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Tonometry

A tonometry test measures the pressure inside your eye, which is called intraocular pressure (IOP). This test is used to check for glaucoma, an eye disease that can cause blindness by damaging the nerve in the back of the eye (optic nerve camera.gif). Damage to the optic nerve may be caused by a buildup of fluid that does not drain properly out of the eye.

Tonometry measures IOP by recording the resistance of your cornea camera.gif to pressure (indentation). Eyedrops to numb the surface of your eye camera.gif are used with most of the following methods.

Tonometry methods

  • Applanation (Goldmann) tonometry. This type of tonometry uses a small probe to gently flatten part of your cornea to measure eye pressure and a microscope called a slit lamp to look at your eye. The pressure in your eye is measured by how much force is needed to flatten your cornea. This type of tonometry is very accurate and is often used to measure IOP after a simple screening test (such as air-puff tonometry) finds an increased IOP.
  • Electronic indentation tonometry. Electronic tonometry is being used more often to check for increased IOP. Although it is very accurate, electronic tonometry results can be different than applanation tonometry. Your doctor gently places the rounded tip of a tool that looks like a pen directly on your cornea. The IOP reading shows on a small computer panel.
  • Noncontact tonometry (pneumotonometry). Noncontact (or air-puff) tonometry does not touch your eye but uses a puff of air to flatten your cornea. This type of tonometry is not the best way to measure intraocular pressure. But it is often used as a simple way to check for high IOP and is the easiest way to test children. This type of tonometry does not use numbing eyedrops.

Why It Is Done

Tonometry may be done:

  • As part of a regular eye examination to check for increased intraocular pressure (IOP), which increases your risk of glaucoma.
  • To check the treatment for glaucoma. Tonometry can be used to see if medicine is keeping your IOP below a certain target pressure set by your doctor.

How To Prepare

Tell your doctor if you or someone in your family has glaucoma or risk factors for glaucoma.

If you wear contact lenses, remove them before the test. Do not put your contacts back in for 2 hours after the test. Bring your eyeglasses to wear after the test until you can wear your contact lenses.

Loosen or remove any tight clothing around your neck. Pressure on the veins in your neck can increase the pressure inside your eyes. Stay relaxed.

How It Is Done

Tonometry takes only a few minutes to do.

Applanation (Goldmann) method

This type of tonometry is done by an ophthalmologist or an optometrist. Your doctor will use eyedrops to numb the surface of your eyes so that you will not feel the tonometer during the test. A strip of paper containing a dye (fluorescein) will be touched to your eye, or eyedrops containing the dye will be applied. The dye makes it easier for your doctor to see your cornea.

WebMD Medical Reference from Healthwise

Last Updated: February 28, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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