(a) What is hypermetropia?
(b) What are the two causes of this defect of vision?
(c) How can this defect of the eye be corrected? Illustrate your answer by drawing ray diagram to show the formation of image by (i) a hypermetropic eye,(ii) a hypermetropic eye corrected with a suitable lens.

Hypermetropia is also known as long-sightedness. In this defect, a person can see the distant objects clearly but cannot see the nearby objects clearly. 

Cause of hypermetropia:
This defect arises due to either of the following two reasons:
(i) The eyeball becomes too small along its axis so that the distance between the eyelens and the retina is reduced.
(ii) The focal length of the eyelens becomes too large resulting in the low converging power of the eyelens.

As a result of the above mentioned causes, the rays coming from an object placed at 25 cm (normal near point) from the eye meet at a point behind the retina. So the object cannot be seen clearly.

Fig. Hypermetropia and its correction

The object has to be moved away from the eyes to a distance greater than 25 cm inorder to focus the rays again on the retina. Thus, the near point of the eye is not at 25 cm but it has shifted to N' at a distance greater than 25 cm from the eyes. 

Correction of hypermetropia:

A hypermetropic eye is corrected using a convex lens of suitable focal length. This lens diverges the rays such that the rays coming from normal near point N appear to come from near point N' after refraction. That is a virtual image of the object placed at N is formed at N'. Then the eyelens forms a clear image at the retina, as shown in Fig. (c).