Effect of a Cyclooxygenase (COX) Inhibitor on Iris Color Darkening Induced by Topical Latanoprost in Sympathectomized (SX) Rabbit Eyes

Abstract

Abstract: : Purpose: To determine whether diclofenac, a COX inhibitor, can inhibit iris color darkening in SX rabbit eyes treated with latanoprost, a prostaglandin F_2α analogue. Methods: Thirteen Dutch belted rabbits underwent bilateral superior cervical ganglionectomy. Starting the next day and for seven months, diclofenac 0.1% was administered four times a day to one eye and vehicle to the contralateral eye in a randomized, masked fashion, and both eyes were treated with latanoprost 0.005% twice-daily. Color photographs of rabbit irides were taken at monthly intervals. Observers rated paired photographs using scores ranging from "0" for no obvious decision as to a difference in iris color between paired eyes, to "3" for very certain of a color difference. The scores were analyzed using a random effects model. Scheffe multiple comparisons were made to compare scores by months. At seven months, aqueous humor was measured for protein and PGE₂ levels, and iris tissue was assayed for tyrosinase. Values from diclofenac-treated vs vehicle treated eyes were compared by a paired t-test. Results: Based on an analysis of observer scores, the latanoprost/diclofenac-treated eyes were judged to be lighter than the contralateral latanoprost/vehicle- treated eyes starting at month 1 and continuing through month 7 (p=0.0001). There were no differences between eyes in protein or PGE₂ levels in the aqueous humor, or tyrosinase in the iris. Conclusions: Diclofenac can inhibit the iris color darkening induced by treatment with latanoprost in an experimental rabbit model.

Keywords: animal model • iris • drug toxicity/drug effects