Comparative study of the measurement of central corneal power using the manual keratometer, the IOLMaster® and Sirius® tomography

Objective: To assess the repeatability and comparability of the central keratometric power measurements obtained from a novel Scheimpflug camera with a Placido-disc topographer (Sirius®), manual keratometer and IOLMaster®. Material and methods: In a sample of 30 unoperated eyes of healthy subjects, the central corneal power was analyzed by a single examiner using the Sirius®, the manual keratometer and the IOLMaster®. Repeatability of 3 sets of measurements from each device were evaluated using the coefficient of variation, standard deviation, and intraclass correlation coefficient. T-test with Bonferrioni adjustment and Bland and Altman plots were used to assess agreement between devices. Results: All instruments showed high reproducibility with coefficient of variation less than 0.30% for all measurements (0.291% and 0.237%, 0.238% and 0.361%, 0.238% and 0.208% for the flattest (FK) and steepest keratometry of Sirius®, manual keratometer and IOLMaster® respectively) and a higher intraclass correlation coefficient of 0.95 in all measurements. The manual keratometer has the lowest keratometric power (FK 41,988 and SK 43,277 D), followed by Sirius® (FK 42.285 D and SK 43.510 D) and finally the IOLMaster® (FK 42.483 D and SK 43.763 D), with a statistically significant differences. Conclusion: In the assessment of normal corneas, central corneal power measured with this 3 devices showed high repeatability however there was no agreement between the equipments and the differences were statistically significant.