The Oxygen Saturation in Vascular Abnormalities Depends on the Extent of Arteriovenous Shunting in Diabetic Retinopathy

PURPOSE. Diabetic retinopathy is characterized by disturbances in retinal blood flow mediated by capillary occlusion, intraretinal microvascular abnormalities (IRMAs), neovascularizations, and omega loops and reduplications. It is likely that the study of oxygen saturation in these abnormalities can provide knowledge about their role in the development of diabetic retinopathy. METHODS. The oxygen saturation in IRMA vessels and venous loops and reduplications were studied in 40 diabetic patients with severe nonproliferative or proliferative diabetic retinopathy. The saturation values in the studied vascular abnormalities were compared to those of the larger retinal arterioles and venules. RESULTS. There was a similar oxygen saturation (mean 6 SD) in IRMAs observed to connect arterioles with venules (78.6% +/- 11.8%, n = 22) and IRMAs connecting venules with venules (79.2% +/- 9.0%, n = 12; P > 0.999). The saturation in IRMAs was significantly lower (P < 0.0002) than in arterioles (97.4% 6 5.2%, n = 40) and significantly higher (P < 0.0001) than the saturation in omega loops and reduplications (54.2% +/- 19.3%, n = 6), which in turn showed no significant difference from the saturation in the venules (61.8% +/- 6.8%, n = 40, P = 0.4). CONCLUSIONS. The findings suggest that the oxygen saturation in vascular abnormalities in diabetic retinopathy depends on the extent of arteriovenous (A-V) shunting, with venous saturation due to no A-V shunting in venous loops and reduplications, and intermediate oxygen saturation due to moderate shunting in IRMAs. This may precede the development of neovascularizations with arterial oxygen saturation due to high A-V shunting.