What Causes Glaucoma In The Eyes And Whos At Risk?

Glaucoma is not one disease. It is a group of eye conditions that damage the optic nerve, the bundle of nerve fibers that carries visual information from the eye to the brain. In most cases the damage is linked to increased pressure inside the eye, but pressure is not the whole story. Some people develop glaucoma with normal eye pressure, and some people with high pressure never develop it. The biggest risk factors are age, family history, and race or ethnicity — particularly Black, Hispanic, and Asian ancestry depending on the type.

What makes glaucoma dangerous is that it usually causes no symptoms until vision is already lost. The vision lost to glaucoma cannot be restored. That is why regular eye exams matter more for this condition than for almost any other.

What Causes Glaucoma In The Eyes And Whos At Risk?

Glaucoma happens when the optic nerve is damaged, most often because fluid in the eye cannot drain properly and pressure builds up. Risk rises with age, family history, certain ancestry groups, and several medical conditions.

The eye constantly produces a fluid called aqueous humor. It flows through the pupil into the front part of the eye and drains out through a tissue called the trabecular meshwork. When that drainage system becomes blocked or works poorly, fluid builds up and intraocular pressure rises. Normal eye pressure is generally considered to fall between 10 and 21 millimeters of mercury (mmHg).

High pressure alone does not define glaucoma. It is the damage to the optic nerve that does. Many people with pressures above 21 mmHg never develop glaucoma — a condition called ocular hypertension. Others develop optic nerve damage at pressures in the normal range, which is called normal-tension glaucoma. This is one of the genuinely non-obvious points about the disease: eye pressure is a major risk factor, not a diagnosis.

The exact reason optic nerve fibers die is still not fully understood. Research points to poor blood flow to the nerve, mechanical strain from pressure, and possibly immune or inflammatory processes. No single mechanism explains every case.

What Are The Different Types Of Glaucoma?

Glaucoma comes in several forms, and they behave very differently. The two main categories are open-angle and angle-closure.

Open-angle glaucoma is the most common form in the United States and in most of the world. The drainage angle where the iris meets the cornea is open, but the meshwork drains too slowly. It develops gradually over years and causes no pain.

Angle-closure glaucoma happens when the iris bulges forward and blocks the drainage angle. It can be chronic or acute. Acute angle-closure is a medical emergency. Pressure spikes rapidly, and symptoms include severe eye pain, headache, nausea, blurred vision, and seeing halos around lights. Anyone with these symptoms needs emergency care immediately.

Normal-tension glaucoma causes optic nerve damage even though eye pressure stays within the normal range. Its causes are less clear, and researchers have looked at factors such as blood flow to the optic nerve and underlying vascular conditions.

Secondary glaucoma develops as a result of another condition or event — eye injury, inflammation, long-term use of steroid medications, diabetes-related changes in the eye, or tumors. Congenital glaucoma is rare and is present at birth, usually from abnormal development of the drainage system.

Who Is Most At Risk Of Developing Glaucoma?

Some risk factors cannot be changed and some can. Knowing where you stand helps you decide how often to get checked.

The strongest established risk factors include:

• Age. Risk rises steadily after age 40 and climbs more sharply after 60.
• Family history. Having a parent or sibling with glaucoma raises your risk substantially. A first-degree relative with the condition is one of the most significant risk factors known.
• Race and ethnicity. Black adults have a higher risk of open-angle glaucoma, and it tends to appear earlier and progress faster. Hispanic and Latino adults also face elevated risk. People of Asian descent have a higher risk of angle-closure glaucoma. Everyone in these groups should discuss screening timing with an eye care professional.
• High eye pressure. Measured pressure above the normal range is a leading risk factor, though as noted, it does not equal glaucoma.
• Thin corneas. A thin central cornea is linked to higher glaucoma risk, which is why corneal thickness is sometimes measured during evaluation.
• Severe nearsightedness. High myopia is associated with increased risk.
• Diabetes, high blood pressure, and poor circulation. These conditions are associated with higher risk, though the relationships are complex and not fully settled.
• Long-term steroid use. Steroid eye drops, pills, and even some inhaled or topical steroids can raise eye pressure in some people.
• Eye injury or certain eye surgeries. Trauma and some procedures can disrupt normal drainage.

Risk factors stack. A 65-year-old with a parent who had glaucoma and elevated eye pressure is in a very different position than a 45-year-old with none of these factors.

Why Do So Many People Not Know They Have Glaucoma?

Open-angle glaucoma is silent in its early stages. There is no pain, no redness, and no noticeable change in vision until a significant portion of the optic nerve is already damaged.

Vision loss typically begins in the peripheral field — the edges of what you can see. The brain fills in missing information so smoothly that most people do not notice the loss. Central vision, the sharp part used for reading and recognizing faces, is usually affected late. By the time someone notices a problem, substantial and permanent damage may already exist.

This is why glaucoma is sometimes called the “sneak thief of sight.” The label is not marketing. It reflects the actual clinical pattern of the disease.

There is no way to detect open-angle glaucoma at home. Checking eye pressure requires equipment. Examining the optic nerve requires a dilated eye exam. Visual field testing maps peripheral vision. Optical coherence tomography (OCT) can measure the thickness of the nerve fiber layer. None of these can be replaced by noticing symptoms, because early on there are none.

How Is Glaucoma Diagnosed?

Diagnosis rests on a combination of eye pressure measurement, optic nerve examination, and visual field testing. No single test confirms glaucoma on its own.

A comprehensive dilated eye exam is the core of evaluation. The eye care professional measures pressure, examines the drainage angle, and looks directly at the optic nerve for signs of damage such as cupping, where the center of the nerve appears hollowed out.

Visual field testing checks peripheral vision. Because glaucoma damages side vision first, this test can detect loss that the person has not noticed. Repeating it over time shows whether vision is stable or worsening.

Optic nerve imaging, including OCT, measures nerve fiber thickness and can detect thinning before visual field loss appears. Corneal thickness measurement helps interpret pressure readings — a thick cornea can make pressure read falsely high, and a thin cornea can make it read falsely low.

Because glaucoma is progressive and often slow, diagnosis sometimes requires monitoring over months rather than a single visit. A single normal exam does not rule out future risk.

Can Glaucoma Be Prevented?

There is no proven way to prevent glaucoma. There are, however, well-established ways to catch it early and to slow its progression once it is found.

Regular comprehensive eye exams are the most reliable approach. The American Academy of Ophthalmology recommends a baseline dilated eye exam by age 40 for adults with no risk factors, with follow-up intervals determined by the eye care professional. People with risk factors — family history, Black or Hispanic ancestry, diabetes, or elevated pressure — should discuss earlier or more frequent screening with their eye doctor. Screening intervals are individualized, not fixed.

Once glaucoma is diagnosed, lowering eye pressure slows progression. This is one of the best-supported findings in ophthalmology. Treatment usually begins with prescription eye drops, and options include laser therapy and surgery. Some people with elevated pressure but no nerve damage are offered treatment to reduce the chance of developing glaucoma, a decision made case by case.

What does not have strong evidence: dietary supplements marketed for eye pressure, eye exercises, and lifestyle changes promoted as glaucoma prevention. Some research has looked at caffeine, exercise, and sleep position, but none of these substitutes for medical evaluation and treatment. Anyone with glaucoma should talk to their eye doctor before making changes that could affect eye pressure.