Correction of short-sightedness. Illustration of cross section of an eye with short-sightedness corrected with a concave lens (blue). In short-sightedness, or myopia, the eyeball is longer than it should be, or the eye's lens (grey) is the wrong shape, and light is focussed in front of the retina. This causes difficulty focussing on distant objects, which appear blurred. The concave lens causes light passing through it to diverge slightly, allowing a sharp image to be focussed on the retina.