title: Combining ocular response analyzer metrics for corneal biomechanical diagnosis.
abstract: OBJECTIVE
  To evaluate corneal biomechanical properties in non-keratoconic myopic eyes and to identify descriptors for improving the specificity of the Ocular Response Analyzer (ORA) (Reichert Ophthalmic Instruments, Depew, NY) testing for subclinical keratoconus detection.
  
  
  METHODS
  Observational case series of 52 non-keratoconic non-myopic eyes and 97 non-keratoconic myopic eyes (spherical equivalent < -5 diopters [D]) in dataset 1 and 87 non-keratoconic eyes and 73 eyes with subclinical keratoconus in dataset 2. Examination included corneal topography, tomography, and biomechanical testing with the ORA. Receiver operating characteristic curves and logistic regression were used to identify optimal combinations of biomechanical indices for keratoconus detection. Main outcome measures were corneal thickness-corrected hysteresis (DifCH) and resistance factor (DifCRF), the difference between these two (CH-CRF), and the diagnostic performance of their combinations.
  
  
  RESULTS
  Compared to non-keratoconic non-myopic eyes, non-keratoconic myopic eyes with flat corneas (average corneal power < 44.0 D) had reduced DifCH (mean ± standard deviation, 0.11 ± 1.27 vs -0.79 ± 1.50, P < .01) and DifCRF (0.24 ± 1.16 vs -0.70 ± 1.59, P < .01) values, whereas non-keratoconic myopic eyes with steep corneas showed no difference. Keratoconic eyes exhibited lower DifCH and DifCRF values than non-keratoconic myopic eyes. Combinations of DifCH, DifCRF, and CH-CRF had increased specificity (> 80%) for subclinical keratoconus compared to the DifCRF index alone (71%).
  
  
  CONCLUSIONS
  In biomechanical keratoconus screening, some non-keratoconic myopic eyes show altered ocular biomechanical properties and are identified as false-positive cases. The low specificity of DifCRF when dealing with these non-keratoconic eyes could be improved by considering additional biomechanical descriptors such as DifCH and CH-CRF, which seem to be indicative of the aforementioned biomechanical profile.
authors.affiliation: Hospital de Clinicas Jose de San Martin, University of Buenos Aires, Argentina.
authors.forename: Pablo R
authors.initials: PR
authors.lastname: Ruiseñor Vázquez
authors.forename: Marianella
authors.initials: M
authors.lastname: Delrivo
authors.forename: Fernando Fuentes
authors.initials: FF
authors.lastname: Bonthoux
authors.forename: Tomás
authors.initials: T
authors.lastname: Pförtner
authors.forename: Jeremías Gastón
authors.initials: JG
authors.lastname: Galletti
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology / Q000503:physiopathology*; D019781:Corneal Topography; D004548:Elasticity; D005500:Follow-Up Studies; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D009216:Myopia / Q000175:diagnosis* / Q000503:physiopathology; D012372:ROC Curve; D012720:Severity of Illness Index