The corneal and conjunctival surface in vitamin A deficiency: a scanning electron microscopy study.

A model system of acute vitamin A deficiency in the guinea pig was used to investigate changes in corneal and conjunctival morphology. Hypovitaminosis A was induced by feeding experimental animals a purified gel diet deficient in vitamin A, while a control group received a vitamin A enriched diet. By the fifth week experimental animals exhibited a significant decrease in plasma vitamin A levels compared to controls. Animals were sacrificed at intervals from 5 to 9 weeks, and the corneas and conjunctivae were examined histologically and by scanning electron microscopy. Conjunctivae from control animals showed large numbers of goblet cells, whereas 16 of 18 experimental conjunctivae were completely devoid of goblet cells. Tarsal, palpebral, and cul-de-sac epithelia from deficient animals all showed many superficial squamous cells uplifted from the surface. Also, rugae were notably absent from the palpebral and cul-de-sac conjunctivae. The corneas of vitamin A--deficient animals exhibited varying degrees of superficial epithelial cell desquamation and keratinization. In addition, reduced numbers of microprojections and membrane breakdown were observed. These morphological and clinical findings are correlated with the possible role of vitamin A in cellular physiology.