Autoregulative behavior of retinal arteries and veins during changes of perfusion pressure: a clinical study.

PURPOSE: To investigate the autoregulative response of large retinal vessels to artificial reduction of perfusion pressure. METHODS: The diameters of a venous and an arterial segment (each approx.1.5 mm in length) in one eye of each of 13 healthy volunteers (age 54.5+/-18 years) were measured continuously using the Retinal Vessel Analyzer (Imedos, Weimar, Germany). The intraocular pressure (IOP; mean before examination 13.7+/-2.9 mmHg) was increased by 21.2+/-3.5 mmHg by means of a suction cup in order to produce a temporary reduction of the retinal perfusion pressure. The RVA measurements were taken for 2 min without artificial intervention (baseline), for 100 s during IOP elevation, and for up to 10 min after removal of the suction cup. RESULTS: A significant response of arterial and venous diameters to the provocation was found ( P<0.02, ANOVA). The arterial and venous responses were opposite: Whereas the artificially elevated IOP increased the arterial diameter by +1.9+/-4.5%, the venous vessel diameter decreased by -2.6+/-3.5% ( P<0.02, Mann-Whitney U-test). After normalization of the IOP the arterial diameter fell slightly below the baseline value, while the veins underwent temporary dilation by +5.9+/-3.3% ( P<0.001). The mean systemic blood pressure did not change significantly during the investigation. CONCLUSION: Retinal arteries and veins of healthy volunteers exhibited opposite autoregulative behavior in response to perfusion pressure changes. This is believed to be due to the different regulative functions of arteries and veins.