Lower Incidence of Iris Darkening in Primates With Bimatoprost Compared to Latanoprost

Abstract

Abstract: : Purpose: To determine whether bimatoprost causes iris darkening in the primate eye. Methods: Cynomolgus monkeys were unilaterally treated in the left eye for one year with one drop per day of bimatoprost (0.03%; n = 8) or latanoprost (0.005%; n = 8). Two other animals served as untreated controls. Iris photographs were taken at baseline and after 3, 6 and 12 months of treatment. Iris darkening was judged by an independent panel of 9 masked observers comparing baseline images with images taken after one year of treatment. Differences were scored using an arbitrary scoring scale. Results: Based on 4 eyes from 2 untreated animals the iris color darkened slightly over the 1 year period. In the bimatoprost treatment group overall the eye color changes were not different from the age–related changes seen in untreated animals. In contrast, iris hyperpigmentation in the latanoprost treatment group was significantly greater (P<0.05; Two–Factor ANOVA) than in the bimatoprost group. The pigmentary effects of latanoprost in our study are in agreement with an earlier report (Selen et al, Surv Ophthalmol 1997;41). Conclusions: The risk to develop iris hyperpigmentation appears to be much lower with bimatoprost than with latanoprost in primates. These findings are consistent with the substantially lower incidence of eye color changes after 1 year of treatment reported for bimatoprost (1.5%; Higginbotham et al, Arch Ophthalmol 2002;120) compared to latanoprost (16.1%; Wistrand et al, Surv Ophthalmol 1997;41) in long–term clinical trials. The cynomolgus monkey appears to be a good model to study drug effects on iris pigmentation in vivo.

Keywords: pharmacology • iris