Health encyclopaedia

Health encyclopaedia - Alphabetical Topic List

Short-sightedness

Myopia, (short-sightedness) is a vision defect resulting from the eye being too long from front to back, or from a steeply curved cornea, so that there is an inadequate correlation between the focusing power of the cornea and lens and the length of the eye. Myopia causes light rays to focus on the front of the retina and so close objects are seen clearly, whilst distant objects appear blurred.

The focusing power of a lens is measured in dioptres. Myopia up to 3 dioptres (D) is termed mild degree, 3 to 6D is moderate degree and high degree is 6D and over. (A dioptre is 1 divided by the focal length of the lens in centimetres. So a 1-dioptre lens has a focal length of 1m; a 2-dioptre lens has a focal length of 50cm; a 5D lens has a focal length of 20cm.)

Approximately 30% of people in Britain are short-sighted and approximately 5% of those will have high degree myopia. A

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