Lasers have been used in eye surgery for more than 25 years. They can cut tissue or aid in coagulation [17]. The laser allows the ophthalmologist to apply heat to a location in the eye in a controlled manner. Many procedures use the retina as a laser target. The retina is the thin sensory tissue that rests on the inner surface of the back of the eye and is the actual transducer of the eye, converting light energy into electrical pulses. On occasion, this layer will detach from the wall, resulting in death of the detached area from lack of blood and leading to partial or total blindness in that eye. A laser can be used to "weld" the retina into its proper place on the inner wall.
Automated control of position enables the ophthalmologist to indicate to the controller where lesions should be inserted. The controller then monitors the retina and controls the laser's position so that each lesion is placed at the proper location. A wide-angle video-camera system is required to monitor the movement of the retina, as shown in Figure DP4.4(a). If the eye moves during the irradiation, the laser must be either redirected or turned off. The position-control system is shown in Figure DP4.4(b). Select an appropriate gain for the controller so that the transient response to a step change in r(t) is satisfactory and the effect of the disturbance due to noise in the system is minimized. Also, ensure that the steady-state error for a step input command is zero. To ensure acceptable transient response, require that K Figure DP4.4
Laser eye surgery system.

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