title: Comparison of ultrasound pachymetry and partial coherence interferometry in the measurement of central corneal thickness.
abstract: OBJECTIVE
  To compare central corneal thickness (CCT) measurements obtained with 3 ultrasound pachymeters and with partial coherence interferometry (PCI) and evaluate the effect of repeated contact by a pachymetry probe on corneal thickness.
  
  
  METHODS
  Department of Ophthalmology, University of Vienna, Vienna, Austria.
  
  
  METHODS
  Central corneal thickness was measured in 20 eyes of 20 healthy volunteers with 3 different ultrasound pachymeters (DGH 500, DGH Technology Inc.; SP 2000, Tomey Inc.; Paxis, Biovision Inc.) and with PCI. In each eye, 5 measurements with PCI were followed by 5 measurements with each ultrasound pachymetry device and another 5 measurements with PCI.
  
  
  RESULTS
  The mean CCT measured with the DGH 500, SP 2000, and Paxis was 541.0 microm, 539.2 microm, and 545.1 microm, respectively. Although the differences among the 3 ultrasound pachymetry devices were within 6.0 microm, they were statistically significant (P<.05). The PCI measurements were significantly smaller (P <.05) than the ultrasound measurements: 518.8 microm before and 517.5 microm after repeated contact with the ultrasound pachymetry probe (P <.05). The mean precision (standard deviation) was 0.77 microm for PCI and between 2.40 microm and 3.58 microm for ultrasound pachymetry measurements. The correlation coefficients for the intraobserver variability were 0.999 for PCI and between 0.987 and 0.995 for ultrasound pachymetry measurements.
  
  
  CONCLUSIONS
  Partial coherence interferometry was the more precise method of measuring CCT and had better intraobserver variability. Repeated contact by a pachymetry probe reduced corneal thickness by 1.3 microm. However, the reason for the smaller measurements with PCI than with ultrasound pachymetry remains unclear.
authors.affiliation: Department of Ophthalmology, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. georg.rainer@akh-wien.ac.at
authors.forename: Georg
authors.initials: G
authors.lastname: Rainer
authors.forename: Vanessa
authors.initials: V
authors.lastname: Petternel
authors.forename: Oliver
authors.initials: O
authors.lastname: Findl
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
authors.forename: Christian
authors.initials: C
authors.lastname: Skorpik
authors.forename: Alexandra
authors.initials: A
authors.lastname: Luksch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Drexler
mesh_terms: D000328:Adult; D003315:Cornea / Q000033:anatomy & histology*; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007368:Interferometry / Q000379:methods; D008297:Male; D015588:Observer Variation; D015203:Reproducibility of Results; D014463:Ultrasonography / Q000379:methods