title: Comparability and repeatability of pachymetry in keratoconus using four noncontact techniques.
abstract: OBJECTIVE
  To compare and determine the repeatability of central corneal thickness (CCT) measurements using four noncontact pachymetry instruments in eyes with keratoconus.
  
  
  METHODS
  The CCT of consecutive patients with keratoconus was measured during a single visit using the swept source optical coherence tomography (SS-OCT, Casia SS-1000°CT, Tomey, Nagoya, Japan), a rotating Scheimpflug camera system (Pentacam, Oculus Optikgerate GmbH, Wetzlar, Germany), scanning slit topographer (Orbscan IIz topography, Baush and Lomb Surgical Inc., San Dimas, CA, USA), and a hand-held spectral domain OCT (HHSD-OCT, Bioptigen Inc., Durham, North Carolina, USA). Test-retest variability, correlation between measurements and interdevice agreement were analyzed.
  
  
  RESULTS
  Fifty eyes of 25 participants were analyzed in this study. All measurement methods correlated well with each other (r > 0.9, P < 0.001). Mean ± standard deviation CCT measured by HHSD-OCT, Orbscan IIz, SS-OCT, and Pentacam was 462 ± 41 mm, 458 ± 41 mm, 454 ± 40 mm, and 447 ± 42 mm, respectively. While the HHSD-OCT over-estimated the CCT (P < 0.001), there was a good correlation between the measurements obtained from the other three devices. However, the numerical difference was high and this trend was seen in all the paired comparisons.
  
  
  CONCLUSIONS
  Though the measurements by different devices correlated well, the numerical agreement may be inadequate for their interchangeable use in clinical practice.
authors.affiliation: Department of Cornea and Refractive Surgery, Narayana Nethralaya Super Specialty Eye Hospital, Bengaluru, Karnataka, India.
authors.forename: Mukesh
authors.initials: M
authors.lastname: Kumar
authors.forename: Rohit
authors.initials: R
authors.lastname: Shetty
authors.forename: Chaitra
authors.initials: C
authors.lastname: Jayadev
authors.forename: Debarun
authors.initials: D
authors.lastname: Dutta
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003315:Cornea / Q000000981:diagnostic imaging*; D063171:Corneal Pachymetry / Q000379:methods*; D019781:Corneal Topography / Q000379:methods*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D010781:Photography; D011446:Prospective Studies; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000379:methods*; D055815:Young Adult