Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2001-09-19
2003-04-15
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
C606S005000
Reexamination Certificate
active
06547393
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system and method for correcting corneal irregularities through reshaping of an eye's cornea to provide a desired corrective corneal curvature. A preferred embodiment of the invention includes a topography device for mapping in detail the irregularities and surface deviations of a cornea, an interface system for receiving and manipulating topographical data and for providing directions to a laser system or the like to carry out a predetermined ablation profile on a substrate such as a corneal stroma and for providing a variety of actual and simulated pre and post operative visual depictions. The interface system provides a tool for use by a surgeon or the like which allows a surgeon to review and simulate a wide variety of potential surgical alternatives for a wide variety of corneal defects including irregular eye shapes and corneal surface irregularities.
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, and in some situations even glasses and contacts cannot provide complete correction due, for example, to a localized, highly irregular shaped corneal defect. 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 relatively 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, for most applications, 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 and low thermal effect resulted in it being well suited as an eye laser. That is, many eye lasers are extremely accurate and remove only 0.25 microns (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. A fast treatment time is important in that, for some procedures, an overextended treatment period can slow the post operative curing process to final vision level obtainment.
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 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. Any surface contour irregularities can also result in the improper focusing of the eye due to the irregularities causing light rays to land away from the desired focal point on the retina.
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.
Presbyopia is a problem considered to be due to an aging process occurring in the natural lens of the eye, and thus does not fall under the same category as the refractive errors of myopia, astigmatism and hyperopia noted above, although combinations of presbyopia and one or more of the refractive errors are possible. U.S. Pat. No. 5,533,997 to Dr. Luis A. Ruiz describes a presbyopia corrective apparatus and method which involves the use of a laser system to remove tissue from the eye in presbyopic corrective patterns discovered to be effective by the inventor.
One of the prior art laser treatment methods is known as photorefractive keratectomy (PRK), in which 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 comeal 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.
The ablation profiles for the prior art PRK and LASIK laser treatments described above are based on mathematical equations and formulas that assume the eye as a perfect optical body or one that conforms to an optical model having very regular spherical shapes. The prior art ablation profiles thus fail to take into consideration the fact that each eye is unique and possesses many i
Manuel George
Smith Gambrell & Russell
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