Light paths in retinal vessel oxymetry

The oxygen utilization and, therefore, the metabolic state, of a distinctiv e area of the retina may be calculated from the diameter of the supplying a rtery and vein, the haemoglobin oxygenation, and the velocity of the blood. The first two parameters can be determined by imaging spectrometry at the patients ocular fundus, However, the reflected light emerging from a vessel followed different pathways through the ocular fundus layers and the vesse l embedded in the retina. The contribution of the single pathways to the ve ssel reflection profile is investigated by a Monte Carlo simulation. Consid ering retinal vessels with diameters of 25-200 mum we found the reflection from a thin vessel to be determined by the single and double transmission o f light at 560 nm, The backscattering from the blood column determines the reflectance in the case of a thick vessel. However, both components are in the same order of magnitude. This has to be considered in the calculation o f the oxygen saturation of blood in retinal vessels from their reflection s pectra.