Repeatability of Automated Vessel Density Measurements Using Optical Coherence Tomography Angiography

Aims: To determine the repeatability of optical coherence tomography angiography (OCT-A)-derived automated vessel density measurements in the superficial retinal layer (SRL) and deep retinal layer (DRL) in healthy individuals.

Methods: 41 eyes of 21 healthy individuals were included in this study. OCT-A was performed using the NIDEK RS-3000 Advance with prototype OCT-A software. Each subject underwent two scanning sessions with 5-10 min in between. En face images of the retinal vasculature were generated using the default segmentation for SRL and DRL. Automated vessel density measurements were compared between the two sessions. The intraclass correlation coefficients (ICCs) and coefficient of repeatability were used as a measure for repeatability.

Results: The mean±SD age of the subjects was 36.8±7.5 years. Overall vessel density measured in the first and second session was 19.43±3.10 and 19.72±3.78 for the SRL, and 34.67±1.801 and 34.55±1.64 for the DRL, respectively. The mean difference in vessel density between sessions was -0.3 (95% CI 3.3 to -3.9) for the SRL and 0.1 (95% CI 2.6 to -2.5) for the DRL. The two measurements were highly correlated with an ICC=0.90 (p=0.33) for the SRL and 0.83 (p=0.589) for the DRL. The coefficient of variation was 0.052 for the SRL and 0.02 for the DRL.

Conclusions: Commercial automated vessel density measurements using OCT-A showed excellent repeatability in healthy individuals. Although repeatability will also need to be established in the setting of disease, the level of reproducibility should be useful for assessing the significance of differences in capillary density over time or under different conditions.