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Complete or partial opacity of the ocular lens. SYN: cataracta. [L. cataracta, fr. G. katarrhaktes, a downrushing, a waterfall, fr. katarrhegnymi, to break down, rush down]

- anular c. congenital c. in which a central white membrane replaces the nucleus. SYN: disk-shaped c., life-belt c., umbilicated c..

- atopic c. a c. associated with atopic dermatitis.

- axial c. a lenticular opacity in the visual axis of the lens.

- black c. a c. in which the lens is hardened and a dark brown. In the 19th century, German black c. meant gutta serena (q.v.). SYN: cataracta brunescens, cataracta nigra.

- blue c. coronary c. of bluish color. SYN: cataracta cerulea.

- capsular c. a c. in which the opacity affects the capsule only.

- capsulolenticular c. a c. in which both the lens and its capsule are involved. SEE ALSO: membranous c..

- central c. congenital c. limited to the embryonic nucleus.

- cerulean c. [MIM*115660] a congenetal c. with bluish coloring and radial lesions; autosomal dominant inheritance in some cases.

- complete c. SYN: mature c..

- complicated c. SYN: secondary c. (1).

- concussion c. traumatic c. occurring with or without a hole in the lens capsule.

- congenital c. c., usually bilateral, present at birth. It occurs as an autosomal recessive condition in calves of the Jersey breed. In humans approximately 25% of bilateral congenital cataracts are autosomal dominant [MIM*116200, *116700]; X-linked forms also exist [MIM*302200, *302300]. Most congenital cataracts are sporadic, some the result of prematurity, intrauterine infection, drug-related toxicity, injury, or chromosomal or metabolic disorders.

- copper c. SYN: chalcosis lentis.

- coralliform c. congenital c. with round or elongated processes radiating from the center of the lens.

- coronary c. peripheral cortical developmental c. occurring just after puberty; transmitted as a hereditary dominant characteristic.

- cortical c. a c. in which the opacity affects the cortex of the lens. SYN: peripheral c..

- crystalline c. a hereditary c. with a coralliform or needle-shaped accumulation of crystals in the axial region of an otherwise clear lens.

- cuneiform c. cortical c. in which the opacities radiate from the periphery like spokes of a wheel.

- cupuliform c. a common form of senile c. often confined to a region just within the posterior capsule. SYN: saucer-shaped c..

- dendritic c. a congenital sutural c. with complicated branching.

- diabetic c. c. occurring in insulin-dependent diabetes mellitus.

- disk-shaped c. SYN: anular c..

- electric c. a c. caused by contact with a high-power electric current, or a lightning bolt. SYN: cataracta electrica.

- embryonic c. [MIM*115650] a congenital c. situated near the anterior Y suture of the fetal lens nucleus. Inheritance heterogeneous.

- embryopathic c. congenital c. as a result of intrauterine infection, e.g., rubella.

- fibroid c., fibrinous c. a sclerotic hardening of the capsule of the lens, following exudative iridocyclitis.

- floriform c. a congenital c. with opacities arranged like the petals of a flower.

- furnacemen's c. SYN: infrared c..

- fusiform c. SYN: spindle c..

- galactose c. a neonatal c. associated with intralenticular accumulation of galactose alcohol. See galactosemia.

- glassworker's c. SYN: infrared c..

- glaucomatous c. a nuclear opacity usually seen in absolute glaucoma.

- gray c. a c. of gray color, usually seen in senile, mature, or cortical c..

- hard c. SYN: nuclear c..

- hook-shaped c. congenital c. with hooklike figures between the fetal and embryonic nuclei.

- hypermature c. a c. in which the lens cortex becomes liquid, with the nucleus gravitating within the capsule (Morgagni c.). SYN: overripe c..

- hypocalcemic c. a c. occurring with low serum calcium.

- immature c. a stage of partial lens opacification.

- infantile c. a c. affecting a very young child.

- infrared c. a c. secondary to absorption of heat by the lens, or by transmission from the adjacent iris. SYN: furnacemen's c., glassworker's c..

- intumescent c. a c. swollen because of fluid absorption.

- juvenile c. a soft c. occurring in a child or young adult.

- lamellar c. a c. in which the opacity is limited to the cortex. SYN: zonular c..

- life-belt c. SYN: anular c..

- mature c. a c. in which both the nucleus and cortex are opaque. SYN: complete c., ripe c..

- membranous c. a secondary c. composed of the remains of the thickened capsule and degenerated lens fibers.

- Morgagni c. a hypermature c. in which the nucleus gravitates within the capsule. SYN: sedimentary c..

- myotonic c. c. occurring in myotonic dystrophy.

- nuclear c. a c. involving the nucleus. SYN: hard c..

- overripe c. SYN: hypermature c..

- perinuclear c. a lamellar c. in which the nucleus is clear but is surrounded by a ring of opacity.

- peripheral c. SYN: cortical c..

- pisciform c. a hereditary c. with bilateral fish-shaped opacities in the axial region of the fetal nucleus.

- polar c. a capsular c. limited to an area of the anterior or posterior pole of the lens.

- posterior subcapsular c. a c. involving the cortex at the posterior pole of the lens.

- progressive c. a c. in which the opacification process progresses to involve the entire lens.

- punctate c. an incomplete c. in which there are opaque dots scattered through the lens.

- pyramidal c. a cone-shaped, anterior polar c..

- radiation c. a c. caused by excessive or prolonged exposure to ultraviolet rays, x-rays, radium, gamma rays, heat, or radioactive isotopes.

- reduplicated c. a type of congenital c. with opacities situated at various levels in the lens.

- ripe c. SYN: mature c..

- rubella c. embryopathic c. secondary to intrauterine rubella infection.

- saucer-shaped c. SYN: cupuliform c..

- secondary c. 1. a c. that accompanies or follows some other eye disease such as uveitis; SYN: complicated c.. 2. a c. occurring in the retained lens or capsule after a c. extraction.

- sedimentary c. SYN: Morgagni c..

- senile c. a c. occurring spontaneously in the elderly; mainly a cuneiform c., nuclear c., or posterior subcapsular c., alone or in combination.

- siderotic c. a c. resulting from deposition of iron from an iron-containing intraocular foreign body.

- soft c. an advanced or mature c. in which the nucleus is not well developed.

- spindle c. a c. in which the opacity is fusiform, extending from one pole to the other. SYN: fusiform c..

- stationary c. a c. that does not progress.

- stellate c. congenital c. with lens opacities radiating toward the periphery, with subcapsular and cortical changes.

- subcapsular c. a c. in which the opacities are concentrated beneath the capsule.

- sugar c. any c. associated with intralenticular accumulation of pentose or hexose alcohols.

- sunflower c. SYN: chalcosis lentis.

- sutural c. a congenital type of c. with opacities along the Y sutures of the fetal lens nucleus; usually does not affect vision.

- tetany c. a c. that develops in hypocalcemia.

- total c. a c. involving the entire lens.

- toxic c. a c. caused by drugs or chemicals.

- traumatic c. a c. caused by contusion, rupture, or a foreign body.

- umbilicated c. SYN: anular c..

- vascular c. congenital c. in which the degenerated lens is replaced with mesodermal tissue. SYN: cataracta adiposa, cataracta fibrosa.

- zonular c. SYN: lamellar c..

cat·a·ract 'kat-ə-.rakt n a clouding of the lens of the eye or its surrounding transparent membrane that obstructs the passage of light

any opacity in the lens of the eye that results in blurred vision. Cataracts may be congenital or due to metabolic disease (such as diabetes), direct or indirect injury to the lens, or prolonged exposure of the eye to infrared rays (e.g. glass-blowers' cataract) or ionizing radiation, but they are most commonly a result of age (senile cataract). A type commonly related to ageing is nuclear sclerotic cataract, which results from increasing density and yellowing of the centre of the lens. A posterior subcapsular cataract, which develops at the rear surface of the lens within the lens capsule, is also related to ageing but occurs in addition with prolonged use of steroids and chronic ocular inflammation. Brunescent cataracts are dark brown and very dense, and a cortical cataract is one in which the opacity occurs in the soft outer part (cortex) of the lens. A Morgagnian cataract is a longstanding very opaque cataract in which the cortex has started to shrink and liquefy, leaving a central shrunken nucleus. Minor degrees of cataract do not necessarily impair vision seriously.

Cataract is treated by removal of the affected lens (see cataract extraction, phacoemulsification); patients may wear a contact lens or appropriate spectacles to compensate for the missing lens but in modern practice a plastic intraocular lens implant is routinely placed inside the eye after surgery.