Repeatability of corneal power and wavefront aberration measurements with a dual-Scheimpflug Placido corneal topographer

Abstract

To evaluate the repeatability of the Galilei dual-Scheimpflug analyzer in measuring corneal curvature, wavefront aberrations, pachymetry, and anterior chamber depth (ACD). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Three consecutive measurements were performed in 1 eye of each subject. The following were evaluated: (1) mean total corneal power at the central, paracentral, and peripheral zones (0.0 to 4.0 mm, 4.0 to 7.0 mm, and 7.0 to 8.0 mm, respectively) and posterior corneal power (K(avg)); (2) corneal higher-order wavefront aberrations (6.0 mm pupil); (3) mean pachymetry at the central, paracentral, and peripheral zones; and (4) ACD. Repeatability was assessed by calculating the within-subject standard deviation (SD), coefficient of variation (COV), and intraclass correlation coefficient (ICC). The study enrolled 20 subjects. The SD was 0.09 diopter (D), 0.05 D, and 0.19 D for central, paracentral, and peripheral total corneal power, respectively, and 0.03 D for posterior K(avg). The COV ranged from 0.10% to 0.35%, and the ICC was 0.996 or more (P<.001). For 3rd-order coma and trefoil, the SD was 0.08 mum and 0.09 mum, respectively. For 4th-order spherical aberration, astigmatism, and tetrafoil, the SDs were lower (0.02 mum, 0.04 mum, and 0.09 mum, respectively). The SD was 1.68 mum, 1.98 mum, and 2.82 mum for central, paracentral, and peripheral pachymetry, respectively, and 0.04 mm for ACD. Dual-Scheimpflug measurements of corneal power, pachymetry, ACD, and corneal aberrations for Zernike terms in the middle of the Zernike tree showed excellent repeatability.