Keratocyte density in vivo after photorefractive keratectomy in humans

Purpose: To determine changes in keratocyte density in central human corneas in vivo after photorefractive keratectomy (PRK). Methods: Fifteen patients (25 eyes) received excimer PRK (VISX Star) with epithelial removal by laser-scrape (43 μm ablation followed by manual scrape) to correct myopia between -1.5D and -7.25D. Corneas were examined by using confocal microscopy in vivo before PRK and at 1 day, 5 days, 1 month, and 3 months after PRK. A custom automated image-processing algorithm identified bright objects (keratocytes) against a dark background and estimated keratocyte density by using the number and size of the objects. Cell density was quantified in anteroposterior stromal regions after PRK and compared to cell density in corresponding pre-PRK regions. Results: One day after PRK, keratocyte density increased 9% in the anterior third of the stroma (II=.003), was unchanged in the middle third of the stroma (II=.481), and decreased 6% in the posterior third of the stroma (II=.038). Keratocyte density remained elevated in the anterior stroma to 3 months after PRK; at this time, there was a 13% increase in keratocyte density throughout the full-thickness stroma (II<.001). Conclusions: Keratocyte density was increased in the anterior stroma immediately after PRK in humans. Three months later, keratocyte density was increased in all anteroposterior stromal regions, suggesting that PRK affects keratocytes throughout the entire central cornea.