title: Clinical evaluation of the dynamic observing tonometer.
abstract: OBJECTIVE
  The Dynamic Observing Tonometer (SmartLens, Ophthalmic Development Company AG, Zürich, Switzerland) is a diagnostic contact lens that allows continuous measurement of intraocular pressure, in addition to providing the investigator with a view of the posterior pole and anterior chamber angle. The purpose of this study was to determine the accuracy of this tonometer and the repeatability of the intraocular pressure measurements.
  
  
  METHODS
  The intraocular pressure was measured by Goldmann applanation tonometry in one randomly chosen eye of 40 subjects (median age 66 years, range 21-77 years). The intraocular pressure, pulse amplitude and 10-second continuous tonometric recordings were then taken using the Dynamic Observing Tonometer and a pneumatonometer. Accuracy was determined by calculating the mean bias and 95% limits of agreement of measurements made with the Dynamic Observing Tonometer against measurements made with the Goldmann and pneumatonometer. Repeatability was evaluated by calculating the differences between pairs of repeated measurements against the mean value and by calculating reliability coefficients.
  
  
  RESULTS
  Intraocular pressure measurements made with the Dynamic Observing Tonometer had a mean bias of +2.1 mm Hg (95% limits of agreement: -4.0 to +8.2 mm Hg) compared with Goldmann tonometry. There was a reasonable correlation between Goldmann and Dynamic Observing Tonometer intraocular pressure readings (r = 0.78, P < 0.01). In measuring pulse amplitude, the Dynamic Observing Tonometer was found to have a mean bias of +0.4 mm Hg (95% limits of agreement: -1.6 to +2.3 mm Hg) compared with the pneumatonometer (r = 0.78, P < 0.01). In assessing the repeatability of intraocular pressure measurements, the first Dynamic Observing Tonometer reading was on average 0.4 mm Hg higher than the second (95% limits of agreement: -3.8 to +4.6 mm Hg) with a coefficient of reliability of 0.91. For pulse amplitude readings, the first reading was on average 0.1 mm Hg lower than the second (95% limits of agreement: -1.4 to +1.2 mm Hg) with a coefficient of reliability of 0.90.
  
  
  CONCLUSIONS
  Intraocular pressure measurements taken with the Dynamic Observing Tonometer had a small positive bias compared with Goldmann tonometry. The pulse amplitude values correlated well with those obtained with a pneumatonometer and the repeatability of intraocular pressure measurements was similar to that found in other commercially available tonometers.
authors.affiliation: Neurosciences Research Institute, School of Life and Health Sciences, Aston University, Birmingham, England.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Morgan
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Hosking
authors.forename: John F
authors.initials: JF
authors.lastname: Salmon
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000592:standards*