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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.
Common abbreviations that cause medication errors include U (unit), mg (milligram), QD (every day), SC (subcutaneous), TIW (three times per week), D/C (discharge or discontinue), HS (at bedtime or "hours of sleep"), cc (cubic centimeters), and AU (each ear).
The human body produces and destroys 15 million blood cells every second.
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.
The ratio of hydrogen atoms to oxygen in water (H2O) is 2:1.