Segmented Swept Source OCT Angiography Assessment of the Foveal Avascular Zone Ratio in Ultra Wide-Field Imaged Non-Proliferative and Proliferative Diabetic Retinopathy: New Biomarker of Prognosis

Abstract

Purpose : Segmented Swept-Source OCT Angiography (SS-OCTA) imaging of the foveal avascular zone (FAZ) and the parafoveal vasculature shows microvascular changes that can be correlated with the severity of diabetic retinopathy (DR). We aim to assess whether alterations in the parafoveal capillary plexuses can be interpreted as a clinical biomarker of disease progression.

Methods : Observational and retrospective study of diabetic patients diagnosed with Non-Proliferative (NPDR) and Proliferative (PDR) DR between January and October 2016. All eyes were imaged on Optos California® (Optos®, UK) and the retinopathy classified by two independent observers into three groups: mild/moderate NPDR, severe NPDR and PDR. SS-OCTA (Triton Plus®, Topcon Corp., Japan) images were acquired using the 6 mm x 6 mm fovea-centred cubes scanning protocol. Surface Area (SA) was measured using the Topcon IMAGEnet® (version 1.19) proprietary software after automated segmentation of the FAZ into superficial vascular (SVP) (SVP-FAZ) and deep vascular plexus (DVP) (DVP-FAZ). Eyes with Clinically Significant Macular Oedema (CSMO) and with previous panretinal photocoagulation (PRP) were excluded. The difference and ratio between SAs in SVP-FAZ and DVP-FAZ in each group were analysed.

Results : Five (PRP) and ten (CSMO) eyes were not included in the statistical analysis. Imaging results from seventy-four eyes (36 patients, 15 females and 21 males, mean age was 60.3 years (±11.65, range 35-83)) were included in this study. In all eyes, the SA of DVP-FAZ was larger than that of SVP-FAZ. Mild/moderate NPDR graded eyes showed the smallest SA of FAZ in both DVP and SVP (p<0.01), whereas PDR eyes showed the largest FAZ area in both plexuses (p<0.01). The ratio of SAs of SVP-FAZ over DVP-FAZ (rFAZ) was significantly lower in severe NPDR eyes vs. mild/moderate NPDR and PDR eyes (p<0.01).

Conclusions : The SA of FAZ in both plexuses is correlated with DR severity, increasing with severity of retinopathy. Capillary rarefaction in DVP compared to that in SVP is more evident in severe NPDR than in the other groups. The enlargement of SA of DVP-FAZ may indicate further enlargement of the SA of SVP-FAZ and progression to PDR. Therefore rFAZ could serve as a prognostic tool for the monitoring of DR.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.