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Out-of-tune Goldmann applanation tonometers may overestimate IOP
Ophthalmology. 2009;116(1):9-13.
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Calibration errors on a Goldmann applanation tonometer may lead to inaccurate assessment of a patient’s IOP.
Researchers examining 125 eyes of 125 patients measured IOP with a Goldmann tonometer set to zero calibration error and compared results with tonometers known to have calibration errors ranging from zero to +5 mm Hg.
Out-of-tune tonometers routinely overestimated IOP, but the degree of error did not match the value of overestimation at a one-to-one level. For instance, mean IOP measured by a tonometer with a +1 mm Hg error was +1 mm Hg higher than the zero-error tonometer, but a tonometer with a +2 mm Hg error returned an IOP that was +1.2 mm Hg compared with the zero-error tonometer. The +3 mm Hg error tonometer measured IOP at +1.6 mm Hg, the +4 mm Hg error measured IOP at +3.6 mm Hg and the +5 mm Hg error measured IOP at +3.3 mm Hg compared with the zero-error tonometer.
In some situations, such as when a tonometer is used frequently and the manufacturer may not be available to reset the calibration, it may be clinically acceptable to use tonometers with a calibration error of less than +3 mm Hg because the error is typically less than +2 mm Hg compared with zero-error tonometers.