Reproducibility and repeatability of central corneal thickness measurement in keratoconus using the rotating Scheimpflug camera and ultrasound pachymetry

PURPOSE: To assess repeatability, reproducibility, and agreement of rotating Scheimpflug camera (Pentacam Oculus, Wetzlar, Germany) and ultrasound pachymetry in measuring central thickness of keratoconic corneas. DESIGN: Method-comparison study. METHODS: In 33 patients with keratoconus (one eye per patient), two examiners each used both pachymetric methods to measure central corneal thickness (CCT); in the same session, measurements then were repeated by examiner 1 (A.M.). The difference between two examiners, and between first and second measurements by examiner 1, with both methods and the difference between the two pachymetric methods in measuring central thickness of keratoconic corneas were noted. RESULTS: With the rotating Scheimpflug camera, interexaminer correlation was higher (intra-class correlation coefficient [ICC], 0.98 vs 0.76) and inter-examiner variability was lower (95% limits of agreement [95% LoA], -14.8 to 13.8 microm vs -18.0 to +49.5 microm) than with ultrasound pachymetry. Both methods showed close first- to second-measurement correlation (ICC, > 90), but the rotating Scheimpflug camera had lower variability (95% LoA, -14.5 to 14.2 microm vs -27.4 to 26.0 microm). Mean CCT was 478.9 +/- 34.6 microm with the rotating Scheimpflug camera and 486.6 +/- 30 microm with ultrasound pachymetry. Although the mean difference was small (-7.8 microm), the 95% LoA (-43.8 to 28.2 microm) showed that the difference between the two methods can be considerable. CONCLUSIONS: In keratoconic corneas, the rotating Scheimpflug camera provides measurements of central thickness that are more reproducible and repeatable than those obtained with ultrasound pachymetry. The rotating Scheimpflug camera seems to be suitable for disease staging and follow-up, when corneal thickness measurements may be repeated over time by different examiners.