The importance of the corneal epithelium in excimer laser PRK: The role of EGF

Purpose: Although clinical results of excimer laser PRK are promising some unexpected results have been observed throughout the dioptric range with individual patients showing excessive myopic regression and prolonged disturbances in corneal transparency ("haze"). The magnitude of both regression and haze in any given cornea may be predominantly determined by the genetic control of wound healing implicit in each individual. Corneal wound healing involves a complex and well-regulated sequence of events which are regulated mainly by growth factors. Among those EGF is well known for its potential to enhance corneal wound healing. Methods: In order to evaluate the importance of EGF for the postoperative outcome of PRK we have measured the EGF concentration in the tear fluid of PRK patients prior and after the surgery by using an ELISA kit. We have also measured the m-RNA concentration in corneal epithelial cells of those patients by using the technique of RT-PCR. Results: Twenty-four patients showed EGF levels between 0.22 and 0.84 ng/ml tear fluid. These patients had a postoperative refraction of +/-1 diopter of the intended correction. In contrast, six patients showed significant higher EGF levels between 2.45 and 10.65 ng/ml. Clinically, these patients showed severe regression. These datas were similar to the m-RNA concentration of EGF in corneal epithelial cells, in that patients with high levels of EGF in the tear fluid showed higher amounts of EGF m-RNA. Conclusion: Screening of unsuitable P_P patients prior to PRK might be possible by measuring the EGF concentration in the tear fluid or the m-RNA.