What glaucoma actually damages

The optic nerve carries visual information from your retina to your brain, and glaucoma is fundamentally a disease of that nerve. It damages the nerve fibers and the ganglion cells that feed into them, and because this damage is not reversible, any vision lost to glaucoma is generally lost for good. This is different from a cataract, which clouds the lens but doesn't harm the optic nerve itself — the two conditions can occur together in the same eye, but they affect entirely different structures.

Glaucoma usually starts at the edges of your vision rather than the center. Peripheral vision narrows first, often so slowly and symmetrically between the two eyes that the brain compensates and the person notices nothing unusual. Only in more advanced stages does central vision become involved.

Eye pressure is the main — but not the only — risk factor

Inside the eye, a fluid called aqueous humor is constantly produced and drained to maintain a stable internal pressure. In most people with glaucoma, this drainage system doesn't work as efficiently as it should, and pressure inside the eye (intraocular pressure, or IOP) rises. Elevated IOP is the single most important and most common risk factor for optic nerve damage, and it's also the main thing treatment aims to control.

That said, eye pressure isn't the whole story. Some people develop optic nerve damage typical of glaucoma even with pressure readings in the normal range — a pattern sometimes called normal-tension glaucoma — while others have elevated pressure for years without ever developing nerve damage. This is one reason glaucoma is diagnosed by evaluating the optic nerve directly, not by pressure numbers alone.

The main types

The two broad categories are open-angle and angle-closure glaucoma. Open-angle glaucoma is by far the more common form: the drainage angle of the eye looks structurally normal, but fluid outflow is gradually and painlessly reduced, so the disease develops slowly over years. Angle-closure glaucoma is less common and involves the drainage angle becoming physically blocked; it can develop gradually as well, but it can also occur suddenly, causing a rapid pressure spike, eye pain, redness, blurred vision, and nausea — a true eye emergency that needs immediate care. Beyond these two main categories, there are other, rarer types linked to injury, inflammation, other eye diseases, or medications.

Why it's called "the silent thief of sight"

The hardest thing about glaucoma is that, in its early and even moderate stages, it usually causes no pain, no redness, and no obvious symptoms. Because vision loss starts at the periphery and progresses gradually, many people don't notice anything wrong until a significant — and by then irreversible — portion of their peripheral vision is already gone. By the time symptoms are noticeable without testing, meaningful damage has often already occurred.

This is exactly why glaucoma is a leading cause of irreversible blindness worldwide despite being, in most cases, manageable if caught early. Regular comprehensive eye exams — including eye pressure measurement and a direct look at the optic nerve, sometimes combined with visual field testing or imaging — are the main way glaucoma is caught before it causes noticeable vision loss. There's usually no early symptom to prompt you to book that appointment on your own; the exam has to come first.

How glaucoma is treated

There's currently no cure for glaucoma, and vision already lost to it typically cannot be restored. Treatment instead focuses on lowering intraocular pressure to slow or stop further optic nerve damage, preserving as much of your remaining vision as possible for as long as possible. Depending on the type and severity, this may involve:

  • Eye drops, usually the first line of treatment, which lower IOP by reducing fluid production or improving drainage. They're generally well tolerated but can cause side effects such as stinging, redness, or temporarily blurred vision.
  • Laser procedures, which can improve drainage of aqueous humor for certain types of glaucoma and are often effective at lowering pressure, sometimes reducing the need for drops.
  • Surgery, reserved for cases where drops and laser treatment aren't sufficient to control pressure, using various techniques to create or improve drainage pathways.

These approaches are often combined, and because glaucoma is a chronic, lifelong condition, treatment isn't a one-time event — it requires ongoing monitoring, periodic testing, and adjustment over time to keep pressure in a safe range.

Why glaucoma matters when you're planning cataract surgery

If you have glaucoma — or a family history of it — it's worth raising directly with your surgeon before you have cataract surgery, for a few practical reasons.

First, cataract surgery and glaucoma management are sometimes combined into a single procedure. Certain minimally invasive glaucoma surgery (MIGS) techniques can be performed at the same time as cataract removal, addressing both the cloudy lens and elevated eye pressure in one visit. Whether this is appropriate depends on your specific type and stage of glaucoma, which your ophthalmologist will assess.

Second, glaucoma is a significant factor in IOL selection. Glaucoma can already reduce contrast sensitivity — your ability to distinguish subtle differences between an object and its background — even when visual acuity looks fine on a standard eye chart. Diffractive multifocal and trifocal lenses split incoming light between multiple focal points, which further reduces contrast and can introduce glare or halos around lights. Stacking that trade-off on top of an optic nerve that's already compromised by glaucoma is generally avoided, which is why patients with glaucoma are usually steered toward monofocal or enhanced monofocal IOLs rather than multifocal designs. See how to think through this choice →

Third, having glaucoma doesn't change the fact that it needs its own ongoing care. Cataract surgery treats the lens; it does nothing to treat glaucoma itself. Regardless of which IOL you choose, your glaucoma should continue to be actively monitored and managed by an ophthalmologist, both before and after your cataract procedure.

A final note

Glaucoma is a serious condition, but it's also one of the more manageable causes of vision loss when it's caught early and treated consistently. The single most useful thing you can do is keep up with regular comprehensive eye exams, even when your vision feels fine — and if you're diagnosed with or suspect glaucoma, work directly with an ophthalmologist for diagnosis, treatment, and any decisions about cataract surgery or IOL choice. This page is educational only and isn't a substitute for a professional eye exam.