Comparison of the measurement of central corneal thickness measured by a new device of tomography with Scheimpflug camera and Placido rings (Sirius ^®) and ultrasonic pachymetry in healthy subjects

Objective: To assess the repeatability and comparability of the central corneal thickness measurements obtained from a novel Scheimpflug camera with a Placido-disc topographer (Sirius ^®) and ultrasound pachymetry. Material and methods: In a sample of thirty unoperated eyes of healthy subjects, the central corneal thickness was analyzed by a single examiner using the Sirius ^® and the ultrasound pachymeter. Repeatability of three sets of measurements from each device were evaluated using the coefficient of variation, standard deviation, and intraclass correlation coefficient. T-test with Bonferroni adjustment and Bland and Altman plots were used to assess agreement between devices. Results: For the Sirius ^® the coefficient of variation was 0.291%, and for the ultrasound pachymeter was 0.238%. The standard deviation was 0.123μm and 0.101μm for Sirius ^® and US respectively and the intraclass correlation coefficient was higher than 0.95 in all measurements. Ultrasound pachymetry systematically yielded higher values and statistically significant (mean 543.867 vs 558.267μm Sirius ^® and ultrasound pachymeter respectively), but the difference was not clinically significant. Conclusion: In the assessment of normal corneas, central corneal thickness measured with both devices showed high repeatability and good agreement. Even though central corneal thickness measurements obtained by Sirius ^® were systematically lower than those obtained by ultrasound pachymeter, they do not have clinical significance.