How Often the Goldmann Applanation Tonometer Should be Checked for Calibration Error?

To evaluate the frequency of Goldmann applanation tonometer (GAT) calibration error (CE) check.

One observer at each of the 3 tertiary care ophthalmic centers was involved. The tonometers were checked at baseline for CE. A tonometer was defined as faulty when CE exceeded 2 mm Hg at any testing level. Faulty GATs were repaired in-house. Subsequent CE check was done once per month for 6 months. GATs were divided into 3 groups: group 1 (G1)≤1 year, group 2 (G2)>1 to 10 years, and group 3 (G3)>10 years of usage.

In total, 76 slit-lamp mounted GATs were included. The number of GATs in groups 1 to 3 was 19, 36, and 21, respectively. Seven (9.2%) tonometers were faulty at the baseline. None in G1, 5 in G2, and 16 in G3 demonstrated unacceptable CE over the study course (P<0.01). The survival function of G1 tonometers was 1.0 throughout, whereas that (95% confidence interval) of the G2 and G3 tonometers were 0.97 (0.81-0.99) and 0.76 (0.51-0.89) at 1 month, and 0.86 (0.69-0.93) and 0.23 (0.08-0.43) at 6 months, respectively. The probability of CE development increased with increasing age of the tonometer. The frequency of use of the tonometer was not associated with the development of CE (odds ratio=1.00).

CE occurs more frequently in older tonometers. Although newer GATs (<1 y old) can be checked twice yearly, GATs older than a year should be checked at least monthly.