The incidence and time-course of latanoprost-induced iridial pigmentation as a function of eye color

Latanoprost, a phenyl-substituted analogue of prostaglandin F-2 alpha administered as eye drops, induces increased melanogenesis in the iridial melanocytes of monkeys. Similar effects were seen in 12, 23 and 11% of patients in the USA, United Kingdom (UK) and Scandinavia, respectively, during one year of treatment. The highest incidence of induced pigmentation was seen in green-brown, yellow-brown and blue/grey-brown eyes, in that order. The relatively high proportion of patients with green-brown eyes in the UK explains the larger number of affected patients in this country. Typically, a concentric increase of the iris pigmentation appeared after six months (range: 3-17) and was judged to be noticeable by the patient in about 2/3 of the cases. After cessation of latanoprost, no change of the induced pigmentation has been seen in patients followed for two years, and there have been no signs of dispersion of pigment into the anterior chamber. Irides, homogeneously blue, grey, green or brown, were seldom affected. Naevi or freckles on iris, conjunctiva, or eye lids were not affected. It is intriguing that many patients with mixed eye color, particularly the blue-brown eyes, have not developed increased pigmentation even during two years of treatment. This could be due to a relatively slow melanogenesis or to refractory melanocytes in these individuals.