The optics of retinal blood vessels and their significance for scanning laser Doppler flowmetry

Recently,the scanning laser Doppler flowmetry (SLDF) has been developed as a standard method for the quantification of retinal blood flow. However the measured quantities flow,volume,and velocity depend on the angle between t he direction of the blood flow and of the light. The underlying theory assu mes isotropic illumination of the vessel. This assumption, however, is not valid for light back-scattered from retinal vessels. This paper investigate s the contribution of different pathways of the light to the SLDF signal by a Monte Carlo simulation. It is shown that the light measured on a vessel having a thickness of 50 mum is predominantly backscattered from the blood inside the vessel, whereas the measurement on vessels 20 mum in diameter or less also includes light transmitted through the vessel.