Latanoprost and pigmentation.

Latanoprost is a prostaglandin analogue with well-established efficacy in the treatment of open-angle glaucoma and ocular hypertension. Once-daily administration of this drug for up to 5 years is generally well tolerated both locally and systemically. While most reported side effects have been classified as mild in intensity, an increase in iris, eyelash, and periocular pigmentation has been associated with prostaglandin analogue use in some patients. Follow-up studies of patients withdrawn from latanoprost treatment suggest that the increased iridial pigmentation is irreversible while changes in eyelash and periocular skin pigmentation are reversible after cessation of therapy. Concern as to whether latanoprost affects proliferation of iridial melanocytes or other cellular components prompted investigation into its mechanism of action. All available evidence from in vitro, in vivo, and clinical studies suggests that latanoprost does not induce melanocyte proliferation. Morphologic study of human peripheral iridectomy specimens did not reveal any significant latanoprost-induced pathologic change in the iris. There was no evidence of melanin granules blocking the outflow pathways in treated patients. Stimulation of melanogenesis in iridial melanocytes, perhaps through an effect on tyrosinase, appears to account for induction of melanin production. Additional studies are in progress to further elucidate the mechanism of latanoprost-induced increased iridial pigmentation.