Purpose: To study the effect of a single dose of topical dorzolamide hydrochloride 2%, a carbonic anhydrase inhibitor, on the retinal circulation of normal subjects.
Methods: Measurements of the effect of dorzolamide hydrochloride were performed in 20 normal subjects using bidirectional laser Doppler velocimetry and monochromatic fundus photography. In a double-masked randomized design, one eye received one drop of dorzolamide hydrochloride 2 % and the other eye one drop of placebo. Vessel diameter, maximum erythrocyte velocity and volumetric blood flow rate were measured in a main temporal vein of each eye before the drops, and then, 2 h later.
Results: Following treatment, intraocular pressure decreased by 12% in the dorzolamide-treated eye (p = 0.0004, paired Student's t-test) and by 4% in the placebo-treated eye, p = 0.04). No significant changes in venous diameter, maximum erythrocyte velocity, and volumetric blood flow rate were observed in the dorzolamide-treated eyes (0.6%, 2.6% and 1.4%, respectively) or the placebo-treated eyes (1%, 3.7% and 1.6%, respectively).
Conclusions: A single drop of dorzolamide hydrochloride does not cause any significant change in any of the hemodynamic parameters measured. With the variability of our measurements, we have about 89% power to detect average 10% change in volumetric blood flow rate if significance testing is performed at p = 0.05 level.