title: Corneal and epithelial thickness in keratoconus: a comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography.
abstract: OBJECTIVE
  To compare corneal thickness measurements in individuals with keratoconus using optical coherence tomography (OCT), Orbscan II, and ultrasonic pachymetry and to measure epithelial and stromal thickness in these individuals using OCT.
  
  
  METHODS
  Twenty individuals with keratoconus and 20 controls (without keratoconus) were enrolled. The Orbscan II was used to locate the steepest area of the cornea, which was taken to represent the cone apex. Each instrument was used to obtain four total corneal thickness measurements-from the cone apex, corneal center, mid-nasal, and mid-temporal cornea. Optical coherence tomography scans were analyzed to provide epithelial and stromal thickness readings.
  
  
  RESULTS
  In individuals with keratoconus, mean central corneal thickness (CCT) measured by ultrasonic pachymetry, Orbscan, and OCT was 494.2 +/- 50.0 microm, 438.6 +/- 47.7 microm, and 433.5 +/- 39.7 microm, respectively. The central keratoconic cornea was 57.7 microm thinner than the normal cornea (post-hoc P<.001). The cone apex was thinner than the central cornea (P<.001). Keratoconic epithelium was 48.2 +/- 5.5 microm centrally and 42.1 +/- 4.5 microm at the apex. Central keratoconic epithelium was 4.7 microm thinner and central keratoconic stroma was 57.8 microm thinner than the normal cornea (P<.001, respectively). Comparing instruments, Orbscan and OCT correlated in CCT measurement (r=0.890) and apical thickness (r=0.846). All instruments produced similar readings for mid-nasal and mid-temporal corneal thickness in participants with keratoconus (P>.05).
  
  
  CONCLUSIONS
  Ultrasonic pachymetry produced the highest corneal thickness readings in the center and apex, compared to Orbscan II and OCT. Centrally, the total cornea, epithelium, and stroma were thinner in individuals with keratoconus than in normal individuals.
authors.affiliation: Centre for Contact Lens Research, School of Optometry, University of Waterloo, Ontario, Canada. s2haque@uwaterloo.ca
authors.forename: Sameena
authors.initials: S
authors.lastname: Haque
authors.forename: Trefford
authors.initials: T
authors.lastname: Simpson
authors.forename: Lyndon
authors.initials: L
authors.lastname: Jones
mesh_terms: D000293:Adolescent; D000328:Adult; D019781:Corneal Topography; D019573:Epithelium, Corneal / Q000000981:diagnostic imaging* / Q000473:pathology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D041623:Tomography, Optical Coherence; D014463:Ultrasonography