title: Geometric ray tracing analysis of visual acuity after laser in situ keratomileusis.
abstract: OBJECTIVE
  Using a geometric ray tracing model, we explain the increase in visual acuity observed in myopic patients after laser in situ keratomileusis (LASIK).
  
  
  METHODS
  This study included 37 eyes of 23 patients who underwent LASIK. All patients had myopia and a spectacle-corrected visual acuity of 0.95 or worse. Clinical tests included biometry, corneal topography, pachymetry, and refraction (with and without cycloplegia). Calculations were made by tracing rays through all the refractive surfaces of the eye based on a Le Grand-type theoretical model of the whole eye.
  
  
  RESULTS
  Comparison of spectacle-corrected visual acuity of the eye before surgery, the size of the blur circle calculated by ray tracing, and the magnification for the ocular system facilitated a numerical criterion to assess visual acuity by geometric calculation. This criterion was applied to myopic eyes that underwent LASIK, and the maximum increase in spectacle-corrected visual acuity was predicted. An actual increase in visual acuity of approximately 40% of the predicted maximum was observed in patients.
  
  
  CONCLUSIONS
  With geometric ray tracing, it was possible not only to obtain an estimate of the visual acuity before LASIK but also to assess the value of the maximum and probable increases in visual acuity after LASIK.
authors.affiliation: Instituto Cántabro de Oftalmología-Clínica Cotero, and the Universidad de Cantabria, Santander, Spain.
authors.forename: J N
authors.initials: JN
authors.lastname: Fernández del Cotero
authors.forename: F
authors.initials: F
authors.lastname: Moreno
authors.forename: D
authors.initials: D
authors.lastname: Ortiz
authors.forename: E
authors.initials: E
authors.lastname: Vélez
authors.forename: F
authors.initials: F
authors.lastname: González
authors.forename: J M
authors.initials: JM
authors.lastname: Saiz
authors.forename: J I
authors.initials: JI
authors.lastname: Velarde
authors.forename: L
authors.initials: L
authors.lastname: De Valentín-Gamazo
authors.forename: P
authors.initials: P
authors.lastname: García-Antón
mesh_terms: D000328:Adult; D001699:Biometry; D019781:Corneal Topography; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D012029:Refraction, Ocular; D014792:Visual Acuity / Q000502:physiology*