As light enters our eye, it must be brought to a focus on the retina in order to perceive a clear image. About two thirds of the focusing power of the eye comes from the cornea, the rest comes from the lens inside the eye. As the light enters the eye, it is focused a fixed amount by the cornea. As the light passes through the pupil, the lens then adjusts the focus a variable amount with the exact amount of focusing power applied dependent on the distance of the object being viewed. Objects at near like a book or knitting require more power than distance objects like movies or traffic signs.