Open-angle glaucoma is often called the “silent thief of sight” because it gradually damages vision without warning signs until significant harm has occurred, making regular eye examinations the only reliable way to catch this common eye disease before permanent damage takes hold.

What Is Open-Angle Glaucoma?

Open-angle glaucoma is the most common type of glaucoma, an eye disease that damages the optic nerve—the vital structure that carries visual information from the eye to the brain. In this condition, the eye’s natural drainage system begins to malfunction, typically so slowly that people don’t notice anything wrong at first. The drainage angle where fluid should exit the eye appears open and normal, which is why it’s called “open-angle” glaucoma. However, deeper inside this drainage system, within a spongy tissue called the trabecular meshwork (the network of tiny channels that filter eye fluid), resistance builds up and prevents fluid from draining properly.^[1]

When the eye’s natural fluid, called aqueous humor (the clear fluid that nourishes the front part of the eye), cannot drain normally, it accumulates inside the eye. This buildup increases the pressure inside the eye, known as intraocular pressure or IOP (the fluid pressure inside the eyeball). Over time, elevated pressure damages the optic nerve, leading to vision loss that cannot be reversed. The damage typically affects peripheral vision first—the ability to see objects to the side while looking straight ahead—and gradually moves inward toward central vision.^[2]

What makes open-angle glaucoma particularly dangerous is its deceptive nature. The condition progresses slowly and painlessly, often over many years. Most people experience no symptoms in the early stages, and by the time they notice vision problems, significant and irreversible damage has already occurred. Without treatment, open-angle glaucoma can progress to complete blindness.^[1]

How Common Is Open-Angle Glaucoma?

Open-angle glaucoma represents a significant public health challenge worldwide. It accounts for more than 90 percent of all glaucoma cases in the United States, making it by far the most prevalent form of the disease. Approximately 2.5 million people in the United States have glaucoma, affecting about 3 percent of people older than 55 years. However, roughly half of those with the condition don’t know they have it because it develops without noticeable symptoms.^[6]

The disease is the second most common cause of legal blindness in the United States overall, but among Black Americans, it holds the unfortunate distinction of being the leading cause of legal blindness. About 120,000 Americans are blind as a result of glaucoma, creating substantial costs—approximately $1.5 billion per year—in disability benefits, lost tax revenues, and health expenses.^[6]

Certain populations face higher risks than others. The condition is more common in older adults, with risk increasing significantly with age. It typically affects people over 50 years old, though it can occur at any age. The disease usually affects both eyes, but the damage is typically asymmetric, meaning one eye is usually more affected than the other. This asymmetry makes the condition even harder to detect, as the stronger eye compensates for the weaker one, masking vision loss.^[2]

What Causes Open-Angle Glaucoma?

The eye has a built-in drainage system to manage the fluid it continuously produces. The ciliary body (a ring of tissue behind the iris) produces aqueous humor, which flows through the pupil and should drain out through the trabecular meshwork, a spongy network of channels in the drainage angle where the cornea meets the iris. In open-angle glaucoma, something goes wrong with this drainage process, even though the angle appears structurally normal and open.^[1]

Experts believe the problem lies within the trabecular meshwork itself. This tissue appears to develop an abnormality in its structure, similar to accelerated aging. The extracellular matrix—the material between cells—changes in ways that impede fluid flow. The number of cells in the trabecular meshwork may also decrease over time. These changes create resistance that prevents aqueous humor from draining properly, even though the entrance to the drainage system remains open.^[14]

In most cases of open-angle glaucoma, it isn’t clear what causes these changes in the drainage system. This is why the condition is called “primary” open-angle glaucoma—there’s no identifiable underlying cause. However, certain factors can contribute to the problem. The eye may produce too much fluid, overwhelming the drainage system’s capacity. Or the drainage channels may become clogged with cellular debris and abnormal protein deposits over time.^[5]

Some cases of open-angle glaucoma do have identifiable causes and are called “secondary” open-angle glaucoma. Known causative factors include eye trauma, inflammation inside the eye called uveitis, and steroid therapy. Steroids of any kind may contribute to elevated eye pressure, but topical eye drops and injections near the eye seem most likely to increase pressure. Other secondary causes include developmental abnormalities of the drainage system, scarring from infection, and toxic effects from detached iris pigment or abnormal protein deposits.^[6]

Elevated intraocular pressure is the major modifiable risk factor and the primary target of treatment. However, the relationship between pressure and damage is complex. Not everyone with high eye pressure develops glaucoma—more than two-thirds of people with elevated pressure (above 21 mm Hg) do not lose vision or develop optic nerve damage. Conversely, about 15 percent of people with glaucoma have consistently normal eye pressure yet still develop characteristic nerve damage and vision loss, a condition called normal-pressure glaucoma.^[6]

Who Is at Risk?

Several factors increase a person’s likelihood of developing open-angle glaucoma. Age is a significant risk factor—the condition primarily affects people over 50, and risk rises steadily as people get older. Among whites, those over 65 years are at increased risk, while among Black individuals, risk increases significantly after age 40.^[6]

Race and ethnicity play important roles in glaucoma risk. African Americans face substantially higher risk than people of other racial backgrounds, with prevalence rates about four times higher than whites. The disease also tends to develop at an earlier age in Black individuals and progresses more severely. Blindness from glaucoma is six to eight times more likely among Black people compared to whites. Hispanic populations also experience higher rates of open-angle glaucoma compared to non-Hispanic whites.^[14]

Family history significantly increases risk. People with a close relative who has glaucoma face higher chances of developing the condition themselves. This genetic connection suggests that inherited factors influence susceptibility to the disease, though specific genetic causes haven’t been fully identified.^[6]

Certain medical conditions are associated with increased glaucoma risk. People with diabetes have higher rates of open-angle glaucoma. Those with high blood pressure also face elevated risk. Severe nearsightedness, called myopia, is another risk factor. Additionally, people with thinner corneas—the clear front surface of the eye—are at increased risk. Corneal thickness matters because it can affect pressure measurements and may indicate structural differences in eye tissues that influence vulnerability to damage.^[5]

Vascular problems may also contribute to risk, particularly for normal-pressure glaucoma. People with conditions that affect blood flow, such as migraines or Raynaud syndrome (a disorder that causes reduced blood flow to fingers and toes), have higher rates of glaucoma. This suggests that inadequate blood supply to the optic nerve may play a role in nerve damage, especially when eye pressure is in the normal range.^[14]

What Are the Symptoms?

Open-angle glaucoma is particularly insidious because most people experience no symptoms until substantial vision loss has occurred. The disease is often discovered during routine eye examinations rather than because someone noticed a problem. This is one reason why regular eye check-ups are so important for detecting the condition early.^[7]

When symptoms do appear, they reflect the pattern of vision loss. Because damage typically begins in peripheral vision and progresses slowly inward, people may not notice problems with everyday activities at first. Early signs might include missing a step when walking downstairs because the bottom step isn’t visible in the affected area of peripheral vision. Someone might miss some letters in a word while reading, or have trouble seeing road signs while driving. Difficulty seeing contrast in low light conditions is another early sign.^[1]

The loss of peripheral vision creates specific patterns of blind spots that eye doctors can detect during testing. These visual field defects have descriptive names. A nasal step defect is a blind spot on the side of the visual field near the nose. An arcuate scotoma appears as an arc-shaped blind spot on the top or bottom of vision. A paracentral scotoma is a small, rounded blind spot just off-center. A temporal wedge defect creates a wedge-shaped dark area on the temple side of the visual field.^[1]

As open-angle glaucoma advances, it leads to progressively worsening tunnel vision—the sensation of looking through a narrow tube, with only central vision remaining while peripheral vision disappears. In advanced stages, even central vision can be affected. Vision loss from open-angle glaucoma is usually painless, which is another reason people don’t seek help until damage is extensive. However, some patients develop a complication called retinal venous occlusion (a blockage of veins in the retina) that can cause eye pain along with vision loss.^[1]

Most people with open-angle glaucoma do not experience eye pain from high eye pressure itself. This differs dramatically from acute angle-closure glaucoma, where eye pressure suddenly spikes, causing severe eye pain, headache, cloudy vision, and eye redness. In primary open-angle glaucoma, pressure typically increases gradually over time, so there’s no sudden spike that would trigger pain. The eyes don’t turn red, and central vision remains good until late stages, all of which contribute to the disease’s ability to progress unnoticed.^[7]

Can Open-Angle Glaucoma Be Prevented?

For primary open-angle glaucoma—the most common type—diet and exercise cannot prevent someone from developing the disease. The genetic and biological factors that make someone susceptible cannot currently be changed through lifestyle modifications. However, this doesn’t mean lifestyle is irrelevant. Certain habits and practices may help reduce risk or slow progression once the disease is diagnosed.^[20]

The most important preventive measure is regular eye examination. Early detection through screening is the best way to preserve vision, because treatment can slow or stop progression once glaucoma is found. People at higher risk—including Black individuals over 40, whites over 65, and anyone with a family history of glaucoma—should have comprehensive eye exams regularly. Even people without risk factors should have periodic eye examinations as they age.^[6]

For secondary causes of glaucoma, some prevention is possible. Wearing protective eyewear during activities that could injure the eyes can prevent trauma-related glaucoma. Managing conditions like diabetes and high blood pressure through medical care may help reduce glaucoma risk associated with these conditions. If steroids are necessary for medical treatment, discussing alternatives with a doctor or using the lowest effective dose for the shortest time may minimize risk of steroid-induced pressure elevation.^[20]

Certain dietary and lifestyle practices may support overall eye health, though they cannot prevent glaucoma. A diet rich in fruits and vegetables, particularly dark leafy greens and colorful produce, provides antioxidants that may benefit the optic nerve. Foods containing omega-3 fatty acids, such as fish, may also support eye health. Moderate aerobic exercise like walking, jogging, or swimming can help reduce intraocular pressure and improve blood flow to the optic nerve.^[16]

Stress management may also be beneficial. High stress levels can affect eye pressure, so practices like meditation and mindfulness might help. Recent studies have shown that regular meditation can lead to reductions in eye pressure in some patients. While not a substitute for medical treatment, stress reduction techniques offer a low-risk addition to glaucoma care.^[19]

How Does Glaucoma Damage the Eye?

Understanding how open-angle glaucoma damages the eye requires looking at the normal functioning of eye fluid and the optic nerve. The ciliary body continuously produces aqueous humor, which fills the front chambers of the eye, providing nutrients to tissues that don’t have blood vessels. This fluid should flow through the pupil and exit through the drainage angle, maintaining a healthy balance between fluid production and drainage.^[6]

In open-angle glaucoma, the drainage system malfunctions at the level of the trabecular meshwork. Even though the entrance to the drainage angle is open, fluid cannot pass through efficiently. This is similar to a clogged pipe beneath a sink drain—the drain opening looks clear, but deep in the pipe, a blockage prevents water from flowing freely. The backup of aqueous humor raises pressure inside the eye.^[4]

The optic nerve is particularly vulnerable to damage from elevated pressure. This nerve is made up of approximately one million nerve fibers called retinal ganglion cells (specialized nerve cells whose long fibers carry visual signals from the retina to the brain). At the point where the optic nerve exits the eye—called the optic disc or optic nerve head—these delicate nerve fibers can become pinched and compressed by increased pressure.^[6]

When pressure damages these nerve fibers, they die and cannot regenerate. The loss of nerve fibers causes progressive thinning of the neural rim—the ring of healthy tissue around the central depression of the optic nerve called the cup. As nerve fibers die, the cup enlarges, creating an increased cup-to-disc ratio that eye doctors can observe during examination. This characteristic change in optic nerve appearance is a hallmark of glaucoma.^[14]

The death of retinal ganglion cells creates permanent blind spots in the visual field. The pattern of vision loss typically follows the arrangement of nerve fibers in the retina. Peripheral nerve fibers are often affected first, which is why peripheral vision loss is the earliest symptom. As more nerve fibers die over time, blind spots expand and eventually merge, progressively narrowing the field of vision.^[2]

In normal-pressure glaucoma, damage occurs even without elevated pressure. Researchers believe that in these cases, the optic nerve may be unusually vulnerable to pressure that would be normal for most people, or that blood flow problems compromise the nerve’s health. Insufficient blood supply may deprive nerve fibers of oxygen and nutrients, making them more susceptible to damage. People with vascular disorders that affect blood flow, such as migraines or Raynaud syndrome, have higher rates of normal-pressure glaucoma, supporting this theory.^[14]

The progressive nature of the damage means that once nerve fibers are lost, they cannot be recovered. This is why early detection and treatment are so critical—the goal is to preserve remaining nerve fibers and prevent further loss. Treatment focuses on lowering intraocular pressure to a level that stops or slows progression, protecting the optic nerve from additional damage.^[2]