Therapeutic applications of excimer photorefractive keratectomy (PRK) are limited by epithelial regrowth mechanisms that produce a flattening of the cornea. This physiological healing response can cause a high degree of hyperopia to result in patients who have avoided corneal transplants by having had anterior corneal scars and irregularities removed with excimer laser treatment. Patients manifesting large amounts of hyperopic astigmatism, e.g., from eye surgery, could benefit from excimer PRK astigmatic treatment, but would be left with an overall hyperopic correction, due to the excimer PRK flattening of the steeper meridian. Current methods of sculpturing the cornea with excimer lasers are not versatile enough to produce the complex types of ablations necessary to stop flattening from epithelial regrowth. Since the regrowth flattening is in response to edges in the stroma, stable hyperopic excimer PRK also requires complex contouring at the edge of the ablation zone. VISX, a demonstrated leader in excimer laser PRK, proposes to develop prototype instrumentation for generating complex ablations to be used in hyperopic excimer PRK procedures. It will be tested on plastic to evaluate the predictability and reliability of the system. Human clinical studies will be conducted in Phase II.
