title: Effect of central corneal thickness and corneal hysteresis on tonometry as measured by dynamic contour tonometry, ocular response analyzer, and Goldmann tonometry in glaucomatous eyes.
abstract: OBJECTIVE
  The dynamic contour tonometer (DCT; Pascal tonometer) and the Ocular Response Analyzer (ORA) are novel tonometers designed to measure intraocular pressure (IOP) independent of corneal properties and central corneal thickness (CCT), respectively. We wanted to compare the corneal compensated IOP (IOPcc) as measured by ORA with IOP values measured by DCT and Goldmann applanation tonometry (GAT) with respect to IOP readings and the influence of corneal hysteresis (CH) and CCT in glaucoma patients.
  
  
  METHODS
  In a study of 94 glaucomatous eyes, IOP measurements by ORA, DCT, and GAT were compared, and the effects of CCT and CH were analyzed. All measurements were taken by 1 of the authors only.
  
  
  RESULTS
  The Mean CCT was 550+/-44 mum and mean CH 10.24+/-3.3 mm Hg. The mean value for IOPcc was 17.94+/-5.9 mm Hg, 15.14+/-3.7 mm Hg for DCT, and 14.3+/-4.3 mm Hg for GAT. The mean difference was 3.65+/-3.85 mm Hg between IOPcc and GAT and 2.80+/-4.9 mm Hg between IOPcc and DCT (P<0.001) and -0.85+/-3.3 mm Hg between GAT and DCT (P=0.015). None of the methods was related to CCT. In contrast, CH was highly statistically significant related to IOPcc (P<0.0001), whereas GAT and DCT showed only weak relation to CH (P=0.05).
  
  
  CONCLUSIONS
  IOP measurements with the ORA are significantly higher than DCT or GAT with no apparent linear correction factor. To date, we cannot estimate the impact of differences in CH in relation to IOP and its measurement.
authors.affiliation: Department of Ophthalmology, Asklepios Klinik Nord-Heidberg, Tangstedter Landstr. 400, 22419 Hamburg, Germany. anhager@gmx.de
authors.forename: Annette
authors.initials: A
authors.lastname: Hager
authors.forename: Hager
authors.initials: H
authors.lastname: Annette
authors.forename: Kristina
authors.initials: K
authors.lastname: Loge
authors.forename: Loge
authors.initials: L
authors.lastname: Kristina
authors.forename: Bernd
authors.initials: B
authors.lastname: Schroeder
authors.forename: Schroeder
authors.initials: S
authors.lastname: Bernd
authors.forename: Mark-Oliver
authors.initials: MO
authors.lastname: Füllhas
authors.forename: Füllhas
authors.initials: F
authors.lastname: Mark-Oliver
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wiegand
authors.forename: Wiegand
authors.initials: W
authors.lastname: Wolfgang
mesh_terms: D001696:Biomechanical Phenomena; D003315:Cornea / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004547:Elastic Tissue / Q000503:physiopathology; D005901:Glaucoma / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008875:Middle Aged; D014065:Tonometry, Ocular / Q000295:instrumentation*