title: Discriminant value of custom ocular response analyzer waveform derivatives in keratoconus.
abstract: OBJECTIVE
  To evaluate the performance of corneal hysteresis (CH), corneal resistance factor, and 16 investigator-derived Ocular Response Analyzer (ORA) variables in distinguishing keratoconus (KC) from the nondiseased state.
  
  
  METHODS
  Retrospective case series.
  
  
  METHODS
  Fifty-four eyes of 27 unaffected patients and 49 eyes of 25 KC patients from the Instituto de Olhos, Rio de Janeiro, Brazil.
  
  
  METHODS
  Sixteen candidate variables were derived from exported ORA signals to characterize putative indicators of biomechanical behavior. Area under the receiver operating characteristic curve (AUC) and the Z statistic were used to compare diagnostic performance.
  
  
  METHODS
  Discriminant value of standard and derived ORA variables as measured by AUC.
  
  
  RESULTS
  Fifteen of 16 candidate variables performed significantly better than chance (AUC, >0.5) at discriminating KC. Diagnostic performance was greatest for a custom variable related to the depth of deformation as defined by the minimum applanation signal intensity during corneal deformation (concavity(min); mean AUC ± standard error, 0.985 ± 0.002) and a new measure incorporating the pressure-deformation relationship of the entire response cycle (hysteresis loop area, 0.967 ± 0.002). Z statistics assessing the discriminative value of each of the top 5 variables demonstrated superiority to CH (AUC, 0.862 ± 0.002). Concavity(min) had the best overall predictive accuracy (cutoff value, 50.37; 94.9% sensitivity, 91.7% specificity, and 93.2% test accuracy), and the top 4 variables demonstrated the most consistent relationships to KC severity.
  
  
  CONCLUSIONS
  Investigator-derived ORA variables related to the depth of deformation and the pressure-deformation relationship demonstrated very high test accuracy for detecting the presence of KC. Beyond their diagnostic value, the candidate variables described in this report provide mechanistic insight into the nature of the ORA signal and the characteristic changes in corneal dynamics associated with KC.
authors.affiliation: Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Katie M
authors.initials: KM
authors.lastname: Hallahan
authors.affiliation: Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Sinha Roy
authors.affiliation: Instituto de Olhos, Rio de Janeiro, Brazil; Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil.
authors.forename: Renato
authors.initials: R
authors.lastname: Ambrosio
authors.affiliation: Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio; Instituto de Olhos, Rio de Janeiro, Brazil.
authors.forename: Marcella
authors.initials: M
authors.lastname: Salomao
authors.affiliation: Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio; Biomedical Engineering, Cleveland Clinic Lerner Research Institute, Cleveland, Ohio. Electronic address: bjdupps@sbcglobal.net.
authors.forename: William J
authors.initials: WJ
authors.lastname: Dupps
mesh_terms: D000328:Adult; D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography; D016002:Discriminant Analysis; D004548:Elasticity / Q000502:physiology*; D054459:Elasticity Imaging Techniques; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D007640:Keratoconus / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity