title: Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography.
abstract: OBJECTIVE
  To investigate the association of a novel metric, percent tissue altered, with the occurrence of ectasia after laser in situ keratomileusis (LASIK) in eyes with normal corneal topography and to compare this metric with other recognized risk factors.
  
  
  METHODS
  Retrospective case-control study.
  
  
  METHODS
  The study included 30 eyes from 16 patients with bilateral normal preoperative Placido-based corneal topography that developed ectasia after LASIK (ectasia group) and 174 eyes from 88 consecutive patients with uncomplicated LASIK and at least 3 years of postoperative follow-up. The following metrics were evaluated: age, preoperative central corneal thickness, residual stromal bed, Ectasia Risk Score System scores, and percent tissue altered, derived from [PTA = (FT + AD)/CCT], where FT = flap thickness, AD = ablation depth, and CCT = preoperative central corneal thickness.
  
  
  RESULTS
  In the ectasia group, percent tissue altered ≥40 was the most prevalent factor (97%), followed by age <30 years (63%), residual stromal bed ≤300 μm (57%), and ectasia risk score ≥ 3 (43%) (P < .001 for all). Percent tissue altered ≥ 40 had the highest odds ratio (223), followed by residual stromal bed ≤ 300 μm (74) and ectasia risk score ≥ 4 (8). Stepwise logistic regression revealed percent tissue altered ≥ 40 as the single most significant independent variable (P < .0001).
  
  
  CONCLUSIONS
  Percent tissue altered at the time of LASIK was significantly associated with the development of ectasia in eyes with normal preoperative topography and was a more robust indicator of risk than all other variables in this patient population.
authors.affiliation: Department of Ophthalmology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; Department of Ophthalmology, University of Sao Paulo, Sao Paulo, Brazil. Electronic address: marconysanthiago@hotmail.com.
authors.forename: Marcony R
authors.initials: MR
authors.lastname: Santhiago
authors.affiliation: University Center Hospital of Bordeaux, Bordeaux, France.
authors.forename: David
authors.initials: D
authors.lastname: Smadja
authors.affiliation: Department of Ophthalmology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Beatriz F
authors.initials: BF
authors.lastname: Gomes
authors.affiliation: Department of Ophthalmology, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Glauco R
authors.initials: GR
authors.lastname: Mello
authors.affiliation: Department of Ophthalmology, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Mario L R
authors.initials: ML
authors.lastname: Monteiro
authors.affiliation: Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Wilson
authors.affiliation: Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia.
authors.forename: J Bradley
authors.initials: JB
authors.lastname: Randleman
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003315:Cornea / Q000473:pathology; D063171:Corneal Pachymetry; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis / Q000209:etiology; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis / Q000209:etiology*; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D011183:Postoperative Complications; D012372:ROC Curve; D012189:Retrospective Studies; D012307:Risk Factors; D013524:Surgical Flaps / Q000473:pathology; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult