Addition of dorzolamide to timolol in primary open-angle glaucoma shows augmented reduction of intraocular pressure. It is unknown as yet if addition of dorzolamide will alter hemodynamics.Fifteen patients with primary open-angle glaucoma were placed on a medication-dependent 1-week to 4-week washout that included maintenance on timolol. After washout, baseline measurements were taken (timolol). They were studied after a month on timolol or dorzolamide-timolol (Cosopt; Merck, Inc, Whitehouse Station, New Jersey), with the second drug preceded by another month of timolol maintenance and second baseline measurements. At each visit, visual function, intraocular pressure, and ocular hemodynamics were monitored, including indocyanine green and fluorescein angiography and color Doppler imaging.Cosopt significantly reduced intraocular pressure (14.7 to 13.4 mm Hg, P <.05) and increased arteriovenous passage time (superior temporal artery) of fluorescein dye (2.13 to 1.76 seconds, P =.01) but had no effect on visual function.When compared with timolol in primary open-angle glaucoma, Cosopt augments ocular tension reduction and reduces the amount of time required for blood to pass through the superior retinal vasculature.