Cataract
A common cause of gradual vision loss, a cataract is an opacity of the lens or the lens capsule of the eye. Light shining through the cornea is blocked by the clouded lens. This, in turn, blurs the image cast onto the retina. As a result, the brain interprets a hazy image.
Cataracts commonly affect both eyes, but each cataract progresses independently. Exceptions are traumatic cataracts, which are usually unilateral, and congenital cataracts, which may remain stationary. Cataracts are most prevalent in persons older than age 70. Surgery restores vision in about 95% of patients.
Causes
Cataracts are classified by their causes:
Senile cataracts develop in elderly people, probably because of chemical changes in lens proteins.
Congenital cataracts occur in neonates from inborn errors of metabolism or from maternal rubella infection during the first trimester of pregnancy. These cataracts may also result from a congenital anomaly or from genetic causes. Transmission is usually autosomal dominant; however, recessive cataracts may be sex-linked.
Traumatic cataracts develop after a foreign body injures the lens with sufficient force to allow aqueous or vitreous humor to enter the lens capsule.
Complicated cataracts occur secondary to uveitis, glaucoma, retinitis pigmentosa, or retinal detachment. They can also occur with systemic disease, such as diabetes, hypoparathyroidism, or atopic dermatitis, or from ionizing radiation or infrared rays.
Toxic cataracts result from drug or chemical toxicity with ergot, dinitrophenol, naphthalene, and phenothiazines.
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