Abstract

We have developed a stabilized, bidirectional, laser Doppler velocimeter with a retinal tracking and beam directing system for maintaining a laser beam on a target retinal blood vessel in the presence of eye movement. Light scattered by moving red blood cells is Doppler-shifted and heterodyned with light scattered from the vessel wall. The light is collected along two paths that are separated by a known angle. The photocurrent signal is stored on computer disk as 89 data-segment pairs. The computer produces a power spectrum for each data segment. The power spectrum exhibits a sharp cutoff at the maximum Doppler shift, f_max. Δf_max is the difference of two/max values taken along two paths separated by a known angle. Δf_max determines the instantaneous centerline blood speed. The system displays a record of blood speeds from a retinal artery or vein sampled at ~5 ms intervals during several complete cardiac cycles. Mean blood flow is calculated as the product of the mean blood speed and the vessel cross section. The ability to precisely place a stabilized beam on a retinal vessel improves the reliability of the measurement and permits a detailed study of retinal hemodynamics.

© 1990 Optical Society of America