 Background It has recently been shown that diffuse luminance flicker increases retinal and optic nerve head blood flow. This indicates that a neuro-vascular coupling between neural activity and blood flow exists as described previously for the brain. Although a lot of mediators such as NO, pO2, pCO2, H and K have been proposed, the mechanism of this coupling is still a matter of controversy. However, it has been shown in an animal experiment, that an increase in blood flow, evoked by diffuse luminance flicker stimulation is paralleled by an decrease in pO2 in the tissue. Thus, in this study we set out to investigate the flicker light induced increase in blood flow under elevated blood pO2. 