Refraction occurs when light enters the eye through the cornea and lens.
There are three available methods to help correct refractive errors. The first two use lenses to redirect the incoming light to focus and include glasses and contact lenses. This reshapes the corneal surface, allowing it to better focus the image on the retina, with the goal of reducing a patient's reliance on eyeglasses or contact lenses. This differs from PRK in which the laser treatment is performed on the surface of the cornea after the surface epithelial cells are removed. Similarly, the goal of the treatment is to reduce a patient's reliance on glasses and contact lenses.