1. Loss of the sense of sight; absolute b. connotes no light perception. SEE ALSO: amblyopia, amaurosis. 2. Loss of visual appreciation of objects although visual acuity is normal. 3. Absence of the appreciation of sensation, e.g., taste b.. SYN: typhlosis.
- change b. failure to observe large changes in the vision field that occur simultaneously with brief disturbances.
- color b. misleading term for anomalous or deficient color vision; complete color b. is the absence of one of the primary cone pigments of the retina. See protanopia, deuteranopia, tritanopia.
- day b. SYN: hemeralopia.
- eclipse b. SYN: solar maculopathy.
- flash b. a temporary loss of vision produced when retinal light-sensitive pigments are bleached by light more intense than that to which the retina is physiologically adapted at that moment.
- hysterical b. loss of vision or blurring of vision following a psychologically traumatic event such as seeing one's child being killed in an accident.
- legal b. generally, visual acuity of less than 6/60 or 20/200 using Snellen test types, or visual field restriction to 20° or less in the better eye; the criteria used to define legal b. vary among different groups.
- letter b. visual agnosia for letters, in which letters are seen but not identified; caused by a lesion in the occipital cortex.
- mind b. visual agnosia for objects, in which objects are seen but not identified; caused by a lesion in area 18 of the occipital cortex. SYN: object b., psychanopsia, psychic b..
- music b. SYN: musical alexia.
- night b. SYN: nyctalopia.
- note b. SYN: musical alexia.
- river b. SYN: ocular onchocerciasis.
- solar b. SYN: solar maculopathy.
- text b., word b. SYN: alexia.
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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.
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blind·ness (blīndґnis) lack or loss of ability to see; lack of perception of visual stimuli, due to disorder of the organs of sight or to lesions in certain areas of the brain; see also amaurosis.Medical dictionary. 2011.