Surgery – Instruments – Light application
Reexamination Certificate
1998-11-06
2001-10-16
Nasser, Jr., Robert L. (Department: 3736)
Surgery
Instruments
Light application
Reexamination Certificate
active
06302877
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system and method for correcting presbyopia through a reshaping of the eye's corneal curvature, so as to have a desired corrective corneal curvature based upon a predetermined eye material removal profile. The removal of eye material is carried out in the corneal stroma preferably with a laser system with means for forming a sculptured corneal stroma having the predetermined profile in cross-section, which profile is based on a predetermined profile equation and the specific input of parameters including measurable eye parameters. The laser system includes control means which relies on corrective presbyopia directive means for ablative resculpturing of the corneal stroma, which directive means facilitates formation of the presbyopia correcting profile deemed best suited for the patient based on preestablished profile parameters.
BACKGROUND OF THE INVENTION
For many, many years, humans have sought ways to correct visual problems. The ancient Chinese slept with small bags of mercury on their eyes, flattening their corneas and improving their shortsightedness. Unfortunately, the effects only worked for a few minutes after waking. Spectacles are thought to have been first introduced by the Arabs in the 11th Century and were introduced into Europe about 200 years later. This century has seen the development of contact lenses, initially the hard variety and later soft and disposable soft lenses.
Although these optical aids allow patients to see well while wearing them, they do not offer a permanent cure for the visual disorder or problem. Also, in many situations, they are inappropriate, for example, when swimming or wearing contacts in the laboratory. Another problem is that in some instances dangerous situations can arise when they become dislodged. This can occur while they are being used by firefighters and police officers.
Roughly two decades ago, surgical techniques were introduced in an effort to permanently correct shortsightedness and astigmatism. The radial keratotomy procedure used a diamond blade to make incisions into the cornea, the front surface or “window of the eye”. Although this technique worked well, there have been problems with long term stability of vision and weakening of the cornea as a result of the cuts often having to be made up to 95% of the corneal thickness.
More recently, these older techniques have been replaced with laser treatment techniques which have replaced the surgeon's blade with a computer controlled laser that gently re-sculptures the shape of the cornea without cutting or weakening the eye. These laser techniques are typically carried out with a photoablation process using an excimer laser.
Excimer lasers were chiefly developed for the manufacture of computer microchips, where they were used to etch the circuits. However, the laser's extreme accuracy resulted in it being well suited as an eye laser. That is, many eye lasers are extremely accurate and remove only 0.25 microns ({fraction (1/4000)}
th
millimeter) of tissue per pulse. During the re-sculpturing, the excimer laser gently “evaporates” or vaporizes tissue; there is no burning or cutting involved. In most cases, the laser treatment takes only 20 to 45 seconds, depending on how severe the refractive error is.
In the normal eye, light rays entering the eye are accurately focused on the retina and a clear image is formed. Most of the bending or focusing of the light rays occurs at the cornea, with the natural lens inside the eye being responsible for fine adjustments. If light is not focused on the retina, then the eye is said to have a refractive error. Common refractive errors include: myopia or shortsightedness, hyperopia or farsightedness, and astigmatism. The excimer laser has been used to accurately re-sculpture the cornea in myopia, hyperopia and astigmatism corrections in an effort to make the curve of the cornea focus light rays normally on the retina.
Myopia, or shortsightedness, is a condition whereby light rays come to a focus in front of, rather than on, the retina at the back of the eye. This results in blurry vision, especially when looking at objects far away. Myopia results from the length of the eye being too long or the cornea being too steeply curved.
In hyperopia, or farsightedness, light rays are focused behind the retina. This results in blurry vision especially when looking at objects that are close. Hyperopia results from the length of the eye being too short or the cornea being too flat.
In astigmatism, the cornea, or window of the eye, has an irregular curvature being shaped more like a rugby ball, rather than a soccer ball. Light rays are focused at different points. A person often has some degree of astigmatism and myopia or hyperopia at the same time.
In myopia laser correction procedures, the cornea is flattened to better focus light rays normally on the retina, whereas in hyperopia, the cornea is made more curved. With astigmatism, the surface of the cornea is re-sculptured to a regular curvature.
Under one method of treatment, known as photorefractive keratectomy (PRK), the, laser beam is applied directly to the surface of the cornea, after the thin surface layer of epithelium cells has been removed (e.g., through solvent with wiping, preliminary laser treatment, or minor abrasion). After the direct laser re-sculpturing of the cornea, a bare area of the cornea is left which takes a few days to heal (e.g., 2 to 6 days) and can be uncomfortable during this period. The healing process can sometimes lead to regression (some refractive error returns) or to scarring (which may blur the vision), especially in patients with large refractive errors. Although still used for low degrees of myopia and hyperopia, PRK is generally being replaced by the LASIK method for these same disorders, in which the laser treatment is applied under a protective corneal flap. Under the “Laser in situ Keratomileusis” (LASIK) treatment, a thin protective corneal flap is raised, rather like a trapdoor. The front surface of the exposed cornea is treated by the excimer laser. The net result being that the cornea is altered in a manner directed at allowing light rays to be focused normally on the retina. At the end of the procedure, the protective flap is simply replaced. The LASIK technique leaves the original surface of the cornea virtually intact, hence, there is no bare area to cause pain. In addition, the mild healing process results in minimal regression and avoids scarring problems.
Presbyopia is a problem that is due to an aging process occurring in the natural lens of the eye, and thus is not linked to the cornea being incorrectly shaped as in myopia, hyperopia and astigmatism. As a person ages, the lens expands, becomes harder and less pliable and, because of these factors, is not as capable of changing its shape to focus. In a typical situation, once a person reaches about 40 years of age, the loss of elasticity and the expansion in the natural lens of the eye results in that person experiencing problems with focusing close, for example, during reading. Most people, as they age, suffer from a presbyopia problem. The usual way to correct this problem is to use bifocal lenses. However, some people dislike wearing glasses, particularly bifocals, for many reasons. For example, bifocal lenses present lines where the two portions of the lens are joined together and thus can be unsightly unless more expensive “no line” bifocals are relied upon. Furthermore, people must become accustomed to reading through the one relatively smaller portion of the bifocals.
Because of the underlying differences in the causes for presbyopia and the group of myopia, hyperopia and astigmatism, many ophthalmologists have concluded that there is no cure for presbyopia and that the only solution is to wear reading glasses to compensate for the loss of ability to focus on close objects.
Chapter 4 of the book
Surgery for Hyperopia and Presbyopia
of Neal A. Sher, M.D., F.A.C.S., 1997 (which book is incorporated by reference in its entirety)
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