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

PURPOSE: To evaluate the frequency of Goldmann applanation tonometer (GAT) calibration error (CE) check. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

A Simplified (Screening) Approach to Check the Calibration Status of the Goldmann Applanation Tonometer.

BACKGROUND: To investigate whether a lower-end calibration error check alone can identify a Goldmann applanation tonometer (GAT) with acceptable calibration error as per Asia-Pacific Glaucoma Society (APGS) and World Glaucoma Association (WGA) guidelines. METHODS: This was a multicentric prospective study in a tertiary eye-care institutional setting. Seventy-six slit-lamp-mounted Haag-Streit GATs (Model AT 900 C/M) were included in the study. All GATs were checked for calibration error at 0, 20, and 60 mm Hg testing levels as recommended by the manufacturer. The ability of 2 screening criteria (calibration error within ±1 or ±2 mm Hg, respectively, at the 0 mm Hg testing level without using the calibration error check weight bar) to identify a tonometer within acceptable calibration limits defined by APGS (calibration error within ±2, ±3, and ±4 mm Hg at 0, 20, and 60 mm Hg testing levels, respectively) and WGA (calibration error within ±1 mm Hg at all testing levels) was determined. MAIN OUTCOME MEASURE: The negative likelihood ratio of the screening criteria RESULTS:: Five (6.6%) and 42 (55%) GATs were outside of the APGS and the WGA calibration limits, respectively. Negative likelihood ratios of the first and the second screening criteria at the APGS definition of calibration error tolerance were 0.11 and 0.25, respectively, and at that of the WGA definition of calibration error tolerance were 0.38 and 0.90, respectively. CONCLUSIONS: The screening criteria of calibration error within ±1 mm Hg at the 0 mm Hg testing level seem to be clinically useful to detect GAT with an acceptable calibration error as per the APGS guideline.