title: Repeatability of corneal power and wavefront aberration measurements with a dual-Scheimpflug Placido corneal topographer.
abstract: OBJECTIVE
  To evaluate the repeatability of the Galilei dual-Scheimpflug analyzer in measuring corneal curvature, wavefront aberrations, pachymetry, and anterior chamber depth (ACD).
  
  
  METHODS
  Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.
  
  
  METHODS
  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).
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  Dual-Scheimpflug measurements of corneal power, pachymetry, ACD, and corneal aberrations for Zernike terms in the middle of the Zernike tree showed excellent repeatability.
authors.affiliation: Department of Ophthalmology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Mariko
authors.initials: M
authors.lastname: Shirayama
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Koch
mesh_terms: D000328:Adult; D000867:Anterior Chamber / Q000033:anatomy & histology; D003315:Cornea / Q000033:anatomy & histology / Q000502:physiology*; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010781:Photography / Q000295:instrumentation; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D055815:Young Adult