title: Central corneal thickness measurements: using an ultrasonic instrument and 4 optical instruments.
abstract: OBJECTIVE
  Both between-session and within-session repeatability were determined for measurement of corneal thickness with the following techniques: ultrasound pachymetry (UP), confocal microscopy (CS), Orbscan pachymetry (ORB), spectral oscillation interferometry (SOI), and optical coherence tomography (OCT).
  
  
  METHODS
  The right eyes of 20 normal subjects were tested on 2 different days. For each session, 2 central corneal thickness measurements were determined using the ConfoScan 3 microscope, the Orbscan system, and the Stratus OCT system; 5 measurements were found with the Sonogage ultrasound pachymeter; and between 2 and 10 measurements were found with the SOI system.
  
  
  RESULTS
  This study showed that SOI had the best repeatability, whereas CS had the worst repeatability for both within-session and between-session repeatability. Based on 95% limits of agreement (LoA), the within-session repeatability can be ranked as: (1) SOI; (2) UP; (3) OCT; (4) Orbscan pachymetry; and (5) CS. SOI had a bias of 0.13 and 95% LoA of -1.07 to 1.33, whereas UP had a bias of -0.98 and 95% LoA of -7.35 to 5.40. The between-session repeatability of the instruments can be ranked as: (1) SOI; (2) OCT; (3) UP; (4) Orbscan pachymetry; and (5) CS. Of the optical methods, SOI had the best repeatability with a bias of 1.26 and 95% LoA of -6.14 to 8.66, followed by OCT with a bias of 0.75 and 95% LoA of -16.22 to 17.27.
  
  
  CONCLUSIONS
  Of the 4 instruments that are commercially available, the UP was the most repeatable for within sessions, and the OCT was the most repeatable for between sessions.
authors.affiliation: College of Optometry, The Ohio State University, Columbus, OH 43210-1280, USA.
authors.forename: Ravaughn
authors.initials: R
authors.lastname: Williams
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Fink
authors.forename: P Ewen
authors.initials: PE
authors.lastname: King-Smith
authors.forename: G Lynn
authors.initials: GL
authors.lastname: Mitchell
mesh_terms: D000328:Adult; D003315:Cornea / Q000033:anatomy & histology*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007368:Interferometry / Q000295:instrumentation; D008297:Male; D033401:Microscopy, Acoustic / Q000295:instrumentation; D018613:Microscopy, Confocal / Q000295:instrumentation; D008875:Middle Aged; D015588:Observer Variation; D012016:Reference Values; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000295:instrumentation; D055815:Young Adult