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Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
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Approximately 500,000 babies are born each year in the United States to teenage mothers.
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In 1864, the first barbiturate (barbituric acid) was synthesized.
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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
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More than 20 million Americans cite use of marijuana within the past 30 days, according to the National Survey on Drug Use and Health (NSDUH). More than 8 million admit to using it almost every day.