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Vision Disorders


A cataract is the clouding or opacity of the crystalline lens which alters the amount of light entering the eye. Developmental cataracts are relatively minor and harmless, primarily present at birth or developing in early childhood, but which can occur later in life. No reduction in vision is noticeable with this type, which are thought to be hereditary. Congenital cataracts are present at birth and may appear as a white or gray pupil; they create a squint like that apparent in strabismus and cause visual impairment. In most instances, the cause is unknown; however, diseases and disorders contracted by the child's mother during pregnancy—such as rubella, syphilis, diabetes mellitus, or birth defects as a result of Down syndrome, are thought to be causative. Systemic disease-associated cataracts develop as a result of such disorders as diabetes, high doses of steroids over long periods, and a dysfunctioning thyroid. Some cataracts develop secondary to ocular diseases like keratitis (inflammation of the cornea), iritis (inflammation of the iris), radiation (either from radiation therapy or the sun), or from trauma, such as intraocular surgery or penetration of the eye.

The most common cataracts are senile cataracts, a phenomenon of aging that occurs in almost all people over 65 years of age. Sometimes they develop in younger people whose nutrition is poor and are then termed presenile cataracts. Both types are probably caused by changes in or loss of enzyme production, which synthesizes nutrients that in turn feed the layer of cells on the lens surface. Senile cataracts grow slowly over months Suturing of a donor's cornea onto the eye of a transplant recipient. The transplant replaces the patient's own damaged cornea, which was impairing his vision. Photograph by Chet Szymecki. © Chet Szymecki/Phototake. Reproduced by permission.
or years, cause no pain, usually affect both eyes, and gradually reduce visual acuity. Symptoms include two or more images from one eye, dark spots in the center of vision, extreme sensitivity to the glare of bright lights or sunshine, and reduced color vision. If not removed surgically, they eventually cause blindness.

Additional topics

Science EncyclopediaScience & Philosophy: Verbena Family (Verbenaceae) - Tropical Hardwoods In The Verbena Family to WelfarismVision Disorders - Refractive Errors, Hyperopia/presbyopia, Other Refractive Errors, Strabismus, Nonparalytic Strabismus, Paralytic Strabismus - Myopia, Astigmatism, Glaucoma, Secondary glaucomas, Degeneration of the macula, Retinal dystrophies