Measurement of Goldmann applanation tonometer calibration error

Area of Science:

• Ophthalmology and Optometry
• Biomedical Engineering
• Medical Device Technology

Background:

• The Goldmann applanation tonometer is a standard instrument for measuring intraocular pressure (IOP).
• Accurate IOP measurement is critical for diagnosing and managing glaucoma and other eye conditions.
• Calibration errors in tonometers can lead to misdiagnosis and inappropriate treatment.

Purpose of the Study:

• To determine the frequency and potential causes of calibration errors in Goldmann applanation tonometers.
• To assess the intraobserver and interobserver agreement in measuring these calibration errors.
• To evaluate the reliability of tonometer calibration over time.

Main Methods:

• Evaluated 132 slit-lamp-mounted Haag-Streit Goldmann tonometers (Model AT 900 C/M).
• Calibration error testing performed using a standard check weight bar at 0, 20, and 60 mmHg.
• Intraobserver and interobserver agreement assessed through repeated measurements by single and multiple observers.

Main Results:

• Only 4% of tonometers met the manufacturer's tolerance (+/-0.5 mmHg) at 20 mmHg.
• 28% of instruments showed errors > +/-2 mmHg at 20 mmHg; 12.12% showed errors > +/-2 mmHg at 0 or 60 mmHg.
• After repair, 20.75% of faulty instruments again exhibited unacceptable errors; good intraobserver and interobserver agreement was noted.

Conclusions:

• A substantial proportion of Goldmann tonometers exhibit clinically unacceptable calibration errors.
• While measurement agreement is good, frequent calibration error testing is necessary.
• Automation of the calibration error check process is recommended for improved reliability.