Abstract
PURPOSE: To elucidate the relationship between vessel density (VD) measurements and signal strength in OCT angiography (OCTA). DESIGN: Cross-sectional study. PARTICIPANTS: Healthy volunteers. METHODS: OCT angiography images obtained from healthy volunteers were analyzed to demonstrate the relationship between signal strength index (SSI) and VD. Experiments were performed to determine the effects of signal strength reduction on VD measurements on the Optovue/AngioVue (Optovue, Inc, Fremont, CA) and Cirrus/AngioPlex OCTA (Carl Zeiss Meditec, Inc, Dublin, CA) systems. Signal strength reduction was generated by either neutral density filters (NDFs) or defocus. MAIN OUTCOME MEASURES: Regression analysis of signal strength effects on VD. RESULTS: Vessel density decreased linearly with signal strength with high statistical significance on both OCTA systems tested and for all analyzed sources of variation in signal strength. The slope of VD versus SSI was greatest when signal strength was adjusted by NDFs, followed by defocus, interscan difference, interindividual variation, and left-right eye difference. Multivariate analysis revealed that both SSI and age had a significant effect on the interindividual variation in VD. CONCLUSIONS: Vessel density measurements using OCTA were affected significantly by OCT signal strengths on 2 OCTA platforms. Investigators should exercise caution when interpreting VD data from OCTA scans. Quantification algorithms for OCTA should ideally remove the signal strength bias.