Effect of timolol maleate on the retinal circulation of human eyes with ocular hypertension.

We studied the effect of topical timolol maleate 0.5% on the retinal circulation of eyes with ocular hypertension using laser Doppler velocimetry and monochromatic fundus photography. Patients with ocular hypertension had normal eye examinations and had documented elevated intraocular pressures of 23 mmHg or higher on two or more separate occasions. In a double-masked randomized design, one eye of each subject received timolol maleate 0.5% and the fellow eye received placebo. Vessel diameter, maximum velocity of red blood cells, and volumetric blood flow rate were determined in a major retinal vein of each eye just prior to the instillation of drops, and then 2 hr later. In comparison to the baseline value, there was an increase of 12.0% in average red blood cell velocity (P less than 0.005, statistically significant) and of 8.4% in volumetric blood flow rate in the timolol-treated eyes (P less than 0.05, statistically significant). No significant changes in these quantities were observed in the placebo-treated eyes. Also, no significant change in venous diameter was detected in the placebo- and the timolol-treated eyes. In comparison to the baseline, a significantly larger increase in red blood cell velocity was observed in the timolol-treated eyes than in the placebo-treated eyes (P less than 0.05). The difference between the increase in blood flow observed in the timolol-treated eyes and the placebo-treated eyes achieved a probability value of P = 0.058. The increase in blood flow observed in the timolol-treated eyes may be related to the increase in perfusion pressure produced by this drug.