cataract

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Related to Cataracts: macular degeneration, 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 ?
There was a lake here, in the lap of the great mountains, the green slopes that rose toward the lower crags were graced with scattered Swiss cottages nestling among miniature farms and gardens, and from out a leafy ambuscade in the upper heights tumbled a brawling cataract.
From her feet the ground sloped sharply into view, and violets ran down in rivulets and streams and cataracts, irrigating the hillside with blue, eddying round the tree stems collecting into pools in the hollows, covering the grass with spots of azure foam.
The roar of the cataract simply threw up that immense stillness in relief.
Of a sudden the man broke out into blasphemies and cataracts of incredulous words.
When we were seated in the little ferry-boat, and were crossing the swollen river immediately before both cataracts, I began to feel what it was: but I was in a manner stunned, and unable to comprehend the vastness of the scene.
Just as Alice veiled her eyes in horror, under the impression that they were about to be swept within the vortex at the foot of the cataract, the canoe floated, stationary, at the side of a flat rock, that lay on a level with the water.
Were Niagara but a cataract of sand, would you travel your thousand miles to see it?
Presently a fair slip of a girl, about ten years old, with a cataract of golden hair streaming down over her shoulders, came along.
Then came the hill--a cataract, A dusty swirl, before us; The world stood round--a village world-- In fearful chorus
Like the fabulous Gordon Pym, at every moment I expected to see "that veiled human figure, of larger proportions than those of any inhabitant of the earth, thrown across the cataract which defends the approach to the pole.
He reeled back with a shudder and the same moment the drops became a crimson cataract.
Down came the whole side of the mountain, in a cataract of ruin.