Plasmin in the tear fluid: A new therapeutic concept to reduce postoperative myopic regression and corneal haze after excimer laser photorefractive keratectomy

Some individuals have shown excessive regression and prolonged corneal haze after excimer laser photorefractive keratectomy. Both regression and haze relate to the wound healing process of the cornea. Wound healing is a balanced process involving three elements: (1) removal of damaged tissue; (2) repair of partially damaged tissue; and (3) replacement of irreparable tissue. There are two main systems involved in the regulation of wound healing. These are: (1) degradation of damaged tissue by the plasminogen- activator/plasmin system, and (2) tissue replacement by epithelial cells and activated keratocytes. Current postoperative treatment regimens have ignored process (1), i.e., the control of the removal of damaged tissue and have concentrated on (2), namely the inhibition of keratocytes by the use of corticosteroids in the hope that excessive collagen synthesis would be prevented. However, in a recent clinical trial steroid therapy was shown to be ineffective in modulating the final patient outcome in terms of both, haze and regression. In this study the authors examined aspects of process (1) by determining the presence and time course of plasminogen-activator/plasmin activity subsequent to PRK by monitoring the levels of plasmin in the tear fluid. In 17 patients plasmin was not measurable preoperatively (levels were less than 0.2 μg/ml) and increased to a mean value of 38.2 μg/ml subsequent to surgery. However, in three patients preoperative levels were up to 35 μg/ml and each of these patients showed marked postoperative regression.