Retinal blood flow response to posture change in glaucoma patients compared with healthy subjects

Purpose: To characterize the retinal vascular autoregulatory response to ocular perfusion pressure (OPP) changes in patients with glaucoma and in healthy control subjects. Design: Observational cohort study. Participants: Eighteen patients with open-angle glaucoma (OAG) and 8 control subjects, all females ages 40 to 60 years, were studied. Only subjects with known maximum intraocular pressure less than 22 mmHg in both eyes were included. Methods: Arterial diameter and blood speed in the inferior temporal retinal artery of the left eye were measured simultaneously at baseline while sitting, while reclining for approximately 30 minutes, and once again sitting using a retinal laser Doppler instrument. Blood flow rate was computed automatically. Brachial artery blood pressure and heart rate also were measured. Main Outcome Measure: Change in blood flow rate while reclining for approximately 30 minutes compared with baseline blood flow rate measured while seated. Results. In control subjects, arterial diameter decreased by 7.5 +/- 3.4% (P = 0.0003) and blood speed increased by 24.6 +/- 10.8% (P = 0.004) while reclining compared with baseline. The concomitant change in the blood flow rate (6.5 +/- 12.0%; P = 0.15) compared with baseline was not statistically significant. In contrast, OAG patients showed a much broader range of blood flow changes in response to posture change (14.9 +/- 37.7%; P = 0.086) compared with baseline. Although there were no significant differences in the flow changes compared with baseline in either group, there was a significant difference in the variance of the blood flow changes in the OAG patients compared with the controls (P = 0.0025). Division of the OAG patients into subgroups revealed a significant (P = 0.031) association between baseline OPP and the retinal blood flow response to posture change. Conclusions: The authors describe the hemodynamic details of retinal vascular autoregulation in response to posture-induced changes in OPP in healthy subjects and document the lack of such autoregulation in a selected group of patients with OAG.