Refractive surgery improves vision by permanently changing the shape of the cornea, the clear front window of the eye. When treating myopia, or nearsightedness, refractive surgery techniques reduce the curvature of the cornea to lessen the eye's focusing power. Images that focused in front of the retina, due to an elongated eye or steep corneal curve, are pushed closer to or directly onto the retina.
When treating hyperopia, or farsightedness, refractive surgery techniques make the cornea steeper to increase the eye's focusing power. Images that focused beyond the retina, due to a short eye or thin cornea, are pulled closer to or directly onto the retina.
Astigmatism occurs when the cornea is more curved in one direction than the other. If astigmatism is significant, light passing through the cornea is scattered. Images reaching the retina are distorted and vision is blurred. When treating astigmatism, refractive surgery techniques selectively reshape portions of the cornea to make it symmetrical and smooth, so that images focus clearly on the retina.
Common refractive surgery procedures include: