunken collagen fibers can be used to reshape the cornea.
The original thermokeratoplasty technique used was the applic
Alison de Runtz K.
Laser Biotech, Inc.
Shay David M.
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