Repeatability and agreement of central corneal thickness measurement with non-contact methods: a comparative study

To compare the central corneal thickness (CCT) measurements and reliability of RTVue XR-100 anterior segment optical coherence tomography (AS-OCT), AL-scan optical biometer and Schwind Sirius anterior segment analysis system.

The CCT was measured in one hundred and twenty-seven eyes of 127 healthy subjects with AS-OCT, AL-scan and Sirius system. Mean CCT was compared among the instruments, and the level of agreement was assessed using Bland-Altman plots. One eye each of 30 subjects was randomly assigned for intrasession intraoperator and interoperator repeatability which was assessed using coefficient of variation and intraclass correlation coefficient.

Mean CCT with AS-OCT, AL-scan and Sirius system was 496.72 ± 32.75, 507.43 ± 33.54 and 512.08 ± 33.1 µm, respectively. There was no statistically significant difference between AL-scan and Sirius system (p = 0.26). Significant difference was found between AS-OCT/AL-scan (p = 0.01) and AS-OCT/Sirius system (p < 0.0001). Bland-Altman analysis showed a high level of agreement between AL-Scan/Sirius system (Mean difference -4.6 µm) and a low level of agreement between AS-OCT/AL-scan (Mean difference -10.7 µm) and OCT/Sirius system (Mean difference -15.4 µm).

AS-OCT underestimated CCT measurements when compared to other two devices in healthy subjects. Hence, one must be cautious when analyzing the results from different machines and should be aware that the measurement values are not interchangeable.