What is hypermetropia? Give its causes. Explain with the help of a labelled ray diagram, how it is corrected.

The defect of the human eye in which a person can see the objects lying at long distances clearly, but cannot see the nearby objects distinctly is called hypermetropia. In a hypermetropic eye, the rays from the normal near point are focussed at a point beyond retina of the eye. The hypermetropic eye is caused by the following two defects: (i) Increase in the focal length of the eye lens (ii) The size of the eyeball becomes too short The following diagram represents a hypermetropic eye. To correct a hypermetropic eye, the person is allowed to wear spectacles with a convex lens of suitable power or focal length as indicated in the following figure. When a convex lens or converging lens of suitable power is placed in front of the hypermetropic eye, then the diverging rays of light coming from the nearby object are first converged by this convex lens. Thus, the convex lens forms a virtual image of the nearby object (lying at O ' ) at the point O of the hypermetropic eye which can be easily focused by the eye lens to form an image on the retina.