WHAT YOU NEED TO KNOW
- Glaucoma damages the optic nerve, and lost vision cannot be recovered.
- In the early stages it has no symptoms: only an eye examination detects it in time.
- With early diagnosis and regular treatment, the vast majority of people keep useful vision throughout their lives.
This guide brings together, on one page, the essentials of glaucoma: what it is, who is most at risk, how it is diagnosed, how it is treated and how to live with it. Each chapter ends with links to the articles where each topic is covered in depth.
What glaucoma is
Glaucoma is a chronic disease of the optic nerve, the “cable” of more than a million fibres that carries the images captured by the eye to the brain. Throughout life a small proportion of these fibres is naturally lost; in glaucoma, the loss is too fast.
The result is a progressive loss of visual field, the whole area an eye sees when fixing on a point. The defects usually start in the periphery and only reach central vision in advanced stages. It is one of the leading causes of irreversible blindness worldwide; in Portugal, according to the Directorate-General of Health, it affects about 100,000 people, many of whom do not yet know they have it.
There are several types. Glaucoma can be primary, with no other identifiable cause, or secondary, when it results from another condition such as inflammation, trauma, pseudoexfoliation or corticosteroid use. There is also normal-tension glaucoma and, more rarely, congenital or childhood glaucoma.
Eye pressure
A clear fluid, the aqueous humour, circulates inside the eye. It is produced behind the iris, passes through the pupil and leaves mainly through the trabecular meshwork, in the angle between the iris and the cornea. Intraocular pressure results from the balance between production and outflow of this fluid, and it rises almost always because drainage is insufficient.
On average, pressure is close to 16 mmHg, and values above 21 mmHg are usually considered high. But a single value does not allow conclusions: corneal thickness affects the measurement, pressure varies during the day and the optic nerve’s tolerance varies from person to person.
That is why high pressure does not mean glaucoma. When pressure is high but the optic nerve is healthy, this is called ocular hypertension: a risk factor that needs monitoring, but not always treatment. And glaucoma can exist with pressures considered normal.
Read moreWhat is intraocular pressure? Ocular hypertension and glaucoma: what is the difference?
Who is most at risk
A risk factor does not mean a person will develop glaucoma, but it justifies closer monitoring. The main ones are:
- Raised intraocular pressure, the most important factor and the only one that can be treated.
- Age: the risk increases from the age of 40.
- Close relatives with glaucoma: in a population study, the lifetime risk was about nine times higher in siblings and children of patients.
- Ancestry African (open angle) or Asian (closed angle).
- Eye diseases, such as high myopia, pseudoexfoliation, uveitis and injuries.
- General diseases and medicines, such as diabetes, familial amyloid polyneuropathy and long-term corticosteroid use.
Having relatives with glaucoma is not a sentence: relatives of patients tend to be diagnosed earlier, precisely because they are monitored, and that changes the outlook.
QuizAnswer 9 simple questions and find out whether an eye examination makes sense. Do I have risk factors?
Read moreWhat are the risk factors for glaucoma? I have relatives who are blind from glaucoma. Is the same likely to happen to me?
Why it goes unnoticed
In the vast majority of cases, glaucoma causes no symptoms until advanced stages, for three reasons: high pressure cannot be felt; the defects start in the periphery, not in the detailed central vision we pay most attention to; and the brain and the other eye compensate for the gaps. Seeing well and having no pain does not rule out glaucoma.
The exception is acute angle closure, in which pressure rises suddenly. It can cause intense eye pain, a red eye, blurred vision, coloured halos around lights, headache, nausea or vomiting. It is an emergency: with these symptoms, go immediately to an eye emergency department.
Read moreWhat symptoms should I watch for?
How it is diagnosed
Early diagnosis is the most important measure in glaucoma: lost vision cannot be recovered, so the earlier the disease is detected and treated, the more vision is preserved throughout life.
Because it causes no symptoms, glaucoma is almost always detected at an eye examination, routine or screening, and not because the person noticed any change. At the consultation:
- the intraocular pressure is measured (tonometry);
- the optic nerve is examined at the back of the eye, sometimes with the pupil dilated;
- the drainage angle is assessed with a special lens (gonioscopy).
Further tests confirm the diagnosis and are then used to monitor progression. Optical coherence tomography (OCT) measures the nerve fibre layer and can show loss before visual field defects appear. The visual field test shows areas of reduced sensitivity. Pachymetry measures corneal thickness, which affects the pressure reading.
Read moreHow is glaucoma detected?
Open angle and closed angle
The type of glaucoma depends on whether the aqueous humour can reach the trabecular meshwork.
- In open-angle glaucoma, about three in four cases, the fluid reaches the meshwork freely, but it drains poorly. Pressure rises slowly and without symptoms.
- In angle-closure glaucoma, the iris moves close to or touches the meshwork and blocks the outflow. This can happen gradually or suddenly, in an acute attack. It is rarer, but tends to be more destructive.
Gonioscopy is essential for this distinction: with a special lens placed on the eye, the drainage angle is viewed directly to assess whether it is open, narrow or closed. It is performed in a specialised glaucoma consultation.
Knowing which type of glaucoma you have matters in daily life: for example, many “contraindicated in glaucoma” warnings in medicine leaflets refer mainly to untreated angle closure.
Read moreHow do open and closed angles differ? Is open-angle or angle-closure glaucoma worse?
Treatment with eye drops
As there is no definitive cure, the aim of treatment is to stop progression. Lowering pressure to a level suited to each eye, the so-called target pressure, is at the heart of treatment.
In open-angle glaucoma, eye drops are usually the first line of treatment, alongside selective laser trabeculoplasty (SLT). They only work if used every day, at the right time and correctly. After putting in the drop, closing your eyes for 2 to 3 minutes keeps more medicine in the eye and reduces effects on the rest of the body. If you use more than one drop, wait at least 5 minutes between them.
Most side effects are mild, and there are almost always alternatives: another drop, a preservative-free version, a combination of two medicines in one bottle, laser or surgery. Side effects are a reason to talk to your doctor, not to stop treatment.
Read moreHow is glaucoma treated? How to use eye drops Side effects of eye drops
Laser treatment
Selective laser trabeculoplasty (SLT) improves the outflow of aqueous humour through the natural route, in open-angle glaucoma and ocular hypertension. It can be the first treatment or add to eye drops. It is done in the clinic in a few minutes, and its effect is assessed over 3 to 8 weeks. Some eyes respond little, and the benefit may wane over time; the treatment can be repeated.
Peripheral iridotomy creates a small opening in the outer iris and is used in angle closure with pupillary block, or to prevent it in eyes at significant risk. Iridoplasty and goniopuncture are used in more specific situations.
Surgical treatment
Surgery is considered mainly when pressure is not controlled with drops and laser, when the disease progresses despite treatment, when drops are not tolerated or when the person wants to rely less on them. No single technique suits everyone:
- Trabeculectomy: creates a new drainage route, controlled by a flap of the eye’s own tissue.
- Non-penetrating deep sclerectomy: filters fluid through a thin membrane that is preserved.
- Canaloplasty: dilates and tensions the eye’s natural drainage canal.
- Drainage implants: a small tube carries fluid to a reservoir behind the eye, in more difficult cases.
- Lens surgery: in selected angle-closure cases, it can widen the angle lastingly.
The choice depends on the type of glaucoma, the stage of the disease and the condition of the eye. After the operation, pressure and healing are closely monitored, and medication may still be needed.
Read moreSafer trabeculectomy Deep sclerectomy Canaloplasty Drainage implants Care after surgery
What treatment can and cannot do
No treatment, whether drops, laser or surgery, restores vision already lost: optic nerve fibres do not regenerate. Treatment protects the remaining fibres and the vision that still exists. That is why the earlier glaucoma is detected, the more vision is preserved.
The good news is that, with early diagnosis and treatment, only a minority of patients lose their sight. Success rests on three pillars: early diagnosis, controlling progression with proper follow-up, and sticking to treatment every day without missing appointments.
Read moreDoes having glaucoma mean I will go blind? Can lost vision be recovered? Can laser or surgery cure glaucoma?
Living with glaucoma
Living with glaucoma is, in the vast majority of cases, living normally. Regular aerobic exercise is recommended. There are just a few precautions: avoid staying head-down for long periods, don’t hold your breath when lifting weights, and don’t drink large amounts of water at once. You can fly without restrictions, with your drops in your hand luggage.
Keep an up-to-date list of your medicines, including eye drops, and show it whenever something new is prescribed. Corticosteroids are the group that matters most in open angle. For driving, what counts is the visual field: at your appointments, your ophthalmologist will tell you whether you meet the legal requirements.
Finally, tell your close relatives that you have glaucoma, so that they can be checked too.
Read moreGlaucoma in daily life Which medicines can affect glaucoma? Driving licence
Clinical sources
European Glaucoma Society · Terminology and Guidelines for Glaucoma, 6th edition
This information does not replace an individual medical assessment. Follow the advice of the team looking after you.
Clinical responsibility: Dr. Nuno Lopes · Ophthalmology
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