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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.
Serum cholesterol testing in adults is recommended every 1 to 5 years. People with diabetes and a family history of high cholesterol should be tested even more frequently.
Drugs are in development that may cure asthma and hay fever once and for all. They target leukotrienes, which are known to cause tightening of the air passages in the lungs and increase mucus productions in nasal passages.
Cyanide works by making the human body unable to use oxygen.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."