What are glaucoma tests?

Glaucoma tests are eye tests that help diagnose glaucoma. Glaucoma is a group of eye diseases that can damage a nerve in the back of your eye called the optic nerve. This nerve connects your eyes to your brain, allowing you to see. Damage to the optic nerve can cause vision loss and blindness. Glaucoma tests can help find the disease before you know you have it, so you can start treatment to protect your eyes against serious vision loss.

Researchers aren't sure exactly what causes the most common types of glaucoma. But having high fluid pressure in one or both eyes increases your risk for the disease. Your eyes are always making fluid that nourishes the tissues inside the eye. The fluid leaves your eyes through a drainage system with openings in the space where your iris (the colored part of your eyes) and your cornea (the clear front layer of your eyes) meet.

The pressure inside of each eyes stays in a healthy range when there's a balance between how much fluid your eye makes and how much drains out of your eye. If the drainage system becomes clogged or blocked, fluid can't drain at a normal rate. If your eye makes new fluid faster than it can drain, the fluid backs up, which increases the pressure in your eye. The high pressure may damage the optic nerve and lead to serious vision problems.

There are several types of glaucoma. The main types are:

• Open-angle glaucoma, also called primary open-angle glaucoma. This is the most common type. It's called "open" because the canals that lead to your eye's drainage system are open. But deeper inside the drainage system, clogs develop. These clogs slow the fluid drainage.

  Open-angle glaucoma tends to affect both eyes. In the early stages, Most people don't have any symptoms or vision changes. But without treatment, peripheral (side) vision is usually lost first.

• Closed-angle glaucoma, also called angle-closure or narrow-angle glaucoma. In this uncommon type of glaucoma, the canals that drain fluid from your eye are "closed" because your iris covers them. This condition usually affects one eye at a time. There are two main types:
  • Acute closed-angle glaucoma is a medical emergency. No fluid can drain out of your eye, so eye pressure increases suddenly. This causes eye pain, blurry vision, and other symptoms. Without prompt treatment, it can cause blindness in a few days.
  • Chronic closed-angle glaucoma develops slowly over time. You may not have any symptoms. Or you may have symptoms such as eye discomfort, blurry vision, redness, or headaches. The symptoms often get better with sleep. Without treatment, vision loss develops slowly.

What are they used for?

Glaucoma tests are used to screen for and diagnose glaucoma. If glaucoma is diagnosed early, treatment may help slow or prevent vision loss.

Why do I need glaucoma testing?

Anyone can get glaucoma. To protect your vision, it's important to be tested for glaucoma before symptoms start. When to start testing and how often to get tested will depend on your risk for glaucoma.

Your risk for glaucoma may be high if you:

• Are over age 60. Glaucoma is much more common in older people. The risk is especially high if you are an older Hispanic/Latino American.
• Are an African American over age 40. Glaucoma is the leading cause of blindness in African Americans.
• Are an Asian American. Asian Americans have a higher risk for getting a type of open-angle glaucoma called normal-pressure or normal-tension glaucoma. With this condition, optic nerve damage begins when eye pressure is normal or a little higher than normal. But treatments that lower eye pressure often help.
• Have a family history of glaucoma. You can inherit certain types of glaucoma from your parents.
• Have certain medical conditions. They include diabetes and high blood pressure.

If your risk of glaucoma is high, ask your health care provider or eye care specialist when you should start getting tested and how often you need to have your eyes checked. Getting an eye exam with glaucoma testing by age 40 can help catch glaucoma and other eye diseases early.

If you have symptoms of acute closed-angle glaucoma, you need to be tested for glaucoma right away to prevent blindness. Symptoms may start suddenly and be severe. They include:

• Blurry vision
• Severe eye pain
• Red eyes
• Colored halos around lights
• Nausea or vomiting
• Headache

If you have glaucoma, you may need regular testing to monitor your condition and check whether your treatment is working.

What happens during a glaucoma test?

Glaucoma tests are done as part of a comprehensive (complete) eye exam. A complete eye exam checks both your vision and your eye health. These exams can be done by:

• An ophthalmologist, a medical doctor who specializes in preventing, diagnosing, and treating all types of eye disease, including doing eye surgery.
• An optometrist, a health care professional who specializes in diagnosing and treating vision problems and certain eye disorders.

If you're unsure which type of eye specialist should check you for glaucoma, talk with your provider.

Glaucoma tests check different parts of your eyes and vision, including:

• Your eye pressure. There are a few ways to measure eye pressure using tonometry tests:
  • Air-puff test. You'll rest your chin on a machine and your eye care specialist will blow a puff of air into your eye. This quick and painless test is used as part of a routine glaucoma screening. If the results show that your eye pressure is high, your provider will do other eye-pressure tests to get a more accurate measurement.
  • Applanation tonometry. Your provider will numb your eyes with drops before measuring your eye pressure using one of these methods:
    • You'll rest your chin on a special magnifying device called a slit lamp. Your eye care specialist will examine your eye through the slit lamp while gently pressing a special tool on your eye to test the pressure.
    • Your eye care specialist will gently press a handheld device against your eye. The device measures your eye pressure.
• The thickness of your corneas. The cornea is the clear outer layer at the front of your eye. Its thickness can affect the results of your eye-pressure measurements. If your eye pressure is high, a pachymetry test gives your eye care specialist more information about how high it may be. To do the test, your eye will be numbed with drops and your eye care specialist will place a small device on your cornea to measure the thickness.
• Your optic nerves. Your eye care specialist will do a dilated eye exam to look for damage to your optic nerve. This exam is part of a routine glaucoma check-up. It's also called ophthalmoscopy. You'll be given eye drops that widen (dilate) your pupils (the openings that let light into your eyes). You'll look straight ahead while your eye care specialist looks into your eye using a device with a light and magnifying lens.
• Your peripheral (side) vision. A visual field test, also called perimetry, measures how well you can see using your side vision. There are different ways to do the test. In general, you'll look straight ahead. Objects will be shown off to the sides of your vision. Without moving your eyes, you'll say when you can see the objects.
• The canals where fluid drains out of your eyes. If your eye care specialist thinks you have glaucoma, you may have a gonioscopy to see if your eye's drainage system is opened (open-angle glaucoma) or closed (close-angle glaucoma). Your eyes will be numbed with drops. Then your provider will hold a special contact lens on your eye. The lens has a mirror that shows the area where fluid drains out of your eye.

Some eye care specialists may use other tests to check for glaucoma, such optical coherence tomography (OCT). This test makes images of the back of your eye that can show damage to the optic nerve.

Will I need to do anything to prepare for a glaucoma test?

If you wear glasses or contact lenses, bring them with you. Bring sunglasses to wear after your exam in case your eyes are sensitive to light. Also, plan to have someone take you home because your vision may be blurry.

Are there any risks to the tests?

There is no risk to having glaucoma testing. Some of the tests may feel a bit uncomfortable. If your eyes were dilated, you may have blurry vision and be light sensitivity for a few hours.

What do the results mean?

If your test results aren't normal, you may have glaucoma or a high risk for developing glaucoma.

If your eye care specialist diagnoses glaucoma, your treatment will depend on the type of condition you have. Treatment won't cure the disease or restore any vision you have already lost. But it can prevent more vision loss. Your eye care specialist may recommend one or more treatments, such as:

• Medicines to lower eye pressure or reduce the amount of fluid your eye makes.
• Eye surgery or laser therapy to improve fluid drainage from the eye.

If an optometrist examined your eyes, you may be referred to an ophthalmologist for more testing and/or treatment.

You will probably have more glaucoma testing to see if the treatment is helping. Ask your eye care specialist to explain your test results and be sure to find out how often you should have your eyes checked.

Learn more about laboratory tests, reference ranges, and understanding results.