Can zinc prevent apoptosis of anterior keratocytes after superficial keratectomy?

Objective. To determine whether zinc, which blocks apoptosis in many systems, including in leukemic cells and possibly in retinal dystrophies, can prevent the unwanted loss of anterior stromal keratocytes after superficial keratectomy. Methods. After mechanical central corneal epithelial debridement, the left eyes of nine New Zealand white rabbits were treated with 25 mM zinc chloride (ZnCl₂) in Earle's salts minimal essential medium (MEM) either every 30 min (n = 3), every 2 h (n = 3), or every 4 h (n = 3). The left eyes of nine additional animals, divided into three equal groups, were deepithelialized, and each received pure culture medium at one of the same three frequencies. One eye of each of another six rabbits was deepithelialized but received no drops. After 24 h, all 24 animals were sacrificed and the globes were enucleated. The corneas were processed and sections were stained with hematoxylin and eosin. Results. The cell count of MEM-treated corneas exceeded that of untreated corneas (p = 0.03, analysis of variance [ANOVA]), but there was no difference among eyes that received the different frequencies of MEM application (p = 0.36, ANOVA). Cell counts increased with frequency of zinc application, but the differences were not statistically significant (p = 0.09, ANOVA). Only in the group receiving the most frequent zinc applications were superficial keratocytes retained. This group also possessed a greater number of stromal keratocytes than untreated controls and MEM-treated corneas (p = 0.01). Conclusions. At a significantly high dosage, zinc can prevent loss of superficial keratocytes to a greater extent than culture medium alone can. Moreover, zinc has the advantage of preserving the most anterior layer of keratocytes. Retention of these cells may prevent the reactive overproliferation that constitutes haze after photorefractive surgery.