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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.
If all the neurons in the human body were lined up, they would stretch more than 600 miles.
As of mid-2016, 18.2 million people were receiving advanced retroviral therapy (ART) worldwide. This represents between 43–50% of the 34–39.8 million people living with HIV.
In the United States, there is a birth every 8 seconds, according to the U.S. Census Bureau's Population Clock.
Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.