Short-term increase of intraocular pressure does not alter the response of retinal and optic nerve head blood flow to flicker stimulation

PURPOSE. It has been shown that stimulation with diffuse luminance flicker induces vasodilatation in the human retina and increases optic nerve head (ONH) blood flow. The present study was designed to investigate the influence of a short-term increase in intraocular pressure on flicker-induced changes in ONH blood flow and retinal vessel diameters. METHODS. In a group of 15 healthy volunteers, IOP was increased by the episcleral suction cup technique. ONH blood flow was assessed with a laser Doppler flowmeter, and retinal vessel diameters were measured with the retinal vessel analyzer. Flicker responses of retinal vessel diameters and ONH blood flow were determined at baseline conditions and during suction of 70 and 140 mm Hg. Flicker light consisted of 8-Hz square-wave flashes at a wavelength below 550 nm and produced a retinal irradiance of 140 μW/cm². RESULTS. Suction increased IOP from 12 ± 2 to 27 ± 4 mm Hg and 43 ± 4 mm Hg. Stimulation with diffuse luminance flicker induced an increase in ONH blood flow of +24.0% ± 20.7%. Increased IOP did not significantly change the flicker response in the ONH (+19.3% ± 26.6% and +22.1% ± 25.1%). In retinal veins, flicker induced an increase in vessel diameter of +3.0% ± 2.0%. Flicker responses in retinal veins were not significantly altered after the IOP was increased, compared with those recorded at baseline IOP (+2.8% ± 2.5% and +3.2% ± 2.2%). The flicker response in retinal arteries at baseline IOP was + 3.5% ± 2.0%. Again, the increase in IOP did not significantly alter this flicker response (+2.8% ± 1.6% and +3.1% ± 2.4%). CONCLUSIONS. A short-term increase in IOP does not alter the response of retinal vessel diameters and ONH blood flow to diffuse luminance flicker, which indicates that increased IOP does not alter retinal or ONH regulation during neuronal stimulation.