Comparison of Foveal Avascular Zone Metrics in Diabetic Retinopathy

Abstract

Purpose : Foveal avascular zone (FAZ) abnormalities are known in diabetic retinopathy (DR) and may prove useful as a biomarker in DR diagnosis and management. Fundus photography and fluorescein angiography (FA) as shown in the ETDRS are the gold standard for staging DR. Recently, optical coherence tomography angiography (OCTA) provides noninvasive imaging of foveal microvasculature. Here we compare FA and OCTA FAZ area and circulatory index measurements to better understand if these techniques are comparable.

Methods : Twenty-eight eyes with DR and no diabetic macular edema underwent FA and OCTA macular scans (RTVue-XR; Optovue, Inc or AngioPlex, Carl Zeiss Meditec, Inc). FAZ area and perimeter were calculated by using in-house software by 2 experienced graders (SW,CH) for FA images and with commercial instrument software for OCTA macular scans. Final FA image adjudication was done by a third grader (KS) when >10% difference between graders existed. Circularity index, the ratio of measured area to the expected area, (closer to 0, more irregular; closer to 1.0, more circular), was calculated for FA and OCTA FAZ measurements. Additionally, 21 eyes also underwent both 3x3 mm and 6x6 mm OCTA macular scans and calculated FAZ area was compared.

Results : Twenty-five of 28 FA studies were gradable for FAZ area and perimeter. FAZ area difference between graders of >10% occurred in 14 of 25 eyes and >20% in 12 of 25 eyes. Calculated FAZ area was greater when measured by FA images compared to OCTA images. For 20 eyes with both FA and OCTA 6x6mm scans, mean FA FAZ area was 0.355mm²+/- 0.1081 and mean OCTA FAZ area was 0.280mm² +/- 0.0983. For 5 eyes with both FA and OCTA 3x3mm scans, mean FA FAZ area was 0.463mm²+/- 0.0705 and mean OCTA FAZ area was 0.3224mm² +/- 0.1387. Circularity index for FA was lower (0.6489mm² +/- 0.1275), indicating more irregularity, than for OCTA (0.7175 mm² +/- 0.1105). OCTA FAZ area could be calculated for 17 of 21 eyes undergoing both 3x3 and 6x6mm scans. Measured FAZ areas were larger by 3x3mm scans (mean 0.3269mm² vs 0.2953mm² for 6x6mm scans).

Conclusions : Calculating FAZ area in DR shows significant variability between different imaging modalities and scans. Calculated FAZ area by FA images may over represent area and irregularities. FAZ area measurement also vary in OCTA imaging depending on scan type. These obstacles in measurement highlight possible challenges in using FAZ area as a reliable DR biomarker.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.