Visual impairment

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The eye is made of three parts.

The cornea and lens, which focus light at the front of the eye,
The retina, a light sensitive film at the back of the eye,
and optic nerves, a large collection of communication wires to the brain.

Many people have some sight problems and need to wear glasses or contact lenses. The three most common causes of sight problems are:

Long-sightedness

The medical name for long-sightedness is hypermetropia. People with long-sightedness have difficulty seeing close-up objects. This is because the eyeball is too short, causing the light rays around objects to travel behind the retina, because they havenâ€™t been bent enough by the cornea and lens.

Long-sightedness often becomes worse as you get older and can also affect the way you see distant objects. People with long-sightedness usually need to wear corrective eyewear such as glasses or contact lenses to read, write and carry out detailed tasks.

Short-sightedness

The medical name for short-sightedness is myopia. People with short-sightedness have difficulty seeing distant objects because the eyeball is too long, causing the light rays from objects to travel to the front of the retina, having been bent too much by the cornea and lens.

Between a quarter and a third of people in the UK are shortsighted. People with short-sightedness usually need to wear corrective eyewear such as glasses or contact lenses to drive and carry out tasks that involve looking at far-off objects. Shortsightedness may also sometimes be treated with laser surgery.

Astigmatism

Astigmatism is when the cornea is unevenly shaped, causing light be focussed on some, but not all parts of an object. People without sight difficulties have basketball-shaped corneas, whereas people with astigmatism have rugby ball-shaped corneas.

People with astigmatism usually need to wear glasses or contact lenses to correct their vision.

Visual impairment is used to describe people who are blind or partially sighted, as opposed to long or short-sighted. A person with a visual impairment has some loss or distortion of their vision. Depending on how severe the sight loss is, the conditions are usually known as partial sightedness or blindness.

Partial sightedness

A person with partial sight or severe low vision has a serious loss of sight but is not blind. This has been defined by the World Health Organisation as a person who cannot clearly see how many fingers are being held up at a distance of 6 metres or less (even with their glasses or lenses on).

Blindness

A person who is blind has very severe sight loss and is unable to clearly see how many fingers are being held up at a distance of three metres or less (even with their glasses or lenses on). However, they may still have some degree of vision.