title: Agreement between placido topography and Scheimpflug tomography for corneal astigmatism assessment.
abstract: OBJECTIVE
  To evaluate inter-device agreement between Placido topography (iTrace; Tracey Technologies, Houston, TX) and Scheimpflug tomography (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) for measuring corneal power and cylinder and axis of astigmatism.
  
  
  METHODS
  Observational case series of 54 eyes from 54 subjects with no ocular disease. Main outcome measures were corneal power, cylinder power, and axis of astigmatism and their agreement was assessed by Bland–Altman analysis.
  
  
  RESULTS
  For corneal power and corneal cylinder, 95% limits of agreement (LoA) were considered good (−0.38 to 0.45 diopters [D] and −0.49 to 0.27 D, respectively). In contrast, the 95% LoA for corneal astigmatism axis exceeded the clinically relevant margins (−14.8 to 13.5): 28 eyes (52%) had a greater than 5° difference, 10 eyes (19%) had a greater than 10° difference, and 4 eyes (7%) had a greater than 20° difference between instruments. This absolute difference was significantly correlated with average corneal cylinder (Spearman’s r = −0.379, P = .005) but not with average corneal power. In eyes with corneal astigmatism 2 D or greater, the 95% LoA for axis were −8.7° to 6.7°, whereas in those with corneal astigmatism less than 1 D, the 95% LoA for axis were −19.1° to 16.6°.
  
  
  CONCLUSIONS
  Placido topography and Scheimpflug tomography show good agreement for corneal power and cylinder, but not for corneal astigmatism axis. These instruments could be used interchangeably only in eyes with corneal astigmatism of 2 D or greater.
authors.forename: Marianella
authors.initials: M
authors.lastname: Delrivo
authors.forename: Pablo R
authors.initials: PR
authors.lastname: Ruiseñor Vázquez
authors.forename: Jonatán David
authors.initials: JD
authors.lastname: Galletti
authors.forename: Martín
authors.initials: M
authors.lastname: Garibotto
authors.forename: Fernando
authors.initials: F
authors.lastname: Fuentes Bonthoux
authors.forename: Tomás
authors.initials: T
authors.lastname: Pförtner
authors.forename: Jeremías Gastón
authors.initials: JG
authors.lastname: Galletti
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000175:diagnosis* / Q000503:physiopathology; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000295:instrumentation / Q000379:methods*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D014054:Tomography / Q000379:methods