Impaired Retinal Vascular Reactivity in Diabetic Retinopathy as Assessed by Optical Coherence Tomography Angiography

To assess retinal vascular reactivity in healthy controls and subjects with diabetic retinopathy (DR).

A total of 22 healthy control eyes and 16 eyes with DR were enrolled. Images were acquired using a commercially available swept-source optical coherence tomography angiography (SS-OCTA) system. Three conditions were tested for each patient (hyperoxia, hypercapnia, and room-air) by employing a non-rebreathing apparatus that delivered appropriate gas mixtures (100% O2, 5% CO2, room air). Vessel skeleton density (VSD) and vessel diameter index (VDI) were compared between the conditions using mixed-model ANOVA adjusting for age and hypertension. Significant gas or interaction effects were followed by a Bonferroni adjusted pairwise post hoc analysis. Statistical significance was defined at P < 0.05.

The mixed-model ANOVA of the VSD found a significant intraindividual gas effect (F[2, 70] = 20.3, P < 0.001) and intergroup effect (F[1, 35] = 6.9, P = 0.001), and interaction effects (F[2, 70] = 4.6, P = 0.03). The post hoc pairwise comparison found significant differences among all three gas conditions in the healthy controls. In the subjects with DR, there were significant differences in VSD between hyperoxic and room air, and between hyperoxic and hypercapnic conditions, but not between hypercapnic and room-air conditions. Similar results were found for VDI.

The retinal capillaries, assessed with SS-OCTA, in subjects with DR preferentially reacted to hyperoxia but not hypercapnia, while the healthy controls reacted to both. The difference in the vascular reactivity may be indicative of the underlying pathophysiology of DR.