Repeatability, reproducibility, and agreement of two scheimpflug-placido anterior corneal analyzers for posterior corneal surface measurement

PURPOSE: To evaluate the intraoperator repeatability and interoperator reproducibility of two Scheimpflug- Placido anterior corneal analyzers (Sirius; Costruzione Strumenti Oftalmici, Florence, Italy, and TMS-5; Tomey, Nagoya, Japan) for the measurement of posterior corneal surface in normal eyes and the agreement between the two devices. METHODS: The current prospective study investigated 55 right eyes of 55 healthy patients in a random order. The posterior steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), and astigmatism were randomly measured by two independent experienced operators using the Sirius and TMS-5 Scheimpflug-Placido systems. Three consecutive measurements were obtained. Vector analysis was used for astigmatism. To assess intraoperator repeatability and interoperator reproducibility, withinsubject standard deviation (Sw) and test-retest repeatability (TRT, 2.77 Sw) were calculated. The Bland-Altman plots and 95% limits of agreement (LoA) were used to evaluate the agreement between the two systems. RESULTS: In the Sirius Scheimpflug-Placido system, the Sw and TRT of keratometry and astigmatism were less than 0.04 and 0.12 diopters (D), respectively. The interoperator Sw and TRT were less than 0.03 and 0.07 D, respectively. In the TMS-5 Scheimpflug-Placido system, the intraoperator Sw and TRT did not exceed 0.03 and 0.08 D, respectively. The interoperator Sw and TRT were no greater than 0.02 and 0.05 D, respectively. All parameters showed minor fluctuations in the 95% LoA. CONCLUSIONS: Both Scheimpflug-Placido systems show high repeatability and reproducibility for posterior corneal surface measurement. A high concordance between the two devices suggests interchangeable use in normal eyes.