Precision of a new Scheimpflug and Placido-disk analyzer in measuring corneal thickness and agreement with ultrasound pachymetry

Purpose To assess the precision of corneal thickness measurements obtained by a new Scheimpflug camera combined with Placido-disk corneal topography (Sirius) and compare the measured values with those obtained by ultrasound (US) pachymetry. Setting Eye Hospital of Wenzhou Medical College, Wenzhou, China. Design Comparative evaluation of a diagnostic test or technology. Methods Eyes of healthy subjects were examined with the Scheimpflug–Placido topographer. Central (CCT) and thinnest (TCT) corneal thickness were recorded after 3 consecutive measurements. For US pachymetry, only CCT was measured. Measurements were repeated within 1 week. The within-subject standard deviation (Sw), test–retest repeatability, coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were calculated to evaluate intrasession repeatability and intersession reproducibility. Interdevice comparison was analyzed with paired t tests and Bland-Altman plots. Results The intrasession repeatability of Scheimpflug–Placido measurements was high, with test–retest and CoV close to 9 μm and 0.6% for CCT and TCT, respectively. The intersession test–retest and CoV were close to 10 μm and 0.7%, respectively. The ICC was higher than 0.98 for repeatability and reproducibility. High agreement was found between Scheimpflug–Placido and US pachymetry measurements, with narrow 95% limits of agreement. Conclusions The Scheimpflug–Placido instrument showed excellent intrasession repeatability and intersession reproducibility of CCT and TCT measurements in healthy eyes. High agreement and lack of statistically significant difference suggest that the instrument's TCT and the US pachymetry–CCT measurements can be used interchangeably in subjects with normal corneal thickness. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.