sight test


Glaucoma is a group of eye diseases in which the optic nerve, which connects your eye to your brain, is damaged by the pressure of the fluid inside your eye.

This may be because the pressure is higher than normal, or because the nerve is more susceptible to damage from pressure. This may affect one or both of your eyes. There are two main types of glaucoma – chronic glaucoma, which happens slowly, and acute glaucoma which happens quickly. Chronic glaucoma is much more common than acute glaucoma. The most common form of chronic glaucoma is called primary open angle glaucoma (POAG).

Chronic glaucoma

Who is at risk of chronic glaucoma?

Anyone can develop chronic glaucoma. The risk of developing chronic glaucoma increases if you:
• are aged over 40
• are very short-sighted
• are of African or Caribbean origin
• are closely related to someone with chronic glaucoma
• have raised pressure in your eye. This is called ocular hypertension (OHT)
• are diabetic
• have high blood pressure.

If one of your parents or children, or a brother or sister, has glaucoma, and you are over 40, the NHS will pay for your eye examination. (In Scotland all eye examinations are provided under the NHS.)

A person with glaucoma may see blurring around the outside of their vision, but this is usually when glaucoma is well advanced. Catch it early to avoid this.

Will I go blind if I have glaucoma?

If left untreated, glaucoma can lead to tunnel vision and blindness, but most people who go blind from glaucoma are those in whom it was detected at a late stage. As a result, it is important to detect it early.

How is chronic glaucoma detected?

Because the early stages of chronic glaucoma do not cause symptoms, the best way to catch it early is to have regular eye examinations.

A person with glaucoma may see blurring around the outside of their vision, but this is usually when glaucoma is well advanced. Catch it early to avoid this.

There are three main tests to see if you have chronic glaucoma. The first one is where your optometrist looks at the nerve at the back of your eye using an ophthalmoscope, or a slit lamp to shine a light into your eye. They may also take a photograph or a scan of the nerve.
This can be useful for future visits, to help them see if things have changed.

The second test is where the optometrist measures the pressure inside your eye. This may be done by using a machine which gently blows a puff of air at your eye, or by numbing your eye with drops and then gently pressing an instrument called a tonometer against it.
The tests do not hurt, although the puff of air may make you jump a bit.
The third test is where the optometrist tests how wide your visual field is – how far you can see around you when you are looking straight ahead.

Sometimes you can have chronic glaucoma even if you have normal eye pressure, which is why you will usually have at least two of these three tests. If the results are not clear, you may be asked to do one or more of the tests again on a different day.

I have been told that the pressure inside my eye is high, but I do not have glaucoma

Some people naturally have pressure that is above the normal range, but this pressure does not cause any damage to their eyes. This means they do not have glaucoma. However, they are more likely to develop chronic glaucoma, so your optometrist or ophthalmologist (a specialist eye doctor) will tell you how often you should have this checked.

What will happen if I have chronic glaucoma?

If your optometrist suspects that you may have glaucoma, they will refer you to an ophthalmologist. If you have chronic glaucoma, you will be given eye drops to use every day. The drops will reduce the pressure and help control the build-up of fluid. They will not hurt.

Because you will not feel different in any way, you will not be able to tell that the treatment is working. This is why it is very important that you:
• go to your follow-up appointments
• keep on using the drops. If you find it hard to use the eye drops, you can get special bottles or holders to make it easier.

In a small number of cases, your ophthalmologist may recommend that you have an operation to help drain away the fluid. There is no cure for chronic glaucoma but it can be treated effectively, normally with eye drops. Any existing eye damage will probably be permanent, but your sight could get much worse if you stop the treatment. It is very important that you use the eye drops every day, even if you cannot tell that they are helping.

I have glaucoma. Can I drive?

If you drive a car and have been diagnosed with glaucoma in both eyes, this will affect the amount you can see around you, and the law says that you must tell the DVLA (Driver and Vehicle Licensing Authority), or DVA if you are in Northern Ireland. You may have to take some extra tests, but most people are still allowed to carry on driving. You can find out more at

Acute glaucoma

This is a type of glaucoma where the drainage channels inside your eye are blocked or damaged in some way. This causes the pressure inside your eye to increase rapidly. It may be called acute angle closure glaucoma.

Sometimes the increased pressure can come and go, and some people get short bursts of pain or discomfort and blurred vision. This can happen when your pupils get bigger, so you may notice it at night or when you are in a dark area (like the cinema) or when you are reading.

Other symptoms are an ache in the eye which may come and go, nausea and vomiting, red eyes, or seeing coloured rings around white lights, or it can be a bit like looking through a haze or mist.

If you get these symptoms it is important to act quickly, even if the symptoms appear to go away, as your vision may be damaged each time you notice the symptoms.

If you have these symptoms but they have gone away, you should see your optometrist as soon as possible and mention that you have had these symptoms. If you have these symptoms and they have not gone away, you should go to the Accident and Emergency department immediately so that they can reduce the pressure in your eye and get rid of the pain.

People who are more likely to get acute glaucoma are:
• people over the age of 40
• women
• people of East Asian or South Asian origin
• people with a family history of closed-angle glaucoma
• people who are long-sighted.

For more information, look up glaucoma on the NHS Choices website, or phone SightLine on 01233 648170. Sightline is an information, support and advice service provided by the International Glaucoma Association.

Charles Bonnet syndrome

Some people with poor vision may experience silent visual hallucinations called Charles Bonnet syndrome. These may be quite vivid. They are caused by the brain trying to ‘fill in’ detail in the blind areas. They are not a sign of mental illness. You can find help and more information at

More information

Call Sightline, an information, support and advice service provided by the International Glaucoma Association, on 01233 648170