Effects of 0.2% brimonidine on ocular anterior structures

The aim of the study was to evaluate the effect of an alpha2-adrenergic agonist, 0.2% brimonidine, on a number of echobiometry and ultrasound biomicroscopy ocular parameters. Ten healthy subjects ranging in age from 20 to 40 years (mean age 29+/-3.39) were recruited into this prospective open-label trial. After instillation of 0.2% brimonidine eye drops, the following parameters were assessed: refraction, visual acuity, pupil diameter, intraocular pressure, five A-scan echobiometric parameters and 15 ultrasound biomicroscopy parameters. As early as the first hour after administration of the drug, a marked ocular hypotensive effect was detected associated with a miotic effect, without any refractive or visual acuity alterations. The A-scan echobiometry parameters were unchanged, while, as far as the ultrasound biomicroscopy variables were concerned, we observed an increase in iris-lens contact distance and a reduction in iris root thickness with a resulting increase in posterior chamber depth and in iris-ciliary process distances. No changes were observed in either the anterior chamber or the anterior iris profile. Brimonidine 0.2% proved to be an ocular hypotensive agent which is also endowed with a mild miotic effect, without giving rise to refractive or visual acuity alterations. The drug does not alter the thickness and position of the lens and does not facilitate pupil block; it reduces the iris thickness with an increase in posterior chamber depth and in iris-ciliary process distance but with no changes in anterior chamber depth or chamber angle width.