Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2001-02-27
2003-06-24
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
C606S010000
Reexamination Certificate
active
06582078
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to refractive eye surgery, and more particularly to a software tool for assisting surgeons in planning this surgery.
BACKGROUND
Refractive errors result when the optical elements of the eye, namely the cornea and the lens, do not focus a clear image onto the retina. An eye is considered emmetropic if it has no refractive error. Most eyes have at least some degree of refractive error. In myopia, the optical elements are too strong for the length of the eye, and the image is focused in front of the retina. In hyperopia, the optical elements are too weak for the length of the eye, and the image is focused behind the retina. In astigmatism, the optical elements cannot focus an image to a single point, and the image is split and focused at two separate points.
When a refractive error is present, a lens may be used to refocus light onto the retina. This lens may be in the form of a spectacle lens or contact lens. Additionally, a lens surgically implanted within the eye (intrastromal or intraocular) can be used.
The cornea is the strongest refracting lens of the eye. Therefore, small changes in the shape of the cornea result in large changes in the overall refractive properties of the eye. By making the cornea flatter or steeper in a controlled fashion, a surgeon can affect changes in the eye's refractive power. Using mathematical calculations and review of surgical results, a surgeon can predict the amount of refractive change induced by a given amount of corneal reshaping. Surgeons use these calculations to predict the outcome of corneal refractive surgery.
Radial Keratotomy (RK), Arcuate Keratotomy (AK), and Photo Refractive Keratectomy (PRK) are refractive corneal surgical techniques that have been commonly used in the past to induce controlled changes in the shape of the cornea, and subsequently in the refractive error. In RK and AK procedures, surgeons use a diamond-bladed scalpel to make small incisions in the cornea. Radial incisions, used in RK, reduce myopic refractive errors while arcuate incisions, used in AK, reduce astigmatic refractive errors. These incisions induce changes in the corneal curvature and, consequently, alter the eyes' refractive properties.
PRK procedures use a laser to reshape the corneal surface. The laser sculpts a thin layer, between 5 and 10 mm in diameter, on the corneal surface. This technique has many advantages over RK/AK since it usually cuts less than 10 percent of the way through the cornea, as opposed to about 90 percent with RK/AK, and can correct a wider range of myopic, hyperopic, and astigmatic refractive errors.
Laser Assisted In Situ Keratomileusis (LASIK) offers additional advantages over both RK/AK and PRK. The LASIK procedure consists of two distinct surgical procedures. The first part of the procedure involves the surgical creation of a corneal flap. The laser is then used to treat deeper corneal stroma tissue in much the same way as PRK treats the stroma near the corneal surface. The flap is then replaced after the laser treatment. This offers the advantage of leaving much of the corneal surface intact, leading to faster and more comfortable recovery for the patient.
Despite its advantages over other corneal refractive surgery techniques, LASIK refractive surgery still has a number of shortcomings. This invention addresses, among other things, one of these shortcomings, namely, the fact that many excimer lasers now used for LASIK were built for the purpose of performing PRK refractive surgery. Consequently, when a surgeon enters patient data such as refractive error and patient age, the laser calculates a treatment based on the expected results of PRK, not LASIK. Therefore, a surgeon must compensate for the fact that LASIK and PRK differ in refractive treatment effects by making appropriate adjustments to the refractive error information that is entered into the machine. This means that the surgeon often cannot use the patient's actual refractive error to achieve the best surgical result. Instead, the refractive error information that is actually entered must be adjusted by as much as 25 percent in order to optimize the treatment. These adjustments are calculated using a nomogram that is created on the basis of previous surgical results. An example of a nomogram for myopia is shown in FIG.
1
. There are different nomograms utilized for each type and combination of refractive errors including myopia, hyperopia, and astigmatism. It should also be understood that these charts are specific to particular surgical laser equipment, and somewhat dependent on variations in surgical technique. Different surgical laser equipment manufactured by different suppliers would therefore require different chart nomograms. The chart nomogram (
FIG. 1
) has patient age in years on one axis and diopters of refractive error on the other axis. Each axis contains a range for each data entry. Where the x and y-axis meet, a correction percentage is given. This represents the amount that the programmed refractive error must be changed in order to perform LASIK. A problem arises in that a large amount of surgeon judgment is required in utilizing a chart nomogram. This judgment is required because each axis includes range data that will affect the percent correction factor in setting the laser. For example, if the patient is at the low end of an age range on one axis and has a spherical equivalent at the low end of the refractive range on the other axis, the surgeon may adjust the percentage of correction suggested in the chart nomogram by a different amount than if the patient's age or refractive error were at a different point within the same range on the x or y axis. The correction percentage indicates that the refractive laser should be set for the desired diopters of correction by adjusting the spherical refraction. The surgical plan may also include a simultaneous but different formula to adjust the cylindrical portion (astigmatism) of the manifest refraction.
The growing body of clinical evidence suggests that a nomogram must take into consideration a number of factors including but not limited to the refractive error of the eye and the patient's age at the time of surgery. Other parameters may influence the refractive effect of the laser treatment on the eye, including the vertex distance of the refraction, and the patient's gender. Despite this accumulation of data, LASIK, like all surgical procedures, can vary in effectiveness from surgeon to surgeon and from patient to patient. It should be emphasized that, as more information is collected, the nomograms can, and should, be revised to include statistical data indicative of a particular surgeon's procedural results.
The beginning surgeon has no personal surgical data, and therefore cannot predict the effectiveness of an excimer laser, built and programmed for PRK, when used for LASIK. With experience, a surgeon may begin to understand the variables that will result in over- or under-correction, however, with no personal experience; a beginning surgeon must rely on nomograms based on the results of others. What is needed is a tool to assist such surgeons in developing a standardized technique and nomogram based on the results of other surgeons. What follows is a brief review of the decisions a surgeon must make in preparation for LASIK surgery.
LASIK DECISIONS
Refractive Error Correction. One of the most important decisions involves understanding the design of the laser system being used. As stated, many lasers were designed and programmed for the purpose of performing PRK. If a surgeon wishes to perform LASIK using one of these machines, he or she must understand that the programmed correction must be adjusted based on the known differences between PRK and LASIK. These differences are currently addressed using published chart nomograms, however, more precise adjustment calculations would be desirable. Currently, the clinical evidence suggests that age and refractive error have a bearing on the effectiveness of LASIK
Gallagher Shawn P.
Halpern Barton L.
Barley Snyder
Halpern Barton L.
Manuel George
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