Effect of apraclonidine in long-term timolol users.

A double-blind, randomized study was undertaken to determine if the alpha-agonist apraclonidine has an additive effect in eyes treated with long-term timolol. Seventeen patients (15 with primary open-angle glaucoma, 1 with pigmentary glaucoma, and 1 glaucoma suspect) on long-term timolol treatment in both eyes received a single dose of apraclonidine in one eye and a placebo in the other. Aqueous flow and intraocular pressure were compared in the treated and untreated eyes. There was no statistically significant difference in pretreatment aqueous flow between the two eyes. When flow in the apraclonidine-treated eyes (1.39 +/- 0.41 microliter/min, mean +/- standard deviation) was compared with that of the untreated eyes (1.66 +/- 0.38 microliter/min), a statistically significant difference was found (P less than 0.01). Apraclonidine reduced intraocular pressure by 1.3 mmHg (P = 0.05). The implications of these findings on the understanding of the mechanism of action of adrenergic drugs in the human eye is discussed.