**5.3 Prospective uncontrolled single-centre study ROXINEGLYD (Contribution of Retinal OXimetry to the assessment of impact of INternal Environment, GLYcaemia and Diabetes control on retinal vessel oxygen saturation in PWD) (2016–2020)**

Retinal oximetry is a method for measuring retinal oxygen saturation (SatO2). Changes of retinal oxygen saturation were described in various clinical conditions such as retinal vein occlusion, retinitis pigmentosa, glaucoma, cataract, after pars plana vitrectomy, Alzheimer's disease and also in diabetic retinopathy [129, 130]. An increase in venous oxygen saturation was shown to be related to the severity of retinopathy [131–133]. Lower arteriovenous difference of oxygen saturation reflects reduced oxygen delivery to tissues [134]. The question is whether early regular investigations of retinal oxygen saturation might help to assess the risk and progress of diabetic retinopathy.

*Purpose* of the pilot study [135] was to find an association of retinal oxygen saturation with acid-base balance, carboxyhaemoglobin concentration, current

plasma glucose concentration (PG), mean PG and PG variability over the last 72 hrs, HbA1c. and other conditions.

*Methods:* Forty-one adults (17 men) with T1D (n=14) or T2D (n=27), age 48.613.5 years, diabetes duration 9 (0.1–36) years, BMI 29.46.3 kg/m<sup>2</sup> , HbA1c 5212.7 mmol/mol completed the study. The 4-day study comprised two visits (Day l, Day 4) including 72 hrs of CGM by iPro®2 Professional CGM (Medtronic, MiniMed, Inc., Northridge, CA, USA). Retinal oximeter Oxymap T1 (Oxymap ehf., Reykjavik, Iceland) was used to assess retinal oxygen saturation.

*Results:* Wilcoxon signed-rank test showed no SatO2 difference between eyes and visits. A significant correlation between arterial SatO2 and PG variability in T2D, a positive correlation of venous SatO2 with HbA1c and with finger pulse oximetry was found. No correlation of retinal oxygen saturation with acid-base balance, carboxyhaemoglobin, current PG, mean PG over the 72 hrs, age, diabetes duration, BMI, lipoproteinaemia, body temperature, systolic and diastolic blood pressure, heart rate, central retinal thickness and retinal nerve fibre layer thickness was shown.

*Conclusion:* This study confirmed the association of venous retinal oxygen saturation with long-term but not with short-term diabetes control and not with acid-base balance or other conditions. The increased oxygen saturation and questionable impact of PG variability should be clarified further on.
