What Is Tonometry?

Tonometry is a quick and simple test that checks the pressure inside your eyes. The results can help your doctor see if you’re at risk for glaucoma.

Glaucoma is a disease that boosts the pressure inside your eyes. It can cause blindness. Early screening can help protect your eyesight and slow down vision loss.

Why Do I Need This Test?

Your eyes are filled with different fluids that keep them healthy. New fluid is constantly being made and old fluid drained out. But if this drainage system gets plugged, the fluids build up. That causes the pressure inside your eyes to rise.

Sometimes the pressure is caused by an eye injury or trauma. Once your eye heals, everything may go back to normal. But some people have a drainage system that doesn’t work like it should.

Over time, high pressure inside your eye can damage your optic nerve, which sends images from your eyes to your brain. Left untreated, it can cause glaucoma.

Since the disease doesn’t always have symptoms, regular eye exams are a good idea. Your eye doctor will check your eye pressure by doing a tonometry test. She can also track any changes in pressure over time.

Anyone can get glaucoma, but your odds are higher if you:

  • Are over 40
  • Have a family member with glaucoma
  • Are African, Hispanic or Asian
  • Have had an eye injury
  • Are far-sighted or near-sighted
  • Have been told your corneas are thin in the middle
  • Have diabetes
  • Get migraines
  • Have high blood pressure
  • Have circulation (blood flow) problems

What Happens During a Tonometry Test?

Your doctor can check your eye pressure a couple of different ways:

  • Tonometer. After special numbing drops are put in your eye, your doctor gently holds this pencil-shaped device against the outside of your eyeball. The reading tells how well your cornea pushes back.
  • “Puff of air.” Your doctor could also use an instrument that blows a small puff of air at your eye while you look into a light. This also measure the pressure inside your eyeball.

Both these methods are painless and only last a few seconds. If your doctor does the “puff of air” test, you may feel a small amount of pressure against your eye.

Your doctor will share the results with you right away.

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What Do the Results Mean?

Eye pressure is different from person to person. Normally, it lies somewhere between 12-22 mmHg (“millimeters of Mercury”). Most people diagnosed with glaucoma have an eye pressure above 20 mmHg.

If your eye pressure is high but your optic nerve looks normal, you may have what’s called “ocular hypertension.” You might not have any symptoms, but this could lead to glaucoma over time.

Some people with ocular hypertension never end up with glaucoma. Others develop it even though their eye pressure falls within a normal range. Because of this, tonometry is only part of a complete eye exam. These results, along with other vision tests, help your doctor get a better idea of your eye health. She’ll also talk to you about your health history and any symptoms you’re having.

If the test shows you have high pressure in your eyes, your doctor may keep a close watch on it by having you come in for regular testing. Or, she could decide to lower the pressure by prescribing eye drops that you’ll take every day. They’ll help protect your optic nerve from future damage and, in the long run, could save your sight.

WebMD Medical Reference Reviewed by Alan Kozarsky, MD on January 28, 2017

Sources

SOURCES:

Glaucoma Research Foundation: “Five Common Glaucoma Tests,” “How Glaucoma Affects the Optic Nerve,” “Ocular Hypertension Treatment.”

See Jane See: “Living with High Intraocular Pressure (IOP).”

JAMA: “Clinical Methods: The History, Physical, and Laboratory Examinations.”

American Academy of Ophthalmology: “What Causes High Eye Pressure?” “Glaucoma Diagnosis,” “What is Glaucoma?” “Who Is at Risk for Glaucoma?”

National Eye Institute: “Facts About Glaucoma.”

Mount Sinai: “Tonometry,” “Hyphema.”

Air Force Center of Excellence for Medical Multimedia: “Intraocular Pressure Test.”

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