Under normal conditions, the light passing through the cornea and the crystalline lens will focus precisely on the retina. This is the ideal situation in which there is no refractive error and is called "Emmetropia". Therefore, emmetropia occurs when the refractive media of the eye (cornea and crystalline lens) and their distances from the retina are in complete harmony with each other. The cornea and the lens focus the light rays emitted from an object directly onto the retina, creating the right image. But vision is not perfect for all people. In some eyes the light is focused on the front and not on the retina (myopia). In other eyes the light focuses behind it (hyperopia). In refractive surgery, a specially trained ophthalmologist uses very precise lasers to gild the surface of the cornea and thus change its curvature so that the light focuses directly on the retina.