Glaucoma is usually picked up during a routine eye test, often before it causes any noticeable symptoms. Other tests are usually needed afterwards to diagnose and monitor the condition.

It's important to have regular eye tests so problems such as glaucoma can be diagnosed and treated as early as possible. Early treatment can help stop your vision becoming severely affected.

You should have an eye test at least every 2 years. If you're at a higher risk of glaucoma – for example, if you have a close relative with it – you may be advised to have more frequent tests.

You can get an eye test at a local opticians, and the tests are carried out by an optometrist. Find an optician near you.

Some people can receive free eye tests on the NHS. Find out if you're entitled to free NHS eye tests.

There are different tests that can be carried out by an optometrist if they suspect you have glaucoma after a routine eye test.

Eye pressure test

An eye pressure test (tonometry) uses an instrument called a tonometer to measure the pressure inside your eye.

The optometrist will put a small amount of painkilling medicine (anaesthetic) and dye into the front of your eye. They will then shine a light into your eye and gently touch the surface of it with the tonometer.

Some optometrists use a different instrument, which uses a puff of air and doesn't touch the eye, to check pressure.

Gonioscopy

Gonioscopy is an examination to look at the front part your eye – the fluid-filled space between the coloured part (iris) and the clear window of the front of the eye (cornea). This is where the fluid should drain out of your eye.

A gonioscopy can help to determine whether this area (the "angle") is open or closed (blocked), which can affect how fluid drains out of your eye. It will tell your optometrist what type of glaucoma you have.

Visual field test

A visual field test (sometimes called perimetry) checks for missing areas of vision.

You may be shown a sequence of light spots and asked to press a button to indicate which ones you can see. Some dots will appear at the edges of your vision (your peripheral vision), which is often the first area to be affected by glaucoma.

If you can't see the spots in the periphery, it may mean glaucoma has damaged your vision.

Optic nerve assessment

The optic nerve, which connects your eye to your brain, can become damaged in glaucoma, so an assessment may be carried out to see if it's healthy.

For the test, eyedrops will be used to enlarge your pupils. Your eyes are then examined using either:

• a slit lamp (a microscope with a bright light)
• optical coherence tomography – a type of scan where special rays of light are used to scan the back of your eye and produce an image of it

The eyedrops used to widen your pupils could temporarily affect your ability to drive, so you'll need to make arrangements for getting home after your appointment.

If glaucoma is picked up during an eye test, you should be referred to a specialist eye doctor (ophthalmologist) for further tests. They will confirm your diagnosis and find out:

• how far the condition has developed
• how much damage the glaucoma has done to your eyes
• what may have caused the glaucoma

They will then be able to advise on treatment. See treating glaucoma for more information.

In some cases, your ophthalmologist will continue to treat you. But for less serious types of glaucoma, you may be referred back to the opticians.