Retinal Oximetry Demonstrates Differences in Vessel Oxygen Saturation by Severity of Diabetic Retinopathy

Abstract

Purpose: To measure retinal vessel oxygen saturation (SO₂) using retinal oximetry in healthy subjects and in diabetic patients with one of three clinical stages: no diabetic retinopathy (DR), mild non-proliferative DR (NPDR) and moderate NPDR. In order to evaluate SO₂ in the context of diabetic status and retinal vascular perfusion, HbA1c, urine microalbumin and fluorescein angiography (FA) were obtained.

Methods: Retinal vessel SO₂ was measured in 16 diabetics with no DR, 16 diabetics with early DR (5 with mild NPDR and 11 with moderate NPDR) and 27 age-matched healthy subjects using a retinal oximeter (Oxymap ehf., Reykjavik, Iceland). Arterial saturation (SaO₂), venous saturation (SvO₂) and arteriovenous (A-V) difference for each subject were calculated within a ring-shaped measurement area concentric to the optic disc. For diabetic patients, HbA1c, urine microalbumin and FA (% ischemia in ring) were also analyzed for correlation.

Results: Patients with moderate NPDR showed a significant increase in SvO₂ compared to healthy subjects and diabetics with no DR (p=0.018, 0.047; respectively) and a nearly significant increase compared to diabetics with mild NPDR (p=0.057). Moderate NPDR patients also showed a significant decrease in A-V difference compared to healthy subjects, diabetics with no DR and diabetics with mild NPDR (p=0.003, 0.033, 0.016; respectively). SaO₂ was approximately equal across all groups. Age showed significant negative correlation with SaO₂ (r =-0.449, p=0.0004) and SvO₂ (r =-0.466, p=0.0002) and nearly significant positive correlation with A-V difference (r=-0.243, p=0.064). In diabetic patients, no correlation between SO₂ or A-V difference was found with HbA1c, urine microalbumin or FA (% ischemia in ring). In multivariate regression analysis, age and history of hypertension were significant determinants of A-V difference (β=1.507, p=0.012; β=-1.208, p=0.018, respectively).

Conclusions: In this preliminary study, increased SvO₂ and decreased A-V difference were found in patients with moderate NPDR compared to earlier stages of DR and healthy subjects. This may signify decreased delivery of oxygen to retinal tissues in patients with early DR and/or decreased tissue extraction of oxygen. Future studies of diabetic patients across all DR stages are ongoing to correlate retinal oxygenation with FA and systemic markers of diabetic severity.

Keywords: 499 diabetic retinopathy • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 688 retina