Changes in Choroidal and Optic Nerve Head Blood Flow Regulation During an Experimental Increase in Ocular Perfusion Pressure

Abstract

Purpose: : The aim of the present study was to compare choroidal blood flow (ChBF) and optic nerve head blood (ONHBF) in response to an increase in ocular perfusion pressure (OPP) induced by isometric exercise.

Methods: : 48 healthy subjects were included. Subjects performed 6 minutes of squatting to increase OPP. Either ONHBF (n = 24) or ChBF (n = 24) was measured continuously by the means of laser Doppler flowmetry. OPP was calculated as 2/3*mean arterial pressure-intraocular pressure.

Results: : The response in blood flow was less pronounced than the response in OPP indicating for some degree of blood flow regulation. ChBF and ONHBF increased during isometric exercise (p < 0.001 each). However, ChBF was better autoregulated in response to isometric exercise than ONHBF (p = 0.023). ChBF remained constant until an OPP of about 60% above baseline, whereas ONHBF started to increase when OPP rose about 40% over baseline. In 3 subjects, an interesting phenomenon was observed: During squatting ONHBF decreased considerably below baseline when OPP fluctuated due to exhaustion, although OPP was still much higher than at baseline.

Conclusions: : The results of the present study indicate that ChBF shows better regulatory properties than ONHBF during isometric exercise, most likely due to the rich neural innervation. In the ONHBF experiments, a slight decrease in OPP during the squatting periods was accompanied by a pronounced decrease in ONH blood flow. Whether this plays a role in ocular disease remains unclear.

Clinical Trial: : http://www.clinicaltrials.gov NCT00912665

Keywords: choroid • optic disc • intraocular pressure