Prevalence of Calibration Errors in Goldmann Applanation Tonometers

PURPOSE To determine the prevalence of calibration errors in Goldmann applanation tonometers at Farabi Eye Hospital. METHODS 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. RESULTS 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. CONCLUSION 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.