Evaluation of Automatically Quantified Foveal Avascular Zone Metrics in Diabetic Retinopathy Using OCTA

Abstract

Purpose : To test an automated algorithm to identify the foveal avascular zone (FAZ) in eyes with diabetic retinopathy (DR), and to compare the performance of novel FAZ metrics to that of conventional FAZ metrics and extrafoveal avascular area (EAA) for the diagnosis of DR.

Methods : A generalized gradient vector flow (GGVF) model based algorithm detected the FAZ in 3×3-mm macular OCTA scans from diabetic and healthy subjects. Automated FAZ detection was compared to manual delineation and within-visit repeatability was tested. The correlations of two novel FAZ metrics (STD4 and NR300, Fig. 1), two conventional FAZ metrics (FAZ area and acircularity index), and EAA with ETDRS DR severity and BCVA were assessed.

Results : Eighty eyes from 66 diabetic patients and 33 control eyes from 19 healthy subjects were included. The agreement between automated and manual FAZ delineation had a Jaccard index > 0.82, and the repeatability of FAZ detection was excellent at all DR grades. Novel FAZ metrics that incorporated both FAZ size and irregularity, and partially controlled for physiologic FAZ variation, had stronger correlations with DR grade and BCVA than conventional FAZ metrics (Fig. 2). Of all tested OCTA metrics, EAA had the greatest sensitivity in differentiating diabetic from healthy eyes at all DR severity when specificity was held at 95%.

Conclusions : The GGVF algorithm tested in this study allows for rapid FAZ delineation and performs well on the more complicated FAZ borders present in advanced DR, where traditional semi-automated algorithms are more likely to fail. FAZ metrics that partially control for physiologic variation in FAZ by utilizing a maximum inscribed circle, such as STD4 and NR300, show stronger correlations with DR grade and BCVA than conventional FAZ metrics. While FAZ metrics can provide clinically useful information regarding macular ischemia, EAA measurements may be a better biomarker for the presence and severity of DR.

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

 

Quantitative FAZ metrics. (A) FAZ area, (B) acircularity index defined as the ratio of perimeter of the FAZ to the perimeter of a circle of equal area, (C) STD4 defined as the standard deviation of the areas of 4 sectors of the FAZ after excluding the maximum inscribed circle, (D) NR300 defined as the area of intersection of the FAZ and R300 annulus divided by the area of R300 annulus.

 

OCTA metrics by DR grade and corresponding correlation coefficient. *=P-value<0.05