HOW THE EYE WORKS

Light rays enter the eye through the clear cornea, pupil and lens.  These light rays are focused directly onto the retina, the light-sensitive tissue lining the back of the eye.  The retina converts light rays into impulses, sent through the optic nerve to your brain, where they are recognized as images.  Seventy percent of the eye's focusing power comes from the cornea and 30% from the lens.

Many forms of refractive surgery improve vision by permanently changing the shape of the cornea, the clear front window of the eye.