night blindness

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Related to congenital night blindness: congenital glaucoma, Nightblindness

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.

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]

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.

night blindness

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.

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]

blindness

(blind'nes)
Inability to see. The leading causes of blindness in the U.S. are age-related macular degeneration, diabetic retinopathy, and glaucoma.

Blindness may be caused by diseases of the lens, retina, or other eye structures; diseases of the optic nerve; or lesions of the visual cortex or pathways of the brain. A small number of infants are born blind, but far more people become blind during life. In the U.S., blindness due to infection is rare, but worldwide diseases like trachoma and onchocerciasis are relatively common causes of severe visual impairment. In malnourished people, vitamin A deficiency is an important cause of blindness.

A variety of free services are available for the blind and physically handicapped. Talking Books Topics, published bimonthly in large-print, cassette, and disc formats, is distributed free to the blind and physically handicapped who participate in the Library of Congress free reading program. It lists recorded books and magazines available through a national network of cooperating libraries and provides news of developments and activities in library services. Subscription requests may be sent to Talking Books Topics, CMLS, P.O. Box 9150, Melbourne, FL 32902-9150.

amnesic color blindness

Inability to remember the names of colors.
Enlarge picture
TEST FOR COLOR BLINDNESS

color blindness

A genetic or acquired abnormality of color perception. Complete color blindness, a rare disease, is called achromatopsia. Red-green color blindness, which affects about 8% of the male population, is an X-linked trait. Although color blindness is the term most commonly used, it is inaccurate:color deficiency and color vision deficiency are preferred. See: illustration

cortical blindness

Blindness due to lesions in the left and right occipital lobes of the brain. The eyes are still able to move, and the pupillary light reflexes remain, but the blindness is as if the optic nerves had been severed. The usual cause is occlusion of the posterior cerebral arteries. Transitory cortical blindness may follow head injury.
Synonym: cerebral visual impairment

day blindness

Hemeralopia.

eclipse blindness

Blindness due to burning the macula while viewing an eclipse without using protective lenses. Looking directly at the sun at any time can damage the eyes. Synonym: solar blindness; solar maculopathy

green blindness

Aglaucopsia.

hysterical blindness

An inaccurate term for functional blindness, i.e., blindness caused by psychological disorders rather than by demonstrable organic pathology.

legal blindness

A degree of loss of visual acuity that prevents a person from performing work requiring eyesight. In the U.S. this is defined as corrected visual acuity of 20/200 or less, or a visual field of 20° or less in the better eye. In the U.S. there are about three quarters of a million blind people, and about 8 or 9 million people with significant visual impairment.

letter blindness

A form of aphasia marked by an inability to understand the meaning of letters.

night blindness

Nyctalopia (1).

note blindness

The inability to recognize musical notes. It is due to a lesion of the central nervous system.

object blindness

A disorder in which the brain fails to recognize things even though the eyes function normally.
See: apraxia

psychic blindness

Sight without recognition due to a brain lesion.

red-green blindness

Red-green color blindness

red-green color blindness

Inability to see red hues. It is the most common kind of color blindness. Synonym: red-green blindness

river blindness

See: onchocerciasis

snow blindness

Blindness, usually temporary, due to the glare of sunlight on snow. It may result in photophobia and conjunctivitis, the latter resulting from effects of ultraviolet radiation.

solar blindness

Eclipse blindness.

taste blindness

An inability to taste certain substances such as phenylthiocarbamide. This inability is due to an autosomal recessive trait.

transient monocular blindness

A temporary loss of vision affecting one eye. In older adults it is usually a form of transient ischemic attack, caused by carotid atherosclerosis, and is therefore a harbinger of stroke. In young adults it may be caused by migraine. Synonym: amaurosis fugax

Etiology

In older adults, causes of carotid atherosclerosis include smoking, diabetes mellitus, hypertension, obesity, and hypercholesterolemia. When atherosclerotic plaques form within the carotid artery, they may ulcerate. The exposed endothelium within the artery becomes a focus of inflammation and blood clotting. Blindness occurs when tiny clots from the carotid arteries embolize to the ophthalmic arteries.

Symptoms

Patients often describe a dark shade descending into the field of vision. At the same time they may have other stroke symptoms, e.g., difficulty with speech or weakness of the hand on the side opposite the affected eye.

Treatment

A patient who may have carotid atherosclerosis should begin taking aspirin or other antiplatelet drugs if these are tolerated. Blood pressure and lipid levels should be controlled. The patient should be referred for noninvasive evaluation of blood flow through the carotid arteries, e.g., ultrasonography. If the carotid arteries are significantly blocked, the patient and physician should consider the risks and benefits of carotid endarterectomy.

violet blindness

Inability to see violet tints.

word blindness

Alexia.

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.

night blindness

see VITAMIN A.

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.

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.

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