Superficial and deep foveal avascular zone size and characteristics evaluated using optical coherence tomography angiography

Abstract

Purpose : To evaluate the size and characteristics of the foveal avascular zone (FAZ) in the superficial and deep capillary plexus in normal, healthy adults using optical coherence tomography angiography (OCTA).

Methods : In a prospective cohort study of 85 healthy volunteers, 3mm x 3mm OCTA scans were performed on both eyes using the AngioVue OCTA system. The superficial and deep FAZ boundaries were manually traced by trained graders and the FAZ area and characteristics were calculated. Circularity represents the degree of resemblance of the area to a perfect circle (a value of 1.0 denotes a perfect circle).

Results : The mean age of the 85 participants (44 males and 41 females) was 22.7 years, with mean axial length and spherical equivalent of 25.4 mm and, -4.3 D, respectively. The mean areas of the superficial and deep FAZ were 0.25 mm² (range, 0.04 to 0.48 mm²) and 0.38 mm² (range, 0.12 to 0.66 mm²) respectively. The 25^th, 50^th and 75^th percentiles for the superficial FAZ were 0.20, 0.25 and 0.31 mm², respectively. Comparing the 2 vascular layers, the deep FAZ size correlated significantly with the superficial FAZ (correlation coefficient 0.707, p<0.001) and was significantly larger compared to the superficial FAZ (mean difference 0.13 mm², p<0.001). No retinal vessels were visualized within the outer retinal layer. Comparing the right and left eyes, the superficial and deep FAZ sizes correlated strongly (correlation coefficients of 0.94 and 0.89, respectively), with mean differences between contralateral eyes of 0.001 mm² (p=0.720) and 0.005 mm² (p=0.408), respectively. The mean circularity index was 0.81 (range 0.54 to 0.95) for the superficial FAZ, and 0.89 (range 0.76 to 0.97) for the deep FAZ. The mean maximum diameter was 0.65 mm for the superficial FAZ and 0.78 mm for the deep FAZ (p<0.001), with Feret’s angle of 92.3^o for the superficial FAZ and 78.4^o for the deep FAZ. The mean central choroidal thickness was 315.3 µm (range, 119 to 537 µm). Neither superficial nor deep FAZ correlated with central choroidal thickness.

Conclusions : The FAZ area of the superficial and deep capillary plexus varies significantly among healthy adults. There is strong correlation between the areas of the superficial and deep FAZ, and between the contralateral eyes. Deep FAZ area and Feret’s diameter are significantly larger than the superficial FAZ.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.