Goldmann Applanation Tonometer Calibration Error Frequency | FitEyes.com
This study investigated how quickly Goldmann applanation tonometers used in clinical practice develop calibration errors and the frequency of checks required to detect these errors. Checks of the calibration error of all Haag-Streit Goldmann applanation tonometers at Month Zero, Month One, and Month Four were performed according to the Haag-Streit method using a standard calibration weight bar by two independent observers. Calibration errors were classed as +/- 0.5 to 2.5 mmHg, +/- 3 to 4 mmHg or greater than +/- 4 mmHg.
Tonometers with a calibration error greater than +/- 2.5 mmHg were returned to the manufacturer for re-calibration.
The following numbers of tonometers were found to be within the manufacturer's recommended calibration range of +/-0.5 mmHg at each period listed below:
- At Month Zero, only two of 34 (5.9 percent) were found to be within the manufacturer's recommended calibration;
- At Month One, only three of 29 (10.3 percent) were found to be within the manufacturer's recommended calibration;
- At Month Four, zero of 33 (0.0 percent) tonometers fell within the manufacturer's recommended calibration range of +/-0.5 mmHg.
The following numbers of tonometers were found to be outside the clinically acceptable error range of +/-2.5 mmHg at each time period listed below:
- At Month Zero, 14 of 34 (41.2 percent) tonometers were identified to have calibration errors greater than +/-2.5 mmHg;
- At Month One 10 of 29 (34.5 percent) tonometers were identified to have calibration errors greater than +/-2.5 mmHg.
At Month Four, 17 of 33 (51.5 percent). tonometers were identified to have calibration errors greater than +/-2.5 mmHg.
Goldmann applanation tonometers are not as accurate as the manufacturer's recommended calibration error tolerance of +/- 0.5 mmHg would suggest. Calibration error of less than +/- 2.5 mmHg is clinically acceptable. Calibration error checks should be carried out monthly and tonometers with calibration error greater than +/- 2.5 mmHg returned to the manufacturer for re-calibration.
I originally published this at http://www.fiteyes.com/blog/dave/goldmann-applanation-tonometer-calibration-error-frequency
SOURCE: Sandhu SS, Chattopadhyay S, Birch MK, Ray-Chaudhuri N. Frequency of Goldmann applanation tonometer calibration error checks. J Glaucoma 2005;14(3):215-8.
It is alarming enough to consider that up to 50% of Goldmann tonometers used in clinical practices are out of calibration. However, according to the study cited in the post above, it is possible that more than 50% of Goldmann tonometers are out of calibration.
Source: [Ophthalmology Times: Should IOP be adjusted for corneal thickness alone?]: http://www.fiteyes.com/ophthalmology-times-should-iop-be-adjusted-for-corneal-thickness-alone