Retinal oxygen extraction and hyperemic response in patients with Type II diabetes at different stages of non‐proliferative diabetic retinopathy

Abstract

Purpose: Diabetic retinopathy (DR) is a worldwide cause of irreversible vision loss. Vascular factors such as reduced oxygen supply and impaired neurovascular coupling play a major role in the development of DR. We therefore investigated retinal oxygen metabolism and functional hyperemia in patients with Type II diabetes at different stages of non‐proliferative DR and healthy controls.Methods: To study retinal oxygen metabolism, a total of 67 patients with Type II diabetes (34 patients with no, 15 with mild and 18 with moderate‐to‐severe DR) and 20 healthy controls were recruited. We used the oxygen module of a Retinal Vessel Analyzer to measure retinal oxygen saturation in arteries and veins, and a custom‐built Doppler optical coherence tomography (DOCT) system to assess total retinal blood flow (TRBF). Values of retinal oxygen saturation and TRBF were then used to calculate retinal oxygen extraction. To measure the hyperaemic response, 29 patients with no, 12 with mild, 15 with moderate‐to‐severe DR and 20 healthy controls were included. Retinal blood flow was assessed before and during visual stimulation by combined measurement of retinal vessel calibres and blood velocity using the Dynamic Vessel Analyzer (Imedos, Germany) and DOCT.Results: Retinal oxygen extraction was lowest in patients with moderate‐to‐severe DR (1.78 ± 0.57 μL O2/min, p = 0.040 vs. healthy controls), followed by mild DR (1.90 ± 0.77 μL O2/min), no DR (2.14 ± 0.6 μL O2/min) and healthy controls (2.24 ± 0.57 μL O2/min). Compared to healthy controls (40.4 ± 27.2%), flicker responses were significantly decreased in patients with DR depending on the stage of DR (no DR 37.7 ± 26.0%, mild DR 26.2 ± 28.2%, moderate‐to‐severe DR 22.3 ± 13.9%; p = 0.035, ANOVA).Conclusions: Our results indicate that retinal oxygen extraction as well as hyperaemic response decreases with increasing severity of DR. Further studies are needed to assess whether these retinal functional changes can be used to identify high‐risk patients.