How an intraocular pressure test works

Tonometer is a measured test Eye intraocular pressure (IOP). This term describes the pressure inside your eye.

Tonometry is an important part of a comprehensive eye exam.When your eye pressure is higher than normal, you may be at risk for: glaucoma. High intraocular pressure can damage the delicate nerve fibers in the back of the eye, sometimes leading to blindness.

A tonometer is an instrument that measures eye pressure. It does this by calculating your cornea’s resistance to indentation. Your healthcare provider may use one of several methods to measure the pressure inside your eye.

This article looks at the different kinds of IOP tests, what they are used for, and who should get them.

Why do I need an IOP test?

An intraocular pressure test is used to check for glaucoma. This is a serious eye disease that causes damage to the optic nerve. The optic nerve is the nerve at the back of the eye.

There are several different types of glaucoma. Open angles, the most common type, can take many years to develop. It doesn’t cause pain, and most people don’t experience symptoms until later in life. If left untreated, blindness can result. The damage to the eye from glaucoma cannot be reversed.

Because vision loss is often the first sign of disease, it is important to diagnose at an early stage. That’s why it’s important to have an IOP test even if you have good vision. When you receive an early diagnosis, your healthcare provider can prescribe medication to stop the disease from progressing before it causes vision loss.


Tonometers can help diagnose glaucoma early, before it causes vision loss. That’s why it’s important to have this test as part of your routine eye exam.

Who should be tested?

Healthy adults with good vision should have a complete eye exam, including an IOP test, in their 20s, 30s, and 40s. Your eye doctor will recommend a schedule for future exams based on your results.

Certain conditions put you at risk for eye disease. You will need to schedule earlier and more frequent tests if you have any of these risk factors:

  • Family history of glaucoma or other eye disease
  • hypertension
  • diabetes
  • heart disease

Your eye doctor may also perform this test if you have any of the following symptoms:

  • peripheral vision loss
  • Tube perspective

Tonometers can also be used to diagnose angle-closure glaucoma, a type of glaucoma that appears suddenly. Symptoms may include:

  • severe eye pain
  • headache
  • blurred vision
  • See the rainbow halo around the lights
  • loss of vision
  • nausea and vomiting
  • blurred vision
  • red eyes

After being diagnosed with glaucoma, you may also need regular eye pressure tests. These will help your healthcare provider monitor how well your treatment is working.

Normal intraocular pressure varies from person to person. There is a range that is considered normal. If your eye pressure is higher than the normal range, you may be at increased risk of developing glaucoma.


It is most important to have an IOP test if you are over 40 and/or if you have risk factors such as diabetes, high blood pressure, heart disease or a family history of glaucoma.

Types of Tonometry Tests

There are several different types of eye pressure tests. Some are more accurate than others, but each has distinct advantages.

Goldman Tonometer

The Goldmann applanation tonometer is the most common intraocular pressure test. Your healthcare provider will put anesthetic eye drops and a small amount of dye in your eye before the test. Blue light illuminates the dye. A small probe is gently pressed into the cornea, and the device measures the force required to flatten that small part of the cornea. Your healthcare provider will record this number and compare it with future test results.

non-contact tonometer

A non-contact tonometer (NCT) is also known as a “puff” test. Many people like this test because it doesn’t involve touching the eyes. Conversely, a gentle blow will flatten the cornea. Although some studies have shown that the NCT tonometer is not as accurate as the Goldmann tonometer, it is still a good choice for children or sensitive adults.


The Goldman tonometer test is the most common. During this test, a small probe applies pressure to your cornea. For children and sensitive adults, “puff” IOP testing may be preferred.

Electronic tonometer

An electronic tonometer is a handheld mobile device that looks like a writing pen. It can be applied lightly and quickly on your cornea. Typically, this test needs to be repeated several times to produce accurate measurements. Overall, it is not as reliable or accurate as the Goldmann tonometer.

Schiotz Tonometer

The Schiotz tonometer uses a small metal plunger to press into the eye. The device calculates intraocular pressure by measuring the depth of the indentation on the cornea. Modern eye care practitioners do not use this type of tonometer like other types. However, it is sometimes used in more remote settings.


Electronic tonometers and Schiotz tonometers are not as commonly used as other modalities. Electronic tonometers are used when portability is required, and Schiotz tonometers are sometimes used in remote settings.


A tonometer measures the pressure in the eye. Higher pressure in the eye can put you at risk for glaucoma.

You may have an eye pressure test as part of a complete eye exam. This test is most important when you are over 40 or have risk factors such as diabetes and high blood pressure.

There are several different types of eye pressure tests. Most involve touching the eye with a probe. If you’re sensitive, you can also opt for a test that measures eye pressure with a puff of air.

VigorTip words

Glaucoma progresses slowly. The most common type has no symptoms in the early stages. If you wait until you have lost your vision to have an IOP test, your eye damage cannot be reversed. That’s why it’s important to get this test done before symptoms of glaucoma appear.

Consult your eye care practitioner if you are uncomfortable having the probe touch your eye. A blow test might be a good option for you.

Frequently Asked Questions

  • What is an OCT glaucoma test?

    An optical coherence tomography (OCT) test is a non-invasive test that can help diagnose glaucoma and many other eye diseases, including:

    • macular edema
    • macular hole
    • diabetic retinopathy
    • age-related macular degeneration
    • optic nerve disorder

    During this test, a machine uses light waves to create an image of your retina.

  • Is the puff test for glaucoma accurate?

    Non-contact tonometers are sometimes called “suction tests.” Many patients prefer it because the machine does not physically touch the cornea. The aspiration test is considered accurate, but it can sometimes overestimate eye pressure. For this reason, many eye care providers prefer other types of tonometers. It’s still a good option for children and adults sensitive to more traditional IOP tests.

  • How long does it take to do an IOP test?

    An IOP test usually only takes a minute or two. With a contact test, the probe will only touch your eye for a few seconds. Test results should be available immediately. Your healthcare provider will discuss these issues with you before you complete your appointment.