Influence of scan direction on subfoveal choroidal vascularity index using optical coherence tomography

We investigated the influence of scan direction on subfoveal choroidal vascularity index (CVI) measurements using spectral-domain optical coherence tomography (SD-OCT) in young healthy subjects. Seventy-eight eyes of 41 healthy volunteers were included. Choroidal structures were obtained using SD-OCT with enhanced depth imaging (EDI) through radial scans at the center of the macula. The subfoveal choroidal images in the horizontal (0°), 45°, vertical (90°) and - 45° directions were recorded and CVIs were analyzed according to their respective directions using image binarization. Additionally, subfoveal choroidal thickness (SFCT), and axial eye length were measured. The SFCT and subfoveal CVI showed a negative correlation but were only significant for the 45° scan (Pearson's r = - 0.262, P = 0.021). The axial eye length and subfoveal CVI had no significant correlation in any direction (all P > 0.05). In the Bland-Altman plot, the subfoveal CVI measurement showed high agreement among the four scan directions. When the SFCT was ≥ 300 µm, there was no difference in the measured values of the subfoveal CVI among the four scan directions; however, when the SFCT was < 300 µm, there was a significant difference in subfoveal CVI among the scan directions (one-way analysis of variance, F = 4.685, P = 0.004). In subfoveal CVI measurement, it is considered that the horizontal (0°) scan can represent the vertical (90°) or oblique (45°, - 45°) scans. However, when the SFCT is thinner, the subfoveal CVI in each direction of radial scan may vary significantly. Hence, caution is required in the interpretation.