The difference between open-angle and closed-angle glaucoma is where the eye's drainage system fails. In open-angle glaucoma, the drain stays open but slowly works less well, usually with no symptoms. In angle-closure glaucoma, the colored iris blocks the drain. In the United States, more than 80% of glaucoma cases are the open-angle type.
Both types damage the optic nerve, the cable that carries vision to the brain, and both can cause permanent vision loss. But they affect different people and are treated differently.
The Drainage Angle, Explained Simply
Your eye constantly makes a clear fluid called aqueous humor, which then drains out. The balance between fluid made and fluid drained sets your eye pressure.
The fluid leaves through the drainage angle. This is the corner where the iris (the colored part of the eye) meets the cornea (the clear front window). Inside that corner sits the trabecular meshwork, a tiny sponge-like filter that lets fluid out of the eye.
Think of a kitchen sink. In open-angle glaucoma, the drain is uncovered but partly clogged. In angle-closure glaucoma, something is sitting on top of the drain.
Open-Angle Glaucoma: The Silent Type
In open-angle glaucoma, the angle looks open, but fluid moves through the trabecular meshwork with more resistance than normal. Pressure can rise slowly over years, and the damage is painless.
Most people have no symptoms until the disease is advanced. Vision loss usually starts in the side (peripheral) vision, so it often goes unnoticed. The National Eye Institute (NEI) reports that half of people with glaucoma do not know they have it. Learn more on our open-angle glaucoma page.
According to the NEI, people at higher risk include those who are over age 60, those who are African American or Hispanic/Latino and over age 40, and those with a family history of glaucoma. If a parent, brother, or sister has glaucoma, read why family members should get checked.
Some people develop damage with pressure in the normal range, called normal-tension glaucoma.
Angle-Closure Glaucoma: When the Drain Gets Blocked
In angle-closure glaucoma, the iris presses against the drainage angle, so fluid cannot reach the filter and pressure builds. An eye with a crowded angle is called "narrow angle." Not everyone with narrow angles develops glaucoma. See our narrow-angle glaucoma page.
What is narrow angle glaucoma, and who is at risk?
Narrow angles come mostly from the shape of the eye. A large review in JAMA lists these risk factors:
- Older age
- Female sex
- Asian ancestry, especially East Asian (for example, Chinese) ancestry
- A small, crowded front of the eye, including a shorter eye, which is common in farsighted people
- A thicker lens that sits farther forward
The natural lens inside your eye thickens as you age. That is one reason angle closure becomes more common later in life.
Acute angle-closure attack: a true emergency
Sometimes the angle closes suddenly. Pressure can shoot up quickly, usually above 30 mm Hg. Symptoms of very high eye pressure include:
- Severe eye pain
- Headache
- Nausea or vomiting
- Halos or rainbow rings around lights
- A red eye
- Blurred vision
If you have these symptoms, go to an emergency room or call an eye doctor right away. Do not wait to see if it passes. Prompt treatment to lower the pressure gives the best chance of protecting vision.
Chronic angle closure can be silent too
The JAMA review notes that angle-closure glaucoma is mostly a disease without symptoms, with an acute attack in less than a third of cases. The angle can close slowly and painlessly. That is why an exam of the angle matters even if your eyes feel fine.
Medications That Can Trigger Angle Closure
In people with narrow angles, some medicines can close the angle. A review in Current Opinion in Ophthalmology lists:
- Some decongestants and other adrenergic drugs, such as nasal ephedrine, phenylephrine eye drops, and nebulized salbutamol (albuterol).
- Anticholinergic drugs, which dry secretions and widen the pupil, including some older antidepressants and certain eye drops.
- Sulfa-based drugs, including topiramate (a seizure and migraine medicine), acetazolamide, and hydrochlorothiazide. These work through a different mechanism, swelling of the tissue behind the iris, and a laser iridotomy does not fix that type.
Most people who have a drug-related attack did not know they had narrow angles. See medication-associated glaucoma.
Important: never stop a prescribed medication without talking to the doctor who prescribed it.
How Doctors Tell the Two Types Apart
You cannot tell the two types apart by symptoms alone. A specialist looks directly at the drainage angle.
Gonioscopy is the key test. After numbing drops, the doctor places a small mirrored lens on the eye to see whether the angle is open, narrow, or closed, and to look for scar-like adhesions.
Anterior segment imaging adds a picture. Anterior segment optical coherence tomography (OCT) is a painless, no-touch scan that shows a cross-section of the front of the eye and how wide the angle is. Learn more about glaucoma screening and diagnosis.
How Treatment Differs
Treating open-angle glaucoma
The goal is to lower eye pressure to protect the optic nerve. Options include:
- Eye drops, used daily.
- Selective laser trabeculoplasty (SLT), a gentle in-office laser that helps the trabecular meshwork drain better. In the LiGHT trial of 718 patients, at 36 months 74.2% of the SLT group needed no drops to keep their pressure at target. The authors concluded SLT should be offered as a first-line treatment.
- Minimally invasive glaucoma surgery (MIGS), tiny devices or procedures that improve drainage, often done at the same time as cataract surgery.
Treating angle-closure glaucoma
The goal is to open the blocked angle. See angle-closure glaucoma treatment. Options include:
- Laser peripheral iridotomy (LPI). The laser makes a tiny opening in the iris, giving fluid a new path so the iris falls back from the drain.
- Lens extraction. Removing the eye's natural lens, as in cataract surgery, makes more room in the front of the eye.
Two major trials shape these choices:
The ZAP trial (Lancet, 2019) studied 889 people in China, aged 50 to 70, who had narrow angles but no glaucoma. One eye of each person got LPI and the other did not. Over 72 months, angle-closure disease developed at 4.19 per 1000 eye-years in treated eyes versus 7.97 per 1000 eye-years in untreated eyes. Because the risk was low, the authors did not recommend widespread preventive LPI.
The EAGLE trial (Lancet, 2016) enrolled 419 people aged 50 or older who did not have cataracts. All had angle closure with high pressure (30 mm Hg or greater) or angle-closure glaucoma. Compared with LPI plus drops, clear lens extraction gave better quality-of-life scores and pressure 1.18 mm Hg lower on average at 36 months. The authors concluded lens extraction should be considered as an option for first-line treatment.
The right choice depends on your age, angle anatomy, any glaucoma damage, and your lens. It is a decision to make with your specialist.
Open-Angle vs. Closed-Angle Glaucoma at a Glance
| Feature | Open-angle glaucoma | Angle-closure glaucoma |
|---|---|---|
| What happens | The drain is open but works less well | The iris blocks the drain |
| Speed | Slow, over years | Can be sudden (acute) or slow (chronic) |
| Symptoms | Usually none until late; side vision fades | Acute: severe eye pain, headache, nausea, halos, red eye, blurred vision. Chronic: often none |
| Who is at risk | Over 60; African American or Hispanic/Latino and over 40; family history | Older age, female sex, Asian ancestry, farsightedness, thicker lens |
| How diagnosed | Eye pressure, optic nerve exam, OCT, visual field, gonioscopy shows an open angle | Gonioscopy and anterior segment imaging show a narrow or closed angle |
| Main treatments | Eye drops, SLT laser, MIGS | Laser peripheral iridotomy, lens extraction, plus drops if needed |
From the Glaucoma Specialists
If you have been told you have "narrow angles," keep a note in your phone and share it with every doctor and pharmacist. Before taking a new decongestant, allergy pill, or migraine medicine, ask whether it is safe for narrow angles. And if you ever have sudden eye pain with a headache, nausea, and halos around lights, treat it as an emergency, not a migraine.
Glaucoma Care in Upland and the Inland Empire
Inland Glaucoma Center in Upland, California, is an independent practice, not a corporate chain. It is led by Robert Gunzenhauser, MD, a Harvard-educated, UCLA fellowship-trained glaucoma specialist, and Marc Shomer, MD, PhD, Adjunct Associate Professor of Ophthalmology at the Keck School of Medicine of USC. Both are board certified.
We see patients from Upland, Rancho Cucamonga, Ontario, Claremont, Montclair, Pomona, Fontana, Chino, Riverside, and San Bernardino, and offer both laser and surgical glaucoma care.
Call 909-315-6891 or request an appointment.
Works Cited
- Weinreb RN, Aung T, Medeiros FA. The pathophysiology and treatment of glaucoma: a review. JAMA. 2014;311(18):1901-1911. https://doi.org/10.1001/jama.2014.3192 (PMID 24825645)
- He M, Jiang Y, Huang S, et al. Laser peripheral iridotomy for the prevention of angle closure: a single-centre, randomised controlled trial (ZAP). Lancet. 2019;393(10181):1609-1618. https://doi.org/10.1016/S0140-6736(18)32607-2 (PMID 30878226)
- Azuara-Blanco A, Burr J, Ramsay C, et al. Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE): a randomised controlled trial. Lancet. 2016;388(10052):1389-1397. https://doi.org/10.1016/S0140-6736(16)30956-4 (PMID 27707497)
- Gazzard G, Konstantakopoulou E, Garway-Heath D, et al. Selective laser trabeculoplasty versus eye drops for first-line treatment of ocular hypertension and glaucoma (LiGHT): a multicentre randomised controlled trial. Lancet. 2019;393(10180):1505-1516. https://doi.org/10.1016/S0140-6736(18)32213-X (PMID 30862377)
- Lachkar Y, Bouassida W. Drug-induced acute angle closure glaucoma. Curr Opin Ophthalmol. 2007;18(2):129-133. https://doi.org/10.1097/ICU.0b013e32808738d5 (PMID 17301614)
- Jain NS, Ruan CW, Dhanji SR, Symes RJ. Psychotropic drug-induced glaucoma: a practical guide to diagnosis and management. CNS Drugs. 2021;35(3):283-289. https://doi.org/10.1007/s40263-020-00790-w (PMID 33604881)
- National Eye Institute. Glaucoma. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma (accessed October 2026)