Low vision is often a loss of sharpness or acuity. It may also present as a loss of field of vision, light sensitivity, distorted vision or a loss of contrast.
A person is said to have low vision when their eyesight is limited or impaired and cannot be adequately corrected with surgery, conventional glasses or contact lenses.
Low vision can affect people of all ages and have an impact on many aspects of their life. It may cause problems with reading, using the computer, dialling the telephone, and watching TV. Low vision can make it difficult to recognise faces, see stairs, cross the road and undertake daily living and leisure activities. Low vision services are essential in helping the individual and their family, carers and friends to cope with the challenges of low vision.
How low vision is measured
Low vision is measured by distance visual acuity. When a person has normal vision their visual acuity is rated 6/6 or 20/20. This rating indicates that the person can read the letters on an eye chart, which is designed to be seen at a distance of six metres or twenty feet away.
A person is said to have low vision when they see fewer letters on the eye chart from this distance. For example 6/18 means that the patient can see at 6 metres, what a person with normal vision is able to see at 18 metres. A person is considered legally blind if they cannot see at six metres what someone with normal vision can see at 60 metres or if their field of vision is less than 20 degrees in diameter.