Significance of the lacunar hydration pattern after corneal cross linking.

Purpose: The aim of the present study was to investigate the characteristic honeycomb hydration pattern after corneal cross linking using in vivo rabbit cornea.
Methods: After removal of the central epithelium, the right corneas of 4 New Zealand white rabbits were cross-linked applying a photosensitizing 0.1% riboflavin-dextran solution and UV-A light of 370 nm wavelength with a surface irradiance of 3 mW/cm for 30 minutes. Two animals were euthanized 3 days postoperatively and another 2 were euthanized 6 weeks postoperatively. The corneas of the enucleated eyes were evaluated using 4-mum light microscopic sections with tangential en face and cross-sectional orientation.
Results: By day 3 after treatment, complete apoptotic damage and loss of the stromal keratocytes and endothelial cells were found in the central irradiated area through the entire thickness of the stroma. There was marked lacunar edema in the former positions of the apoptotic keratocytes in the anterior 250 microm of the stroma and diffuse edema in the adjacent posterior and lateral zones. Lacunar edema was identified best on tangential sections. By week 6, the cytoarchitecture of the cornea appeared normal again, and complete resolution of both lacunar and diffuse corneal edema had occurred.
Conclusions: After riboflavin/UV-A cross linking of in vivo rabbit cornea, a characteristic lacunar hydration pattern can be observed in the anterior stroma with maximum cross linking, whereas diffuse edema is present in the adjacent areas without significant cross linking. The lacunar edema may explain the temporary demarcation of the anterior stroma after cross linking on biomicroscopy because of increased light scattering. The network pattern of cross linking may contribute to the elasticity of the cornea after cross linking.