Glaucoma does not usually cause any symptoms to begin with.
It tends to develop slowly over many years and affects the edges of your vision (peripheral vision) first.
For this reason, many people do not realise they have glaucoma, and it's often only picked up during a routine eye test.
If you do notice any symptoms, they might include blurred vision, or seeing rainbow-coloured circles around bright lights.
Both eyes are usually affected, although it may be worse in 1 eye.
Very occasionally, glaucoma can develop suddenly and cause:
Visit an opticians or a GP if you have any concerns about your vision.
If you have glaucoma, early diagnosis and treatment can help stop your vision getting worse.
Without treatment, glaucoma can eventually lead to blindness.
This is a medical emergency that may require immediate treatment.
There are several different types of glaucoma.
The most common is called primary open angle glaucoma. This tends to develop slowly over many years.
It's caused by the drainage channels in the eye becoming gradually clogged over time.
Other types of glaucoma include:
Glaucoma can occur for a number of reasons.
Most cases are caused by a build-up of pressure in the eye when fluid is unable to drain properly.
This increase in pressure then damages the nerve that connects the eye to the brain (optic nerve).
It's often unclear why this happens, although certain things can increase the risk, including:
It's not clear whether you can do anything to prevent glaucoma, but having regular eye tests should pick it up as early as possible.
Glaucoma can usually be detected during a routine eye test at an opticians, often before it causes any noticeable symptoms.
The tests are carried out in the opticians by an optometrist.
You should have a routine eye test at least every 2 years.
Several quick and painless tests can be carried out to check for glaucoma, including vision tests and measurements of the pressure inside your eye.
If tests suggest you have glaucoma, you should be referred to a specialist eye doctor (ophthalmologist) to discuss treatment.
It's not possible to reverse any loss of vision that occurred before glaucoma was diagnosed, but treatment can help stop your vision getting worse.
The treatment recommended for you will depend on the type of glaucoma you have, but the options are:
You'll also probably need regular appointments to monitor your condition and check the treatment is working.