title: Corneal biomechanical properties: precision and influence on tonometry.
abstract: OBJECTIVE
  To assess the precision and reproducibility of the corneal biomechanical parameters, and their relationships with the intraocular pressure (IOP) measured with the Goldmann tonometer and a noncontact tonometer.
  
  
  METHODS
  Readings for biomechanical properties and for IOP measured with the Goldmann and noncontact tonometers, were taken on one randomly selected eye of 106 normal subjects, on each one of two measurement sessions. Measurements with the ocular response analyzer (ORA) and the noncontact tonometer were randomized, followed by the measurement of central corneal thickness and with the Goldmann tonometer.
  
  
  RESULTS
  Repeatability coefficients for CCT, corneal hysteresis (CH) and corneal resistance factor (CRF) in Session 1 were ± 0.01 μm, ± 3.05 mmHg and ± 2.62 mmHg, respectively. The mean CCT, CH, CRF, Goldmann and noncontact tonometry did not vary significantly between sessions. Reproducibility coefficients for CCT, CH and CRF were ± 0.02 μm, ± 2.19 mmHg and ± 1.97 mmHg, respectively. Univariate regression analysis showed that CCT, CH and CRF significantly (P<0.0001) correlated with the IOP measured with the Goldmann and noncontact tonometers (and with the differences between tonometers) in Session 1. There were no significant correlations with the differences between tonometers in Session 2. Multivariate analysis revealed a minimal effect of CCT on Goldmann measurements but a significant effect on those of the noncontact tonometer.
  
  
  CONCLUSIONS
  Measurement of the biomechanical properties of the cornea, using the ORA, are repeatable and reproducible, affect Goldmann tonometry less than noncontact tonometry, and have a minimal influence on the difference in measured intraocular pressure between tonometers.
authors.affiliation: Cornea Research Chair, Department of Optometry and Vision Sciences College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433, Saudi Arabia. Electronic address: kelogb@hotmail.com.
authors.forename: Kelechi C
authors.initials: KC
authors.lastname: Ogbuehi
authors.affiliation: Cornea Research Chair, Department of Optometry and Vision Sciences College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433, Saudi Arabia. Electronic address: uosuagwu@ksu.edu.sa.
authors.forename: Uchechukwu L
authors.initials: UL
authors.lastname: Osuagwu
mesh_terms: D000328:Adult; D016477:Artifacts; D003315:Cornea / Q000502:physiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014065:Tonometry, Ocular / Q000295:instrumentation* / Q000379:methods; D055815:Young Adult
keywords: Goldmann tonometer; Noncontact tonometer; ORA; Ocular Response Analyzer; Repeatability; Tonometry.