title: Thickness mapping of the cornea and epithelium using optical coherence tomography.
abstract: OBJECTIVE
  To measure corneal and epithelial thickness across four meridians using Optical Coherence Tomography (OCT) and to compare these measurements between normal non-lens wearers (NLW), rigid gas permeable (RGP) lens wearers, and RGP-wearing keratoconics (KC).
  
  
  METHODS
  Both eyes of 60 subjects were measured (20 NLW, nine female:11 male, 27.6 +/- 5.9 years; 20 RGP, 20 female, 23.9 +/- 7.6 years; and 20 KC, seven female:13 male, 32.4 +/- 8.1 years). A customized fixation target employing LEDs in eight directions of gaze was attached to the OCT and corneal images obtained. Raw OCT scans were analyzed to yield values for corneal and epithelial thickness and color-coded maps were compiled.
  
  
  RESULTS
  Central corneal thickness (CCT) was thinnest in KC (447 +/- 68 microm) and similar between RGP (518 +/- 32 microm; pKC < 0.001) and NLW (517 +/- 21 microm) (p(KC) < 0.001 NLW pRGP > 0.05). Peripheral corneal thickness in NLW was thickest in the superior temporal and thinnest in the inferior (I) regions (superior temporal(thickest) vs. I(thinnest) p < 0.001). Central epithelial thickness was thinnest in KC (44 +/- 7 microm), followed by RGP (50 +/- 4 microm), then NLW (54 +/- 2 microm) (pKC < 0.001 NLW p(RGP) < 0.05). Central epithelial thickness in the KC group was significantly thinner than in the RGP group (p < 0.001). In the NLW group, peripheral epithelial thickness was thicker (63 +/- 5 microm) than central (p < 0.001) and was thickest in the superior (S) region and thinnest in the inferior (I) region (S(thickest) vs. I(thinnest) p < 0.001). KC epithelium was thinnest in the inferior temporal meridian (42 +/- 5 microm).
  
  
  CONCLUSIONS
  Thickness of the normal cornea and epithelium was greatest in the superior region. In all groups, the inferior cornea and epithelium was thinnest, and to a greater extent in the KC group.
authors.affiliation: Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. sameena.haque-khan@cibavision.com
authors.forename: Sameena
authors.initials: S
authors.lastname: Haque
authors.forename: Lyndon
authors.initials: L
authors.lastname: Jones
authors.forename: Trefford
authors.initials: T
authors.lastname: Simpson
mesh_terms: D000328:Adult; D003261:Contact Lenses; D003315:Cornea / Q000473:pathology*; D003319:Corneal Stroma / Q000473:pathology; D019781:Corneal Topography / Q000379:methods*; D019573:Epithelium, Corneal / Q000473:pathology*; D004867:Equipment Design; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000473:pathology* / Q000534:rehabilitation; D008297:Male; D041623:Tomography, Optical Coherence / Q000295:instrumentation; D055815:Young Adult