Prevalence of calibration errors in Goldman applanation tonometers

ABSTRACT

To determine the prevalence of calibration errors in Goldmann applanation tonometers at Farabi Eye Hospital. This cross-sectional study was performed on all tonometers in use at Farabi Eye Hospital. All Haag-Streit Goldmann applanation tonometers were checked according to the manufacturer's method by two independent observers and by a third observer in case of mismatched results. Calibration errors were classified into 6 categories of +/- 0.5, +/- 1, +/- 1.5, +/- 2, +/- 2.5 and more than +/- 2.5 mmHg. Overall, 43 Goldmann tonometers were evaluated. There were 3 [7%], 10 [24.3%], 16 [38.3%], 24 [56.9%], 31 [72.1%] and 12 [27.9%] tonometers within calibration errors of +/- 0.5, +/- 1, +/- 1.5, +/- 2, +/- 2.5 and more than +/- 2.5 mmHg respectively. Goldmann tonometers were not within the manufacturer's recommended range [ +/- 0.5 mmHg] in 93%, and not within the acceptable range of +/- 2.5 mmHg in 28% of checked devices. Further study is needed to demonstrate the correlation between calibration errors and clinical errors