A Comparison between Scheimpflug Imaging and Optical Coherence Tomography in Measuring Corneal Thickness

Purpose: To assess the repeatability and reproducibility of 3 rotating Scheimpflug cameras, the Pentacam (Oculus, Wetzlar, Germany), Sirius (Costruzione Strumenti Oftalmici, Florence, Italy), and Galilei (Ziemer, Biel, Switzerland), and 1 Fourier-domain optical coherence tomography (FD-OCT) system, the RTvue-100 OCT (Optovue Inc., Fremont, CA), in measuring corneal thickness. Design: Evaluation of diagnostic test. Participants: Sixty-six right eyes of 66 healthy volunteers, whose mean age +/- standard deviation (SD) was 35.39 +/- 10.06 years (range, 18-55 years). Methods: Corneal thickness measurements obtained by each system included central corneal thickness (CCT), thinnest corneal thickness (TCT), and midperipheral corneal thickness (MPCT), measured at superior, inferior, nasal, and temporal locations at a distance of 1 and 2.5 mm from the corneal apex. In the first session, 3 consecutive measurements were performed by the same operator to assess intraobserver repeatability and by a second operator to assess interobserver reproducibility. Measurements were repeated in the second session scheduled 1 day to 1 week later. The mean values obtained in the 2 sessions by the first operator were used to investigate the intersession reproducibility. Main Outcome Measures: Intraobserver repeatability and interobserver and intersession repeatability of corneal thickness measurements, as calculated by means of within-subject SD, testeretest repeatability, coefficient of variation (COV), and intraclass correlation coefficients. Results: The precision of CCT, TCT, CT2 mm (midperipheral corneal thickness [MPCT] with a distance of 1 mm from the corneal apex), and CT5 mm (midperipheral corneal thickness [MPCT] with a distance of 2.5 mm from the corneal apex) measurements was high with all 4 systems. The COV was <= 1.16%, 0.94%, and 1.10% for repeatability, interobserver reproducibility, and intersession reproducibility, respectively. The 4 devices offered better interobserver reproducibility than intersession reproducibility for all measurements. The CTsuperior-5 mm (midperipheral corneal thickness [MPCT], measured at superior locations with a distance of 2.5 mm from the corneal apex) measurements showed the poorest repeatability and reproducibility. The Galilei revealed the best precision of CCT, TCT, and CT2 mm measurements. Conclusions: Both Scheimpflug imaging and FD-OCT offer highly repeatable and reproducible measurements of CCT and MPCT. The precision was lower in the midperipheral superior quadrant.