Reproducibility of retinal thickness measurements on normal and pathologic eyes by different optical coherence tomography instruments

Purpose: To compare retinal thickness measurements produced by different time-domain and spectral-domain optical coherence tomography (TD-OCT and SD-OCT) devices when imaging normal and pathologic eyes. Design: Prospective, observational study in an academic institutional setting. Methods: 110 eyes were imaged by six different OCT devices: Stratus and Cirrus (Carl Zeiss Meditec Inc., Dublin, CA, USA), Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany), RTVue-100 (Optovue Inc., Fremont, CA, USA), SDOCT Copernicus HR (Optopol Technology S.A., Zawiercie, Poland) and 3D OCT-1000 (Topcon Corporation, Tokyo, Japan). Eyes were normal or affected by different pathologies of the retina, including exudative and non-exudative age related macular degeneration, epiretinal membrane, cystoid macular edema and macular hole. For each instrument we used standard analysis protocols for macular thickness evaluation. Mean retinal thickness values between the instruments in the ETDRS central, circular, 1000 µm diameter areas, and in the ETDRS mid peripheral, circular, 3000 µm diameter areas were compared. Results: The 6 different devices produced measurements that differ in variance (Bartlett test p=0.006), and mean values (Friedman test p<0.001). Altman-Bland analysis revealed that the limits of agreement for all the comparisons were not acceptable. Regression was calculated and it was elaborated into a conversion table, despite a high standard error for both intercepts and slope conversion values. Conclusions: This study suggests that retinal thickness measurements obtained with various OCT devices are different beyond clinical practice tolerance, according to Altman-Bland analysis. Furthermore, regression analysis reveals high standard error values. These differences appear to be primarily due to the analysis algorithms used to set retinal inner and outer boundaries.