Retinoic acid and the ocular surface.

Retinoic acid is known to improve cutaneous wound healing and, in recent years, its application in ophthalmology has been investigated. This review looks at the role of retinoic acid on the ocular surface. Retinoic acid can be produced synthetically, and its mechanism of action includes both nuclear and non-nuclear receptor mediated pathways. It has been shown to improve full and partial thickness corneal lacerations as well as corneal epithelial defects. Retinoic acid plays a critical role in cell differentiation at the cornea, conjunctiva, and limbus, and may have an anti-tumor role. Its positive effect is only achieved at the correct concentration, however; excess concentrations of retinoic acid have a deleterious effect. The main limiting factor of retinoic acid use is its detrimental effect on meibomian glands, resulting in cell death, atrophy of acini, hyposecretion of oils, and altered gene expression, eventually resulting in dry eye symptoms. This effect is reversible on discontinuation of the drug. Crown