title: Corneal biomechanical evaluation in healthy thin corneas compared with matched keratoconus cases.
abstract: To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in healthy eyes with a central corneal thickness (CCT) < 505 µm with CH and CRF in gender-, age-, and CCT-matched keratoconus cases, and to estimate the sensitivity and specificity of these parameters for discriminating between the two groups.
  
  
  
  Prospective, comparative case series. In total 46 eyes from 30 healthy patients with CCT < 505 µm, and 42 eyes from 30 CCT-, gender- and age-matched keratoconus cases were enrolled. Biomechanical metrics (CH and CRF) were measured using the Ocular Response Analyzer (ORA) and then compared. A receiver operating characteristic (ROC) curve was used to identify cut-off points to maximize the sensitivity and specificity for discriminating between the groups.
  
  
  
  The CCT was 485.96 ± 17.61 µm (range, 438 - 505) in healthy thin corneas and 483.64 ± 16.19 µm (range, 452 - 505) in keratoconus; p=0.5225. CH was 8.63 ± 1.23 mmHg (range, 5.95 - 12.2) and 8.07 ± 1.17 mmHg (range, 4.9 - 9.85), respectively; p=0.0312. CRF was 8.43 ± 1.29 mmHg (range, 5.45 - 11.10) and 7.22 ± 1.34 mmHg (range, 4.7 - 9.45), respectively; p<0.001. ROC curve analysis showed a poor overall predictive accuracy of CH (cut-off, 8.95 mmHg; sensitivity, 63%; specificity, 23.8%; test accuracy, 44.30%) and CRF (cut-off, 7.4 mmHg; sensitivity, 28.3%; specificity, 40.5%; test accuracy, 34.12%) for detecting keratoconus in the eyes studied.
  
  
  
  CH and CRF were statistically lower in keratoconus than in healthy thin corneas. However, CH and CRF offered very low sensitivity and specificity for discriminating the groups.
authors.affiliation: Department of Ophthalmology, Federal University of São Paulo, São Paulo, SP, Brazil. brunomfontes@terra.com.br
authors.forename: Bruno Machado
authors.initials: BM
authors.lastname: Fontes
authors.forename: Renato
authors.initials: R
authors.lastname: Ambrósio
authors.forename: Guillermo Coca
authors.initials: GC
authors.lastname: Velarde
authors.forename: Walton
authors.initials: W
authors.lastname: Nosé
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003315:Cornea / Q000033:anatomy & histology / Q000502:physiology*; D019781:Corneal Topography; D004547:Elastic Tissue / Q000502:physiology*; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D011446:Prospective Studies; D012372:ROC Curve; D012680:Sensitivity and Specificity