If you have glaucoma, it can take a long time before you realise that 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.
It is therefore very important to have regular eye tests so that any problems can be detected and treated as early as possible.
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 that you have more frequent eye tests if you have a close blood relative with glaucoma, such as a parent, brother or sister.
Tests for glaucoma
There are several glaucoma tests that your optometrist can perform. They are painless and quite quick. The tests should be carried out during the same appointment to ensure that the results are as accurate as possible.
The tests that you may have for glaucoma 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 your cornea (the transparent layer of tissue that covers the front of the eye). 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 (perimetry)
A visual field test (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 cannot see the spots in your peripheral vision, it may indicate that 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 that are used to widen your pupils could affect your ability to drive. Therefore you may need to make alternative arrangements for getting home after your appointment, such as asking a family member to collect you.
Referral
If your optometrists suspects that you have glaucoma, they will refer you to an ophthalmologist (see box, right) for further tests. Your ophthalmologist will confirm your diagnosis and find out:
- how developed the glaucoma is
- how much damage the glaucoma has done to your eyes
- what may have caused the glaucoma
They will then be able to advise you about the treatment that you need (see Glaucoma - treatment).
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.
