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Did you know?
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.
Did you know?
More than 4.4billion prescriptions were dispensed within the United States in 2016.
Did you know?
There are 20 feet of blood vessels in each square inch of human skin.
Did you know?
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).
Did you know?
It is difficult to obtain enough calcium without consuming milk or other dairy foods.