Inability to see. Definitions of blindness and partial sight vary. In the UK, 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.)
Blindness |
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