Short-sightedness (myopia) is corrected by using concave lens. These lens work by bending the light rays slightly outwards, so that they can focus further back on the retina.
Myopia is an eye defect in which the eyeball grows slightly too long. This means that light does not focus on the light sensitive tissue (retina) at the back of the eye properly. Instead, the light rays focus just in front of the retina, resulting in distant objects appearing blurred.