Purpose: This double-masked, prospective and randomized clinical trial was planned to investigate with color Doppler imaging the 1-month vascular effects of betaxolol, dorzolamide and apraclonidine treatment on patients with newly diagnosed primary open-angle glaucoma (POAG). Methods: 22 consecutive patients with newly diagnosed POAG between the ages of 46 and 72 years were enrolled in this study. All patients were newly diagnosed cases and had not received any antiglaucoma medication before. Patients who had a systemic vascular disease (including systemic hypertension) or were taking P-blockers, nitrates or calcium channel blockers were excluded from the study. The patients were randomly divided into three groups. Groups A and B contained 7 patients, group C contained 8 patients. Group A patients were treated with topical betaxolol, group B patients received topical dorzolamide eye drops, and group C patients were treated with topical apraclonidine eye drops. Peak systolic velocities (PSV), end-diastolic velocities (EDV) and resistive indices (RI) in the right ophthalmic arteries (OA), central retinal arteries (CRA) and posterior ciliary arteries (PCA) were measured at baseline by using color Doppler imaging on a masked basis. On days 15 and 30 of treatment, the same measurements were repeated. The inter- and intragroup results were compared statistically. Results: Compared to pretreatment measurements, topical betaxolol therapy significantly decreased PSV only in the PCA and only on day 30 of treatment (p = 0.011). On days 15 and 30, dorzolamide decreased RI measurements in the PCA compared to pretreatment measurement (p = 0.013 and p = 0.011, respectively). Apraclonidine also decreased PSV in the OA on days 15 and 30 of treatment when compared to pretreatment values (p = 0.013 and p = 0.012, respectively). When 15-day measurements were compared between the groups, PSV in the CA were significantly higher in dorzolamide-treated patients compared to other groups (p = 0.013 and p = 0.011). On day 30 of treatment, PSV in the OA was also higher in the dorzolamide-treated group than the other groups (p = 0.012 and p = 0.01). Additionally, apraclonidine-treated patients had a significantly lower EDV in the OA than the other groups (p = 0.013 and p = 0.01). The RI in the OA was also significantly lower in the apraclonidine-treated group compared to the other groups (p = 0.01 and p = 0.011). Conclusion: Our study suggests that dorzolamide has the most advantageous 1-month effects on blood flow velocity in the retrobulbar arterial circulation of POAG patients. Betaxolol seems superior to apraclonidine in this regard. Our data may help the clinician when treating patients with POAG medically. Further studies using a larger population size may clarify our results. Copyright (C) 2001 S. Karger AG, Basel.