Blindness Health Dictionary

Inability to see. Definitions of blindness and partial sight vary. In the , blindness is defined as a corrected visual acuity of 3/60 or less in the better eye, or a visual field of no more than 20 degrees in the better eye. Blindness may result from injury to, or disease or degeneration of, the eyeball; the optic nerve or nerve pathways connecting the eye to the brain; or the brain itself. Clouding of the cornea may result from Sjögren’s syndrome, vitamin A deficiency, chemical damage, infections, and injury. Corneal ulcers can cause blindness due to scarring of the cornea. Uveitis and cataracts are other common causes of blindness. Diabetes mellitus, hypertension, or injury can all cause bleeding into the cavity of the eyeball and subsequent loss of vision. Bleeding into the fluid in front of the lens (hyphaema) or behind the lens (vitreous haemorrhage) can also result in loss of vision. Other conditions that may cause blindness include glaucoma; retinal artery occlusion or retinal vein occlusion; age-related macular degeneration; retinopathy; retinal detachment; tumours such as retinoblastoma and malignant melanoma of the eye; and retinal haemorrhage.

Loss of vision may be due to nerve conduction problems. These problems may be the result of pressure caused by a tumour; reduced blood supply to the optic nerve; optic neuritis; or toxic or nutritional deficiencies. Blindness can result if there is pressure on the visual cortex from a brain tumour or brain haemorrhage, or if the blood supply to the cortex is reduced following a stroke.

Treatment depends on the underlying cause. If the loss of vision cannot be corrected, the patient may then be registered as legally blind or partially sighted. (See also eye; vision, loss of.)

The statutory de?nition – 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 ?eld of vision is markedly contracted in the greater part of its extent’. Partial sight has no statutory de?nition, but there are o?cial 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 ?eld, or better with gross ?eld 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 de?ciency (see EYE, DISORDERS OF).

n. the inability to see. Lack of all light perception constitutes total blindness but there are degrees of visual impairment far less severe than this that may be classed as blindness for administrative or statutory purposes. For example, marked reduction in the *visual field is classified as blindness, even if objects are still seen sharply. The commonest causes of blindness worldwide are *trachoma, *onchocerciasis, and vitamin A deficiency (see night blindness) but there is wide geographic variation. In Great Britain the commonest causes are age-related *macular degeneration, *glaucoma, *cataract, myopic retinal degeneration, and diabetic *retinopathy.