Open-angle and angle-closure glaucoma: the differences

One evening, without warning, an eye turns red. It hurts, a dull ache; a headache arrives, and in the mirror the pupil of that eye looks bigger than the other. This is the typical picture of acute angle closure: the pressure inside the eye rises suddenly and, if it is not lowered quickly, it damages the optic nerve³.

It is also the most dramatic way to discover that glaucoma is not a single disease. The most common form, open-angle glaucoma, goes on for years without giving any signs¹. Angle-closure glaucoma, by contrast, can stay silent for a long time⁸ or present as an emergency. Understanding the difference helps you to know what to ask your ophthalmologist and when a problem cannot wait for the next check-up.

In this article

1. What the angle is, and why it makes the difference
2. Angle-closure glaucoma: who is at risk
3. An acute attack is an emergency
4. Drugs and drops that dilate the pupil
5. Laser or lens: what the studies say
6. Frequently asked questions
7. Sources

What the angle is, and why it makes the difference

A clear fluid, the aqueous humour, circulates inside the eye; it nourishes the structures at the front and drains away through a filter, the trabecular meshwork. This filter sits in the angle between the cornea, the transparent window at the front of the eye, and the iris, the coloured disc.

In open-angle glaucoma the access route to the filter is clear, but the fluid drains away with difficulty. In angle-closure glaucoma, by contrast, the iris comes up against the filter and obstructs it. The most common cause is so-called pupillary block in eyes that already have narrow angles, as is often the case in long-sighted people³. With age, the lens, the natural lens of the eye, grows and contributes to narrowing the angle¹⁰.

In both cases the word glaucoma indicates the same consequence: damage to the optic nerve with loss of the visual field¹.

	Open angle	Angle closure
What happens	The filter can be reached, but the fluid drains away poorly	The iris comes up against the filter and blocks access to it
How it presents	Without symptoms until the advanced stages1	At first often without loss of vision8; sometimes with an acute attack3
Main risk factors	Age, high eye pressure, family history, high short-sightedness, sub-Saharan African ancestry1	Age, long-sightedness, East Asian ancestry1
Where it is most common	Africa2	Asia2

Angle-closure glaucoma: who is at risk

A meta-analysis of 50 population studies estimated that angle-closure glaucoma reaches its highest frequency in Asia, affecting 1.1% of people aged 40 to 80². In the pooled studies, there were 786 angle-closure cases among about 112,000 people examined, and 3,770 open-angle cases among about 140,000: the closed form is less common, but far from rare².

The main risk factors are advanced age, long-sightedness (long-sighted eyes are generally shorter, with less room in the front part) and East Asian ancestry¹. One review describes it as an aggressive disease that blinds millions of people worldwide¹⁰. We also discuss this in our article on long-sightedness.

An acute attack is an emergency

In acute angle closure the drainage is blocked suddenly and the pressure rises sharply. A clinical review recommends suspecting it in anyone with a red eye that has appeared suddenly, with a dilated pupil, dull pain and headache, and starting treatment to lower the pressure straight away, with urgent referral to an ophthalmologist³. The same authors point out that other conditions, including ones affecting the nervous system, can cause similar symptoms: that is why a medical assessment is needed, not a guess made at home³.

After an attack, laser in the other eye has a strong preventive effect¹⁰.

Drugs and drops that dilate the pupil

A review of cases caused by drugs lists several families that, in people with narrow angles, can trigger acute closure: adrenergic substances, including in eye drops or nasal sprays, drugs with an anticholinergic effect, including eye drops that dilate the pupil, some antidepressants and a group of drugs derived from sulfonamides, which act through a different mechanism. Most attacks involve people who did not know they had narrow angles⁴. None of these drugs should be stopped on your own initiative: anyone who knows they have narrow angles can mention it to every doctor who proposes a new treatment. We also discuss this in our article on medicines and the eyes.

And what about the drops used to dilate the pupil during an examination? A study in Singapore dilated the pupils of 471 people over 50 with narrow angles, almost all of Chinese ancestry, together with a drug to contain the pressure: in 3 (0.64%) acute closure occurred anyway within six hours. The authors judge the risk to be low, but present⁵.

Laser or lens: what the studies say

For years the answer to narrow angles was laser iridotomy, a small hole in the iris that opens an alternative route for the fluid, used as prevention even with limited evidence¹⁰. Two large trials have changed the picture.

The EAGLE trial took another route: removing the lens. In 30 hospitals in five countries, 419 people aged at least 50, without cataract, with angle-closure glaucoma or with a closed angle and very high pressure (30 mmHg or more) were randomly assigned to removal of the still-clear lens or to laser with eye drops. After three years, those who had been operated on had a higher quality-of-health score and a pressure lower by 1.2 mmHg on average; irreversible loss of sight occurred in one person who had been operated on and in three treated with laser, and there were no serious adverse events⁸.

A 2021 Cochrane review found moderate-certainty evidence that surgery on the lens reduces deterioration of the visual field and the number of eye drops needed, compared with laser; the comparison, however, was based on a single trial, and the trials gathered were too different for an overall numerical synthesis⁹. It is nonetheless a surgical operation: the choice depends on the stage of the disease and on the person. The other glaucoma treatments are described in our article on eye drops, laser and surgery.

Frequently asked questions

Is angle-closure glaucoma more serious than open-angle glaucoma?

It is less common², but it can be more aggressive¹⁰, and an acute attack requires immediate treatment³. There are, however, treatments that in studies have lowered pressure and slowed progression^8,9.

Can the drops that dilate the pupil trigger an attack?

In people with narrow angles it is possible, but rare: in a study of 471 people at risk it happened in 3⁵. That is why the ophthalmologist assesses the angle; you will find more in our article on the back of the eye.

If I have narrow angles, do I need laser?

Not necessarily. In people with narrow angles found through screening, without other signs, the ZAP trial found a limited benefit^6,7. The case of someone who has already had an attack in one eye is different¹⁰. It is a decision to take with the ophthalmologist.

Is removing the lens enough to stop angle-closure glaucoma?

Not necessarily, and the damage already done to the optic nerve remains. In the EAGLE trial, however, the operation gave a lower pressure and a better quality of health than laser⁸.

Open angle and angle closure have the same possible outcome, but different stories. The first has to be looked for with check-ups, because it does not make itself felt. The second can often be recognised before it causes problems, by looking at the angle; and when it appears suddenly, there is only one rule: get seen at once, without putting it off until the next day.