title: Influence of ocular pulse amplitude on ocular response analyzer measurements.
abstract: OBJECTIVE
  To evaluate if the ocular pulse amplitude (OPA) (the difference between systolic and diastolic intraocular pressure) is associated with the measurement variability of IOPg [Goldmann-correlated intraocular pressure (IOP)], IOPcc (corneal compensated IOP), corneal hysteresis (CH), and corneal resistance factor (CRF) obtained from the ocular response analyzer (ORA).
  
  
  METHODS
  Sixty normal participants and 60 glaucoma patients were included. In 1 randomly selected eye in each participant, 4 repeated measurements were obtained with the ORA (Reichert Inc, Depew, NY) followed by OPA measurement by dynamic contour tonometry (Pascal; Swiss Microtechnology AG, Port, Switzerland). The repeatability of IOPg (a mathematically derived value with strong correlation with Goldmann applanation pressure measurement), IOPcc (a mathematically derived measurement less affected by corneal biomechanical properties), CH, and CRF were calculated. The associations between age, refraction, keratometry, central corneal thickness, axial length, OPA, and ORA measurements variability were evaluated with univariate and multivariate regression analyses.
  
  
  RESULTS
  The repeatability of IOPg, IOPcc, CRF, and CH were 4.08 (95% confidence interval: 3.06-5.09) mm Hg, 4.72 (3.54-5.89) mm Hg, 2.14 (1.61-2.68) mm Hg, 2.35 (1.77-2.94) mm Hg, respectively, for the normal group; and 4.18 (3.75-4.61) mm Hg, 5.56 (4.99-6.14) mm Hg, 2.17 (1.95-2.40) mm Hg, 2.78 (2.50-3.07) mm Hg, respectively, for the glaucoma group. Within-subject variances of IOPg and IOPcc, but not CRF and CH, were positively correlated with OPA. No association was found between age, refraction, keratometry, central corneal thickness, axial length, and the measurement variability of ORA.
  
  
  CONCLUSIONS
  The measurement reliability of ORA was only moderate. Eyes with large OPA were associated with high IOP measurement variability. Taking average of multiple repeated measurements is important for reliable measurement of ORA.
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, The People's Republic of China.
authors.forename: Guihua
authors.initials: G
authors.lastname: Xu
authors.forename: Dennis Shun
authors.initials: DS
authors.lastname: Lam
authors.forename: Christopher Kai-shun
authors.initials: CK
authors.lastname: Leung
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology*; D003315:Cornea / Q000502:physiology; D003971:Diastole; D005901:Glaucoma / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D013599:Systole; D014065:Tonometry, Ocular; D014794:Visual Fields; D055815:Young Adult