Comparative study of optic disc measurement by Copernicus optical coherence tomography and Heidelberg retinal tomography

Background Copernicus optical coherence tomography (SOCT) is a new,ultra high-speed and high-resolution instrument available for clinical evaluation of optic nerve.The purpose of the study was to compare the agreements between SOCT and Heidelberg retinal tomography (HRT).Methods A total of 44 healthy normal volunteers were recruited in this study.One eye in each subject was selected randomly.Agreement between SOCT and HRT-3 in measuring optic disc area was assessed using Bland-Altman plots.Relationships between measurements of optic nerve head parameter obtained by SOCT and HRT-3 were assessed by Pearson correlation.Results There was no significant difference in the average cup area (0.306 vs.0.355 mm,P=0.766),cup volume (0.158 vs.0.130 mm,P=0.106) and cup/disc ration (0.394 vs.0.349 mm,P=0.576) measured by the two instruments.However,other optic disc parameters from SOCT were significantly lower compared with HRT-3.The Bland-Altman plot revealed good agreement of cup area and cup volume measured by SOCT and HRT-3.Bad agreement of disc area,rim area,rim volume and cup/disc ratio were found between SOCT and HRT-3.The highest correlations between the two instruments were observed for cup area (r2=0.783,P=0.000) and cup/disc ratio (r2=0.669,P=0.000),whereas the lowest correlation was observed for disc area (r2=0.100,P=0.037),rim area (r2=0.275,P=0.000),cup volume (r2=0.005,P=0.391) and rim volume (r2=0.021,P=0.346).Conclusions There were poor agreements between SOCT and HRT-3 for measurement of optic nerve parameters except cup area and cup volume.Measurement results of the two instruments are not interchangeable.