Patient Basics: Tonometry

Originally published by Harvard Health.

What is the test?

Tonometry is a test to measure pressure in your eyeball. High pressure inside the eye is caused by a disease called glaucoma, which can damage your vision if it is not treated.

How do I prepare for the test?

Remove any contact lenses. Tell your doctor if you have an eye infection or other type of eye problem.

What happens when the test is performed?

The pressure inside your eye is always measured from the outside. In most cases, if you are at an eye clinic, the pressure can even be measured without anything actually touching your eye. The eye doctor has you look up close at an instrument that blows a small puff of air onto your eye. It then uses a special sensor (like a tiny radar detector) to detect the amount of indentation that the air puff causes on the surface of the eye. This indentation is normal and lasts for only a fraction of a second.

Sometimes patients need to have their eye pressure measured but they are not in an eye clinic with this type of machine (for example, some patients need to be checked for glaucoma in an emergency room). In this case, the pressure can be measured with an instrument resembling a pen. One end of the instrument is placed on the surface of the eyeball. This feels like having a contact lens put in your eye.

What risks are there from the test?

The test might make you feel like blinking, but it does not cause any pain. There are no risks from this test.

Must I do anything special after the test is over?

No.

How long is it before the result of the test is known?

You can know the result of the test right away.