Interocular symmetry of the foveal avascular zone area in healthy eyes: a swept-source optical coherence tomography angiography study

Purpose: To determine the presence or absence of interocular differences in the foveal avascular zone (FAZ) area in healthy eyes. Study design: Cross-sectional study. Methods: We examined 236 healthy eyes of 118 consecutive subjects (mean age, 39.1 ± 18.9 years). We used swept-source optical coherence tomography angiography (OCTA) images of the FAZ to measure its area from both the superficial capillary plexus (SCP-FAZ) and the whole retinal capillary plexus (WCP-FAZ). We also investigated the relationship between interocular differences in SCP-FAZ and other factors such as: axial length, spherical equivalent, central retinal thickness, and retinal vascular density. Results: There was no significant difference in the FAZ area between the right and left eyes in either the SCP-FAZ (P = 0.61) or WCP-FAZ (P = 0.80), and the FAZ areas of both eyes showed significant positive correlations (SCP-FAZ; P < 0.001, R² = 0.884, WCP-FAZ; P < 0.001, R² = 0.856). Bland–Altman plots showed that the mean interocular difference in SCP-FAZ area was 0.002 ± 0.037 mm² (95% confidence interval, -0.072–0.075 mm²), and in the WCP-FAZ area, 0.050 ± 0.044 mm² (95% confidence interval, -0.036–0.137 mm²). Multivariate regression analysis showed that none of the investigated factors were significantly associated with interocular differences in SCP-FAZ (P = 0.61, R² = 0.138). Conclusions: There was no significant interocular difference in SCP- and WCP-FAZ areas in healthy eyes. The normal range of values for interocular difference in SCP-FAZ area was 0.002 ± 0.037 mm² and in the WCP-FAZ area, 0.050 ± 0.044 mm².