Optimizing criterion to reduce the variability between observers in the delimitation of the foveal avascular zone in diabetic patients

Aims/Purpose: To reduce the variability when performing manual segmentation of the foveal avascular zone (FAZ) on retinal optical coherence tomography angiography (OCTA) images, and to find a new accurate FAZ delimitation criterion. Methods: Seventy‐three eyes from healthy subjects, 40 eyes from Type 1 diabetes mellitus (DM1) patients without diabetic retinopathy (DR) and 54 eyes from Type 2 diabetes mellitus (DM2) patients with moderate DR and without diabetic macular oedema (DME) were evaluated using OCTA. A manual FAZ segmentation was performed by different observers of each OCTA image of the superficial (SCP) and deep capillary plexuses (DCP). After comparing the results, a new criterion was established to reduce the variability in the segmentations. The FAZ area and circularity were also studied. Results: The novel criterion produces smaller areas (closer to the real FAZ), as well as a diminution of the standard deviation values, with a factor of 0.5, with lower variability than the different criteria of the explorers in both plexuses for the three groups. This was particularly notorious for the DM2 group with damaged retinas, where it was very difficult to define the FAZ limits. The acircularity values were also slightly reduced with the final criterion in all groups. In the DM2 group a significant reduction in the acircularity mean value of both plexuses was obtained. Looking for a relationship between the FAZ area and the acircularity, we found slightly higher values of acircularity for smaller FAZ areas. The number of extremal values was much higher for the initial method, and when the DCP was evaluated. Conclusions: The implementation of a new criterion for FAZ segmentation produced more consistent results with less variability among observers.