Pupillometry Study of Brimonidine Tartrate 0.2% and Apraclonidine 0.5%

This study investigated possible effects of brimonidine tartrate 0.2% and apraclonidine 0.5% on pupil diameter. Ten subjects between 20 and 40 years of age participated. A Colvard pupillometer (Oasis Medical) was used to measure pupil diameter. Baseline and serial measurements were obtained at 3 luminance levels (>6.4, <0.82-0.4, and <0.2-0.02 cd/m(2)) during a 4-hour interval following instillation of 1 drop of brimonidine tartrate 0.2% or apraclonidine 0.5% in one eye versus a placebo in the contralateral eye. The measurements for each drug were obtained on different days. A nested random effects model controlling for subject's age, race, and sex was used for statistical analysis. A maximum reduction in pupil diameter was observed at 90 minutes from instillation (1.40 mm at >6.4 cd/m(2), 1.69 mm at <0.82-0.4 cd/m(2), and 1.55 mm at <0.2-0.02 cd/m(2)) for brimonidine tartrate 0.2%. At all time intervals and illumination levels, miosis (P <.01) occurred. Apraclonidine 0.5% did not produce a significant effect on pupil diameter. Brimonidine tartrate 0.2% produced a moderate miotic effect. No effect was observed for apraclonidine 0.5%. A predominant agonistic effect on alpha-2 receptors of the iris dilator may explain this behavior.