Procedure which consists of measuring the intraocular pressure (IOP), by means of a tonometer. Intraocular pressure is the pressure put on the tunics of the eye by those fluids contained inside the eye (vitreous humor and aqueous humor).

Why the test is performed:

Tonometry is a simple and harmless technique that allows to detect an increase of the pressure inside the eye, either for the first time or as a follow-up.
A steady or sudden increase of the intraocular pressure can lead to irreversible damage of the optic nerve, which in turn may result in partial or complete loss of vision.
Tonometry is a test used to support diagnosis and to follow up eye disorders such as glaucoma.
Intraocular pressure levels and blood pressure are independent.

How it is performed:

Applanation, contact or Goldmann tonometry, measure the IOP by using a tonometer placed in a slit-lamp. It is the most frequently used method. In applanation tonometry, the specialist uses eye drops, to numb the surface of the eye, and fluorescein dye during the test.
Noncontact tonometry or air-puff tonometry consists of delivering a brief puff of air at the eye in order to flatten (applanate) the cornea, thereby measuring IOP.

How to prepare for the test:

The patient cannot be wearing (and must remove) his or her contact lenses before the exam since the fluorescein dye can stain them permanently.