Shortsightedness. Artwork of section through an eyeball affected by shortsightedness, or myopia. This is a condition in which distant objects appear blurred. Light from the bird being observed is brought into focus before it reaches the retina (yellow lining), the light-sensitive membrane at the back of the eye. Focusing is performed by the cornea (blue bulge, far right of eyeball) and the lens (blue oval, left of cornea). Myopia is usually caused by the eyeball becoming elongated, rather than by a defect of the cornea or lens. It can be treated by contact lenses, spectacles or by surgery to adjust the shape of the cornea.