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.
Keywords Glaucoma - iCare - Impedance tonometer - ISO 8612 - Rebound tonometer - TGDc-01 - Transpalpebral tonometer
Parts of the manuscript were presented at the annual meeting of the DOG in September 2005.
No sponsoring organizations.