The oxygen saturation of blood inside retinal vessels is an essential measure for the estimation of oxygen supply to the
tissue as well as its oxygen consumption. In the current approach, the blood oxygenation is measured by a dual-wavelength technique. Using a fundus camera, equipped with a special dual wavelength transmission filter and a color
CCD camera, two monochromatic fundus images at 548 nm and 610 nm were recorded simultaneously. The optical
densities of retinal vessels for both wavelengths and their ratio, which is known to be proportional to the oxygen
saturation, were calculated.
From a health control population, mean arterial and venous oxygen saturations were measured of 98±10.1% and
65±11.7% with reproducibility of 2.52% and 3.25% respectively. In 10 patients with arterial occlusion, a reduction of the
arterial oxygen saturation to 78 ±17% (mean ± standard deviation, branch arterial occlusion) and 91±11% (central
arterial occlusion) respectively was found in the occluded vessel. After 5 days on pentoxifilin therapy, the arterial
saturation increased to an average of 93±12% or 103 ±6% respectively. In 70 eyes of 42 patients suffering from diabetic
retinopathy, an increase of the venous oxygen saturation with the severity of the retinopathy was found (mild nonproliferative
retinopathy: 68.4±8.2%, moderate non-proliferative retinopathy: 70.5±6.8%, severe non-proliferative
retinopathy: 72.4±7.6%, proliferative retinopathy 75.7±8.3%) due to vessel shunting and diabetic changes of the
permeability of vessel walls.
These first clinical results demonstrate the ability of an accurate measurement of retinal vessel oxygenation with a very
simple setup just requiring a special filter in the illumination path of a fundus camera and dedicated software.