Objective: To compare retinal nerve fibre layer (RNFL) thickness measurements acquired using spectral domain (SD) and time domain (TD) optical coherence tomography (OCT) systems.
Study design: Prospective clinical study.
Participants: Twenty eyes of 20 healthy volunteers.
Methods: All patients underwent 3 sets of circular OCT scans around the optic disc using both a TD OCT system, and a new SD OCT system. RNFL thickness measures within each of 4 quadrants, as well as overall mean RNFL thickness, were compared. Bland-Altman plots were also used to assess agreement.
Results: Using the RTVue-100, RNFL measurements in the superior quadrant were, on average, 20 microm greater than those obtained from the Stratus (151.8 microm vs 131.7 microm, p< 0.0001). RNFL measures within other quadrants and overall mean RNFL thickness were not significantly different between systems. Bland-Altman plots indicated large differences between Stratus and RTVue-100 for all variables, with 95% limits of agreement spanning clinically important ranges of >50 microm for all RNFL variables.
Conclusions: Significant differences exist between RNFL measurements obtained from the TD and SD OCT systems used in this study. These related, but distinct, technologies are not interchangeable. Further studies will be required to allow for appropriate clinical use of new SD OCT systems.