Retinal oxygen extraction in individuals with type 1 diabetes with no or mild diabetic retinopathy

Aims/hypothesis The aim of this study was to compare retinal oxygen extraction in individuals with diabetes with no or mild non-proliferative diabetic retinopathy and healthy age- and sex-matched volunteers. Methods A total of 24 participants with type 1 diabetes and 24 healthy age-and sex-matched volunteers were included in this cross-sectional study. Retinal oxygen extraction was measured by combining total retinal blood flow measurements using a custom-built bi-directional Doppler optical coherence tomography system with measurements of oxygen saturation using spectroscopic reflectometry. Based on previously published mathematical modelling, the oxygen content in retinal vessels and total retinal oxygen extraction were calculated. Results Total retinal blood flow was higher in diabetic participants (46.4 +/- 7.4 mu l/min) than in healthy volunteers (40.4 +/- 5.3 mu l/min, p = 0.002 between groups). Oxygen content in retinal arteries was comparable between the two groups, but oxygen content in retinal veins was higher in participants with diabetes (0.15 +/- 0.02 ml O-2/ml) compared with healthy control participants (0.13 +/- 0.02 ml O-2/ml, p < 0.001). As such, the arteriovenous oxygen difference and total retinal oxygen extraction were reduced in participants with diabetes compared with healthy volunteers (total retinal oxygen extraction 1.40 +/- 0.44 vs 1.70 +/- 0.47 mu l O-2/min, respectively, p = 0.03). Conclusions/interpretation Our data indicate early retinal hypoxia in individuals with type 1 diabetes with no or mild diabetic retinopathy as compared with healthy control individuals. Further studies are required to fully understand the potential of the technique in risk stratification and treatment monitoring.