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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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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
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The human body produces and destroys 15 million blood cells every second.
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Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
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The first documented use of surgical anesthesia in the United States was in Connecticut in 1844.