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A cataract is a clouding of the eyes' natural lens. As we age, some clouding of the lens may occur. The first sign of a cataract is usually blurry vision. Although glasses and other visual aids may at first help a person with cataracts, surgery may become inevitable. Cataract surgery is very successful in restoring vision, and it is the most frequently performed surgery in the United States.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.
The first oncogene was discovered in 1970 and was termed SRC (pronounced "SARK").
Approximately one in four people diagnosed with diabetes will develop foot problems. Of these, about one-third will require lower extremity amputation.

