Contact lenses are fine for most myopes (short sighted) as they can usually accommodate to focus close up when wearing the correction. These are concave lenses with, if needed, cylinder to correct for any astigmatism.
With hypermetropes (long sighted) it is quite different. The convex lens corrects properly for close work put it will not allow the wearer to focus on more distant objects. Next time you are in the chemists put on any pair of reading glasses off the rack and check your distance vision, how blurred it is. That is the equivalent of trying to see through a contact lense of any positive power, i.e. convex.