Pachymetric measurements with a new Scheimpflug photography-based system Intraobserver repeatability and agreement with optical coherence tomography pachymetry

PURPOSE: To evaluate the intraobserver repeatability of pachymetric measurements obtained with a new Scheimpflug photography-based system and the agreement of the measurements with those obtained by optical coherence tomography (OCT). SETTING: Vissum Corporation, Alicante, Spain. DESIGN: Evaluation of diagnostic technology. METHODS: Corneal thickness was measured at different locations (center; 2.5 mm and 4.0 mm nasal, temporal, superior, and inferior) in 18 eyes of 18 patients with no ocular pathology or previous surgery with a Scheimpflug photography-based system (Sirius). Three consecutive measurements at each location were obtained with the system to evaluate intraobserver repeatability. Afterward, pachymetric measurements were obtained at the same locations with an OCT system (Visante) to evaluate the agreement between techniques using the Bland-Altman method. RESULTS: The intraclass correlation coefficient of repeated measures ranged from 0.990 to 0.997. The coefficient of variation was lower than 1% and the standard deviations of the repeated measurements (S-w) were below 6 mu m at all corneal locations. Statistically significant differences were found between the coefficient of variation and S-w, values of the repeated measurements corresponding to the 2.5 mm and 4.0 mm locations (P <=.037). The agreement with OCT pachymetric measurements was poor, with ranges of agreement larger than 20 mu m at all corneal locations. Statistically significant differences were found between standard deviations of the differences between the 2 devices at the 2.5 mm and 4.0 mm locations (P <=.017). CONCLUSION: Scheimpflug photography-based technology provided repeatable pachymetric measurements that were not equivalent to those obtained with OCT.