Investigation of the autoregulatory mechanism of human retinal perfusion is conducted with a real-time spectral domain Doppler optical coherence tomography (SDOCT) system. Volumetric, time-sequential, and Doppler flow imaging are performed in the inferior arcade region on normal healthy subjects breathing normal room air and 100% oxygen. The real-time Doppler SDOCT system displays fully processed, high-resolution [512 (lateral) pixels] scans at in volumetric and time-sequential imaging modes, and also displays fully processed overlaid color Doppler flow images comprising 512 (lateral) pixels at . Data acquired following of 100% oxygen inhalation is compared with that acquired postinhalation for four healthy subjects. The average vessel constriction across the population is after oxygen inhalation with a dilation of after a return to room air. The flow decreases by in response to oxygen and in turn increases by as flow returns to normal in response to room air. These trends are in agreement with those previously reported using laser Doppler velocimetry to study retinal vessel autoregulation. Doppler flow repeatability data are presented to address the high standard deviations in the measurements.