The overall objective of the proposed work is to study the nutritive relationship of the tears to the cells of the ocular surface. It has recently been reported that retinol is present in tears. Since vitamin A may affect and be involved in the regulation and maturation of cells in the cornea and conjunctiva, the studies will initially focus on delivery of vitamin A to the ocular surface by the tears based on the hypothesis that ocular surface disease, especially keratinization, in patients with tear film abnormalities may in part be due to inadequate delivery of vitamin A to the ocular surface epithelium by the tears. The specific aims of the project are to: 1) determine the source of retinol in the tears by high pressure liquid chromatography (HPLC) of secretions and extracts of the tear-producing glands and by radioautography of tear-producing glands after system treatment of animals with radiolabeled retinoids. 2) study the relationship of vitamin A in tears to the health of the ocular surface by comparing labeling of the cornea by systematically administered radiolabeled retinoids in normal animals and animals with impaired tear function, by attempting to reverse keratinization of corneas in animals with impaired tear function by topical application of retinoids, and by measuring retinol concentration by HPLC in tears of humans and animals with ocular surface disease. 3) study the mechanisms of action of vitamin A in the cornea, by studies of the effect of retinoids on growth of corneal cells in culture and in vivo, and by HPLC analysis of retinoid metabolism in the cornea by studies of the effect of topical retinoids on endothelial wound healing.