Effect of clonidine on aqueous humor flow in normal human eyes

A randomized, double-blind, placebo-controlled study of the effect of topical 0.125% clonidine, a relatively specific alpha 2-adrenergic agonist, on the rate of aqueous humor flow in the eyes of 24 normal human subjects was performed with fluorophotometry. The effect of clonidine on intraocular pressure, anterior chamber volume, pupil size, pulse, and blood pressure was also studied. Clonidine-treated eyes had a 2 mmHg decrease in intraocular pressure which was statistically significant. Fellow placebo-treated eyes had a smaller but significant decrease in pressure. However, between clonidine and fellow placebo-treated eyes, no significant difference was found in intraocular pressure. Aqueous humor flow was 21% lower in clonidine-treated eyes as compared to fellow placebo-treated eyes, 1.9 microliter min-1 as compared to 2.4 microliters min-1. No significant difference was found in anterior chamber volume, blood-aqueous barrier diffusion constant, and apparent resistance between clonidine and fellow placebo-treated eyes. Clonidine produced a significant miosis of 0.4 mm in treated eyes and miosis of 0.2 mm in fellow eyes. Topical 0.125% clonidine significantly decreased systolic blood pressure by 3 mmHg, but did not affect diastolic blood pressure or pulse.