Retinal oximetry in humans: effect of laser

Abstract

Abstract Purpose: According to theory, laser treatment of the retina decreases the demand for oxygen and increases available oxygen for the remaining retinal tissue. Animal studies have shown that preretinal or intraretinal partial pressure of oxygen (PO2) decreases following experimental branch retinal vein occlusion (BRVO) and the PO2 rises again following laser treatment. Confirming the beneficial effect of laser on retinal oxygenation in humans has been difficult because practical non‐invasive technology for oxygen measurements has been lacking. Our research group has studied retinal oxygenation in humans with retinal vein occlusion. Methods: The retinal oximeter is composed of a fundus camera, beam splitter and a digital camera. It yields fundus images with isosbestic and non‐isosbestic wavelengths of light simultaneously. Custom‐designed software analyses the images and estimates haemoglobin oxygen saturation in retinal vessels. Measurements have been made on 25 patients with retinal vein occlusion, in some cases before and after laser treatment. Results: In the 5 patients with BRVO, who were measured both before and after laser, the oxygen saturation in affected venules rose from 45±10% (mean±SD) before laser treatment to 53±6% after treatment (p= 0.041). Cases of hemivein and central vein occlusion have shown low oxygen saturation before laser and increased oxygen saturation after laser. Conclusions: The preliminary data indicates that, in some cases, low oxygen saturation is measureable in venules affected by retinal vein occlusion and that the saturation increases after laser. In some cases, notably where clinical signs are mild, the saturation appears to be normal even if no treatment has been applied but further studies are needed to establish the variability.