A cataract is any opacity of the crystalline lens sufficient to cause visual impairment. Cataracts have been known about since the beginning of medical history and are the leading cause of blindness throughout the world. Ninety percent of all cataracts are the result of aging and usually there is no other reason for its development. Some loss of transparency of the lens with age is nearly as inevitable as wrinkling of the skin and graying of the hair. More evidence is mounting that exposure to the sun and its ultraviolet rays may be the cause of this loss of transparency.
The other ten percent of cataracts are either congenital (present at birth) or juvenile (early onset) in nature. A large variety of congenital lens opacities exist, but the majority doesn't cause visual impairment. Juvenile cataracts can occur with congenital rubella, congenital syphilis, diabetes mellitus, and inflammation from an infection. Cataracts can also be caused by trauma to the eye. A blunt injury to the eye may cause the rapid formation of a cataract or it may develop months or years later.
Visual Symptoms of Cataracts
Many people with cataracts will experience a slowly progressive and painless decrease in vision, whereas others report a rapid loss of vision over a period of months, weeks, or even days. It is not uncommon for elderly patients with cataracts to notice a renewed ability to read without glasses, despite a decrease in distance acuity. This "second sight" is due to a thickening of the lens that changes their eyeglass prescription. Some cataracts will create glare from lights and "halos" while driving at night. It is not uncommon to experience a loss of color vision. In summary, cataracts can cause loss of vision ranging from very mild to severe impairment. Cataracts alone, however, are not responsible for total blindness.