Surgery – Instruments – Light application
Reexamination Certificate
1999-08-02
2001-09-04
Manuel, George (Department: 3737)
Surgery
Instruments
Light application
C351S212000, C351S210000
Reexamination Certificate
active
06283954
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention is generally concerned with ophthalmic instruments and surgery, and more particularly relates to systems, methods, and apparatus for sensing and/or tracking the position of a human eye. The present invention is particularly useful for tracking the position of the eye during laser eye surgery, such as photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), or the like. In an exemplary embodiment, the present invention is incorporated into a laser ablation system to modify the distribution of laser energy directed at the cornea based on the sensed position of the eye during the laser ablation procedure.
The ability to track or follow the movement of a patient's tissue is recognized as a highly desirable feature, particularly for use in laser delivery systems designed to effect precision surgery in delicate ocular tissue. The eye movements to be tracked include not only the voluntary movements (which can be damped with specialized treatment), but also the involuntary movements which are more difficult to control in a living patient. In other words, even when the patient is holding “steady” fixation on a visual target, eye movement still occurs. This involuntary motion may compromise the efficacy of some ocular surgical procedures, which generally require a rate of precision. In fact, such involuntary movements may occur despite the “total immobilization” of the eye, as such techniques are not fully effective in suppressing involuntary eye motion, and are also rather uncomfortable for the patient. Automatic tracking of the eye may alleviate any need for this uncomfortable immobilization, and may offer a method for more effectively accommodating differing types of eye motion. In other words, augmenting surgery with real time eye tracking may improve the accuracy and speed with which known laser eye surgery can be performed, and may also enable new procedures to be carried out for the first time.
A variety of techniques have been described for tracking eye movements. One general type of eye tracking technique has been called “optical point tracking.” Optical point trackers utilize various lens-like properties of the eye to locate optically distinguishable locations (for example, the first, second, third, and fourth Purkinje points). Unfortunately, such optical point trackers implicitly assume that the eye moves as a rigid body. As the eye actually flexes during movement, transient relative motions of lens structure can lead to fictitious optical point position information. In addition, optical point tracking systems are rather complex, and may exhibit large variability between individuals.
Another class of eye tracking techniques generally involve digital pattern recognition. These digital techniques generally require very fast frame-rate CCD cameras and sophisticated processing algorithms. As tracking frequency response is considerably slower than update frequency, they tend to be relatively slow. Hence, these known digital methods generally require extremely fast repositioning mechanisms to leave time for complex electronic processing within an acceptable total response time.
A recent promising technique for tracking eye movements takes advantage of the difference in the light scattering properties of the iris and sclera. In this technique, light is projected on to the iris/sclera interface or limbus, and the scattered light is detected by photodetectors to determine the boundary location. The relative position of this boundary can then be monitored to track the position of the eye.
Unfortunately, the limbus is more a transition zone between the cornea and the sclera, rather than a sharp boundary. As a result, techniques which rely on edge detection may lack the desired accuracy, and may not be capable of tracking large amplitude movements of the eye. Another disadvantage of known limbus tracking techniques is the relative complexity of signal processing required to effect tracking. In other words, when the eye moves so that the limbus is no longer in the nominal position, effecting realignment using known tracking systems requires fairly complex manipulations of the photodetector signal to properly instruct the repositioning system. These complex signal manipulations increase overall system complexity, and also slow the system down. Work in connection with the present invention indicates that slow tracking system response and less than desirable accuracies may in-part be the result of tracking system non-linearities. While adequate tracking response may be possible using known “pin-point” limbus trackers with accurately aligned photodetectors disposed precisely along the edge of the iris/sclera interface, providing and/or maintaining such alignment adds additional system components and complexity, particularly in light of the variability of eye geometry between differing patients.
In light of the above, it would be desirable to provide improved eye sensing and tracking devices, systems, and methods. It would be particularly desirable if these enhanced techniques improved tracking response times and sensitivity, but without significant increases in cost or complexity of the tracking mechanism. It would be particularly desirable to provide these enhanced capabilities in a system which was adaptable for use in laser eye surgery for accurately sensing and/or tracking a variety of patient eye movements.
SUMMARY OF THE INVENTION
The present invention provides improved devices, systems, and methods for tracking the position of an eye. The techniques of the present invention generally make use of the difference in contrast between features of the eye (such as between the white of the eye or sclera and the colored iris, or between the iris and the pupil) to derive the position of the eye. In many embodiments, linear photodetectors having an elongate sensing area extend from one feature to another across the contrast border. Where the eye is positioned between a pair of such linear photodetectors, movement of the eye from one linear detector toward the other linear detector will change the relative amounts of light striking each linear detector. The amount of misalignment between the linear detectors and the eye will be proportional to the difference in the signal output by the detectors. Therefore, this difference in signal between a pair of opposed linear photodetectors provides an excellent feedback signal, requiring only very simple amplification for use as an input signal for a repositioning mechanism. Such simple signal processing not only reduces the circuitry complexity and cost, but significantly enhances the speed and accuracy of tracking.
Conveniently, linear photodetectors can accurately sense and measure one-dimensional positioning error of a substantially round feature such as the iris or pupil. The tracking systems of the present invention often take advantage of this one-dimensional error measurement by measuring light along two axial segments which cross the contrast border and each other. This arrangement can provide accurate relative position information despite the lack of a sharp contrast boundary, such as when using the gradual contrast boundary often found at the limbus.
In a first aspect, the invention provides a laser eye surgery system for effecting a desired change in optical characteristics of an eye during lateral movements of the eye in X and Y orientations. The eye has a first feature and a second feature with a contrast border therebetween. The system comprises a first linear photodetector having an elongate detector area. The detector area of the first linear photodetector is oriented to receive light from the first and second feature of the eye along a first axis extending across the contrast border. A second linear photodetector has an elongate detector area which is oriented to receive a light from the first and second feature of the eye along a second axis extending across the contrast border. The second axis is disposed at
Barrish, Esq. Mark D.
Manuel George
Townsend & Townsend & Crew LLP
VISX Incorporated
LandOfFree
Linear array eye tracker does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Linear array eye tracker, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Linear array eye tracker will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2526439