Surgery – Instruments – Light application
Reexamination Certificate
2000-07-27
2003-07-15
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Light application
C606S005000, C606S010000, C606S012000, C351S206000, C351S211000, C351S212000
Reexamination Certificate
active
06592574
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to medical devices, systems, and methods. More particularly, the present invention relates to the measurement of a tissue surface such as the surface of the cornea. The invention allows measurement of the tissue surface shape, and/or can provide a measurement of the hydration of the tissue.
Measurements of the surfaces of the eye are useful in diagnosing and correcting vision disorders. Refractive vision errors such as nearsightedness, farsightedness and astigmatism may be corrected surgically. Photorefractive keratectomy (PRK) and phototherapeutic keratectomy (PTK) employ optical beam delivery systems for directing a pattern of laser energy to a patient's eye in order to selectively ablate corneal tissue to reform the shape of the cornea and improve vision. These techniques generally sculpt the corneal tissue to alter the optical characteristics of the eye. Measurement of the eye surface may enhance the accuracy of the sculpting procedure, and could be used to verify that resculpting is proceeding as intended.
Known laser eye surgery techniques often rely on an analysis of the patient's vision to calculate a predetermined pattern of the laser energy so as to effect a desired change in the optical characteristics of the eye. These calculations often assume that the corneal tissue ablates uniformly. The laser pattern is often defined by a beam formed as a series of discrete laser pulses, and known pulse pattern calculation algorithms often assume that each pulse of laser energy removes corneal tissue to a uniform depth, so that the size, location, and number of pulses distributed across the target region of the corneal tissue determine the characteristics of the resculpting. Such techniques work quite well, particularly for eyes having “regular” refractive errors such as myopia, hyperopia, astigmatism, and the like. However, work in connection with the present invention has suggested that pulse ablation depths are not always uniform. Additionally, treatment of irregular corneas can benefit significantly from an accurate measurement of the corneal surface shapes. Hence, a combination of refractive resculpting capabilities with techniques for accurately measuring the shape of the eye would appear to be quite promising.
Current techniques for measuring the eye during surgery suffer from various limitations. Generally, known techniques for measuring the shape of an eye measure either light that is reflected from the surface of the eye, light that scatters from the eye, or the fluorescence of a dye that is applied to the eye. Unfortunately, the surface of the cornea becomes rough during surgery. Light that is reflected from the eye is unevenly scattered, often making measurements with reflected light difficult and inaccurate. Many techniques that employ scatter from the surface of the eye also have limited accuracy because light does not scatter evenly from the rough eye surface. Applying a fluorescent dye to the eye can lead to an inaccurate measurement of the surface shape because it is the shape of the dye covering the eye, rather than the eye itself, that is measured. Also, applying a dye to a tissue structure of the eye can delay a surgical procedure, and generally changes the hydration of the eye.
Hydration of the eye can also be difficult to measure accurately using known techniques, particularly during an ablation procedure. As both the depth of an ablation and the shape of tissue removed can vary with the water content of the tissue, known laser eye surgery techniques often include provisions to control the moisture in the corneal tissue before and/or during the procedure. Nonetheless, variations in moisture content, both locally (on different areas of the same target tissue) and between different patients (in different climates, or the like) can occur, potentially leading to significant differences between the intended resculpting and the actual change in the shape of the corneal tissue.
In light of the above, it would generally be desirable to provide improved tissue surface measurement and ablation systems, devices, and methods. It would be beneficial if the improved surface measurement techniques were suitable for integration with known laser eye surgery systems, particularly if these techniques could provide diagnostic information before, and/or feedback information during, a corneal resculpting procedure. It would further be beneficial to provide information on the shape and/or hydration of the corneal surface itself, and if these measurements could be used to modify the resculpting laser energy pattern for that corneal tissue surface. Some or all of these objectives are satisfied by the devices described below.
2. Description of the Background Art
Techniques for measuring the surface of the cornea using a film covering the cornea are described in U.S. Pat. Nos. 3,169,459; 4,761,071; 4,995,716; and 5,159,361. Moire techniques using specular reflection from the surface of the eye or fluorescent dyes are described in U.S. Pat. Nos. 4,692,003; 4,459,027; and 5,406,342. A technique for measuring the surfaces of the cornea using a vidicon tube is described in U.S. Pat. No. 4,019,813.
A technique for measuring the eye during laser eye surgery is described in U.S. patent application Ser. No. 09/083,773, entitled “Systems and Methods for Imaging Corneal Profiles”, filed on May 22, 1998. Techniques for combining corneal topography and laser eye surgery are described in U.S. Pat. No. 4,669,466 and 4,721,379, respectively entitled “Method And Apparatus For Analysis And Correction Of Abnormal Refractive Errors Of The Eye” and “Apparatus For Analysis And Correction Of Abnormal Refractive Errors Of The Eye.” An exemplary system and method for treating irregular corneas is described in U.S. patent application Ser. No. 09/287,322, entitled “Offset Ablation Profiles For Treatment Of Irregular Astigmatism”, filed on Apr. 7, 1999 now U.S. Pat. No. 6,245,059.
Each of the above references is herein incorporated by reference in its entirety.
SUMMARY OF THE INVENTION
The present invention generally provides improved systems, devices, and methods for measuring and/or changing the shape of a tissue surface, particularly during laser eye surgery. The invention generally takes advantage of fluorescence of the tissue at and immediately underlying the tissue surface. Preferably, the excitation energy will be in a form which is readily absorbed by the tissue within a small tissue depth from the surface to be measured, thereby enhancing the resolution of any surface topography measurements. Conveniently, the excitation light energy to induce this fluorescence may be provided by the same source used for photodecomposition of the tissue. Hence, these measurement techniques may be readily incorporated into laser eye surgery systems and procedures, providing surface shape information before, during, and/or after a resculpting of the cornea. The invention may optionally take advantage of changes in the fluorescence spectrum of a tissue which occur in correlation with changes in the tissue's hydration. Such hydration measurements may be used to revise the ablation algorithm locally and/or globally throughout the treatment region, enhancing the accuracy of the ablation energy pattern by compensating for the changes in ablation rates due to variation in hydration. Alternate hydration measurements may be based on thin film ellipsometry using techniques developed for integrated circuit production to measure a thickness of the fluid film covering the corneal tissue surface.
In a first aspect the invention provides a method for measuring a surface topography of a surface of a tissue. The method comprises exposing the tissue to an excitation light energy so that the tissue produces a fluorescent light energy. The fluorescent light energy is measured from the fluorescent tissue, and the surface topography of the surface is determined using the measured fluorescent light energy.
Often times, the fluoresce
Caudle George
Clapham Terrance N.
Munnerlyn Charles R.
Shimmick John Karl
Barrish, Esq. Mark D.
Dvorak Linda C. M.
Farah A.
Townsend Townsend & CrewLLP
VISX Incorporated
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