The oxygen saturation in retinal vessels from diabetic patients depends on the severity and type of vision-threatening retinopathy

Purpose Diabetic retinopathy is characterized by morphological lesions in the retina secondary to disturbances in retinal blood flow which may influence the supply of oxygen to the retinal metabolism. Using retinal oximetry, it has been shown that the oxygen saturation is increased in retinal arterioles and venules from diabetic patients with retinopathy, but oxygenation before the development of retinopathy and possible differences in retinal oxygenation between diabetic maculopathy and proliferative diabetic retinopathy patients have not been evaluated. Methods One-hundred and fifty-six consecutive patients referred for specialist evaluation of diabetic retinopathy, and eighty normal control persons were subjected to retinal oximetry of the larger retinal arterioles and venules. The diabetic patients were allocated to one of four groups with severity of retinopathy ranging from no retinopathy to vision-threatening retinopathy, and the oxygen saturation in arterioles and venules was compared between these groups. Results Increasing severity of retinal changes from no retinopathy to diabetic maculopathy was accompanied with increasing oxygen saturation in retinal venules and decreasing oxygen extraction, whereas proliferative diabetic retinopathy showed increased oxygen saturation in both retinal arterioles and venules to result in a normal oxygen extraction. Conclusion Prospective observational and interventional studies are needed to show whether changes in retinal oxygen saturation precede or follow the development of diabetic retinopathy. Additionally, studies of regional variations in haemodynamic parameters in patients with vision-threatening diabetic retinopathy might improve the understanding of the pathophysiology of diabetic retinopathy. This is a precondition for improving the prevention and treatment of the disease.