Regulation of optic nerve head blood flow during combined changes in intraocular pressure and arterial blood pressure

Abstract

In the choroid, there is evidence that blood flow does not only depend on ocular perfusion pressure (OPP), but also on absolute mean arterial pressure (MAP) and intraocular pressure (IOP). The present study included 40 healthy subjects to investigate whether such behavior is also found in the optic nerve head (ONH). The ONH blood flow (ONHBF) was studied using laser Doppler flowmetry during a separate increase in IOP and MAP as well as during a combined elevation. Mean arterial pressure was increased by isometric exercise and IOP by the suction method. During both, the change in ONHBF was less pronounced than the change in OPP indicating autoregulation. Correlation analysis was performed for the combined experiments after pooling all data according to IOP and MAP values. A correlation between ONHBF and MAP was found at IOPs 25 mm Hg (P<0.001), but not at IOPs>25 mm Hg (P=0.79). Optic nerve head blood flow and IOP were significantly correlated (P<0.001), and ONHBF was only slightly dependent on MAP. The data of the present study indicate a complex regulation of ONHBF during combined changes in MAP and IOP. Our results may be compatible with myogenic mechanisms underlying autoregulation, and indicate better ONHBF regulation during an increase in MAP than during an increase in IOP.

Figure 1

Effect of isometric exercise on mean arterial blood pressure (MAP) and pulse rate (PR). Asterisks indicate significant changes versus baseline.

Figure 2

Effect of isometric exercise on ocular perfusion pressure (OPP) and optic nerve head blood flow (ONHBF). Data are presented as %change from baseline values. Asterisks indicate significant changes versus baseline.

Figure 3

Effect of application of the suction cup on intraocular pressure (IOP) and mean arterial blood pressure (MAP). Asterisks indicate significant changes versus baseline.

Figure 4

Effect of application of the suction cup on ocular perfusion pressure (OPP) and optic nerve head blood flow (ONHBF). Data are presented as %change from baseline values. Asterisks indicate significant changes versus baseline.

Figure 5

Pressure–flow relationship for optic nerve head blood flow (ONHBF; n=40) during isometric exercise. Data are sorted according to ascending ocular perfusion pressure (OPP) values, and the means as well as the 95% confidence intervals are shown. Asterisks indicate significant changes from baseline ONHBF.

Figure 6

Pressure–flow relationship for optic nerve head blood flow (ONHBF; n=40) during an increase in intraocular pressure (IOP). Data are sorted according to descending ocular perfusion pressure (OPP) values, and the means as well as the 95% confidence intervals are shown. Asterisks indicate significant changes from baseline ONHBF.

Figure 7

Optic nerve head blood flow during a combined increase in intraocular pressure (IOP) and mean arterial pressure (MAP). All data were grouped according to MAP values: MAP⩽85 mm Hg (red triangles, r=−0.67, P<0.01, n=290), 85 mm Hg<MAP⩽115 mm Hg (green squares, r=−0.57, P<0.01, n=251), and MAP>115 mm Hg (blue circles, r=−0.68, P<0.01, n=217), r=correlation coefficient.

Figure 8

Optic nerve head blood flow during a combined increase in intraocular pressure (IOP) and mean arterial pressure (MAP). Data were grouped according to IOP values: IOP⩽15 mm Hg (red squares, r=0.39, P<0.01, n=301), 15 mm Hg<IOP⩽25 mm Hg (blue circles, r=0.39, P<0.01, n=224), and IOP>25 mm Hg (green triangles, r=−0.016, P=0.54, n=234), r=correlation coefficient.