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eye test procedure

How is glaucoma diagnosed?

For most people, the signs of glaucoma are first spotted by an optometrist at a routine eye test. This page talks through the importance of getting your eyes tested, and what will happen if an optometrist identifies warning signs associated with glaucoma.

My sight is fine, why test for glaucoma?

Eye tests aren’t just about how well you can see, or whether you need glasses. During an eye test, an optometrist also looks at the health of your eyes.

Diseases and conditions such as glaucoma, macular degeneration and even diabetes and high cholesterol can be detected during eye tests. So it’s important to get your eyes tested at least every two years unless your doctor tells you otherwise.

It is particularly important to get your eyes tested if you have a close relative with glaucoma, if you are African-Caribbean, East Asian, diabetic, have low blood pressure or are short sighted. All these factors mean you are at increased risk of developing glaucoma.

Am I entitled to free eye tests?

Millions of people in the UK are eligible for free eye tests paid for by the NHS, but many may not know it.

What happens at an eye test?

As well as checking whether you need glasses, the optometrist will carry out different tests to check the health of your eye. Some of these are key to detecting signs of glaucoma.

If any of these tests show you may have glaucoma, you will be referred to a specialist glaucoma service. A referral does not mean that you definitely have glaucoma or that you are at risk of losing sight. It just means your optometrist has found signs you may be at increased risk.

Your optometrist will not diagnose you with glaucoma.

Visual field test

This tests whether your peripheral vision (i.e. the vision away from the centre, or everything you’re not looking directly at) is healthy, or whether there are gaps. Looking into a machine, you are asked to press a button every time you see a dot of light. If you have glaucoma, you may have some gaps in your field of vision so you may miss some of the flashing lights.

Eye pressure test

At an optometrist’s, this is usually an “air puff” test. A small puff of air is directed at your eye and bounces back onto the machine, which measures the pressure within the eye (intraocular pressure or IOP). If you have glaucoma or ocular hypertension, your eye pressure will normally be raised.

Optic nerve assessment

The optometrist looks at the back of the eye and may take a photograph. This is to check the health of the optic nerve. If you have glaucoma, the optic nerve will look different.

What happens if I’m referred to a specialist?

Depending on the risks the optometrist has identified, and where you live, you may be referred directly to an ophthalmologist (an eye doctor) at a hospital. Alternatively, you may be referred to a specially-trained community optometrist.

When you see the glaucoma specialist, they will conduct more tests, including repeating some of those you have already had. The specialist will also look at other risk factors, such as ethnicity or family history of glaucoma. They will then decide whether you have glaucoma, or are at an increased risk, and whether you need to start treatment or not.

Glaucoma can usually be effectively controlled and treated. That’s why it is important that a diagnosis is made early and any treatment begins quickly, to protect your vision. Any vision lost to glaucoma is lost forever.

Download our Eye Clinic Referral Booklet or order a copy for free by clicking the button below. The booklet has lots more information about what to expect, the tests which might be carried out and questions to ask.

Want to know more about glaucoma?

We run or support regular events across the country, providing care and support to people with glaucoma. Sign up for one of our digital support groups below.


If you have questions about being diagnosed with glaucoma, visit our community forum at Health Unlocked. Ask other people with glaucoma about their experiences and read others’ stories.

Call our helpline

If you have any questions about anything on this page, our helpline advisors are here to help (Monday-Friday, 9.30am – 5.00pm)