Blood flow in the human iris measured by laser Doppler flowmetry

A new instrument based on laser Doppler flowmetry (LDF) has been developed to determine noninvasively the relative flux of red blood cells (RBCs) through the microcirculatory network of the iris of the human eye. The probing laser, photodetector, and target fixation devices required by this method were adapted to a slit lamp. Electronic processing and computer analysis of the Doppler signal allow determination of relative velocity, number, and flux of RBCs in the iris, as well as the pulsatility of these flow parameters during the heart cycle. Based on measurements in one eye of eight normal volunteers, the sensitivity of the technique, i.e., the minimum change detectable at the P < 0.05 level, was 4% for the flux. The decrease in blood flow in response to decreases of the ocular perfusion pressure demonstrates the capability of the technique to detect flow changes and its suitability for investigating the physiology and the pharmacology of iris circulation.