Glaucoma: what it is, and why it is almost always caught late

Glaucoma has one feature that sets it apart from almost every other eye disease: for years, you cannot feel it at all. It does not hurt, it does not make the eye red, it does not blur the words on the page. It works at the edges of the field of vision, where the brain fills in the gaps without our noticing, and by the time central vision begins to fail, the damage is already advanced.

That is why the most striking figures on glaucoma concern not the people who have it, but the people who do not know they have it. A 2025 analysis by the European Eye Epidemiology Consortium, which pooled individual data from more than 55,000 adults in 14 population studies, estimates that around 12.3 million people in Europe have glaucoma, and that 6.9 million of them have never been diagnosed¹.

In this article

1. What is glaucoma?
2. How common it is, in Europe and worldwide
3. Who is most at risk
4. What the major studies have shown
5. How glaucoma is detected
6. Frequently asked questions
7. Sources

What is glaucoma?

The word glaucoma covers a group of diseases that share one outcome: the gradual loss of the fibres of the optic nerve, the cable that carries images from the eye to the brain. As the fibres are lost, blind spots appear in the field of vision (ophthalmologists call them scotomas); at first they lie towards the sides, and only later do they move closer to the centre.

The most common form in Europe is primary open-angle glaucoma: the fluid that nourishes the front of the eye, the aqueous humour, drains away less easily than it should, although the drainage route stays open. Then there is angle-closure glaucoma, in which the drainage route narrows or closes; it can develop gradually or suddenly, as an acute attack⁹.

One point needs clearing up straight away: glaucoma does not mean ‘high pressure in the eye’. Raised intraocular pressure is the most important risk factor, and the only one that can currently be modified, but some people with high pressure never develop the disease, while others have glaucoma with pressure in the normal range. The European Glaucoma Society guidelines make exactly this point: a pressure level that is right for one person can be harmful for another, and treatment has to be tailored to the individual patient⁸.

How common it is, in Europe and worldwide

A meta-analysis of 50 population studies, published in 2014, estimated that glaucoma affects 3.5% of people aged 40 to 80 worldwide: about 64 million people in 2013, with the number projected to reach almost 112 million by 2040 as the population ages².

The 2025 European study found an age-standardised prevalence of about 3% in adults over 40. The likelihood of having glaucoma rises by about a third with every five years of age and is slightly higher in men; by 2050, the number of cases in Europe is expected to grow by more than a million¹.

The most striking figure, though, is a different one: 56% of the people with glaucoma identified in those studies did not know they had it, and among those under 55 the proportion was over 80%¹. A systematic review of 55 studies from around the world had reached the same conclusion: in every region, more than half of all cases had gone unrecognised, with Europe in a relatively better position than Africa and Asia³.

Who is most at risk

A 2024 meta-analysis of studies that followed groups of people over time identified the most consistent risk factors for open-angle glaucoma⁴:

• age, the most reliable of them all: the risk rises year after year;
• family history: having a relative with glaucoma is associated with roughly two and a half times the risk;
• short-sightedness, associated with roughly double the risk;
• raised intraocular pressure;
• being male, with a slightly higher risk.

The 2014 meta-analysis had also found glaucoma to be more common in people of African ancestry and in people living in cities². None of these factors, on its own, tells you whether someone will develop the disease: they help to show who has more reason not to neglect their check-ups. If a parent, brother or sister of yours has glaucoma, that is something to tell your ophthalmologist.

What the major studies have shown

Two clinical trials, both published in 2002, underpin the way glaucoma is thought about today.

The second trial, the Ocular Hypertension Treatment Study, involved people with high eye pressure but no damage to the optic nerve. After five years, glaucoma had developed in 4.4% of those using eye drops to lower their pressure and in 9.5% of those who were only monitored. The authors themselves point out that this does not mean everyone with borderline pressure should be treated: the decision depends on each person’s risk⁶. We look at this in our article on high eye pressure.

More recently, the British LiGHT trial compared two ways of starting treatment in 718 people: eye drops, or a laser treatment called selective laser trabeculoplasty. After three years, quality of life was similar in the two groups, and about three in four of the people treated with laser did not need eye drops to keep their pressure at the agreed target⁷. Which route suits a particular person, however, is for the ophthalmologist to decide.

How glaucoma is detected

Precisely because it causes no symptoms, glaucoma is mostly found by looking for it. An eye examination has three key elements: measuring the pressure in the eye, examining the optic nerve at the back of the eye (often with the help of a test called OCT) and, when needed, a visual field test, which maps the areas where you can see and those where you cannot⁸. We explain how these tests work in our articles on the visual field test and on OCT.

Pressure alone is not enough for a diagnosis: what counts is the full picture. That is also part of the reason why a European study found so many missed cases, especially among younger people, who see an ophthalmologist less often¹.

Frequently asked questions

Can glaucoma lead to blindness?

It can if it is not recognised and monitored, and it is one of the leading causes of irreversible blindness worldwide². But the major studies show that lowering eye pressure slows the disease⁵: for most people who are diagnosed and whose treatment is followed up over time, the realistic goal is to keep useful sight for life.

If my eye pressure is normal, can I rule out glaucoma?

No. There is a form of glaucoma with normal pressure and, conversely, high pressure does not always lead to the disease^6,8. A diagnosis also requires an examination of the optic nerve and, if needed, of the visual field.

Is glaucoma hereditary?

It is not inherited in a simple way, but family history matters: having a close relative with glaucoma is associated with roughly two and a half times the risk⁴. It is useful information to give your ophthalmologist.

Can damage from glaucoma be reversed?

No: optic nerve fibres that have been lost do not grow back. The treatments available aim to slow or halt the loss, which is why noticing it early matters so much^5,8.

Glaucoma cannot be felt, but it can be seen: someone just has to look for it. On a continent where millions of people are living with the disease without knowing it¹, the best news comes from the studies of the past twenty years: once it is found and monitored, it can be slowed down.