How to verify the calibration of Goldmann tonometers

measuring the intraocular pressure (IOP), the fluid pressure inside the eye. It is an important test in the evaluation of patients with glaucoma, as damage to the optic nerve is more likely to occur in patients with high IOP. Most tonometers are calibrated to measure pressure in millimeters of mercury (mmHg). Goldmann tonometry is considered to be the gold standard test for IOP and is the most widely accepted method. A disinfected prism is mounted on the tonometer head and placed against the cornea. The force applied to the tonometer head is then adjusted using a dial connected to a variable tension spring until the pressure in the eye can be determined from the force applied (see page 60 for a detailed description of how to use a tonometer). Tonometers in busy clinics have been shown to lose accuracy within months of purchase or calibration by the manufacturer. They are more likely to deviate into the positive range, resulting in higher IOP measurements. It is essential that all eye units develop protocols for calibration checks. Ideally, tonometers should be checked for calibration errors on a monthly basis by individuals who can be held responsible for ensuring their accuracy.