Effect of two weeks of timolol maleate treatment on the normal retinal circulation

The effect of 2 weeks of topical treatment with timolol maleate 0.5% ophthalmic solution on the retinal circulation was investigated using bidirectional laser Doppler velocimetry and monochromatic fundus photography. Fifteen normal healthy volunteers were included in this study. In a double-masked, randomized design one eye of each received one drop of timolol maleate 0.5% twice daily for 14 days, and the fellow eye received placebo. Vessel diameter (D), maximum erythrocyte velocity (Vmax), and volumetric blood flow rate (Q) were determined in one major retinal vein of each eye before treatment, and then, 2 hr after the instillation of drops on the morning of the 15th day of treatment. After treatment, the average change from baseline in D (+0.7%), Vmax (-8.2%) and Q (-7.7%) were not statistically significant in the placebo-treated eyes. In the timolol-treated eyes, the average increase from baseline in D (+0.1%) and Q (+10%) were not statistically significant. Average Vmax, on the other hand, increased significantly from baseline (P less than 0.05) by 9.6%. In comparison to the placebo-treated eyes, Vmax and Q were significantly increased in the timolol-treated eyes (P less than 0.0005 and P less than 0.01, respectively). These results are similar to those reported previously in a study of the effect of a one-time instillation of timolol and, therefore, suggest that the effect of timolol on the retinal circulation is maintained over a 2-week period.