Aim Retinal oxygen metabolism is thought to be affected in diabetic retinopathy. The aim of this study was to test whether retinal vessel oxygen saturation is different in patients with diabetic retinopathy from that in healthy controls.

Methods The retinal oximeter is based on a fundus camera. It estimates retinal vessel oxygen saturation from light absorbance at 586 nm and 605 nm. Retinal vessel oxygen saturation was measured in one major temporal retinal arteriole and venule in healthy volunteers and in patients with diabetic retinopathy.

Results Oxygen saturation in the retinal arterioles of healthy volunteers was 93±4% and 58±6% in venules (mean±SD, n=31). The corresponding values for all diabetic patients (n=20) were 101±5% and 68±7%. The difference between healthy volunteers and diabetic patients was statistically significant (p<0.001 for arterioles and venules). Three subgroups of diabetic patients (background retinopathy, macular oedema and pre-proliferative/proliferative retinopathy) all had higher saturation values than the healthy volunteers (p<0.05 for arterioles and venules).

Conclusion Retinal vessel oxygen saturation is higher in patients with diabetic retinopathy than in healthy controls. Possible explanations include shunting of blood through preferential channels, bypassing non-perfused capillaries in the capillary network. Parts of the retinal tissue may be hypoxic while blood in larger vessels has high oxygen saturation.