In Hypermetropia (long-sightedness), the eye is shorter than normal or the cornea is too flat, so light rays focus behind the retina. Light rays from close objects such as pages of a book cannot be focused on clearly by the retina.
Someone with hypermetropic eyes may find their vision is blurred when looking at objects near to them, and for vision to be clearer when looking at faraway objects. Placing a plus powered (convex) lens in front of a hypermetropic eye allows the image to be moved forward allowing for correct focus on the retina.
A degree of long-sightedness is common in many people, although this only presents a problem when our ability to see is significantly affected or where headaches and eye strain are common.