UV Cross-linking of Donor Corneas Confers Resistance to Keratolysis

Purpose: The aim of this study was to develop a modified ex vivo corneal cross-linking method that increases stromal resistance to enzymatic degradation for use as a carrier for the Boston keratoprosthesis. Methods: Ex vivo cross-linking of human corneas was performed using Barron artificial anterior chambers. The corneas were deepithelialized, pretreated with riboflavin solution (0.1% riboflavin/20% dextran), and irradiated with ultraviolet A (UV-A) light (lambda = 370 nm, irradiance = 3 mW/cm(2)) for various durations. The combined effect of UV-A and gamma (gamma) irradiation was also assessed using the commercially available gamma-irradiated corneal donors. The corneas were then trephined and incubated at 37 degrees C with 0.3% collagenase A solution. The time to dissolution of each cornea was compared across treatments. Results: Deepithelialized corneas (no UV light, no riboflavin) dissolved in 5.8 +/- 0.6 hours. Cross-linked corneas demonstrated increased resistance to dissolution, with a time to dissolution of 17.8 +/- 2.6 hours (P < 0.0001). The corneal tissues' resistance to collagenase increased with longer UV-A exposure, reaching a plateau at 30 minutes. Cross-linking both the anterior and posterior corneas did not provide added resistance when compared with cross-linking the anterior corneas only (P > 0.05). gamma-irradiated corneas dissolved as readily as deepithelialized controls regardless of whether they were further cross-linked (5.6 +/- 1.2 hours) or not (6.1 +/- 0.6 hours) (P = 0.43). Conclusions: Collagen cross-linking of the deepithelialized anterior corneal surface for 30 minutes conferred optimal resistance to in vitro keratolysis by collagenase A.