Short sightedness - Myopia
The image of a distant object is focused in front of the retina, because the eye may be too long or the refractive mechanism is too strong. Shortsighted people will have blurred distance vision, but generally good near vision. A minus (-ve) powered lens is required to correct short sight.

Long sight - Hypermetropia
The image of a distant object is focused behind the retina, because the eye may be too short or the refractive mechanism is too weak. Long-sighted people generally have more difficulty with close work. A plus (+ ve) powered lens is required to correct long sight.