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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
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). 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.
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 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.



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.


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



A waterfall of considerable volume with the vertical fall concentrated in one sheer drop.
An opacity in the crystalline lens or the lens capsule of the eye.


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 periodicals archive ?
In nuclear cataracts, it is predicted that the loss of reduced protein sulfhydryl groups is a major mechanism for cataract growth.
Statins counteract destructive free radicals, which have been linked to nuclear cataracts. This study shows only an association between statin use and fewer nuclear cataracts, Klein cautions.
Editor's Note: While three cross-sectional studies have found a lower risk of nuclear cataract or their progression in association with higher serum levels or dietary intake of lutein and zeaxanthin, the current study's authors note that a recent FDA review concluded that there was no credible evidence to support a protective effect for lutein or zeaxanthin on cataract risk.
Straylight varied as a function of cataract morphology (Table 3); it was significantly higher in the three cataract groups (1.22 [+ or -] 0.20 log units in nuclear cataract, 1.26 [+ or -] 0.23 log units in cortical cataract, and 1.48 [+ or -] 0.34 log units in PSC) compared to the control group (1.12 [+ or -] 0.16 log units, P < 0.05).
The researchers found that cigarette smoking was associated with an increased risk of age-related cataract, especially nuclear cataract.
Healthy diets and the subsequent prevalence of nuclear cataract in women.
"Diet was the strongest risk factor related to reduced risk of nuclear cataract in this sample of postmenopausal women.
According to the study, nuclear cataract was common in the sample with 29 percent (454 women) reporting the eye disease with a lens in at least one eye.
The largest influence on the image quality was demonstrated for nuclear cataract; although due to the small study size, the statistical subgroup analysis was inconclusive.
Higher intakes of protein, vitamin A, niacin, thiamin, and riboflavin were associated with reduced prevalence of nuclear cataract. Intake of polyunsaturated fats was associated with reduced prevalence of cortical cataract.
(30) Elderly age, high rate of pseudoexfoliation co-existence and a dense nuclear cataract were the most common types of comorbidities that may be responsible for the higher zonular dialysis rate and posterior capsular perforation with and without vitreous exposure in our study.
The development of senile cataract, especially nuclear cataract, is associated with progressive oxidative changes in the intrinsic membrane fraction and membrane-related components of the lens, which eventually extends beyond them to also involve the soluble components of lens proteins.