Glaucoma - Diagnosing glaucoma

It's important to have regular eye tests so eye problems, such as glaucoma, can be diagnosed and treated as early as possible.

If you have glaucoma, it can take a long time before you realise you have a problem with your eyesight. This is because glaucoma usually damages the outer edge of the eye and works slowly inwards. You may not notice a problem until the glaucoma is near the centre of your eye.

You should have an eye test at least every two years or more frequently if advised by your optometrist (a healthcare professional who tests sight). For example, they may suggest you have more frequent eye tests if you have a close relative with glaucoma, such as a parent, brother or sister.

NHS eye tests

You qualify for a free NHS-funded sight test if you are:

• aged under 16, or aged under 19 and in full-time education
• aged 60 or over
• registered blind or partially sighted
• diagnosed with diabetes or glaucoma
• aged 40 or over and you are the parent, brother, sister, son or daughter of a person diagnosed with glaucoma, or you have been advised by an ophthalmologist that you are at risk of glaucoma
• eligible for an NHS complex lens voucher

You are also entitled to a free NHS sight test if:

• you receive Income Support or Income-based Jobseeker's Allowance (not contribution based)
• you receive Pension Credit Guarantee Credit
• you receive Income-based Employment and Support Allowanc
• you are awarded Universal Credit
• you are entitled to, or named on, a valid NHS tax credit exemption certificate
• you are named on a valid NHS certificate for full help with health costs (HC2)

People named on an NHS certificate for partial help with health costs (HC3) may also get help.

Also read about the NHS Low Income Scheme (LIS).

Read more information about NHS eye care services.

Tests for glaucoma

There are several glaucoma tests that can be carried out by your optometrist. They are painless and quite quick. The tests should be carried out during the same appointment to ensure results are as accurate as possible.

These tests are explained below.

Eye pressure test (tonometry)

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

A small amount of anaesthetic (painkilling medication) and dye is placed onto the transparent layer of tissue that covers the front of the eye (your cornea). A blue light from the head of the tonometer is held against your eye to measure the intraocular pressure.

Tonometry can diagnose ocular hypertension (OHT – raised pressure in the eye), which is a risk factor for chronic open-angle glaucoma. 

Central corneal thickness

The thickness of your cornea will be measured because this is thought to affect how the intraocular pressure is interpreted.

Gonioscopy

Gonioscopy is an examination of the front outer edge of your eye, between the cornea and the iris (the coloured part of your eye). This is the area where the fluid should drain out of your eye.

A gonioscopy can help to determine whether this angle is open or closed (blocked).

Visual field test

A visual field test – sometimes called perimetry – checks for missing areas of vision. You will be shown a sequence of light spots and asked which ones you can see. Some dots will appear in your peripheral vision (around the sides of your eyeball), which is where glaucoma begins.

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

Optic nerve assessment

Your optic nerve connects your eye to your brain. Your optometrist will use eye drops to enlarge your pupils. They will then examine your eyes using a slit lamp (a microscope with a very bright light) and assess whether your optic nerve has been damaged by the glaucoma.

The eye drops used to widen your pupils could affect your ability to drive. You should make alternative arrangements for getting home after your appointment.

Referral

If your optometrist suspects glaucoma, you will be referred to an ophthalmologist for further tests. Your ophthalmologist 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).

In some cases, your ophthalmologist will continue to treat you. But if you have chronic open-angle glaucoma, you may be referred back to your optometrist who will continue your treatment.