Measurement of central corneal thickness by high-resolution Scheimpflug imaging, Fourier-domain optical coherence tomography and ultrasound pachymetry

Purpose: To compare the repeatability and reproducibility of central corneal thickness (CCT) measurements by high-resolution (HR) rotating Scheimpflug imaging and Fourier-domain optical coherence tomography (FD-OCT). CCT measurements were compared to those determined by ultrasound pachymetry (UP). Methods: In 35 healthy eyes, intra-observer repeatability for HR Scheimpflug (Pentacam) and FD-OCT (RTVue) systems was determined in consecutive images taken by an observer in the shortest time possible. Imaging was repeated again by a second observer to evaluate inter-observer reproducibility. The CCT measurements were compared among Scheimpflug, FD-OCT and UP images. Results: Mean coefficients of repeatability were 0.48% for Scheimpflug and 0.26% for FD-OCT. For Scheimpflug, the coefficient of inter-operator reproducibility was 0.87%. For FD-OCT, the coefficient of inter-operator reproducibility was 0.45%. The CCT measurements by Scheimpflug, OCT and UP images were (mean +/- standard deviation) 521.7 +/- 27.6 mu m, 510.8 +/- 28.6 mu m and 516.5 +/- 27.6 mu m, respectively. The differences between instruments were statistically significant. The 95% limits of agreement in CCT were -0.7 to 22.5 mu m for Pentacam-OCT, -13.4 to 24.0 mu m for Pentacam-UP and -26.7 to 15.4 mu m for OCT-UP. There was a high degree of correlation between CCT measured by all 3 methods. Conclusion: Noncontact measurements of CCT with HR Scheimpflug and FD-OCT systems yielded excellent repeatability and reproducibility and can be used interchangeably. Although both devices were comparable with UP; in clinical practice, the measurements acquired by optical modalities are not directly interchangeable with UP measurements.