title: Role of percent tissue altered on ectasia after LASIK in eyes with suspicious topography.
abstract: OBJECTIVE
  To investigate the association of the percent tissue altered (PTA) with the occurrence of ectasia after LASIK in eyes with suspicious preoperative corneal topography.
  
  
  METHODS
  This retrospective comparative case-control study compared associations of reported ectasia risk factors in 129 eyes, including 57 eyes with suspicious preoperative Placido-based corneal topography that developed ectasia after LASIK (suspect ectasia group), 32 eyes with suspicious topography that remained stable for at least 3 years after LASIK (suspect control group), and 30 eyes that developed ectasia with bilateral normal topography (normal topography ectasia group). Groups were subdivided based on topographic asymmetry into high- or low-suspect groups. The PTA, preoperative central corneal thickness (CCT), residual stromal bed (RSB), and age (years) were evaluated in univariate and multivariate analyses.
  
  
  RESULTS
  Average PTA values for normal topography ectasia (45), low-suspect ectasia (39), high-suspect ectasia (36), low-suspect control (32), and high-suspect control (29) were significantly different from one another in all comparisons (P < .003) except high- and low-suspect ectasia groups (P = .033), and presented the highest discriminative capability of all variables evaluated. Age was only significantly different between the high-suspect ectasia and normal topography ectasia groups, and CCT was not significantly different between any groups. Stepwise logistic regression revealed the PTA as the most significant independent variable (P < .0001), with RSB the next most significant parameter.
  
  
  CONCLUSIONS
  There remains a significant correlation between PTA values and ectasia risk after LASIK, even in eyes with suspicious corneal topography. Less tissue alteration, or a lower PTA value, was necessary to induce ectasia in eyes with more remarkable signs of topographic abnormality, and PTA provided better discriminative capabilities than RSB for all study populations.
authors.forename: Marcony R
authors.initials: MR
authors.lastname: Santhiago
authors.forename: David
authors.initials: D
authors.lastname: Smadja
authors.forename: Steven E
authors.initials: SE
authors.lastname: Wilson
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Krueger
authors.forename: Mario L R
authors.initials: ML
authors.lastname: Monteiro
authors.forename: J Bradley
authors.initials: JB
authors.lastname: Randleman
mesh_terms: D016022:Case-Control Studies; D003316:Corneal Diseases / Q000175:diagnosis / Q000209:etiology*; D003319:Corneal Stroma / Q000601:surgery*; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis / Q000209:etiology; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D009216:Myopia / Q000601:surgery*; D011183:Postoperative Complications; D012189:Retrospective Studies; D012307:Risk Factors