System for detecting, measuring and compensating for lateral movements of a target

This invention relates to tracking systems for aiming a laser beam and/or positioning projected light patterns at a known relation onto moving targets. In particular, the invention is concerned with the detection of, measuring of and compensating transverse movements of optical targets such as an eye during ophthalmic laser surgery as well as non-surgical diagnostic procedures. The present invention is particularly powerful when taken in conjunction with a method for capturing, measuring and compensating for movements along the axial direction such as disclosed by Wm. D. Fountain in U.S. Pat. No. 5,162,642 which is assigned to the same party as the present invention. A method, apparatus and system for a transverse tracker is described that can greatly improve the accuracy, speed, range, reliability, versatility, safety, and efficacy of interventions such as laser microsurgery, particularly ophthalmic surgery, and industrial micromachining. The instrument and system disclosed are applicable to those situations wherein the positioning accuracy of laser lesions is critical, and/or whenever precise operations on a target or series of targets subject to random movement during a procedure are to be effected. The present invention provides means for stabilizing the motion of targets in a plane perpendicular to the axial direction, thus allowing an imaging system, diagnostics illumination, and/or laser beam to maintain a lock on the target area, regardless of its movement. The invention also provides means for recording eye movements in real time and in which data can be stored and manipulated for the purpose of compensating for lateral target motion by either hardware or software means. Unique attributes provided in the tracking system include means for (1) sensing contrast in recognizable large scale boundaries such as the change between the cornea/sclera interface (limbus), thereby to determine the absolute location and orientation of these boundaries, all without having to resort to digital sampling techniques and (2) dual mode operation of an electronic control system compatible with all analog technologies, thereby substantially increasing the speed of operations over other, comparable digital method. The tracking system of the invention is at least comprised of illumination sources, imaging optics, a sensor such as a position-sensitive detector, a movable optical element such as a mirror, a two-dimensional logic board, and a dedicated microprocessor, includ