System to automatically detect eye corneal striae

Details System to automatically detect eye corneal striae System to automatically detect eye corneal striae

2001-04-26

2004-07-20

Johns, Andrew W. (Department: 2621)

Image analysis

Applications

Biomedical applications

C348S078000

Reexamination Certificate

active

06766042

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
Not applicable.
BACKGROUND
1. Field of Invention
The present invention relates to ophthalmic surgical procedures for the correction of refractive error. More particularly, the present invention relates to an ophthalmic refractive correction procedure known as LASIK, wherein a corneal flap is produced. Still more particularly, the present invention relates to an ophthalmic instrument and method which automates the detection of eye corneal striae, or corneal wrinkles, following the LASIK procedure.
2. Description of Prior Art
Laser refractive surgery has become a very popular method for providing patients with better vision. The majority of laser refractive surgery patients will have the procedure termed LASIK (Laser In-Situ Keratomileusis) performed. There are some very important advantages that have caused LASIK to be used over the original Photo-Refractive Keratectomy (PRK) technique. For example, the healing process is usually shorter and more comfortable for the patient and larger refractive corrections can be performed.
In the LASIK procedure a microkeratome device is used to create a thin “flap,” typically 120 to 160-microns in depth, in order to expose the corneal stroma below. The flap is not cut completely across the cornea, thus leaving a hinge. The flap is gently lifted off the cornea and held to the side while the laser system delivers the treatment profile into the cornea stroma (tissue directly underneath the flap). After the laser delivery is completed, the flap is put back in place and smoothed by the surgeon. Within about 2 minutes, the flap is reattached enough such that the lid speculum, which is used to hold the eye open, may be removed. At this point the laser refractive procedure is completed.
Although this procedure does possess many advantages over PRK, it has one drawback that can cause postoperative refractive problems for the patient. This drawback is termed corneal flap striae, which is basically a wrinkle in the corneal flap, created when the flap is not uniformly reattached to the cornea. This striae, or wrinkle, can cause vision problems in the patient ranging from glare to acuity problems due to irregular astigmatism.
Presently, there are two approaches to reducing or eliminating eye corneal striae. The first approach is a preventative method. Here, in one approach, inventors have developed methods and tools to visibly mark the cornea before the LASIK flap is made. These markings are then used to realign the flap when it is put back in place. U.S. Pat. No. 5,934,285 (1999) and U.S. Pat. No. 5,697,945 (1997) both to Kritzinger, et. al. describe tools that provide various visible markings to aid in realignment. However, even this approach does not guarantee that there will be no striae present nor does it automate the detection of striae. In another approach, U.S. Pat. No. 6,019,754 to Kawesch, describes a method to improve flap adherence, by applying filtered compressed air to the corneal flap. Again, it only addresses flap adherence; it does not address the detection of eye corneal striae.
The second current approach attempts to detect striae after the flap has been put back in place. Currently, there are two dominant methods for attempting to detect striae after the LASIK procedure. Both are manual, as opposed to automated, techniques performed by the surgeon. In the most popular method, the refractive surgeon checks the “smoothness” of the cornea, with just the operating microscope and the diffuse, broadband, white light source present with the operating surgical microscope. Here, the surgeon is just making a broad visual determination if striae is present. In a second less popular, but more effective method, the surgeon uses a handheld slit lamp, which projects a thin line of visible broadband, white light onto the cornea. The surgeon scans this line across the cornea and looks for aberrations, or edges, on what otherwise should be a smooth surface. Usually, only two to three scans are made at different angles on the cornea and thus striae can be, and often are, missed at the other angles that are not addressed.
Neither of these two present approaches for reducing or eliminating eye corneal striae addresses the automatic detection of eye corneal striae following LASIK refractive surgery.
Outside the ophthalmic area, U.S. Pat. No. 5,764,345 to Fladd, et. al., presents a method for detecting inhomogeneities, specifically striae, in infused silica glasses. This technique was developed for cases where a sample, such as a glass optical lens, can have a beam of light passed through it such that an instrument on the other side of the lens can detect it. This detector is part of an expensive interferometer system used to measure the striae present in the glass. This approach would not work for eye corneal striae detection as one cannot place a detector on the other side of the cornea. Additionally, the interferometer requires precise alignment and would be too expensive for this application.
Thus, there is no present method for automatically detecting eye corneal striae following LASIK refractive surgery.
SUMMARY
The present invention overcomes many of the problems associated with existing manual methods and tools used to prevent and detect eye corneal striae, or corneal wrinkles, after LASIK refractive surgery, by automating the eye corneal striae detection process with a computer-based analysis system.
OBJECTS AND ADVANTAGES
It is therefore an object of the invention to provide an automated technique for detecting eye corneal striae after LASIK refractive surgery which is more precise and more complete than existing manual techniques.
It is another object of the invention to provide an automated technique for detecting eye corneal striae after LASIK refractive surgery which is faster than existing manual techniques.
It is a further object of the invention to provide an automated technique for detecting eye corneal striae after LASIK refractive surgery which will aid in the reduction of patient revisits to correct eye corneal striae problems.
It is an additional object of the invention to provide an automated technique for detecting eye corneal striae after LASIK refractive surgery which is capable of being retrofit to existing refractive laser systems without modifying any hardware in the existing laser system.
In accord with these objects an automated eye corneal striae detection system is provided for use with a refractive laser system which produces a laser for surgically reshaping the eye. The automated eye corneal striae detection system includes a means for illuminating the cornea of the eye, a means for capturing images of the eye, a computer, and a video display to present possible corneal striae to the surgeon. The means for illuminating the cornea preferably includes an apparatus for concentrating multiple beams of light at predetermined points comprising a ring shaped housing with a plurality of annularly arranged spaced opens. Within the housing at each opening is a holder for a light source for a beam of light, preferably monochromatic, directed out of the opening. A cover for the housing, preferably encasing a diffusing optical element, is threadably engaged with the latter. The computer preferably includes a digital input-output printed circuit board which controls the illuminating apparatus; a video frame grabber which captures images from a camera on the laser system; and is programmed to perform an automated eye corneal striae detection algorithm with respect to the images. The automated eye corneal striae detection algorithm finds possible striae in the image and calculates their position and shape characteristics. The possible striae are then displayed on the video display so that the surgeon can make a determination as to whether the corneal flap should be refloated, adjusted or smoothed again.
The automated eye corneal striae detection system may be retrofit to existing refractive laser systems. Additionally, the automated eye corneal striae detection system may be provided as an integr

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