Stromal degradation in vitamin A-deficient rat cornea. Comparison of epithelial abrasion and stromal incision.

Epithelial abrasions (3-mm diameter) and linear stromal incisions (50-75% depth) were made in vitamin A-deficient (A-) rat corneas to investigate what are contributory factors to the development of keratomalacia. Sixty-four rats were killed at various times after injury, and the corneas were histologically examined. In pair-fed control corneas, wounds healed without stromal degradation. Although abraded A- corneas were infiltrated by numerous polymorphonuclear neutrophil leukocytes (PMNs), reepithelialization eventually occurred and severe stromal degradation was not evident, suggesting that PMN infiltration alone cannot cause keratomalacia. In incised A- corneas, six (20%) exhibited marked stromal degradation, of which three (10%) were infected. Two other corneas studied shortly after incision were in the initial stages of infection. The results suggest that stromal injury importantly contributes to the development of keratomalacia. Bacterial infection might also be contributory. Cytochrome oxidase staining showed that metabolic functional levels of incised A- corneas were accelerated only in the wound zone, whereas abraded A- corneas were metabolically accelerated throughout.