Retinal vessel oximetry made simple and reliable ‐ principle, performance and clinical results

Abstract

Abstract Purpose The regulation of the oxygen supply to the retinal tissue is critical and the detection of alterations in the oxygen supply or consumption may have a diagnostic merit. Quantitative assessment of oxygen supply and oxygen utilization in the tissue requires the measurement of the blood flow as well as the blood oxygenation. While the blood flow can be calculated from laser Doppler velocimetry and the vessel diameter, the intra‐vascular heamoglobin oxygen saturation (SO2) can be determined by a photometric measurement. Methods In the current approach, the SO2 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. Measurements of SO2 were performed in patients with diabetic retinopathy, arterial occlusion, and healthy controls. Furthermore, the changes of SO2 upon flicker light stimulation of the eye were investigated. Results From a healthy control population, mean arterial and venous SO2 were measured to be 98±10.1% and 65±11.7% with reproducibility of 2.52% and 3.25% respectively. In 10 patients with central or branch vein occlusion, a reduction of the arterial SO2 to 62±11% was found in the occluded vessel. After 5 days on pentoxifilin therapy, the SO2 increased to 90±16%. Diabetics showed venous SO2 increasing with the severity of the retinopathy. Flicker increased the venous SO2 by about 5%. Conclusion Dual wavelength oximetry is a simple and reliable method for physiological and clinical investigations. Commercial interest