Influence of diffuse luminance flicker on choroidal and optic nerve head blood flow

Purpose. In the retina there is general agreement that blood flow adapts in response to different conditions of light and darkness including diffuse luminance flicker. By contrast, regulation of choroidal blood flow in response to different light conditions is still a matter of controversy. Thus, we investigated the effect of diffuse luminance flicker on choroidal and optic nerve head blood flow. Methods. In a group of 14 healthy volunteers, choroidal blood flow and ocular fundus pulsation amplitude were assessed with laser Doppler flowmetry and laser interferometry, respectively. Measurements were done before, during and after stimulation with diffuse luminance flicker. Furthermore, the response of optic nerve head blood flow (ONHBF) to flicker stimulation was measured. Flicker stimuli were generated by a Grass® PS2 photostimulator, stimulating at a frequency of 8 Hz. Flicker light consisted of light flashes at a wavelength below 550 nm and produced a retinal irradiance of 140 μW/cm². Blood pressure and pulse rate were measured non-invasively. Paired t-test was used for statistical analysis. Results. ONHBF increased immediately after onset of flicker stimulation. The maximum increase in ONHBF was 30% ± 10% (mean ± SEM, p < 0.008). Both choroidal perfusion parameters were only slightly increased during flicker stimulation, by 2 ± 2% (laser Doppler flowmetry, p < 0.5) and by 4 ± 1% (laser interferometry, p < 0.12). After the end of stimulation all values returned to baseline levels. Conclusion. Our study clearly demonstrates that diffuse luminance flicker increases optic nerve head blood flow. In contrast, increased neural activity in the retina has no effect on choroidal blood flow. Thus, choroidal blood flow appears to be largely independent of alterations in retinal metabolism.