title: Evaluation of the impedance tonometers TGDc-01 and iCare according to the international ocular tonometer standards ISO 8612.
abstract: BACKGROUND
  Two new tonometers have been introduced that are based on the impedance principle. Both the TGDc-01 (transpalpebral measurement) and the iCare (corneal measurement) do not require corneal anaesthesia. The present work presents an evaluation of both devices.
  
  
  METHODS
  Comparative measurements using one of the new tonometers and applanation tonometry were performed by one investigator according to the international standard for ocular tonometer (ISO 8612). Measurements were performed on 445 eyes without corneal pathology from 243 patients. Six measurements were performed for iCare and 3 for TGDc, immediately followed by 3 applanation tonometry measurements.
  
  
  RESULTS
  The correlation coefficient with respect to applanation tonometry was 0.81 for TGDc and 0.95 for iCare. TGDc-01 measurements showed an average deviation of 3.1 +/- 2.6 mmHg to those of Perkins applanation tonometry. The maximum difference was 28.7 mmHg below and 9.8 mmHg above the results of applanation tonometry. iCare showed an average deviation of 2.5 +/- 1.1 mmHg to Goldmann tonometry. The maximum difference was 14.5 mmHg below and 9.8 mmHg above.
  
  
  CONCLUSIONS
  The results of both new tonometers showed a good correlation with the reference applanation tonometric methods, but the strict requirements of ISO 8612 are not fulfilled by either tonometer at present. Additionally, transpalpebral measurements with the TGDc-01 showed unacceptably high variability.
authors.affiliation: Department of Ophthalmology, Charité University Hospital Berlin Campus RVK, Augustenburger Platz 1, 13353 Berlin, Germany. peter.ruokonen@charite.de
authors.forename: Peter Christian
authors.initials: PC
authors.lastname: Ruokonen
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwenteck
authors.forename: Jörg
authors.initials: J
authors.lastname: Draeger
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017097:Electric Impedance; D005901:Glaucoma / Q000175:diagnosis; D006801:Humans; D007429:Intraocular Pressure; D008875:Middle Aged; D012015:Reference Standards; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation*