Retinoid permeability and uptake in corneas of normal and vitamin A-deficient rabbits

In vitro perfusion of corneas of normal and vitamin A-deficient rabbits provided a model in which to study the pharmacokinetics of corneal permeability and uptake of retinoic acid and retinol. The permeability coefficients of retinoic acid and retinol were 1.49 x 10(-5) and 0.61 x 10(-5) cm/s, respectively. Removal of the corneal epithelium did not affect the permeability of these lipid-soluble retinoids; however, diffusion through xerophthalmic, vitamin A-deficient corneas was significantly reduced. The corneal uptake of retinoic acid and retinol was reduced by 50% on removal of the epithelium, was nonspecific, and was not affected by xerophthalmia. High-performance liquid chromatography indicated that these retinoids were not metabolized during diffusion through the cornea. These results show that topical application of retinoids is a rational approach to the treatment of such corneal diseases as xerophthalmia and epithelial defects.