In a normal eye, light is focused by the cornea and lens to form a sharp image on the retina at the back of the eye. Short-sightedness occurs when the eye is too long so that the light comes to a focus in front of the retina. Long-sightedness occurs when the eye is relatively too short. To correct short-sightedness, a laser is used to flatten the cornea slightly. For long-sightedness the laser is used to make the cornea a little steeper. Laser surgery can be used to correct most prescriptions including astigmatism.