Retinal oxygen saturation in relation to retinal thickness in diabetic macular edema

Purpose: Retinal oximetry is a non-invasive measure of retinal metabolism. Diabetic retinopathy is associated with increased oxygen saturation in retinal venules. Hence, we examined if there are regional differences in retinal oxygen saturation, and if retinal oxygen saturation is correlated to retinal thickness in patients with diabetic macular edema (DME). Methods: We included 18 patients with DME that all had central retinal thickness (CRT) >300 µm and were free of active proliferative diabetic retinopathy. Optical coherence tomography (Topcon 3D OCT-2000 spectral domain OCT) was used to evaluate retinal thickness, and oximetry was performed in 50-degree disc-centered images using the Oxymap model T1 (Oxymap, Reykjavik, Iceland). For macular measurements, we used the first traceable macular branches of the superior and inferior temporal arcades with a diameter >6µm. To account for paracentral edema, the oxygen saturation in the upper and lower temporal arcade branches were compared to the corresponding upper and lower subfield thickness. Spearman’s rank was used to calculate correlation coefficients between CRT and retinal oximetry. Results: Median age and duration of diabetes was 59.4 and 3.8 years. Median HbA1c was 61.5 mmol/mol and 22.2% were women. Mean oxygen saturation was higher in retinal macular venules as compared to global venous oxygen saturation (76.7% vs. 66.3%, p=0.0001), whereas there was no difference between macular and global arteriolar oxygen saturations (94.8% vs. 92.3%, p=0.52). We found no correlation between CRT and retinal oxygen saturation, even when accounting for paracentral edema (p>0.05). Furthermore, there was no difference in retinal oxygen saturation between the macular hemisphere that was more or less affected by DME (p>0.05). Conclusion: Patients with DME had higher retinal oxygen saturation in macular venules as compared to the global retinal venous oxygen saturation. No correlation was demonstrated between retinal thickness and retinal oxygen saturation. Retinal oximetry may become an important clinical tool to monitor disease activity in the near future. This study served to further explore the full potential of the method.