Frequency of Goldmann applanation tonometer calibration error checks

Purpose: To investigate how quickly Goldmann applanation tonometers used in clinical practice develop calibration errors, and to determine the frequency of checks required to detect these errors. Materials and Methods: Prospective check of the calibration error of all Haag-Streit Goldmann applanation tonometers in the department at month zero, month one, and month four. The tonometers were checked according to the Haag-Streit method using a standard calibration check weight bar by two independent observers. Calibration errors were classed as +/- 0.5 to 2.5 mm Hg, +/- 3 to 4 mm Hg, or >+/- 4 min Hg. Torrometers with a calibration error greater than +/- 2.5 mm Hg were returned to the manufacturer for re-calibration. Results: At month zero 2 of 34 (5.9%), at month one 3 of 29 (10.3%), and at month four 0 of 33 (0.0%) tonometers fell within the manufacturer's recommended calibration range of +/- 0.5 min Hg. A total of 14 of 34 (41.2%) tonometers at month zero, 10 of 29 (34.5%) tonometers at month one, and 17 of 33 (51.5%) tonometers at month four were identified to have calibration errors greater than +/- 2.5 mm Hg. Conclusions: Goldmann applanation torrometers are not as accurate as the manufacturer's recommended calibration error tolerance of +/- 0.5 mm Hg would suggest. Calibration error of less than +/- 2.5 min Hg is clinically acceptable. Calibration error checks should be carried out once monthly and tonometers with calibration error greater than +/- 2.5 mm Hg returned to the manufacturer for re-calibration. Additional checks should be made if tonometers suffer specific damage. Ideally individual ophthalmologists should check calibration before each session.