Variations in the blood flow of the human optic nerve head

Blood flow in various tissues of the body shows spontaneous variations. The purpose of this study was to analyze variations over time in the blood flow of the optic nerve head. Blood flow was measured by the laser Doppler flowmeter (LDF) in 12 healthy volunteers, and analyzed by spectral Fourier analysis. The LDF technique allows continuous measurement of flow, volume, and velocity in the microcirculation of the optic nerve head. We found variations expressed in cycles per minute (c/min) at frequencies characteristic of vasomotion (< 10 c/min) of breathing, and of cardiac pulsation. Oscillations at frequency < 10 c/min predominated in volume in all subjects and in flow in all but one. Variations in velocity of 60-90 c/min were identified in 10 of the 12 volunteers. Oscillations in the range of breathing frequency made the smallest contribution to changes in blood flow. Fluctuations in the frequency range of 5 c/min and lower were observed most frequently, and the majority of subjects showed fluctuations of several frequencies. Our results provide evidence that blood flow in the human optic nerve head presents some characteristics already known from the general physiology of the microcirculation.