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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.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
The modern decimal position system was the invention of the Hindus (around 800 AD), involving the placing of numerals to indicate their value (units, tens, hundreds, and so on).
The top five reasons that children stay home from school are as follows: colds, stomach flu (gastroenteritis), ear infection (otitis media), pink eye (conjunctivitis), and sore throat.
In the United States, there is a birth every 8 seconds, according to the U.S. Census Bureau's Population Clock.