The statutory deﬁnition – for the purposes of registration as a blind person under the National Assistance Act 1948 – is that the person is ‘so blind as to be unable to perform any work for which eyesight is essential’. Generally this is vision worse than 6/60 in the better eye, or with better acuity than this but where ‘the ﬁeld of vision is markedly contracted in the greater part of its extent’. Partial sight has no statutory deﬁnition, but there are oﬃcial guidelines for registering a person as partially sighted: generally these are a corrected visual acuity of 3/ 60 or less in the better eye with some contraction of the peripheral ﬁeld, or better with gross ﬁeld defects. In the UK more than 100,000 people are registered as legally blind and some 50,000 as partially sighted. The World Health Organisation has estimated that there are over 40 million binocularly blind people in the world. The causes of blindness vary with age and degree of development of the country. In western society the commonest causes are glaucoma, diabetic retinopathy, other retinal diseases and senile cataract. (See also VISION.)
Any blind person, or his or her relatives, can obtain help and advice from the Royal National Institute for the Blind (www.rnib.org.uk).
Night blindness An inability to see in the dark. It can be associated with retinitis pigmentosa or vitamin A deﬁciency (see EYE, DISORDERS OF).