Definition The tonometry test measures the pressure inside the eyeballs. This is called intraocular pressure, or IOP.
Who is a candidate for the test? Tonometry helps to diagnose glaucoma. It is often used as a screening test to detect glaucoma or to follow treatment in someone who has glaucoma. Tonometry is often done as part of a complete eye examination.
How is the test performed? There are 3 methods to measure the pressure inside the eyes. These procedures are all performed in the office of the opthalmologist or doctor.
One method uses a puff of air, and is a noncontact method. The person sits in a chair with the chin resting on a pad. The individual looks straight into the examining instrument. A bright light shines on the front of the eye as a short puff of air is blown at it. The instrument measures the amount of air deflected by the eye, which gives an estimate of the pressure.
Another method is called the Schiotz method. A drop of anaesthetic is placed on the eye. When the eye is numb, the person looks up at the ceiling. A tonometer is lowered until it touches the surface of the eye. The machine measures the intraocular pressure.
Another method is the applanation method. A drop of anaesthetic is placed on the eye. A small amount of fluorescent dye is placed on the cornea. The cornea is then lit with a slit lamp. The front of the eye is touched by the tonometer, and the intraocular pressure is measured.
What is involved in preparation for the test? Specific instructions are available from the doctor. Usually, no preparation is required.
What do the test results mean? The person's intraocular pressure is compared with the normal range available on standard tables.
Elevated intraocular pressure, greater than 21mm Hg, may indicate the presence of glaucoma.
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 15/03/2005 Contributors Potential conflict of interest information for reviewers available on request
