Variability in the calibration error of the goldmann applanation tonometer

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Medical Device Calibration

Background:

• Goldmann applanation tonometry (GAT) is a standard method for measuring intraocular pressure (IOP).
• Consistent calibration of GAT is crucial for accurate IOP measurement.
• Previous studies have highlighted the importance of GAT calibration, but variability with continued use requires further investigation.

Purpose of the Study:

• To investigate the variability in measured calibration error of Goldmann applanation tonometers (GATs).
• To assess the impact of continued usage on GAT calibration error in instruments with pre-existing unacceptable error.

Main Methods:

• 132 slit-lamp mounted Goldmann tonometers (Model AT 900 C/M) were included.
• A single observer assessed intraobserver agreement and prospectively measured calibration error at 0, 20, and 60 mm Hg.
• Faulty instruments (error > ±2 mm Hg) were rechecked multiple times on the same day.

Main Results:

• 21% of instruments were faulty at any testing level; 14% were faulty at 20 mm Hg.
• High variability in calibration error (≥ 2 mm Hg) was observed in 53% of faulty instruments.
• Maximum observed variability was +4 mm Hg for positive error and -23 mm Hg for negative error.

Conclusions:

• Faulty Goldmann applanation tonometers frequently exhibit high variability in calibration error.
• Estimating true intraocular pressure using a faulty GAT without considering its calibration variability is unreliable.
• Regular calibration checks and maintenance are essential for accurate GAT performance.