Calibration of tonometers needs to be tested more often, researchers find

SEATTLE – Researchers investigating the usage of Goldmann tonometry devices at an optometry college found that most practitioners are unaware that those machines should be calibrated quite often for best results.

Otherwise, with the wrong measurements due to poor calibration of the instrument, “glaucoma might be diagnosed later than it could be,” David M. Perrigen, OD, told PRIMARY CARE OPTOMETRY NEWS. “Reading too high or too low gives you a false sense of security.”

The researchers measured 74 Goldmann applanation tonometers at the University of Houston College of Optometry’s University Eye Institute for calibration accuracy at the 20-mm Hg and 60-mm Hg settings, both at 2 weeks and 5 months.

“By the 2-week evaluation, a significant number had drifted outside the recommended range for the 20-mm Hg setting (p=0.039) but not for the 60-mm Hg settings (p=0.404),” according to the poster abstract. “At 5 months, the degree of errors and the number out of calibration had increased. Fifty percent of tonometers off at the 20-mm Hg setting were now also out of calibration at the 60-mm Hg setting.”

They found that the inferior mounted devices were more likely to be out of calibration after 5 months.

The instruments come with devices that help determine calibration, but it is not easily understood how often those devices should be used, Judith A. Perrigen, OD, FAAO, said. “We need to make sure that [information] is incorporated,” she said. “Yearly checks are not adequate.”