Tonometry Overview

Pressure in the eye is called intraocular pressure (IOP). Tonometry tests the amount of pressure in the eye.

There are two main types of tonometry: the noncontact (air puff) method and the applanation (flattening of the cornea with pressure) method. The type of tonometry that is done will depend on the equipment your doctor has and the type of test he or she decides 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.

Noncontact Method

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

Your doctor will place anesthetic drops in your eyes before the test. This will numb your eye. Your doctor may also place a small amount of an orange dye 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 doctor will touch this device 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.

After Test

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.

RESOURCES:

Glaucoma Research Foundation
http://www.glaucoma.org/

National Eye Institute
http://www.nei.nih.gov/

CANADIAN RESOURCES:

Canadian Association of Optometrists
http://www.opto.ca/en/index.html

Canadian Ophthalmological Society
http://www.eyesite.ca/

References:

Brandt JD. Corneal thickness in glaucoma screening, diagnosis, and management. Curr Opin Ophthalmol. 2004;15:85-89.

Brandt JD, Beiser JA, Gordon MO, Kass MA; Ocular Hypertension Treatment Study (OHTS) Group. Central corneal thickness and measured IOP response to topical ocular hypotensive medication in the Ocular Hypertension Treatment Study. Am J Ophthalmol. 2004;138:717-722.

Duch S, Serra A, Castanera J, et al. Tonometry after laser in situ keratomileusis treatment. J Glaucoma. 2001;10:261-265.

Eisenberg DL, Sherman BG, McKeown CA, et al. Tonometry in adults and children. A manometric evaluation of pneumatonometry, applanation, and TonoPen in vitro and in vivo. Ophthalmology. 1998;105:1173-1181.

Kaufmann C, Bachmann LM, Thiel MA. Intraocular pressure measurements using dynamic contour tonometry after laser in situ keratomileusis. Invest Ophthalmol Vis Sci. 2003;44:3790-3794.

Komaroff AL, ed. Harvard Medical School Family Health Guide. New York, NY: Simon and Schuster; 1999.

Krupin T, Liebmann JM, Greenfield DS, et al. Low-pressure glaucoma study group: the low-pressure glaucoma treatment study (LoGTS): study design and baseline characteristics of enrolled patients. Ophthalmology. 2005;112:376-85.

Muir KW, Jin J, Freedman SF. Central corneal thickness and its relationship to intraocular pressure in children. Ophthalmology. 2004;111:2220-2223.

Pache M, Wilmsmeyer S, Lautebach S, et al. Dynamic contour tonometry versus Goldmann applanation tonometry: a comparative study. Graefes Arch Clin Exp Ophthalmol. 2005;243:763-767.

Weigert G, Findl O, Luksch A, et al. Effects of moderate changes in intraocular pressure on ocular hemodynamics in patients with primary open-angle glaucoma and healthy controls. Ophthalmology. 2005;112:1337-1342.