So at the retinal screen, a diffused, defocused image is seen. To correct this defect, a convex lens has to be worn by the person. The focal length of the convex lens is adjusted in such a manner that the image of the object is on the retina. People suffering from long sightedness can see distant objects clearly but are unable to read from a book held close. Hence they need only reading glasses.
Figure below shows the shape of the eye that is suffering from short sightedness or myopia.
In this case the image of an object placed at far off distance is formed in front of the retina. To correct this defect, a concave lens has to be worn by the person. The focal length of the concave lens is such that the parallel light rays coming from distant objects are first diverged a little and then are converged by the eye lens. The adjustment of the focal length of the concave lens has to be in such a manner that a well focused image is formed at the retina. Some people suffer from both short as well as long sightedness.