Complex regulation of optic nerve head blood flow during combined isometric exercise and elevation of intraocular pressure

Abstract

AbstractPurpose For a long time it was assumed that ocular vascular beds are characterized by one specific pressure/flow curve. Recently we have, however, shown that this behavior is much more complex in the choroid, because alterations in arterial and venous pressure lead to different regulatory behaviors. In the present study we tested the hypothesis that this is also the case in the optic nerve head.Methods Two study days were performed in 40 healthy subjects. On the 1st day the effect of isometric exercise and an elevation of IOP on optic nerve head blood flow (ONHBF) were studied separately. On the 2nd day the effect of combined IOP and mean arterial pressure (MAP) increase was investigated. IOP was increased in a stepwise way using the suction cup method. ONHBF was measured using laser Doppler flowmetry. For correlation analysis all values from all subjects were pooled according to IOP and MAP values.Results When data were grouped according to MAP values a highly significant correlation was found between ONHBF and IOP (p<0.001). The regression lines at different MAP levels were almost equal. When data were pooled according to IOP levels a significant correlation was found between MAP and ONHBF for IOP values up to 25 mmHg (p<0.05) and the correlation lines were almost identical. At higher IOP values, however, no correlation between ONHBF and MAP was found.Conclusion Our data are in agreement with previously published studies that ONHBF shows some autoregulatory capacity. The autoregulatory behavior appears to be complex and dependent on the site of perfusion pressure regulation (arterial vs venous). Compared to the choroid the ONH adapts its perfusion better to an increase in IOP