Surgery – Instruments – Light application
Reexamination Certificate
1999-12-22
2001-02-20
Buiz, Michael (Department: 3731)
Surgery
Instruments
Light application
Reexamination Certificate
active
06190375
ABSTRACT:
FIELD OF INVENTION
The invention relates generally to a laser system for corneal sculpting. More specifically, it relates to a system and method for determining the dark adapted pupil size of a patient and reshaping the cornea of the eye based on the dark adapted pupil size.
BACKGROUND OF THE INVENTION
Of the various components in the human eye, the cornea is the principal optical element for refracting incident light onto the retina in the form of a clear image. Photorefractive keratectomy (PRK) is a procedure which typically utilizes an excimer laser beam to vaporize “ablate” corneal tissue in a precise manner to correct for focussing deficiencies of the eye. An excimer laser is preferred for this procedure because pulsed ultraviolet ablation is predictable, discrete, and non-damaging to adjacent tissue. PRK generally involves mechanical removal of the epithelium or outer layer of the cornea to expose the Bowman's layer on the anterior surface of the stroma. Laser ablation usually begins at the Bowman's layer. The laser beam removes corneal tissue to varying depths as necessary for recontouring the anterior stroma. Afterward, the epithelium rapidly regrows and resurfaces the contoured area, resulting in an optically correct (or much more nearly so) cornea. In a variation of the procedure, a surface flap of the cornea is folded aside and the exposed surface of the cornea's stroma is ablated to the desired surface shape with the surface flap then being replaced.
The specific region of the cornea involved in the refractive image formation will vary with the size of the pupil. Only a small central corneal region will refract light onto the cornea when the pupil is constricted under bright lighting conditions. Under dim lighting conditions, when the pupil is substantially dilated, a much larger corneal region is involved forming an image on the retina. This variation in pupil size can become an issue for a PRK patient if the diameter of the laser-treated corneal region (“the optical zone”) is smaller than the dilated pupil diameter. When the ablated optical zone is smaller than the patient's dark adapted pupil size, the patient's night vision is affected. Typically, the patient's vision will be hazy or somewhat blurred, and the patient may perceive halos around bright lights. Approximately 20 percent of patients treated with a 5 mm optical zone have complained of such problems. This is a result of the pupil becoming larger than 5 mm as the pupil adapts for darkness. When a 6 mm optical zone is ablated, it is estimated that only 2 percent of patients complain of night-vision problems.
One apparent strategy for avoiding such night-vision problems would be to treat all patients with an optical zone larger, much larger, than the maximum pupil diameter. However, there are several disadvantages to this approach. First, maximum pupil diameter varies from patient to patient. Second, the maximum depth of laser ablation and the total volume of tissue removed both increase with optical zone diameter. Such increases typically lead to more regression, that is, deterioration, of the refractive change as the cornea heals. In addition, the increased tissue volume to be removed necessitates a longer laser procedure. Variations in corneal ablation behavior over time due to hydration changes in the de-epithelialized tissue (known to occur) maybe degrade the accuracy of the ablative corneal reshaping for lengthy procedures. A much more desirable strategy, not advanced until the present invention, is to tailor the optical zone diameter in each treatment to the maximum pupil diameter of that patient.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a system and method for determining the dark adapted pupil size of an eye.
Another object of the present invention is to provide a system and method for determining the dark adapted pupil size of an eye as a tool in ophthalmic laser surgery to include corneal sculpting procedures.
Yet another object of the present invention is to provide a system and method for determining the dark adapted pupil size of an eye that is surgically eye safe.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a system and method are provided for performing a reshaping of a cornea of an eye for improved vision. The system comprises a first apparatus for determining dark adapted pupil size of an eye; and a second apparatus for reshaping the cornea of the eye in an area approximately equal to the dark adapted pupil size as determined by the first apparatus. The preferable appartus for determining the dark adapted pupil size of an eye permits tracking the eye as ambient lighting is dimmed down to complete or near-complete darkness with an electrical control of a zoom mechanism. The zoom refers to adjusting the diameter of the spot pattern projected onto the eye. Feed back can be utilized to sense the return from the spots, and then to adjust the zoom so that the spot pattern diameter matches the pupil diameter. Laser ablation would then proceed over that circular region (maybe, plus a little outside). Alternatively, a video system with a circular cursor could be used in dim illumination to identify the position and diameter of the dilated pupil. The zoom mechanism has an electrical control for size adjustment of a beam optical radiation or a plurality of such radiation beams (either at a visible or infra-red wavelength) incident on a boundary coincident with the dark adapted pupil size of the eye. The first apparatus may also comprise delivery optics for focusing a plurality of optical radiation beams on a corresponding plurality of positions located on a boundary coincident with the pupil size of the eye to form a pattern. Zoom optics may be used for adjusting the pattern formed by the plurality of optical radiation beams incident on said corresponding plurality of positions. An optical receiving arrangement for detecting reflected energy from each of the plurality of positions is also employed to determine the dark adapted pupil size. The pattern formed by the plurality of optical radiation beams is equivalent to the dark adapted pupil size of the eye. The dark adapted pupil size is entered into a computer program for corneal sculpting.
In performing laser reshaping of an eye for improved vision, the diameter of the optical zone ablated on the cornea is adjusted to match, or nearly match, the diameter of the dilated pupil. The ablation profile at the periphery of the optical zone may be tapered to form a smooth transition between treated and untreated portions of the eye.
This patent application is copending with related PCT patent applications entitled, “Laser Sculpting Method and System”, International publication number WO 95/28890; “Eye Movement Sensing Method and System”, International publication number WO 95/28879; and “Laser Beam Delivery and Eye Tracking System”, International publication number WO 95/28989 all of which were published on Nov. 2, 1995, and owned by a common assignee of subject PCT applications. The disclosures of these three applications all of which are based on United States patent applications, are incorporated herein by reference.
REFERENCES:
patent: 5163934 (1992-11-01), Munnerlyn
patent: 5196027 (1993-03-01), Thompson et al.
patent: 6027494 (2000-02-01), Frey
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Autonomous Technologies Corporation
Buiz Michael
Lewis William
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