The eye is like a camera. Light enters the clear front of the eye (cornea) passes through the opening in the center of the iris (the pupil) and is focused by the lens, which lies behind the pupil and the iris. The lens focuses light rays on the back of the eye (retina), which transmits images to the brain via the optic nerve. This is the process of seeing. If the images are focused on the retina accurately, the result is 20/20 vision.