title: Role of the corneal epithelium measurements in keratorefractive surgery.
abstract: OBJECTIVE
  Refractive surgery has stimulated considerable progress in corneal and anterior segment imaging, and optical characterization of the eye. From front surface corneal topography, we evolved to three-dimensional corneal tomography with limbus to limbus characterization of the front and back corneal surfaces and pachymetric mapping. Corneal anatomical evaluation has further evolved to layered or segmental tomography with the ability to characterize corneal epithelial thickness profile and the elevation of stromal front surface. Further characterization of even more specific structures, such as Bowman's layer and Descement's membrane, has been also demonstrated. The applications of such understanding in keratorefractive surgery are reviewed.
  
  
  RESULTS
  Understanding the corneal epithelial profile is of interest in many areas of ophthalmology, especially in refractive surgery. The most relevant applications include screening candidates at higher risk for complications (i.e. progressive ectasia and tear dysfunction syndrome), planning primary procedures, enhancements, and therapeutic surgery, and also postoperatively understanding the wound healing and clinical outcomes.
  
  
  CONCLUSIONS
  Corneal epithelial thickness was first available using digital very-high-frequency ultrasound. Advances in anterior segment optical coherence tomography enabled such fundamental evaluation, which accelerated progress. Such knowledge significantly impacts safety and efficacy of refractive surgery, and also allows for significant improvement for therapeutic procedures. VIDEO ABSTRACT.
authors.affiliation: aRio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro bDepartment of Ophthalmology, Federal University of São Paulo, São Paulo cDepartment of Ophthalmology, Pontific Catholic University of Rio de Janeiro, Rio de Janeiro, Brazil dDepartment of Ophthalmology, University of Florida, Gainesville, Florida, USA eDepartment of Ophthalmology, Hospital de Braga, Braga, Portugal.
authors.forename: Marcella Q
authors.initials: MQ
authors.lastname: Salomão
authors.forename: Ana Luisa
authors.initials: AL
authors.lastname: Hofling-Lima
authors.forename: Bernardo T
authors.initials: BT
authors.lastname: Lopes
authors.forename: Ana Laura C
authors.initials: ALC
authors.lastname: Canedo
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Dawson
authors.forename: Rui
authors.initials: R
authors.lastname: Carneiro-Freitas
authors.forename: Renato
authors.initials: R
authors.lastname: Ambrósio
mesh_terms: D000869:Anterior Eye Segment / Q000000981:diagnostic imaging; D019781:Corneal Topography / Q000379:methods; D019573:Epithelium, Corneal / Q000000981:diagnostic imaging*; D006801:Humans; D015948:Keratoplasty, Penetrating / Q000379:methods*; D010347:Patient Care Planning; D041623:Tomography, Optical Coherence / Q000379:methods