lack or loss of ability to see (see vision
). Legally, blindness is defined as less than 20/200 vision in the better eye with glasses
(vision of 20/200 is the ability to see at 20 feet only what the normal eye can see at 200 feet). A person with 20° or less vision (pinhole vision
) is also legally blind. In 2002, the number of people classified as legally blind in the United States was estimated at 10 million; millions more had severe visual impairments. The five leading causes of impaired vision and blindness in the United States are age-related macular degeneration
, diabetic retinopathy
, and atrophy of the optic nerve
. Besides health care problems, issues related to employment, independent living, and literacy should all be considered when caring for patients who are blind. The American Foundation for the Blind is a resource center for information related to visual problems. They can be contacted by calling 1-800-232-5463 or consulting their web site at http://www.afb.org.
) popular names for imperfect perception of blue and yellow tints; see tritanopia
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°.
snow blindness dimness of vision, usually temporary, due to the glare of the sun upon snow.
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.
TEST FOR 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
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
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
An inaccurate term for functional blindness, i.e., blindness caused by psychological disorders rather than by demonstrable organic pathology.
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.
A form of aphasia marked by an inability to understand the meaning of letters.
night blindnessNyctalopia (1).
The inability to recognize musical notes. It is due to a lesion of the central nervous system.
A disorder in which the brain fails to recognize things even though the eyes function normally. See: apraxia
Sight without recognition due to a brain lesion.
red-green blindnessRed-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
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 blindnessEclipse 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
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.
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.
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.
Inability to see violet tints.