Magnification Effect of Foveal Avascular Zone Measurement Using Optical Coherence Tomography Angiography

Abstract

Purpose: The aim of this study was to evaluate the foveal avascular zone (FAZ) of healthy subjects and examine the magnification effect. Methods: A total of 33 healthy volunteers were enrolled and all subjects were eligible for analysis. Optical coherence tomography angiography (OCTA) examination scanned 3 × 3 mm of the macular area. The FAZ area was measured on the superficial OCTA en face image with and without correction by axial length. The relationship between changes in the FAZ area after correction with the axial length was examined. Results: The mean age was 21.9 ± 0.6 years. The mean axial length was 24.87 ± 1.17 mm and mean spherical equivalent (SE) value was –3.64 ± 2.83 diopters (D). The FAZ area was 0.26 ± 0.10 mm2 before the axial length correction and 0.27 ± 0.10 mm2 after the correction. In the eyes that had an axial length longer than or equal to 26 mm or SE less than or equal to –6 D, the FAZ area after correction was significantly larger than that before correction (p < 0.01). The change of FAZ area after correction with axial length was significantly correlated with the axial length (R2 = 0.88, p < 0.01) or SE value (R2 = 0.55, p < 0.01). Conclusion: FAZ areas were comparable to previous reports. In high myopic cases, the magnification effect needs to be considered when evaluating the FAZ area.

Keywords

• foveal avascular zone
• magnification effect
• optical coherence tomography angiography
• myopia
• axial length