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What is glaucoma?

Glaucoma is a common eye condition which can affect your vision if it's not diagnosed and treated early enough. 

In glaucoma, the optic nerve, which connects the eye to the brain, becomes damaged. This is usually caused by fluid building up in the front part of the eye, which increases pressure inside the eye.

Video: what is glaucoma?

Professor Pete Shah, Consultant Ophthalmic Surgeon at University Hospitals Birmingham NHS Foundation Trust, explains what glaucoma is, using a model eye to demonstrate what happens in people with the condition.

Video transcript: what is glaucoma?


What is glaucoma?


The glaucomas are a group of diseases that have certain common themes, and I'd like to try and explain and give you a good foundation for understanding what exactly glaucoma is.


Professor Pete Shah picks up a model eyeball.


I'm going to use a model eye, here, and let's start by getting the basics right.

Each of our eyeballs is about the size of a ping pong ball, and it sits inside our eye socket. Let's make that ball a little bit bigger. Here we have magnified eyeball. You've got the eyelids at the front, but the eye is a ball and, just like any ball, it has to have a pressure inside it.

The eye has pressure inside it because within the eye inside, there's a tap that is making fluid every minute of every day. Our eyes make two microlitres of fluid a minute.

What does that mean? Well, that's about enough fluid to fill a small bath for each of our eyes during our life. So the eyes are making a lot of fluid.

Where does that fluid go? The fluid drains into a little drain inside the eye around the coloured part of the eye. (You'll hear the term "the drainage angle".) And if the production of fluid and the drain are balanced, your pressure should be about 15 millimetres of mercury. But if the drain is becoming blocked for a whole variety of reasons, and the tap is still running, then the pressure will build up.

As the pressure builds up inside the eye, it presses on the delicate optic nerve at the back of the eye that sends the picture to the brain, and the pressure inside the eye damages that delicate nerve.

When that nerve is damaged, blank patches start to appear in your vision. You don't notice them at first because the brain fills in the gap. But if the pressure continues, and the nerve is progressively damaged, you'll get progressive blank patches appearing in your vision and, untreated, that can lead to blindness.


© 2021 University Hospitals Birmingham NHS Foundation Trust

Who does glaucoma affect?

The condition can affect people of all ages, but is most common in the over-70s.


Many people do not realise they have glaucoma as it develops very slowly, and symptoms often take a long time to develop.

Initial symptoms may include:

  • blurred vision
  • seeing rainbow-coloured circles around bright lights

Sometimes glaucoma can develop suddenly and cause any of these additional symptoms:

  • Intense eye pain
  • Nausea and vomiting
  • Red eyes
  • A headache
  • Tenderness around the eyes

Video: symptoms in glaucoma

Professor Pete Shah, Consultant Ophthalmic Surgeon at University Hospitals Birmingham NHS Foundation Trust, explains the symptoms of glaucoma.

Video transcript: symptoms in glaucoma


Symptoms in glaucoma.


Glaucoma is called the thief of sight for a reason. That reason is that many patients with moderate, even to quite advanced glaucoma may not be aware they have it.

When blank patches appear in various places in your field of vision, you may not initially notice it. We call this asymptomatic, an absence of symptoms.

As glaucoma progresses, you may notice that you don't see things as well. You don't see in the distance or don't read as well, or that you have blank patches in your vision, or you trip over things.

There are certain types of glaucoma where the drain is blocking quickly, where you can experience pain in the eye - a severe dull ache in the eye and the eye socket or you can get halos around lights, for example when you look at a street lamp. Those are symptoms of angle closure glaucoma, which is a specific type of glaucoma.


© 2021 University Hospitals Birmingham NHS Foundation Trust.

How is glaucoma diagnosed?

Glaucoma can usually be detected during a routine eye test carried out by an optometrist at an opticians. You should have a routine eye test at least once every two years.

The initial tests are quick and painless, and include vision tests and measurements of the pressure inside your eye.

If these tests show that glaucoma may be present, the optometrist may refer you to a specialist eye doctor (an ophthalmologist) for further tests and potential treatment. 

When to get medical help

If you have any concerns about your vision, and you're not already an ophthalmology patient at University Hospitals Birmingham (UHB), please see your GP or an optician.

In an emergency

Please our page on what to do in an emergency if you suddenly develop symptoms, or if you're already a patient at UHB.

Your family

Glaucoma can run in families. If you're diagnosed with glaucoma, it's important to tell close relatives, e.g. parents, brothers and sisters, and cousins. They should arrange to have a simple glaucoma check by an optician once a year to check for the condition.

As glaucoma is more common in the over-40s, if you have glaucoma and you have children, they should get checked regularly by an optician from the age of 40.

Watch our glaucoma video playlist

You may be interested in our YouTube playlist, where you can watch our experts talk about a range of issues affecting glaucoma patients and introduce the service here at UHB.

Further information

For detailed information on glaucoma, including symptoms, diagnosis, testing and treatment, please see the NHS website.

Last reviewed: 12 May 2022