cataract


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Related to cataract: Cataract surgery, glaucoma

cataract,

in medicine, opacity of the lens of the eye, which impairs vision. In the young, cataracts are generally congenital or hereditary; later they are usually the result of degenerative changes brought on by aging or systemic disease (diabetesdiabetes
or diabetes mellitus
, chronic disorder of glucose (sugar) metabolism caused by inadequate production or use of insulin, a hormone produced in specialized cells (beta cells in the islets of Langerhans) in the pancreas that allows the body to use and store
..... Click the link for more information.
). Cataracts brought on by aging are most common; most individuals over 60 exhibit some degree of lens opacity. Injury, extreme heat, ultraviolet light, X rays, nuclear radiation, inflammatory disease, and toxic substances also cause cataracts. There is growing concern that further disintegration of the ozone layerozone layer
or ozonosphere,
region of the stratosphere containing relatively high concentrations of ozone, located at altitudes of 12–30 mi (19–48 km) above the earth's surface.
..... Click the link for more information.
 will increase the incidence of cataracts. Advanced cataracts are usually treated by surgical removal of the lens and implantation of an artificial lens. After cataract surgery, which is the most common surgical procedure in the United States, most patients do not require thick glasses or contact lenses.

Cataract

 

an opacity of the crystalline lens of the eye that prevents light from penetrating into the eye and that results in decreased visual acuity. The term “cataract” reflects the mistaken conception of the ancient Greeks that a cataract is caused by the effusion of a turbid fluid between the iris and the lens. Cataracts are distinguished according to the location of the opacity in the lens: capsular (in the capsule covering the lens), cortical (in the peripheral layers of the lens), and nuclear (in its central layers).

Cataracts may be congenital or acquired. Congenital cataracts develop in the intrauterine period, and the opacity generally does not enlarge or change with age. In congenital cataracts, parts of the lens almost invariably remain transparent, and visual acuity is not completely impaired. Depending on the site of the opacities, cataracts may be anterior or posterior polar (limited opacities of the capsule of the lens), lamellar, and so forth.

Senile cataracts constitute most of the acquired cataracts, and they are characterized by progression of the opacities of the lens. In senile cataracts, opacities appear first in the periphery of the lens (incipient senile cataract), and vision remains unimpaired. The number of opacities then increases and they coalesce, resulting in a marked decrease in visual acuity (immature cataract). As the condition develops, all the layers of the lens become cloudy and it turns grayish white or mother-of-pearl; visual acuity decreases to photoperception—that is, the eye becomes virtually blind (mature senile cataract). Also acquired are complicated cataracts that arise in some systemic diseases (diabetes, cholera, digestive disorders) or result from diseases of the eye itself (inflammation of the uveal tract, progressive myopia). Cataracts resulting from eye injuries, effects of radiation, and so forth constitute a large group of acquired cataracts.

Treatment is generally surgical. In some cases it involves transplanting an artificial lens.

REFERENCE

Dymshits, L. A. “Bolezni khrustalika.” In Mnogotomnoe rukovodstvo po glaznym bolezniam, vol. 2, book 2. Moscow, 1960.

L. A. KATSNEL’SON

cataract

[′kad·ə‚rakt]
(hydrology)
A waterfall of considerable volume with the vertical fall concentrated in one sheer drop.
(medicine)
An opacity in the crystalline lens or the lens capsule of the eye.

cataract

1. a large waterfall or rapids
2. Pathol
a. partial or total opacity of the crystalline lens of the eye
b. the opaque area
References in classic literature ?
We had such a beautiful day, and such endless pictures of limpid lakes, and green hills and valleys, and majestic mountains, and milky cataracts dancing down the steeps and gleaming in the sun, that we could not help feeling sweet toward all the world; so we tried to drink all the milk, and eat all the grapes and apricots and berries, and buy all the bouquets of wild flowers which the little peasant boys and girls offered for sale; but we had to retire from this contract, for it was too heavy.
Surely it is not possible to feel otherwise, any more than it would be possible for a man with cataract to regret the painful process by which his dim blurred sight of men as trees walking had been exchanged for clear outline and effulgent day.
It was not far from the Rue de Louvain, and we stood on the doorsteps of the house we sought ere the clouds, severing with loud peal and shattered cataract of lightning, emptied their livid folds in a torrent, heavy, prone, and broad.
Agamemnon shed tears as it were a running stream or cataract on the side of some sheer cliff; and thus, with many a heavy sigh he spoke to the Achaeans.
This we were obliged to build close to the foot of the cataract, for the current of water extended very nearly to the sides of the gorge.
83, he declared that, as he had seen all the civilized parts of the earth, he was inclined to make a trip to the wilds of America We will not trace him in his brief wanderings, under the influence of that spirit of emigration that some times induces a dapper Cockney to quit his home, and lands him, before the sound of Bow-bells is out of his ears, within the roar of the cataract of Niagara; but shall only add that at a very early day, even before Elizabeth had been sent to school, he had found his way into the family of Marmaduke Temple, where, owing to a combination of qualities that will be developed in the course of the tale, he held, under Mr.
If suddenly startled while feeding in the midst of a forest, the noise they make in getting on the wing is like the roar of a cataract or the sound of distant thunder.
A great cataract of flounces rolled down from the young lady's waist to Newman's feet; he had to step aside to avoid treading upon them.
It was a dull gray landscape, and as I gradually deciphered the details of it I realized that it represented a long and enormously high line of cliffs exactly like an immense cataract seen in the distance, with a sloping, tree-clad plain in the foreground.
Other dispersed fragments of the same great palladium are to be found on the canals of Venice, at the second cataract of the Nile, in the baths of Germany, and sprinkled on the sea-sand all over the English coast.
To-morrow my friends will fly up to the Second Cataract.
Adair's mother had returned from Australia to undergo the operation for cataract, and she, her son Ronald, and her daughter Hilda were living together at 427 Park Lane.