A new imaging technique for retinal vessel oximetry - principles and first clinical results in patients with retinal arterial occlusion and diabetic retinopathy

摘要

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 non-proliferative 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.