[Effect of topical timolol on the blood velocity of the iris microcirculation and the aqueous veins in human subjects].

To clarify the effect of topical timolol on the microcirculation in human eyes, the blood velocity changes of the iris microcirculation and the aqueous veins were measured before and 90 minutes after instillation of timolol in 8 eyes of 8 healthy volunteers by laser speckle flowgraphy. Systemic blood pressure, heart rate and intraocular pressure were measured before and 90 minutes after the instillation. The fellow eyes were measured as controls. The blood velocity decreased in the iris microcirculation (10% decrease, p < .05) and in the aqueous veins (8% decrease, p < .02) 90 minutes after instillation of timolol. The diameter of the aqueous veins did not change, so that the blood flow in the aqueous veins decreased (6% decrease, p < .02) after instillation. The intraocular pressure and pulse rate decreased (20 and 8% decrease, p < .002 and < .001, respectively) 90 minutes after the instillation. The blood velocity, vessel diameter, and intraocular pressure of fellow eyes and systemic blood pressure showed no significant change. These findings indicate that topical instillation of timolol induces decrease of blood flow in the iris, and, possibly, in the ciliary body. The instillation of timolol may decrease aqueous humor formation, and blood flow in aqueous veins.