PURPOSE To examine the retinal blood flow in normal eyes before and during retinal stimulation by flickering light. DESIGN A prospective cross-sectional study. PARTICIPANTS AND TESTING: Twenty-seven eyes of 27 normal subjects with a mean age +/- SD of 38 +/- 15 years (study I) and 21 eyes of 21 normal subjects with a mean age +/- SD of 46 +/- 17 years (study II) were examined with respect to capillary retinal blood flow and central retinal artery and central retinal vein blood flow velocities during flickering light stimulation. A luminance flicker light with a frequency of 8 Hz increased the neuronal activity of retinal ganglion cells. In study I, the retinal capillary blood flow was measured before and during flickering by scanning laser Doppler flowmetry (670 nm, Heidelberg Retina Flowmeter). In study II, the blood flow velocities in the central retinal artery and central retinal vein were examined by pulsed Doppler sonography. MAIN OUTCOME MEASURES Change in blood flow velocities in the central retinal artery and vein and in retinal capillary blood flow after full-field flicker stimulation. RESULTS In study I, measurements of blood flow during retinal flicker stimulation showed a significant increase in the mean value of blood flow +/- SD from 317 +/- 72 arbitrary units to 416 +/- 103 arbitrary units. The change was on average 46 +/- 19%. In study II, the systolic and end-diastolic blood flow velocities in the central retinal artery increased significantly (P < 0.0001): systolic, 9 cm/s to 15 cm/s (+62%); end-diastolic, 2.7 cm/s to 5.3 cm/s (+96%). In the central retinal vein, the systolic and end-diastolic blood flow velocities increased significantly (P < 0.0001): systolic, 4.3 cm/s to 6.7 cm/s (+56%); end-diastolic, 1.8 cm/s to 3.6 cm/s (+100%). The authors found no significant change in blood pressure and heartbeat frequency. CONCLUSIONS Visual stimulation of the retina by flickering light strongly increased the juxtapapillary retinal capillary blood flow and central retinal artery blood flow velocity in normal eyes.