The role of apoptosis in the early corneal wound healing after excimer laser keratectomy in the rat

Background: The potential role of apoptosis in corneal wound healing after excimer laser keratectomy was investigated in a rat model. Methods: Lewis r ats underwent laser keratectomy using a 193-nm excimer laser. The central c orneas were ablated in three depths: group A, epithelium; group B, superfic ial stroma; group C, deep stroma. Eyes were collected at 1, 12, 24, and 36 h and I week. Cellular markers associated with apoptosis - Fas, Fas ligand (FasL), Bcl-2, and Bax - were examined by immunohistochemistry. Keratocyte depletion and endothelial changes were evaluated histologically. In situ en d labeling of double-stranded DNA breaks was used to demonstrate apoptosis in corneal sections. Results: Keratocyte depletion was observed in 6 (50%) of 12 rats (total from groups A, B, and C) at 12 h, 11 (73%) of 15 at 24 h, 3 (20%) of 15 at 36 h, and 2 (15%) of 13 at 1 week after laser surgery. Co rneal endothelial edema was observed in the ablation zone. Expression of Fa s, FasL, Bcl-2, and Bar in corneal cells showed dynamics similar to that of keratocyte depletion and endothelial changes. There was less expression of apoptotic molecules in newly generated epithelial cells and more in endoth elial cells of the stromal ablation groups. Conclusions: Excimer laser kera tectomy triggered apoptosis of corneal keratocytes and endothelial cells. M ore endothelial edema was observed in the stromal ablation than in the epit helial ablation group. The expression of apoptotic molecules coincided with the period of keratocyte depletion and regeneration and of endothelial rec overy, suggesting that apoptosis is a dynamic part of corneal wound healing and remodeling after excimer laser keratectomy.