title: Intraocular pressure measurement precision with the Goldmann applanation, dynamic contour, and ocular response analyzer tonometers.
abstract: OBJECTIVE
  To examine the repeatability and reproducibility of intraocular pressure (IOP) measurements obtained with the Goldmann applanation tonometer (GAT), the Pascal dynamic contour tonometer (DCT; Swiss Microtechnology AG, Port, Switzerland), and the Reichert Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY). A secondary objective was to assess agreement between the devices.
  
  
  METHODS
  Evaluation of technology.
  
  
  METHODS
  One hundred participants; a mixture of glaucoma suspects, patients, and control volunteers.
  
  
  METHODS
  The IOP measurements were obtained with the GAT, DCT, and ORA by 2 of 3 experienced clinicians. Keratometry (CC) measurements were made using the IOLMaster (Carl Zeiss Meditech, AG, Jena, Germany). Three ORA corneal compensated IOP (IOPcc) measurements were obtained before the instillation of anesthesia, after which 2 GAT IOP and 3 DCT IOP measurements were obtained in a randomized order. Central corneal thickness (CCT) was measured using an ultrasound pachymeter. The average ORA corneal response factor (CRF) and the average DCT ocular pulse amplitude (OPA) were determined. Intraobserver variability was calculated by the repeatability coefficient. Interobserver variability (measurement reproducibility) and device agreement were calculated by Bland-Altman analysis (mean difference [bias] and 95% limits of agreement [LoA]). The effect of corneal characteristics (CC, CCT, and CRF) on the IOP measurement differences between tonometers also was determined.
  
  
  METHODS
  Repeatability and reproducibility of the GAT, DCT, and ORA IOPcc and agreement between tonometers.
  
  
  RESULTS
  The repeatability coefficients for GAT, DCT, and ORA were 2.2, 2.3, and 4.3 mmHg, respectively. The intraobserver variability of ORA measurements was shown to be significantly associated with OPA and to a lesser degree with the quality of ORA waveform scans. The interobserver bias (95% LoA) was -0.8 (+/-3.9) mmHg for GAT -0.2 (+/-2.8) mmHg for DCT and -0.3 (+/-3.9) mmHg for ORA IOPcc. On average, GAT under-read both DCT and ORA IOP measurements by approximately 2 mmHg. The IOP measurement differences were better predicted by CRF than CCT.
  
  
  CONCLUSIONS
  The DCT shows excellent measurement precision, displaying the best repeatability and reproducibility of the 3 tonometers. Corneal stiffness, as defined using CRF, was associated significantly with agreement between devices. The IOP measurements with each device are not interchangeable.
  
  
  BACKGROUND
  Proprietary or commercial disclosure may be found after the references.
authors.affiliation: Glaucoma Research Unit, The National Institute for Health Research Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom. aachalkotecha@gmail.com
authors.forename: Aachal
authors.initials: A
authors.lastname: Kotecha
authors.forename: Edward
authors.initials: E
authors.lastname: White
authors.forename: Patricio G
authors.initials: PG
authors.lastname: Schlottmann
authors.forename: David F
authors.initials: DF
authors.lastname: Garway-Heath
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009798:Ocular Hypertension / Q000175:diagnosis; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation*; D055815:Young Adult