(Intraocular Pressure [IOP] Measurement)
Pressure in the eye is called intraocular pressure (IOP). Tonometry tests the amount of pressure in the eye.
Reasons for Test
Elevated eye pressure can lead to eye damage. This may be part of a disease called glaucoma. If left untreated, glaucoma can cause blindness. Tonometry is used to screen for glaucoma. It is also used to monitor the treatment of glaucoma.
You may have ocular hypertension. This happens when pressure is elevated but is not caused by glaucoma.
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There are no major complications associated with this procedure.
What to Expect
There are 2 main types of tonometry: the noncontact air puff method and the applanation method that flattens the cornea with pressure. The type of tonometry that is done will depend on the equipment your doctor has and the type of test they decide to do.
Prior to Test
You may be asked to remove corrective lenses, such as contacts.
Description of the Test
For both methods, you will be asked to sit in an exam chair. You may be asked to place your chin in a special cradle and rest your forehead against a bar. The chin cup and forehead rest will balance and steady your head.
You will be asked to look into an instrument. A puff of air will be blown into the eye. No instruments come in contact with the eye.
Applanation Method or the Goldmann Tonometry
Anesthetic drops will be placed in your eyes before the test. This will numb your eye. A small amount of an orange dye may also be placed into your eye. When your head is balanced and steady, you will be asked to look into an instrument with a blue light. A probe will push against your eye. How hard the probe has to push lets the doctor know how much pressure is in the eye. This test does not hurt because the eye is numb. This test is considered the most accurate method of checking pressure.
Another method of applanation tonometry is the use of a handheld device shaped like a pen. The device will be pushed against the front of your eye to get pressure readings. Again, it does not hurt because the eye is numb.
There are other devices that are used to check eye pressure. The ones listed above are the most common.
The numbing drops and dye wear off in about 20 minutes. It is important not to rub your eye while it is numb.
How Long Will It Take?
A few seconds
Will It Hurt?
This test is painless. Some people do experience a slight sting or tingling due to the anesthetic drops.
If you are having the procedure for glaucoma screening, your doctor will discuss the results with you and determine treatment options, if needed.
If you are having the procedure to monitor an existing diagnosis of glaucoma, your doctor will determine if your current care is helping to lower your eye pressure.
Call Your Doctor
After the test, call your doctor if you have any of the following eye discomforts:
- Excessive itching
- Pink or reddish color that does not go away
- Decreased vision
- Any other eye problem
In case of an emergency, call for emergency medical services right away.
Glaucoma Research Foundation
National Eye Institute
Canadian Association of Optometrists
Canadian Ophthalmological Society
Five common glaucoma tests. Glaucoma Research Foundation website. Available at: http://www.glaucoma.org/glaucoma/diagnostic-tests.php. Updated April 22, 2013. Accessed June 16, 2016.
Tonometers. The College of Optometrists website. Available at: http://www.college-optometrists.org/en/college/museyeum/online_exhibitions/optical_instruments/tonometers.cfm. Accessed June 16, 2016.
Last reviewed May 2018 by Michael Woods, MD Last Updated: 5/26/2015