Correction of long-sightedness, illustration. Cross-section diagram of an eye with the vision defect of long-sightedness, corrected with a convex lens. In long-sightedness, or hyperopia, the eyeball is shorter than it should be, or the eye's lens (grey) is the wrong shape, and light is focussed behind the retina. This causes difficulty focussing on a near object (O, left), which appears blurred. It can be corrected by placing a convex lens (blue) in front of the eye, which refracts light from the object so that it focusses on the retina, creating a sharp image (right).