Retinal nerve fiber layer thickness reproducibility using seven different OCT instruments

Purpose. The clinical utility of new optical coherence tomography (OCT) instruments strongly depends on measurements reproducibility. The aim of this study was to assess retinal nerve fiber layer (RNFL) thickness reproducibility using six different spectral-domain OCTs (SD-OCTs) and one time-domain OCT. Methods. RNFL thickness (average and four quadrant) from six SD-OCTs (Spectral OCT/SLO OPKO/OTI, 3D-OCT 2000 Topcon, RS-3000 NIDEK, Cirrus HD-OCT Zeiss, RTVue-100 Optovue, and Spectralis Heidelberg) and one time-domain OCT (Stratus OCT Zeiss) was measured twice in 38 right eyes of 38 randomly chosen healthy volunteers by two masked operators. Inter- and intraoperator reproducibility was evaluated by the intraclass correlation coefficient (ICC), coefficient of variation (CV), and Bland-Altman test analysis. Instrument-to-instrument reproducibility was determined by ANOVA for repeated measures. We also tested how the devices disagree in terms of systemic bias and random error using a structural equation model. Results. Mean RNFL average thickness ranged from 90.08 μm to 106.51 μm. Cirrus and Heidelberg showed the thinnest RNFL values in all measurements, Topcon the highest. ICC, CV, and Bland-Altman plots showed variable inter- and intraoperator agreement depending on the instrument. Heidelberg demonstrated the best interoperator (ICC, 0.92; CV, 1.56%) and intraoperator (ICC, 0.94 and 0.95; CV, 1.28% and 1.26%, respectively, for operator A and operator B) agreement for average RNFL thickness. Conclusions. Heidelberg demonstrated the higher agreement in inter- and intraoperator reproducibility, Optovue the worst. In light of our error analysis results, we found that a scale bias among instruments could interfere with a thorough RNFL monitoring, suggesting that best monitoring is obtained with the same operator and the same device.