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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.
Increased intake of vitamin D has been shown to reduce fractures up to 25% in older people.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.