Most people with glaucoma have no symptoms at all, especially in the early stages. The most common form, open-angle glaucoma, causes no pain and no noticeable vision changes until significant, irreversible damage has already occurred. Globally, at least half of all open-angle glaucoma cases go undetected, and in developed countries, roughly 7 out of 10 people with the condition don’t know they have it. The only reliable way to catch glaucoma early is through a comprehensive eye exam.
Why You Probably Won’t Feel It
Open-angle glaucoma, which accounts for the vast majority of cases, develops slowly over years. It gradually damages the optic nerve and eats away at your peripheral (side) vision first. Because your brain compensates for small gaps in your visual field, and because the loss happens so gradually, most people don’t notice anything is wrong. By the time you realize your side vision has narrowed, the damage is permanent. There is no way to restore vision that glaucoma has already taken.
This is what makes the condition so dangerous. It earned the nickname “the silent thief of sight” for good reason. You can have elevated eye pressure and progressive nerve damage for years with perfectly clear central vision and no discomfort whatsoever.
Symptoms That Do Appear
There is one form of glaucoma that announces itself loudly. Acute angle-closure glaucoma happens when the drainage system inside your eye becomes suddenly blocked, causing pressure to spike rapidly. Symptoms come on fast and include:
- Severe eye pain
- A bad headache, often on the same side as the affected eye
- Nausea or vomiting
- Blurred vision
- Halos or colored rings around lights
- Redness in the eye
This is a medical emergency. If you experience a sudden onset of severe eye pain with blurred vision and halos, go to an emergency room immediately. Without prompt treatment, acute angle-closure glaucoma can cause permanent vision loss within hours.
With chronic open-angle glaucoma, the first thing you might eventually notice is difficulty seeing things off to the side while looking straight ahead, or bumping into objects you didn’t see. Some people describe it as looking through a tunnel. But again, by the time these changes are obvious to you, you’ve likely lost a substantial amount of vision.
Normal Eye Pressure Doesn’t Rule It Out
Many people assume that if their eye pressure is normal, they’re in the clear. That’s not always true. Normal eye pressure falls between 10 and 20 mmHg, and most glaucoma cases involve pressure above that range. But a form called normal-tension glaucoma causes the same optic nerve damage and vision loss at pressures that never exceed 21 mmHg.
Patients with normal-tension glaucoma tend to have optic nerves that are more vulnerable to damage even at lower pressures. Their visual field loss often appears closer to central vision and can be more severe than what the nerve damage alone would suggest. Diagnosing this form requires ruling out other conditions and sometimes tracking eye pressure at different times of day to confirm that hidden spikes aren’t occurring. This is one reason a pressure check alone isn’t a complete glaucoma screening.
How Glaucoma Is Actually Diagnosed
A comprehensive eye exam for glaucoma involves several tests, most of them quick and painless. Your eye doctor will typically perform some combination of the following:
- Eye pressure check (tonometry): After numbing drops, a tiny instrument gently touches the surface of your eye to measure the pressure inside. It takes only a few minutes and doesn’t hurt.
- Dilated eye exam (ophthalmoscopy): Drops widen your pupil so the doctor can shine a light into the back of your eye and examine the optic nerve directly, checking its color, shape, and size for signs of damage.
- Visual field test (perimetry): You look into a machine and respond when you see small lights flickering in different areas of your vision. This maps out any blind spots or areas of reduced sensitivity.
- Angle exam (gonioscopy): A special lens is placed on your numbed eye to examine the drainage angle where your cornea meets your iris. This tells the doctor whether the angle is open or blocked, which determines the type of glaucoma.
- Corneal thickness measurement (pachymetry): A small probe touches your numbed eye to measure how thick your cornea is. Thinner corneas can make pressure readings less accurate and are themselves a risk factor.
Many eye doctors now also use a scan called optical coherence tomography, which takes a detailed cross-sectional image of the nerve fiber layer at the back of your eye. This technology can detect thinning of that nerve fiber layer before any vision loss shows up on a visual field test, making it one of the most valuable tools for catching glaucoma at its earliest stage. The structural changes in early glaucoma are often so subtle that they’re nearly impossible to spot with a standard exam alone.
Who Is Most at Risk
Certain factors significantly raise your likelihood of developing glaucoma. Age is the biggest one. Risk climbs steadily after 40, and rises sharply after 60. Race matters too: Black individuals are roughly 2.4 times more likely to develop glaucoma compared to white individuals, and they tend to have higher baseline eye pressures. People of East Asian and Hispanic descent also face elevated risk.
Family history is another strong predictor. If a parent or sibling has glaucoma, your own risk is substantially higher. Other risk factors include severe nearsightedness, a history of eye injury, long-term use of corticosteroid medications (especially eye drops), and having thinner corneas. Diabetes and high blood pressure may also contribute.
When and How Often to Get Checked
The American Academy of Ophthalmology recommends a baseline comprehensive eye exam at age 40 for everyone, even if you have no symptoms and no known risk factors. After that baseline, the recommended frequency depends on your age:
- Ages 40 to 54: Every 2 to 4 years
- Ages 55 to 64: Every 1 to 3 years
- Age 65 and older: Every 1 to 2 years
If you have risk factors like family history, African ancestry, or previous eye injuries, your eye doctor will likely recommend starting earlier and screening more frequently. A routine vision check at an optician’s office that only tests your prescription is not the same as a comprehensive eye exam. You need the full workup, including pressure measurement and optic nerve evaluation, to screen for glaucoma.
What Early Detection Changes
Glaucoma can’t be cured, and vision already lost can’t be recovered. But when caught early, treatments can slow or stop further damage. Most people start with prescription eye drops that lower eye pressure. If drops aren’t enough, laser procedures or surgery can improve drainage from the eye. The goal of every treatment is the same: reduce the pressure on your optic nerve to prevent additional vision loss.
People diagnosed early and treated consistently often keep functional vision for their entire lives. People diagnosed late, after significant nerve damage has accumulated, have far fewer options and a much higher chance of serious vision impairment. The difference between these two outcomes is almost entirely a matter of when the condition was found. Since you won’t feel glaucoma developing, the exam is the only thing standing between you and preventable blindness.