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Eye pressure, also known as intraocular pressure (IOP), is the measurement of fluid pressure inside your eye.

The inside of your eye contains a fluid called aqueous humor. This fluid moves throughout the inside of your eye, performing many functions — lubricating, supplying oxygen and nutrients, clearing away waste, and more. As your eye produces new fluid, older fluid drains out.

If your eye is healthy, the amount of new aqueous humor entering your eye is equal to the amount of old fluid draining out. That keeps your eye pressure stable. But if something disrupts the normal flow, it can affect your eye pressure. If your eye pressure becomes too high, it can damage your optic nerve and increase your risk of glaucoma.

How Is Eye Pressure Measured?

Your eye doctor can measure eye pressure during a normal vision exam with a test called tonometry. This test measures the force needed to flatten the cornea. The more force it takes to flatten the cornea, the higher your eye pressure.

There are different methods of tonometry:

• In one method, your eye doctor gives you drops to numb your eye. They then use a handheld device with a blue light or another handheld instrument to gently touch the surface of your eye. This applies a small amount of pressure to the eye.
• In another method, a machine shoots a quick puff of air into your eye.

Either method of the test can flatten the cornea, allowing your doctor to measure your eye pressure.

What Is a Normal Eye Pressure?

Eye specialists measure eye pressure in millimeters of mercury, or mm Hg. Your eye pressure may fluctuate throughout the day. But in general, normal eye pressure is between 10 and 20 millimeters of mercury.

If your eye pressure is in the normal range, it means there is a normal balance of aqueous humor moving through the inside of your eye. Equal shares of fluid are entering into and draining from your eye.

What Is High Eye Pressure?

High eye pressure, or ocular hypertension, is when your eye pressure measures above 20 millimeters of mercury. It happens when something disrupts the normal flow of aqueous humor within your eye, causing excess fluid and pressure. This could mean you are producing too much fluid or that not enough is draining.

Sometimes, high eye pressure is serious. It can cause damage to your optic nerve, which can then lead to glaucoma and vision loss.

Who’s at risk for high eye pressure?

Anyone can develop high eye pressure. But according to the American Academy of Ophthalmology, those who are more at risk include:

• People with a family history of high eye pressure or glaucoma.
• People with diabetes.
• People with high blood pressure.
• People over 40.
• Black Americans and Hispanics.
• Nearsighted people.
• People on certain medications, such as long-term steroids.
• People who had an eye injury or eye surgery.
• People with certain eye conditions, like pigment dispersion syndrome or pseudoexfoliation syndrome.

What Are the Symptoms of High Eye Pressure?

In general, high eye pressure does not cause symptoms. You may not notice anything until it becomes bad enough to cause vision loss. It’s also possible to develop glaucoma even without high eye pressure. For those reasons, it’s important to have regular vision appointments.

You should contact an eye specialist if you notice any changes to your eyes, such as:

• Pain.
• Redness.
• Blurry vision.
• Loss of peripheral vision.
• Tunnel vision.
• Seeing halos around lights.

Sometimes, those symptoms are a sign of a serious eye condition.

Treatment for High Eye Pressure

If you have high eye pressure, your treatment may depend on your risk of developing glaucoma. If you are at low risk, your eye doctor may not prescribe any treatment right away and monitor your condition. If they do determine you need treatment, that could include:

• Prescription eye drops. These are usually the frontline treatment for high eye pressure. They can help lower the pressure in your eye, lowering your risk of glaucoma.
• Laser eye treatment. An eye doctor can use lasers to drain fluid from your eye and relieve pressure.
• Surgery. If medication and laser treatments don’t work, surgery to drain the fluid from your is another option.

If you have high eye pressure, it’s important to talk to your eye doctor about whether you’re a candidate for treatment. You also should keep up with regular eye visits. Sustained high eye pressure without treatment could lead to glaucoma, which can cause vision loss — including blindness.

At the UPMC Vision Institute, our experts specialize in diagnosing and treating eye conditions and diseases. To find eye and vision care near you, visit our website.

Editor's Note: This article was originally published on March 31, 2023, and was last reviewed on July 17, 2023.