The eye is like a camera. Light passes through the front of the eye, to the optic nerve at the back of the eye and to the brain – which then makes a picture of what you see.

If any part of the eye is damaged or not working properly this can affect sight and cause visual impairment.

Visual impairment can be caused by disease, old age, an accident, or it can be inherited. There are 378,000 people in the UK who are registered as blind or partially sighted.

What causes visual impairment and who can get it?

Accidents and disease often cause visual impairment although some people are born with poor sight.

There are several common causes of visual impairment, some of these are treatable and some are not:

Cataracts – Cataracts are clouding of the eye’s lens, which blurs vision. Cataracts can form at any age and some babies are born with cataracts, but most people tend to get them when they are older.

Cataracts are treated in an operation where the cloudy lens is removed and replaced with a plastic lens.

Glaucoma – Glaucoma is a condition, which can cause visual impairment. Glaucoma occurs when there’s an increase in pressure inside the eye. The pressure damages the optic nerve (this nerve that carries light from the eye to the brain).

Glaucoma is more common in older people and in those people who have a family history of glaucoma, but some babies are born with glaucoma. It can be picked up in a simple test done by an optometrist. A person’s sight can be preserved if the condition is found early.

Age-related macular degeneration – Age-related macular degeneration (AMD) is the most common cause of vision loss in older people and is caused by the light sensitive cells in the retina (the back surface of the eye) deteriorating. The condition is not painful, and rarely causes loss of vision, although people with this condition may have a blank spot in their vision, which makes reading and writing difficult. 

Trauma - Any severe trauma to the eye – such as an explosion (like a firework) or a blow to the head can damage the eye and impair vision.

What are the signs and symptoms of visual impairment?

Sight loss can be sudden and severe, such as after a trauma, but it is usually a gradual deterioration over a long period of time.

Symptoms usually depend on the specific eye problem but may include a blurring or fogging of the vision and a restriction of the peripheral field of vision (how well you can see out the corner of your eye). Occasionally visual impairment is accompanied by headache or eye pain.

How is visual impairment normally diagnosed and treated?

A basic sight test, known as a visual acuity test, is used to determine how good your vision is. The test is usually done by an optician and involves reading letters from a chart that become progressively smaller on each line.

If a problem with your eyes is picked up you will then need to be referred by your GP or optician to a hospital eye doctor (ophthalmologist) who will carry out further tests. If a condition such as glaucoma and cataracts are discovered they can then be treated to help preserve your vision.

If you have a significant reduction on your vision, which cannot be corrected with glasses or contact lenses, you may be eligible to be registered as sight impaired or severely sight impaired.

What’s going to help?

Having an eye test at least every two years can help to detect problems that may need treatment before any permanent damage has been done.

It's also important to wear protective eyewear in situations where you could accidentally damage your eyes, for example when playing dangerous sport, or doing DIY.

Looking forward

If you are diagnosed as being visually impaired there are lots of things that can help you to lead a normal life.

Techniques such as Braille help you to read, and you may even get the help of a guide dog. These helper dogs are trained to be a blind person's eyes. They learn to be very alert to surroundings so as well as being your friend they can be your guide and help you to lead an independent life.

For more help and information

RNIB (Royal National Institute of Blind People)

Last reviewed by Great Ormond Street Hospital: 29 September 2007

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