Increasing oxygen saturation in larger retinal vessels after photocoagulation for diabetic retinopathy

Diabetic retinopathy is characterized by retinal vascular impairment resulting in retinal hypoxia. The disease can be treated by retinal photocoagulation, but the mechanism of action of this treatment is unknown. Therefore, it is of interest to investigate whether the effects of retinal photocoagulation are related to changes in oxygen saturation. Retinal oximetry and diameter measurements were performed on larger retinal arterioles and venules in 220 eyes from 149 patients with diabetic maculopathy (DM) and proliferative diabetic retinopathy (PDR) before, immediately after, and 3 months after photocoagulation treatment. Before treatment oxygen saturation was increased in retinal venules in DM patients to result in reduced arteriovenous (AV) saturation difference, and was increased in arterioles and venules in PDR patients to result in a normal AV saturation difference. Immediately after treatment the oxygen saturation in both groups was unchanged in retinal arterioles and increased in retinal venules resulting in a reduced AV saturation difference. Three months after treatment arterial and venous saturations were increased, but the AV saturation difference was not different from the pretreatment level. In both patient groups vascular diameters had decreased 3 months after treatment, which was significant for venules in the PDR group. The effects of retinal photocoagulation on diabetic retinopathy are not correlated with changes in oxygen saturation in larger retinal vessels.