Effect of Brimonidine on Retinal Blood Flow Autoregulation in Primary Open-Angle Glaucoma

Purpose: To determine whether topically applied brimonidine affects the retinal hemodynamic autoregulatory response to posture change in patients with normal tension glaucoma. Methods: Six patients with normal tension glaucoma (primary open-angle glaucoma and maximum untreated intraocular pressure < 22 mmHg) in each eye were studied. We retrospectively reviewed retinal hemodynamic data acquired when the patients were off and on treatment with brimonidine 0.15% (twice a day, both eyes) during the course of their care. At each testing session, vessel diameter and blood speed at the same site along the inferior temporal retinal artery of 1 eye were measured while sitting, while reclining for 30 min, and again while sitting using a retinal laser Doppler instrument. Blood flow was computed automatically. Brachial artery blood pressure and heart rate were also measured. The Wilcoxon signed rank test was used to assess the statistical significance of the differences in each measured parameter while subjects were on and off brimonidine. Results: Off brimonidine, the mean blood flow rate increased by 68.0% +/- 34.3% (range: + 17% to + 108%) after 30 min in reclined posture compared to baseline-seated measures. On brimonidine, the mean blood flow rate increased by 8.9% +/- 16.8% (range: - 9.7 to + 28.0%) after 30 min in reclined posture compared to baseline-seated measures. The difference in the posture-induced changes for blood flow rate while on brimonidine compared to off brimonidine was statistically significant (P = 0.027). Conclusions: Off brimonidine, the patients exhibited marked increases in retinal blood flow while reclining. On brimonidine, the hemodynamic changes were consistent with normal autoregulatory control of retinal blood flow.