Keratocyte density in the human cornea after photorefractive keratectomy

Objective: To perform a quantitative analysis of keratocyte density in human corneas after photorefractive keratectomy (PRK). Methods: In a prospective comparative trial, 24 eyes of 14 patients received PRK to correct refractive errors of between -1.25 diopters (D) and -5.75 D. Corneas were examined by using confocal microscopy before and 1 day, 5 days, and 1, 3, 6, 12, 24, and 36 months after PRK. Keratocyte nuclei were counted in 5 stromal layers in 3 to 6 scans per eye per visit. Keratocyte density in each layer post-PRK was compared with the density in the corresponding layer of the pre-PRK full stroma (included stroma that would later be photoablated) and the pre-PRK future unablated stroma (thickness adjusted by omitting the future ablation depth) (Bonferroni-adjusted paired t test). Results: Keratocyte density in the anterior 10% of the post-PRK stroma decreased by 25% (P=.002), 41% (P<.001), 40% (P<.001), 43% (P<.001), and 45% (P<.001) at 3, 6, 12, 24, and 36 months compared with the anterior 10% of the pre-PRK full stroma and was reduced by 15% at 36 months (P=.02) compared with the anterior 10% of the pre-PRK future unablated stroma. Conclusion: After PRK, keratocyte density in the anterior stroma is not restored to the high-density levels found in the preoperative stroma.