night blindness
inability or a reduced ability to see in dim light; the eyes not only see more poorly in dim light, but are slower to adjust from brightness to dimness. Called also
nyctalopia.
Depending on its brightness, light is perceived by either of two sets of visual cells located in the retina of the eye. One set, the cones, perceive bright light primarily; the other set, the rods, perceive dim light primarily. Dim light produces a change in a pigment called rhodopsin in the rods. This change causes nerve impulses to travel to the brain, where they register as visual impressions. Night blindness occurs when the rods lack rhodopsin.
One cause of night blindness is a deficiency of vitamin A—the primary source of rhodopsin. The defect in vision usually can be cured by proper diet plus therapeutic doses of the deficient vitamin.
In the elderly, there is sometimes a diminution of rhodopsin, with resulting night blindness. Other losses in vision may follow. Diminished blood supply to the eyes is thought to be a cause of this form of the condition. Treatment generally is only of limited effectiveness.
Night blindness sometimes accompanies glaucoma.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
nyc·ta·lo·pi·a
(nik-tă-lō'pē-ă), Decreased ability to see in reduced illumination. Seen in patients with impaired rod function; often associated with a deficiency of vitamin A.
[nyct- + G. alaos, obscure, + ōps, eye]
Farlex Partner Medical Dictionary © Farlex 2012
night blindness
n. A condition of the eyes in which vision is normal in daylight or other strong light but is abnormally weak or completely lost at night or in dim light. The condition may result from vitamin A deficiency, disease, or hereditary factors. Also called nyctalopia.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
night blindness
3. Nyctalopia Defective vision in ↓ illumination, often implying defective rod function with delayed dark adaptation and perceptual threshold; it is either congenital and stationary with myopia and degeneration of the disc–eg, retinitis pigmentosa, hereditary optic atrophy or progressive and acquired with retinal, choroidal or vitrioretinal degeneration–eg, cataract, glaucoma, optic atrophy, retinal degeneration and, the 'classic' cause of nyctalopia, vitamin A deficiency.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
nyc·ta·lo·pi·a
(nik'tă-lō'pē-ă) Decreased ability to see in reduced illumination. Seen in patients with impaired rod function; often associated with a deficiency of vitamin A.
Synonym(s):
night blindness.
[nyct- + G. alaos, obscure, + ōps, eye]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
night blindness
Moderately reduced to severely defective vision in dim light. Night blindness (nyctalopia) occurs in many people with no objectively discernible eye disorder, but is common in short-sighted people, in those with vitamin A deficiency and in the early stages of degenerative diseases of the RETINA including RETINITIS PIGMENTOSA.Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
night blindness
see VITAMIN A.Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
hemeralopia
Term used to mean either
night blindness in which there is a partial or total inability to see in the dark associated with a loss of rod function or vitamin A deficiency; or
day blindness in which there is reduced vision in daylight while vision is normal in the dark.
Syn. nyctalopia (this term is only synonymous with night blindness); night sight (this term is only synonymous with day blindness).
See girate atrophy;
congenital stationary night blindness;
choroideremia;
Oguchi's disease;
retinitis pigmentosa.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann