night blindness

blindness /blind·ness/ (blīnd´nes) lack or loss of ability to see; lack of perception of visual stimuli.

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blue blindness , blue-yellow blindness popular names for imperfect perception of blue and yellow tints; see tritanopia and tetartanopia .

color blindness 

1. popular name for color vision deficiency.

2. see monochromatic vision.

complete color blindness  monochromatic vision.

day blindness  hemeralopia.

flight blindness  amaurosis fugax due to high centrifugal forces encountered in aviation.

green blindness  imperfect perception of green tints; see deuteranopia and protanopia.

legal blindness  that defined by law, usually, maximal visual acuity in the better eye after correction of 20/200 with a total diameter of the visual field in that eye of 20 degrees.

letter blindness  alexia characterized by inability to recognize individual letters.

music blindness  musical alexia.

night blindness  failure or imperfection of vision at night or in dim light.

object blindness , psychic blindness visual agnosia.

red blindness  popular name for protanopia.

red-green blindness  popular name for any imperfect perception of red and green tints, including all the most common types of color vision deficiency. See deuteranomaly, deuteranopia, protanomaly, and protanopia.

snow blindness  dimness of vision, usually temporary, due to glare of sun upon snow.

text blindness  alexia.

total color blindness  monochromatic vision.

word blindness  alexia.

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night blindness

n.

See nyctalopia.

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night blindness.

See nyctalopia.

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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.

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night blindness

inability or a reduced ability to see in dim light. In night blindness, the eyes not only see more poorly in dim light, but are slower to adjust from brightness to dimness. It is a sign of hypovitaminosis A and early progressive retinal atrophy. Testing for night blindness entails construction of an obstacle race and putting an animal through it at dusk. Difficult to interpret results.

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congenital night blindness

occurs in Appaloosa horses. There is a retinal defect which is detectable by electroretinography.

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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.

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night blindness

1 Vitamin A deficiency, see there 2 Retinitis pigmentosa, see there 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