cataract

—cataractal, cataractous, adj. —cataracted, adj.

/kat"euh rakt'/, n.

1. a descent of water over a steep surface; a waterfall, esp. one of considerable size.

2. any furious rush or downpour of water; deluge.

3. Ophthalm.

a. an abnormality of the eye, characterized by opacity of the lens.

b. the opaque area.

[1350-1400; ME cataracte < L catar(r)acta < Gk katarráktes waterfall, floodgate, portcullis (n.), downrushing (adj.), akin to katarássein to dash down, equiv. to kat- CATA- + arássein to smite]

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Opacity of the eye's crystalline lens.

Cataracts causing central visual-field defects are most likely to affect vision. Cataracts may occur in newborns and infants. Diabetes mellitus, prolonged exposure to ultraviolet rays, or trauma can cause them in adults, but they most often occur with age, resulting from gradual loss of transparency of the lens. Treatment is a surgical procedure to replace the lens with an artificial one.

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      a waterfall (q.v.), especially one containing great volumes of water rushing over a precipice.

▪ eye

      opacity of the crystalline lens of the eye (eye, human). Cataracts occur in 50 percent of people between the ages of 65 and 74 and in 70 percent of people over the age of 75. Typical age-related cataracts can cause cloudy vision, glare, colour vision problems, changes in eyeglass (eyeglasses) prescription, and, rarely, double vision (only in the affected eye). Usually, these types of cataracts are bilateral, although one eye may be more affected than the other.

      The three common types of cataract are nuclear sclerotic cataracts, cortical cataracts, and posterior subcapsular cataracts. These cataracts can exist in isolation or in any combination with each other, and each can cause a wide spectrum of vision problems, from unnoticeable to blinding. Nuclear cataracts cause a slow, progressive yellowing or browning of the central core of the lens as it undergoes compression and hardening. Cortical cataracts are spokelike opacities that extend from the lens periphery toward the centre. Advanced cortical cataracts can cause the lens to appear white, a so-called mature cataract. Posterior subcapsular cataracts are located near the very back of the lens and, if present in a troublesome location, can cause vision difficulties even at a relatively small size. In contrast to nuclear or cortical cataracts, posterior subcapsular cataracts tend to occur in younger people and can result from steroid use, exposure to radiation (radiation injury), or trauma. In addition to age-related lens changes, some systemic diseases can promote cataract formation, most notably diabetes mellitus. Management of symptomatic cataracts is surgical, requiring removal of the offending lens and placement of an artificial lens within the eye, if possible.

      Cataracts present at birth are termed congenital cataracts, whereas those that are evident within the first year of life are called infantile cataracts. They can affect one or both eyes and can produce severe visual impairment and amblyopia. They can occur by themselves; in association with genetic and metabolic diseases (metabolic disease), in utero maternal infections, or toxin exposure; or in combination with other congenital eye problems. Treatment involves surgical removal of the cataractous lens if it interferes with vision. However, placement of an artificial lens within the eye requires special considerations and may not be appropriate, depending on the child's age. Eyeglasses or contact lenses (contact lens) are commonly used postoperatively to improve vision, and occlusion patching of the unaffected eye is often necessary to treat associated amblyopia.

Daniel M. Albert David M. Gamm

 

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