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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.
Blood is approximately twice as thick as water because of the cells and other components found in it.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
Since 1988, the CDC has reported a 99% reduction in bacterial meningitis caused by Haemophilus influenzae, due to the introduction of the vaccine against it.