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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.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
The ratio of hydrogen atoms to oxygen in water (H2O) is 2:1.
More than 34,000 trademarked medication names and more than 10,000 generic medication names are in use in the United States.