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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.
More than 150,000 Americans killed by cardiovascular disease are younger than the age of 65 years.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.
Vaccines prevent between 2.5 and 4 million deaths every year.