DIFFERENCES IN KERATOCYTE APOPTOSIS FOLLOWING TRANSEPITHELIAL AND LASER-SCRAPE PHOTOREFRACTIVE KERATECTOMY IN RABBITS

BACKGROUND: Anterior stromal keratocyte cells undergo programmed cell death (apoptosis) in response to corneal epithelial injury. Keratocyte apoptosis may be an initiator of the corneal wound healing response t hat includes keratocyte proliferation and activation, as well as chang es to the overlying epithelium, occurring following refractive surgica l procedures such as photorefractive keratectomy (PRK), This study com pares the effect of laser-scrape and transepithelial PRK on keratocyte apoptosis, METHODS: Photorefractive keratectomy was performed in both eyes of 10 New Zealand white rabbits using the Summit Apex excimer la ser Surgery was performed using transepithelial PRK in one eye and las er-scrape PRK in the other The central cornea was analyzed at 4 hours after surgery using a quantitative TUNEL assay that detects fragmented DNA characteristic of apoptosis. Hepatocyte growth factor (HGF) produ ction by keratocytes was detected by immunocytochemistry. RESULTS: Ave rage apoptotic cells per 400X microscopic field determined by 2 indepe ndent masked observers were 0.9 +/- 0.5 (scanning electron microscopy) and 0.2 +/- 0.2 in the transepithelial PRK group compared with 5.1 +/ - 2.9 and 4.1 +/- 3.2 in the laser-scrape group. The difference betwee n the two groups was statistically significant for both observers (P < .05, ANOVA), HGF was detected within keratocytes throughout the corne al stroma, Less HGF was detected in the anterior stroma in the laser-s crape group at 4 hours after surgery consistent with more anterior ker atocyte apoptosis in this group. CONCLUSIONS: Transepithelial PRPP ind uced less anterior keratocyte apoptosis ire rabbbits than laser-scrape PRK, This suggests that transepithelial PRK could be useful in preven ting or minimizing refractive regression and subepithelial scarring.