Retinal Oxygen Saturation: Novel Analysis Method for the Oxymap

Purpose. To use a novel image analysis approach to consider how oxygen saturation changes as a function of vessel width and distance from the nerve and between superior and inferior retinal hemifields. Methods. Ten images were acquired from one eye of 17 participants (mean [standard deviation] age, 28 [4] years; range, 22-38 years) using the Oxymap T1 retinal oximeter. Every pixel identified by the detection algorithm was extracted, and frequency histograms of retinal vessel oxygen saturation were plotted for each vessel diameter (70-170 mu m). Histograms were fitted with two Gaussian models to identify peak arteriole and venule oxygen saturation. Mean (+/- standard error of the mean) arteriole and venule oxygen saturation at each vessel width were calculated. Data were also analyzed in (1) annuli of 100 mu m centered on the optic nerve or (2) upper and lower hemifields demarcated by the center of the optic nerve. Results. Venous oxygen saturation was higher in smaller vessels than in larger vessels. Arterial oxygen saturation remained relatively constant with vessel width. Oxygen saturation was lower in veins nearer the optic nerve. The upper retinal hemisphere showed higher venous oxygen saturation compared with the lower hemifield. Conclusions. The current objective analysis approach provides a more complete picture of retinal oxygen saturation at the posterior pole as a function of vessel width and retinal location.