Glaucoma is a group of eye conditions that damage the optic nerve, the cable connecting your eye to your brain. It’s one of the leading causes of irreversible blindness worldwide, affecting an estimated 80 million people over age 40 as of 2024. The condition usually develops slowly, stealing peripheral vision so gradually that most people don’t notice anything is wrong until significant damage has already occurred.
How Glaucoma Damages Your Vision
Your eye constantly produces a clear fluid called aqueous humor, which nourishes internal structures and maintains the eye’s shape. Normally this fluid drains out through a meshwork of tissue near the front of the eye at the same rate it’s produced. When drainage slows or gets blocked, fluid builds up and pressure inside the eye rises. That pressure pushes against the optic nerve head, the point where roughly 1.2 million nerve fibers exit the back of the eye on their way to the brain.
The damage happens in stages. Rising pressure first disrupts the transport system within nerve fibers, blocking the flow of survival signals that retinal ganglion cells (the neurons that form the optic nerve) need to stay alive. Without those signals, the cells begin to shrink, their branching connections wither, and they eventually die through a programmed self-destruction process. As nerve fibers are lost, the optic nerve head develops a characteristic “cupping,” a hollowing that your eye doctor can see during an exam. The surrounding tissue also remodels, with scar-like deposits filling in where healthy nerve fibers once were.
This nerve damage translates directly into vision loss. Peripheral vision goes first because the nerve fibers serving your side vision are most vulnerable to pressure changes. You lose it in patchy blind spots that slowly expand. Because your brain compensates for the gaps and your central vision stays sharp until late stages, many people have no idea anything is wrong.
Types of Glaucoma
Open-Angle Glaucoma
Primary open-angle glaucoma accounts for the large majority of cases. The drainage angle where fluid exits the eye looks structurally normal, but the meshwork itself resists fluid flow, like a clogged filter. Pressure builds gradually over months and years, and vision loss creeps in without symptoms. This is the form most people mean when they say “glaucoma.”
A notable subtype is normal-tension glaucoma, where the optic nerve sustains damage even though eye pressure stays at or below 21 mmHg, the traditional upper limit of normal. In these cases, poor blood flow to the optic nerve appears to be a major factor. People with normal-tension glaucoma are more likely to have conditions like low blood pressure, migraines, and problems with blood vessel regulation. It’s more common in people of Asian descent.
Angle-Closure Glaucoma
In angle-closure glaucoma, the iris physically blocks the drainage angle. It comes in two forms. The acute type is a medical emergency: the angle slams shut, pressure spikes rapidly, and you experience sudden eye pain, headache, nausea, blurred vision, and halos around lights. The chronic type involves a slow, partial narrowing of the angle that raises pressure over time, similar in stealth to open-angle glaucoma. People with shallower eye anatomy, including a thicker lens or shorter eyeball, are at higher risk.
Who Is Most at Risk
Age is the strongest non-modifiable risk factor. Glaucoma prevalence climbs steeply after 40, and global rates are projected to rise from 2.8% of people over 40 today to 3.5% by 2060 as populations age, potentially affecting nearly 193 million people worldwide.
Race and ethnicity matter significantly. In the United States, the Baltimore Eye Survey found that glaucoma prevalence in people of African descent was six times higher than in white populations in some age groups. Open-angle glaucoma is also six times more likely to cause blindness in Black Americans, is diagnosed about 10 years earlier, and progresses faster. Elevated eye pressure appears roughly 12 years sooner in this group. Hispanic and Latino populations also face higher-than-average risk.
Family history raises your odds substantially. If a parent or sibling has glaucoma, you’re more likely to develop it yourself. Other risk factors include severe nearsightedness (high myopia), which is expected to contribute over 6 million additional cases by 2060, thin corneas, and previous eye injuries.
Why Early Detection Matters
The core problem with glaucoma is that lost vision cannot be restored. Nerve fibers that die are gone permanently. Because open-angle glaucoma produces no pain and no noticeable vision changes until it’s advanced, the only reliable way to catch it early is through a comprehensive eye exam. Many people discover they have glaucoma during a routine visit for a new glasses prescription.
What Happens During a Glaucoma Exam
A complete glaucoma evaluation typically involves six tests, none of them painful. Tonometry measures the pressure inside your eye, usually by gently touching the eye’s surface with a tiny instrument after numbing drops are applied. Normal eye pressure averages around 14 to 15 mmHg, with a standard range of roughly 9 to 20 mmHg. Pressures above 21 mmHg have traditionally raised a red flag, though plenty of people develop glaucoma below that number.
A visual field test maps your peripheral vision by having you stare straight ahead and click a button each time you notice a small light appear off to the side. Spots you miss may indicate areas of damage. Optical coherence tomography (OCT) scans the optic nerve in fine detail, creating a digital map your doctor can compare over time to detect thinning. During a dilated eye exam, your doctor uses drops to widen your pupil and examines the optic nerve directly, looking for cupping or color changes.
Two additional tests round out the picture. Pachymetry measures corneal thickness with a small probe, because thinner corneas can make pressure readings appear artificially low. Gonioscopy uses a special lens to inspect the drainage angle, which tells your doctor whether you have open-angle or angle-closure disease.
How Glaucoma Is Treated
All current treatments work by lowering eye pressure, the only modifiable risk factor. Lowering pressure slows or halts nerve damage in most people, even in normal-tension cases. Treatment doesn’t recover lost vision; it protects what remains.
Eye Drops
Most people start with prescription eye drops used once or twice daily. The most commonly prescribed type increases fluid drainage out of the eye through an alternative pathway, effectively opening a second exit route. Another class reduces the amount of fluid the eye produces in the first place. A third option does both: it decreases fluid production while also improving drainage. Your doctor may combine classes if one alone isn’t enough. The main challenge with drops is consistency. They only work if you use them every day, and studies show that adherence tends to slip over time.
Laser Procedures
Laser treatment can be offered as a first-line option or when drops aren’t sufficient. For open-angle glaucoma, a laser targets the drainage meshwork to help it filter fluid more efficiently. For angle-closure glaucoma, a laser creates a tiny hole in the iris to relieve the blockage. Both are done in an office setting and take just a few minutes.
Surgery
When medications and laser treatment aren’t enough, surgery creates a new drainage pathway for fluid to leave the eye. Traditional procedures like trabeculectomy have been the standard for decades but involve significant tissue disruption and a longer recovery.
A newer category called minimally invasive glaucoma surgery (MIGS) uses tiny devices inserted through small incisions inside the eye. These cause less tissue disruption, carry a more favorable risk profile, and allow faster recovery. Some devices work by opening a direct channel into the eye’s natural drainage canal. Others route fluid into a space beneath the outer wall of the eye, bypassing the clogged meshwork entirely. A third type drains fluid under the conjunctiva, the clear tissue covering the white of the eye. MIGS is typically offered to people with mild to moderate open-angle glaucoma and is often combined with cataract surgery. For advanced or aggressive disease, traditional surgery remains the more powerful option.
Living With Glaucoma
Glaucoma is a lifelong condition. Once you’re diagnosed, you’ll need regular monitoring, typically every three to six months, so your doctor can track pressure trends, scan for optic nerve changes, and adjust treatment. Many people maintain excellent functional vision for decades with consistent treatment. The biggest threat isn’t the disease itself so much as the temptation to skip drops or miss appointments when you feel fine, because you will feel fine. The damage is silent right up until it isn’t.