Long-term repeatability of optical coherence tomography angiography parameters in healthy eyes

Purpose To determine the long-term repeatability of optical coherence tomography angiography (OCTA) parameters in normal eyes. Methods We prospectively enrolled 104 normal eyes. Participants were divided into three groups based on differences in the signal strength (SS) of OCTA scans obtained at two visits at least 6 months apart: group 1, SS difference = 2; group 2, 1; group 3, 0. We measured a foveal centred scan area of 3 x 3 mm pattern. All measurements were performed twice at 5-min intervals at the initial visit. The second measurements were performed at least 6 months later. Results In short-term vessel density (VD) repeatability, the coefficient of variation (CV) ranged from 3.89% to 8.10% and the intraclass correlation coefficient (ICC) ranged from 0.785 to 0.941. In terms of long-term repeatability, the CV was 5.39-12.62% and the ICC was 0.598-0.867. In group 1, the ICCs of the inner and full VDs were 0.194 and 0.221, respectively. In groups 2 and 3, the ICCs of the inner and full VDs were 0.611 and 0.603, and 0.763 and 0.765, respectively. The central VDs of all groups had high CV besides high ICC. Conclusions Optical coherence tomography angiography parameters showed good short-term and reasonable long-term repeatability in normal individuals. The differences in SSs between measurements affected such repeatability, so physicians should query the reliability of OCTA parameters when the differences in SS are 2 or more even when the SS is high.