Surgery – Instruments – Light application
Reexamination Certificate
1999-04-12
2001-04-17
Peffley, Michael (Department: 3739)
Surgery
Instruments
Light application
C606S006000, C128S898000
Reexamination Certificate
active
06217570
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to laser keratectomy and in particular to properly aligning the visual axis of the patient's eye with the optical axis of the laser beam used to shape the cornea of the eye.
BACKGROUND OF THE INVENTION
The use of an excimer laser to reshape the cornea is now a widely practiced procedure for correcting myopia, astigmatism and hyperopia. As is known, the laser beam is shaped at a point in its pathway or scanned over the cornea to remove tissue by ablation. One of the most serious problems that can occur in any keratorefractive procedure that involves the reshaping of the central cornea is the decentration of the central region of the reshaped cornea from the point where the visual axis intersects the cornea. Such decentration is a known problem with excimer laser keratectomy including but not limited to PRK and LASIK surgery. To overcome the problem, excimer lasers conventionally provide a fixation light. The fixation light is positioned to be centered in the excimer laser beam above its last turning mirror. The optical axis of the fixation light is presumably aligned with the optical axis of the excimer laser allowing the surgeon to align the visual axis with the optical axis of the fixation light and thus presumably the optical axis of the excimer laser. However, since the fixation light can be viewed by the patient's eye when it is in a position other than directly aligned with the excimer laser beam, the ablated area may be decentered with the visual axis intersecting an area of the ablation other than at its center. This introduces astigmatism, irregular astigmatism, hyperopia, decreased visual acuity, “ghost” images and slows the postoperative recovery of vision.
Experience with excimer lasers has shown that a patient can observe the fixation light by rotation of his or her eye so that the eye's visual axis is not parallel to the laser beam. See FIG.
2
. Such rotation will result in decentration of the ablation of the cornea. Accordingly, there is a need for a way to enhance centration of the cornea ablation laser with the visual axis of the eye.
Customarily, the centration of the excimer beam is accomplished by centering the pupil in the path of the excimer ablation either by marking the center of the pupil with two coincident visible laser beams which intersect at the center of the laser ablation or by positioning the pupil so that it falls inside the circle of a reticle in the eye piece of the surgeon's microscope, that reticle having previously been aligned with the excimer laser beam. The patient is then asked to look at a fixation light which has been previously calibrated to set it in the center of the excimer laser beam when the patient's eye is centered under the operating microscope. The problem with this fixation technique is that the patient's visual axis may be directed at the fixation light even when the pupil and eye are not centered in the excimer ablation beam because the eye is tilted, since the patient can still see the fixation light even when the eye is not properly centered.
Put differently, positioning the patient's eye under the laser so that the laser beam for ablating the cornea is centered symmetrically around the visual axis is essential for good optical quality of the corneal ablation. However, no matter how precisely the visual axis is lined up with a conventional fixation light, the laser's optical centration cannot be accurate unless the fixation light itself is located so that it is viewed by the patient in the center of the laser beam. Since the patient's fixation is subjective and the laser beam is invisible, assurance that the instrument has been calibrated so that the fixation light is perfectly centered with an excimer light cannot be obtained with sufficient certainty. The present invention provides assurance of proper alignment and centration between the laser beam and the patient's visual axis and allows the surgeon to align the fixation beam if necessary.
Accordingly, the present invention is directed to a method of assuring centration of the laser beam along the patient's visual axis.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 5,549,597 is directed to an auxiliary apparatus for enabling in situ determination of the astigmatic axis of an eye and for aligning the cylindrical axis of an excimer laser for surgery. In general, the apparatus projects an adjustable target image. The image is adjusted until it can be clearly viewed by the patient. The result is a readout of the astigmatic axis which is used to adjust the excimer laser. The light source for illuminating the projected image is a conventional electric light or a light emitting diode.
U.S. Pat. No. 4,765,336 describes an apparatus for folding a slip lamp light source into the optical axis of a laser beam. A HeNe beam is also folded into the optical axis. All three beams are said to be coaxial or can be made coaxial by use of a mechanism for moving the laser and illuminating beams as viewed through a microscope.
U.S. Pat. No. 4,583,539 is directed to a laser surgical system wherein a HeNe laser and cold light source are optically folded into the optical axis of a CO
2
laser. The HeNe laser is used to properly direct the C
0
2
laser since infrared radiation emitted by the C
0
2
laser is not visible to the human eye.
U.S. Pat. No. 5,281,211 is directed to an apparatus for aiming and/or aligning an excimer laser using a HeNe laser. In particular, a HeNe laser is used to generate visible light which is projected along the optical axis of the excimer laser. Thus the HeNe laser can be viewed through the surgical microscope by the physician.
U.S. Pat. No. 4,409,979 discloses a system for combining both observation beams and illuminating beams in a single optical system for a laser for surgically treating the eye. The light sources can be HeNe laser, a surgical laser and a non-coherent light source.
U.S. Pat. No. 4,830,483 discloses apparatus for providing a visible light guide for an excimer laser.
U.S. Pat. No. 4,881,808 is directed to a system in which a visible light source is coaxially combined with a surgical light source. U.S. Pat. No. 4,887,592 is to the same effect.
U.S. Pat. No. 5,474,548 describes a method for aligning a patient's visual line of sight with the optical axis of an ophthalmic device. The device can be one that is used during laser surgery. The mechanism and method for obtaining alignment according to this patent consists of obtaining two images and then having the patient move his or her eye until the images appear to be in alignment as viewed by the patient's eye.
U.S. Pat. No. 5,214,455 is directed to a system and method for objective eye alignment as opposed to alignment based upon a patient's report of what he or she sees. The patent describes apparatus and a method for obtaining such objective eye alignment by finding and comparing the relationship between the instrument axis and the axis of the patient's eye which is particularly defined.
U.S. Pat. No. 4,620,318 is directed to an apparatus and method using a scanning beam to describe a circular locus of points substantially centered on the fovea.
U.S. Pat. No. 5,442,412 refers to an apparatus and method for fixing the position of the eye using a ring of visible light in combination with a second light source producing a dot of visible light. The system determines when the dot and ring are not concentric.
U.S. Pat. No. 5,024,518 is directed to an ophthalmic contact lens with an external fixation light for determining when the fovea of the eye aligns with a beam of light.
SUMMARY OF THE INVENTION
The present invention relates to a method for properly positioning the patient's eye in the optical axis of a laser beam to be used for reshaping the cornea of the eye. More particularly, the present invention relates to a method of aligning the visual axis of the patient's eye with the optical axis of a laser beam for ablating the eye's cornea.
In accordance with t
Akin Gump Strauss Hauer & Feld L.L.P.
Farah Ahmed
Peffley Michael
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