Causes:

Although older age is the primary risk factor for cataracts, researchers are still not certain about the exact biologic mechanisms that tie cataracts to aging.

Oxygen-Free Radicals (Oxidants) and Glutathione

Researchers have been focusing on particles called oxygen-free radicals as a major factor in the development of cataracts. They cause harm in the following way:

• Oxygen-free radicals (also called oxidants) are molecules produced by natural chemical processes in the body. Toxins, smoking, ultraviolet radiation, infections, and many other factors can create reactions that produce excessive amounts of these oxygen-free radicals.
• When oxidants are overproduced, these chemical reactions can be very harmful to nearly any type of cell in the body. At times these reactions can even affect genetic material in cells.
• Cataract formation is one of many destructive changes that can occur with overproduction of oxidants, possibly in concert with deficiencies of an important protective anti-oxidant called glutathione.
• Glutathione occurs in high levels in the eye and helps clean up these free radicals. One theory is that in the aging eye, barriers develop that prevent glutathione and other protective antioxidants from reaching the nucleus in the lens, thus making it vulnerable to oxidation.

Radiation and Electromagnetic Waves

Sunlight and Ultraviolet Radiation. Sunlight consists of ultraviolet (referred to as UVA or UVB) radiation, which penetrates the layers of the skin. Both UVA and UVB have destructive properties that can promote cataracts. The eyes are protected from the sun by eyelids and the structure of the face (overhanging brows, prominent cheekbones, and the nose). Long-term exposure to sunlight, however, can overcome these defenses.

• UVB radiation produces the shorter wavelength, and primarily affects the outer skin layers. It is the primary cause of sunburn. It is also the UV radiation primarily responsible for cataracts. Long-term exposure to even low levels of UVB radiation can eventually cause changes in the lens, including pigment changes, which contribute to cataract development. (UVB also appears to play a role in macular degeneration, an age-related disorder of the retina.) Some scientists suggest that global warming and ozone depletion may increase peopleâ ' s exposure to UVB, leading to a greater incidence of cataracts.
• UVA radiation is composed of longer wavelengths. They penetrate more deeply and efficiently into the inner skin layers and are responsible for tanning. The main damaging effect of UVA appears to be the promotion of the release of oxidants.

Radiation Treatments. Cataracts are common side effects of total body radiation treatments, which are administered for certain cancers.

Electromagnetic Waves. Questions have been raised about the hazards of low-level radiation from computer screens. To date, no study has demonstrated an association between cataract development and video display terminals. It is a good idea, in any case, to sit at least a foot away from the front of a screen.

Medications

Corticosteroids. Long-term use of oral steroids is a well-known cause of cataracts. Studies have been conflicting, however, over whether inhaled and nasal-spray steroids increase the risk for cataracts. Information on cataract risk from inhaled steroids is important because they are commonly used by asthma patients, and steroid spray use is increasing among allergy sufferers.

Other Medications Associated with Cataracts.

• Psoralens, a class of drugs used along with light therapy to treat skin disorders, such as psoriasis
• Antipsychotic medications such as chlorpromazine (Thorazine)
• Glaucoma medications

Many others drugs have been weakly associated with cataracts, including allopurinol, tamoxifen, amiodarone, tricyclic antidepressants, potassium-sparing diuretics (but not other diuretics), thyroid hormone, tetracyclines, sulfamidase, and mepacrine. Statin drugs (used for managing cholesterol) may possibly reduce the risk for nuclear cataracts.

Glaucoma and Other Eye Conditions

Glaucoma. Glaucoma and its treatments, including certain drugs (notably miotics) and filtering surgery, pose a high risk for cataracts. The glaucoma drugs posing a particular risk for cataracts including demecarium (Humorsol), isoflurophate (Floropryl), and echothiophate (Phospholine).

Uveitis. Uveitis is chronic inflammation in the eye, which is often caused by an autoimmune disease or response. Often the cause is unknown. It is a rare condition that carries a high risk for cataracts.

Causes of Cataracts in Children

Rarely, about 1 in every 10,000 births, a baby is born with cataracts (called congenital cataracts).

• Inherited disorders are often involved in the development of congenital cataracts in children. Such cataracts are most often due to inborn abnormalities in the structure or shape of the lens, including its capsule. Certain types of genetic factors may also play a role.
• Infection during pregnancy can lead to cataracts.
• Pregnant women who abuse alcohol or drugs increase the risk for cataracts (along with other more serious birth defects) in their infants.