title: Corneal topography with Scheimpflug imaging and videokeratography: comparative study of normal eyes.
abstract: OBJECTIVE
  To compare the repeatability within anterior corneal topography measurements and agreement between measurements with the Pentacam HR rotating Scheimpflug camera and with a previously validated Placido disk-based videokeratoscope (Medmont E300).
  
  
  METHODS
  Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia.
  
  
  METHODS
  Normal eyes in 101 young adult subjects had corneal topography measured using the Scheimpflug camera (6 repeated measurements) and videokeratoscope (4 repeated measurements). The best-fitting axial power corneal spherocylinder was calculated and converted into power vectors. Corneal higher-order aberrations (HOAs) (up to the 8th Zernike order) were calculated using the corneal elevation data from each instrument.
  
  
  RESULTS
  Both instruments showed excellent repeatability for axial power spherocylinder measurements (repeatability coefficients <0.25 diopter; intraclass correlation coefficients >0.9) and good agreement for all power vectors. Agreement between the 2 instruments was closest when the mean of multiple measurements was used in analysis. For corneal HOAs, both instruments showed reasonable repeatability for most aberration terms and good correlation and agreement for many aberrations (eg, spherical aberration, coma, higher-order root mean square). For other aberrations (eg, trefoil and tetrafoil), the 2 instruments showed relatively poor agreement.
  
  
  CONCLUSIONS
  For normal corneas, the Scheimpflug system showed excellent repeatability and reasonable agreement with a previously validated videokeratoscope for the anterior corneal axial curvature best-fitting spherocylinder and several corneal HOAs. However, for certain aberrations with higher azimuthal frequencies, the Scheimpflug system had poor agreement with the videokeratoscope; thus, caution should be used when interpreting these corneal aberrations with the Scheimpflug system.
authors.affiliation: Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia. sa.read@qut.edu.au
authors.forename: Scott A
authors.initials: SA
authors.lastname: Read
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Collins
authors.forename: D Robert
authors.initials: DR
authors.lastname: Iskander
authors.forename: Brett A
authors.initials: BA
authors.lastname: Davis
mesh_terms: D000293:Adolescent; D000328:Adult; D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D008297:Male; D010781:Photography; D012029:Refraction, Ocular / Q000502:physiology; D015203:Reproducibility of Results; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult