Brimonidine/Apraclonidine: Anterior Segment Effect

Abstract. This study investigated whether brimonidine tartrate 0.2% and/or apraclonidine 0.5% could alter pupil size and intraocular anterior segment configuration. Methods. Ten healthy subjects between 20 and 40 years of age provided IRB protocol informed consent to participate. Pupil size was measured using a Colvard ® pupillometer (Oasis Medical). Measurements of the peripheral iris, iris root thickness, iris/lens distance, anterior chamber depth and posterior lens-retina depth were obtained with an ultrasound biomicroscope (I3 system ABD v2 Diagnosis Ophthalmic Ultrasound, Software Version 5x, Innovative Imaging Inc). Baseline and serial measurements were obtained at three luminance levels ( > 6.4 cd/m2, < 0.82-0.4 cd/m2 and < 0.2-0.02 cd/m2) during a 4 hour interval following instillation of either one drop of brimonidine tartrate 0.2% or apraclonidine 0.5% in one eye and a placebo in the contra-lateral eye. The measurements for each drug were carried out on different days. A nested random effects model controlling for subject’s age, race and sex was used for statistical analysis. Results. A maximum reduction in pupil size at 90 minutes from instillation (1.40 mm at > 6.4 cd/ m2, 1.69 mm at < 0.82-0.4 cd/m2 and 1.55 mm at < 0.2-.02 cd/m2) was observed for brimonidine tartrate 0.2%. Significant miosis (p < 0.01) occurred at all time intervals and illumination levels. Apraclonidine did not induce a significant difference in pupil size. No significant variation in the intra-ocular anterior segment configuration zones studied was observed for either drug investigated. Conclusion. Brimonidine tartrate 0.2% produced a moderate miotic effect without significantly altering the analyzed intra-ocular anterior segment configuration. A predominant agonistic effect on alpha 2 receptors of the iris dilator may explain this behavior.