Glaucoma Testing Explained: The Tests in a Routine Eye Exam

Published October 1, 2026 · By Dr. Lu Eye Care · 5 min read · Eye health

Glaucoma is sometimes called a silent thief of sight. It damages the optic nerve gradually, usually starting with side vision, and most people do not notice any change until the disease is advanced. Because vision lost to glaucoma cannot be restored, finding it early through testing is essential. This guide explains the tests your eye doctor may use and what the results mean.

What glaucoma is

Glaucoma is a group of eye diseases that damage the optic nerve, the cable of nerve fibers that carries visual information from the eye to the brain. Higher pressure inside the eye is the main known risk factor, but glaucoma can also occur at normal pressure. The most common form in the United States, open-angle glaucoma, develops slowly and painlessly. A less common form, angle-closure glaucoma, can come on suddenly and is an emergency.

Glaucoma is a leading cause of irreversible blindness worldwide. Treatment with eye drops, laser procedures or surgery can slow or stop further damage, but it cannot bring back vision that has already been lost.

Why one test is not enough

No single measurement can confirm or rule out glaucoma. Some people have high eye pressure for years without nerve damage, while others develop glaucoma with pressure in the normal range. That is why eye doctors combine several tests and compare results over time. A routine comprehensive exam includes basic glaucoma screening; if anything looks suspicious, more detailed testing follows.

Tonometry: measuring eye pressure

Tonometry measures intraocular pressure in millimeters of mercury (mmHg). Common methods include:

• Non-contact tonometry, the familiar puff of air.
• Applanation tonometry, in which a small probe gently touches the numbed surface of the eye during the slit lamp exam. It is considered the standard for accuracy.
• Rebound tonometry, a handheld device that lightly taps the eye, often without drops.

Pressure between about 10 and 21 mmHg is usually considered within the normal range, but what matters is how your pressure relates to the health of your optic nerve. Pressure also varies through the day, so a single reading is only part of the picture.

Optic nerve examination

During a dilated exam, the doctor looks directly at the optic nerve head where it leaves the eye. Glaucoma causes a gradual loss of nerve tissue, which enlarges the central depression called the cup. Doctors describe this with the cup-to-disc ratio and watch for thinning of the rim, asymmetry between the two eyes, and small hemorrhages at the edge of the nerve. Photographs make it easier to compare from year to year.

OCT scan

Optical coherence tomography (OCT) uses light to create detailed cross-sectional images of the retina and optic nerve. For glaucoma, it measures the thickness of the retinal nerve fiber layer and other structures, and compares the results with a reference database. OCT can show thinning before any vision loss is detectable, which makes it especially useful for people who are at risk or being monitored.

Visual field test

A visual field test, or perimetry, maps your side vision. You look at a central target and press a button whenever you see a small light appear somewhere in your peripheral vision. Glaucoma typically produces characteristic patterns of missed spots. The test takes several minutes per eye and often becomes more reliable after the first attempt, so a repeat test may be ordered to confirm results.

Pachymetry and gonioscopy

• Pachymetry measures the thickness of the cornea. A thinner cornea can make pressure readings appear lower than they are and is itself associated with higher glaucoma risk.
• Gonioscopy uses a special contact lens to view the drainage angle of the eye, where fluid exits. It shows whether the angle is open or narrow, which helps classify the type of glaucoma and identify people at risk of angle closure.

Who is at higher risk?

• People over 60
• Anyone with a family history of glaucoma
• Black adults, particularly over age 40, and Hispanic and Latino adults as they get older
• People of Asian descent, who have a higher risk of angle-closure glaucoma
• People with diabetes, high nearsightedness or high eye pressure
• Long-term users of steroid medications, including steroid eye drops
• People who have had an eye injury

If you have risk factors, your eye doctor may recommend more frequent exams; see how often you should get an eye exam. People with diabetes should also read our guide to diabetic eye exams.

If you are told you are a "glaucoma suspect"

This label means one or more findings, such as higher pressure, a suspicious-looking optic nerve or a family history, call for monitoring, but glaucoma has not been confirmed. Your doctor will usually gather baseline OCT and visual field tests and repeat them over time to look for change. Keeping these appointments, and taking your records with you if you change doctors, is important. Our guide on requesting eye care records explains how.

If glaucoma is diagnosed

Treatment aims to lower eye pressure to a level that protects the optic nerve. Common approaches include prescription eye drops used every day, laser procedures that help fluid drain from the eye, and surgery when other treatments are not enough. Glaucoma treatment is usually lifelong, and it only works if it is followed consistently. Tell your doctor if drops cause side effects or are hard to use, because there are often alternatives. Regular follow-up testing shows whether the treatment is keeping the disease stable.

Warning signs of acute angle-closure glaucoma

Seek emergency care right away for sudden severe eye pain, a red eye, blurred vision, halos around lights, headache, and nausea or vomiting. These can be signs of a sudden rise in eye pressure that can damage vision within hours.

Bottom line

Glaucoma testing combines eye pressure, an optic nerve exam, imaging and visual field testing to find damage early. Regular comprehensive eye exams are the best protection, especially if you are over 60 or have other risk factors. Learn what else happens at your visit in what to expect during a comprehensive eye exam.

This article is general health information and is not a substitute for an examination or personal advice from a licensed eye care professional. If you have sudden vision changes, eye pain, or new floaters or flashes, seek care promptly.