title: Comparison of front-surface corneal topography and Bowman membrane specular topography in keratoconus.
abstract: OBJECTIVE
  To define the contribution of the corneal epithelium in corneal topography in keratoconus and discuss the implications regarding combined topography-guided photorefractive keratectomy and corneal collagen crosslinking (CXL).
  
  
  METHODS
  French National Reference Center for Keratoconus, Bordeaux, France.
  
  
  METHODS
  Case series.
  
  
  METHODS
  Specular topographies were performed before and immediately after epithelial removal during conventional CXL surgery in patients with keratoconus.
  
  
  RESULTS
  The study included 1 eye with forme fruste keratoconus, 4 eyes in Krumeich stage I, and 3 eyes in stage II. The mean simulated maximum keratometry (K) increased by 2.87 diopters (D) after epithelial removal. The mean effective refractive power increased by a mean of 4.01 D and the astigmatic refractive power, by a mean of 2.17 D. The difference in mean axis deviation was not significant. The mean inferior-superior ratio irregularity index increased 1.51 units. All K and refractive readings except astigmatic refractive axis were significantly increased after epithelial removal. All regularity indices increased significantly without the epithelium. The amplitude of variations in K readings made it difficult to predict the refractive changes after custom laser photoablation based on epithelial-based topography.
  
  
  CONCLUSIONS
  The astigmatism refractive axis did not change significantly; therefore, this axis could be useful for astigmatic corrections, whereas the spherical component would not be useful. Topographic changes after epithelial removal can be important but not intuitive in keratoconus eyes. This should be considered in custom topography-guided photoablation strategies when attempting to correct refractive errors at the time of CXL.
authors.affiliation: French National Reference Center for Keratoconus, Centre Hospitalier Universitaire de Bordeaux, Site Pellegrin, Centre François Xavier Michelet, Service d'Ophtalmologie, Bordeaux Cedex, France. toubould@gmail.com
authors.forename: David
authors.initials: D
authors.lastname: Touboul
authors.forename: Elodie
authors.initials: E
authors.lastname: Trichet
authors.forename: Perry S
authors.initials: PS
authors.lastname: Binder
authors.forename: Delphine
authors.initials: D
authors.lastname: Praud
authors.forename: Camille
authors.initials: C
authors.lastname: Seguy
authors.forename: Joseph
authors.initials: J
authors.lastname: Colin
mesh_terms: D000328:Adult; D050541:Bowman Membrane / Q000187:drug effects / Q000503:physiopathology*; D003094:Collagen / Q000378:metabolism; D003319:Corneal Stroma / Q000378:metabolism; D019781:Corneal Topography; D003432:Cross-Linking Reagents / Q000627:therapeutic use; D019573:Epithelium, Corneal / Q000187:drug effects / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000378:metabolism / Q000503:physiopathology* / Q000628:therapy; D008297:Male; D018903:Photorefractive Keratectomy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D012256:Riboflavin / Q000627:therapeutic use; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin