Question

Explain with the help of a labelled ray diagram, the defect of hypermetropia and how it is corrected.

Answer 1

Hypermetropia is a defect of vision in which the image of the object is not formed on the retina but in front of the retina. It is also called long sightedness. Usually for a healthy eye, it is able to see up to infinity but when it becomes weak due to stress and strain the far point decreases. Similarly, the near point up to which an object can be clearly seen is 25 cm.

Complete step by step answer:
In case of hypermetropia the image of an object is not formed on the retina but Infront of the retina, as shown below.

We can see that the light rays coming from the infinity gets converged Infront of the retina but we want them to get focuses on the retina, thus in order to rectify this defect of eye we use a diverging lens that is concave lens which diverges the incoming light rays, then after passing through it they passes through the lens of the eye and finally converges onto the retina. This can be shown below.

Note:
The major cause of the hypermetropia is that the focal length of the eye lens increases and as a result of it the light rays converge in front of the retina. Another cause can be that the eyeball itself becomes too small. To correct this defect, we use a concave lens of appropriate focal length. In Farsightedness one can see distant objects but cannot see nearby objects.