Regulation of choroidal blood flow during combined changes in intraocular pressure and arterial blood pressure

PURPOSE. To test the hypothesis that human choroidal blood flow (ChBF) may depend, not only on ocular perfusion pressure (OPP), but also on absolute mean arterial pressure ( MAP) and intraocular pressure (IOP). METHODS. There were two study days in an open design. On the first day, OPP was varied by elevating IOP during a squatting-induced increase in MAP (28 subjects). On the second day, only the IOP was increased (17 subjects). IOP was raised in stepwise increments by using the suction cup method. Subfoveal ChBF (laser Doppler flowmetry), MAP, and IOP were assessed, and OPP was calculated as 2/3(MAP - IOP). For correlation analysis, data from all subjects were pooled according to IOP and MAP, and correlation analyses were performed. RESULTS. When data from study day 1 were grouped according to IOP, no correlation was observed between ChBF and MAP; but ChBFs were lower, the higher the IOP (P < 0.001). When data were grouped according to MAP, a significant correlation was found between ChBF and IOP (P < 0.001), but correlations were independent of MAP. When data of study day 2 were pooled according to IOP, a correlation between ChBF and OPP was seen only at IOP > 40 mm Hg (P < 0.05). CONCLUSIONS. The data confirm previously published observations that the choroid shows some autoregulatory capacity during changes in OPP. In addition, the data indicate that the choroid regulates its blood flow better during exercise-induced changes in MAP than during an experimental increase in IOP.