Histologic studies indicate that PGE 2 also enhances melanogenesis. Recently, there have been many reports of iris darkening, hyperpigmentation of the eyelashes, and periocular hyperpigmentation induced by latanoprost . (prostaglandin F 2 α , used for the treatment of glaucoma). 4,5 Although the exact mechanism of this pigmentation is not clear, different mechanisms of the induction of hyperpigmentation by prostaglandins have been suggested, including: (i) influencing the responsiveness of melanocytes to neuronal stimuli; (ii) causing melanocyte proliferation; and (iii) a direct or second messenger mediated interaction with melanocytes via the stimulation of tyrosinase activity.