Someone with short-sight can see near objects clearly, but cannot focus properly on distant objects.
Short sight is caused by one of the following:
Short-sightedness can be corrected by placing a concave lens in front of the eye, as shown in the diagrams below.
Someone who is long-sighted can see distant objects clearly, but they cannot focus properly on near objects.
Long-sightedness is caused by one of the following:
As a result, the lens focuses light behind the retina instead of onto it. Long-sightedness is corrected by putting a convex lens in front of the eye, as shown in the diagrams below.