title: Sensitivity and specificity of posterior and anterior corneal elevation measured by orbscan in diagnosis of clinical and subclinical keratoconus.
abstract: OBJECTIVE
  To determine the sensitivity and specificity of anterior and posterior corneal elevation parameters as determined by Orbscan II (Bausch and Lomb, Rochester, NY, USA) in discriminating between (sub) clinical keratoconus (KCN) and normal corneas.
  
  
  METHODS
  This prospective case-control study included 28 eyes with subclinical KCN, 65 with clinical KCN and 141 normal corneas. Anterior and posterior corneal elevation was measured and compared in the central 5-mm corneal zone using Orbscan II.
  
  
  RESULTS
  Receiver operating curves (ROC) curve analyses for posterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with an area under the curve (AUC) of 0.97 and 0.69, respectively while optimal cutoff points were 51 μm for KCN and 35 μm for subclinical KCN. These values were associated with sensitivity and specificity of 89.23% and 98.58%, respectively, for KCN; and 50.00% and 88.65% for subclinical KCN. ROC curve analyses for anterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with AUC of 0.97 and 0.69, respectively while optimal cutoff points were 19 μm for KCN and 16 μm for subclinical KCN. These values were associated with sensitivity and specificity of 93.85% and 97.16%, respectively, for KCN; and 60.71% and 87.94% for subclinical KCN.
  
  
  CONCLUSIONS
  Anterior and posterior corneal elevation data obtained by Orbscan II can well discriminate between KCN and normal corneas, however the reliability of their indices is lower in differentiating subclinical KCN from normal cases.
authors.affiliation: Ophthalmic Epidemiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Jafarinasab
authors.affiliation: Department of Ophthalmology, Sabzevar University of Medical Sciences, Sabzevar, Tehran, Iran ; Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Shirzadeh
authors.affiliation: Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Sepehr
authors.initials: S
authors.lastname: Feizi
authors.affiliation: Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Farid
authors.initials: F
authors.lastname: Karimian
authors.affiliation: Iranian Applied Research Center for Public Health and Sustainable Development, North Khorasan University of Medical Sciences, Bojnurd, Iran.
authors.forename: Arash
authors.initials: A
authors.lastname: Akaberi
authors.affiliation: Ophthalmologist, Tehran, Iran.
authors.forename: Hosein
authors.initials: H
authors.lastname: Hasanpour
keywords: Corneal Elevation; Keratoconus; Orbscan; Receiver Operating Curve; Sensitivity; Specificity