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Open-Angle Glaucoma
Open-angle glaucoma steals your peripheral vision silently โ€” no pain, no warning, no early symptom you'd think to mention. It's the leading cause of irreversible blindness worldwide, and in developed countries roughly half the people who have it don't yet know. The thing that catches it is a comprehensive eye exam: an eye-pressure reading plus a careful look at the optic nerve, repeated on a schedule that tightens with age. Catch it early, and lowering eye pressure cuts the rate of further vision loss roughly in half across half a dozen landmark trials. Miss it long enough, and the field you've lost doesn't come back.
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This is a settled corner of medicine: treatment works, and the binding constraint is detection. A comprehensive eye exam runs $50 to $200, is often covered by insurance, and takes under an hour. The exam itself is the whole action โ€” once a year or every couple, depending on age and risk. The vision you lose in years you should have been on the calendar does not come back.

How the disease actually works

The eye constantly makes a clear fluid called aqueous humor and constantly drains it through a sieve-like tissue near the front called the trabecular meshwork. In open-angle glaucoma the sieve clogs gradually โ€” the angle between iris and cornea stays anatomically open (hence "open-angle"), but flow resistance climbs Weinreb 2014. Fluid backs up. Pressure inside the eye rises. That pressure presses on the back of the eye where the optic nerve โ€” the cable carrying every visual signal from your retina to your brain โ€” exits through a perforated plate of collagen called the lamina cribrosa. The nerve fibers get pinched and starved. They die. They do not grow back.

The first place the damage shows up is the periphery, in patterns the brain papers over for years: arcs of missing vision above and below the gaze, a step in the nasal field, a paracentral blind spot you'd never spot on your own. Late in the disease the central vision goes too. By the time someone notices a chunk of their world missing, the nerve fibers that used to map it are already gone.

Eye pressure is the cause of glaucoma the way speeding is the cause of crashes โ€” usually, mostly, on average, but not always. Roughly a third of open-angle glaucoma cases worldwide happen at eye pressures inside the "normal" range, called normal-tension glaucoma; the mechanical properties of that perforated plate of collagen and the blood supply to the optic nerve matter alongside pressure itself Tham 2014. But pressure is the only lever the treatment can pull, and pulling it works.

Does treatment actually work

This is one of the most replicated treatment claims in adult medicine. Six trials, four decades, every major eye-care guideline aligned: lowering eye pressure slows glaucomatous vision loss by roughly half.

What no trial has shown: that anything reverses damage already done. Treatment slows the rate of further loss. It does not give back the visual field that's already gone. That asymmetry is what makes detection the load-bearing part of the whole problem.

Who's actually at higher risk

Risk isn't evenly distributed across adults. Five factors do most of the work:

  • Age. Prevalence is about half a percent in adults aged 40 to 49 and roughly seven percent by the late 70s Tham 2014. A 75-year-old is roughly fifteen times as likely to have glaucoma as a 45-year-old.
  • African ancestry. Glaucoma is roughly four times as common in adults of African descent as in adults of European descent, with onset about a decade earlier and faster progression once diagnosed. The Baltimore Eye Survey found around 5% of Black American adults with glaucoma at exam, against about 1% of White American adults across age strata Sommer 1991.
  • Family history. A parent or sibling with glaucoma raises your risk roughly three- to four-fold over the population baseline; siblings in particular run something like a 10% lifetime risk.
  • Thin corneas and high myopia. A thin cornea (under 555 micrometres; measured during the exam) and severe nearsightedness both independently raise risk and were identified in the OHTS prediction model Kass 2002.
  • Previous noted elevated eye pressure. Even if past exams just said "borderline" or "watch this," you're in a higher-risk pool.

If two or more of these apply to you, the higher-frequency exam cadence in the section below applies from your 40s, not your 60s.

If you keep skipping the exam

The disease is silent, so the early years feel like nothing. Years before vision loss is something you'd report to a doctor, the periphery starts thinning โ€” a friend at a barbecue waves at you and you turn before you realise you sensed it; you bump into the corner of a doorway you've passed a thousand times. The brain absorbs it as you-being-tired.

By your late 60s or early 70s, if the disease has been advancing untreated, the pattern is recognisable in retrospect. The book you read every night gets harder to hold at the right angle. You stop driving at night first โ€” too many headlights from the sides you can't quite track. Then you stop driving in the city. Then a grandchild crosses your kitchen and you don't see them. Your spouse starts handling the stairs ahead of you. Falls become a thing that happens, and one of them is the one that breaks a hip Ramulu 2009.

What people around you notice first is that you're quieter at family dinners โ€” across the table is the bit of vision that's already gone, and reading lips at a distance is harder. Then the calls from your kids start checking whether you'd like to move closer to one of them. None of this needs the extreme case to land. Globally, glaucoma is the leading cause of permanent blindness; in 2020 it accounted for an estimated 3.6 million cases of blindness, and the projected number of people with the disease in 2040 is 111.8 million GBD 2020Tham 2014. The vast majority of those outcomes are people who never got the routine exam, or who got it once and never came back.

The asymmetry that does the work: the exam is an hour, every couple of years. The vision you lose if you skip it does not return.

What the exam looks like

A glaucoma-relevant eye exam isn't the eye chart at the DMV. It's a comprehensive dilated exam done by an optometrist or ophthalmologist, lasting under an hour. Five things get done; any one of them in isolation is unreliable, but together they sort you cleanly.

  • Eye-pressure measurement. Either a tiny tip touched gently to the cornea after a numbing drop (the reference standard), or an air-puff machine. A single reading isn't definitive โ€” pressure swings a few mmHg across the day โ€” but it's the number treatment targets.
  • A look at the optic nerve. Drops dilate your pupils; the doctor shines a light through and looks at the disc where the nerve exits the back of the eye. A "cupped" disc with thinned tissue at the edges is the visible signature.
  • An OCT scan of the nerve fibre layer. A non-contact infrared scan that measures the thickness of the nerve fibres around the optic nerve to the micrometre. This typically catches the damage years before a visual-field test can AAO PPP 2020.
  • A visual-field test. You stare into a bowl and click a button when you see flickers of light at the edges. Tedious. Roughly 8โ€“10 minutes per eye. Subjective enough that the doctor will repeat it to confirm any defect.
  • Gonioscopy. A mirrored lens placed on the eye to look at the drainage angle. Confirms the angle is anatomically open (the disease this entry is about) rather than closed (a different disease with a different treatment path).

Total cost in the United States: typically $50 to $200 out of pocket without insurance, and often partially or fully covered by vision or medical insurance from age 40 onward. The two highest-value pieces โ€” the OCT plus the dilated look at the optic nerve โ€” are the parts a primary-care office generally can't do, which is why this lives with eye specialists.

When to get it

Cadence rises with age and with risk. The American Academy of Ophthalmology's recommendation for adults without known risk factors AAO Comprehensive Adult Medical Eye Evaluation PPP 2020:

The cadence isn't arbitrary. Population data show glaucoma prevalence rising from roughly half a percent in your 40s to about seven percent in your 70s Tham 2014; the exam frequency is calibrated so that new disease gets caught within a window where treatment still has decades to work.

What most people get wrong

  • "My eyes feel fine, so I don't need to worry." Open-angle glaucoma is painless and asymptomatic until late. Most damage happens in the periphery โ€” where the brain is good at smoothing over missing pixels โ€” and people with substantial measurable field loss are often unaware of it. Roughly half the people who have glaucoma in countries like the US don't yet know Quigley & Broman 2006.
  • "If my eye pressure is normal, I'm in the clear." Roughly a third of open-angle glaucoma worldwide happens at "normal" pressures (under 21 mmHg on a single reading) Tham 2014. Pressure also varies through the day. A single number is a snapshot; the optic-nerve exam and OCT scan are what actually catch the disease.
  • "I read screening isn't recommended." The 2022 US Preventive Services Task Force statement says the evidence isn't strong enough to recommend that primary-care doctors screen with their own tools, which are limited USPSTF 2022. It does not say the comprehensive dilated exam at an eye specialist's office isn't valuable โ€” that's where actual detection happens, and the American Academy of Ophthalmology still recommends it on the cadence above.
  • "If I'm diagnosed and take the drops, the lost vision will come back." No. Treatment slows the rate of further loss; it does not regenerate dead optic-nerve fibres. The case for catching glaucoma early is that you protect what's still there. And the drops only work if you actually take them โ€” when researchers monitored a group of glaucoma patients with electronic dosing aids, knowing they were being watched, nearly half still used their drops less than 75% of the time Friedman 2009.

What else to look at

Three adjacent topics that ride on the same exam or sit next door:

  • The comprehensive eye exam itself โ€” the same appointment screens for cataracts, age-related macular degeneration, diabetic retinopathy, and refractive change. None of those are open-angle glaucoma, but the visit covers them.
  • Angle-closure glaucoma โ€” a different, acute, painful presentation that's a true ocular emergency. Most relevant for high-risk anatomy (small eyes, far-sighted adults, certain Asian populations); rare enough that the general screening cadence already covers it.
  • Diabetes โ€” diabetes modestly raises glaucoma risk and produces its own retinal disease; the two detection pathways overlap and both benefit from a long-term relationship with an eye-care clinician.
Related in the handbook
Diagnosis
  • โ€” The exam that catches glaucoma early is exactly this comprehensive check โ€” eye pressure plus a careful look at the optic nerve.
Related
  • โ€” Diabetes adds its own silent eye damage on top of glaucoma risk โ€” if you're diabetic, the yearly dilated exam covers both.
  • โ€” The Amsler grid catches a different silent eye disease โ€” glaucoma hides in the periphery and needs the in-clinic exam.
  • โ€” Glaucoma steals vision with no warning at all; sudden flashes, a curtain, or a grey patch are the opposite case โ€” an emergency, not a slow creep.
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