Effect of panretinal photocoagulation on retinal oxygen metabolism and ocular blood flow in diabetic retinopathy

Purpose: To investigate the effects of panretinal photocoagulation (PRP) on retinal oxygen metabolism, calibre of retinal vessels, and blood flow velocity in the optic nerve head (ONH) and choroid in patients with severe nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR). Methods: In this retrospective study, 37 patients (37 eyes) were studied. Retinal oximetry and laser speckle flowgraphy measurements were performed at baseline and after PRP. Results: After PRP, oxygen saturation of retinal arterioles (p = 0.003) and arteriovenous oxygen saturation difference (p = 0.005) significantly increased. On the other hand, the calibre of retinal arterioles significantly decreased (p = 0.016). In the ONH, mean blur rate (MBR)-vessel (p = 0.002), representing blood flow velocity in the retinal vessels, and MBR-tissue (p = 0.002), representing ONH blood flow velocity, and choroidal MBR (p = 0.012) significantly decreased. At baseline, there were significant negative correlations between ONH MBR-overall (r = −0.382, p = 0.026) and ONH MBR-tissue (r = −0.455, p = 0.007) and arteriovenous oxygen saturation difference. After PRP, choroidal MBR had a significant negative correlation with arteriolar oxygen saturation (r = −0.415, p = 0.016). Conclusions: The effects of PRP are correlated with increased arteriovenous oxygen saturation difference, reduction in the calibre of retinal arterioles, and reduction of retinal and choroidal blood flow velocities.