CBSE Class 10 Answered

Hi Abhishek,

Myopia :

This defect may arise due to (i) excessive curvature of the eye lens or (ii) elongation of the eyeball. 

This defect can be corrected by using a concave lens of suitable power. A concave lens of suitable power will bring the image back onto the retina and thus the defect is corrected

Hypermetropia:

This defect may arise because (i) focal length of the eye lens is too long or (ii) the eyeball has become too small. 

This defect can be corrected by using a convex lens of suitable power. Eye glasses with converging lenses provide the additional focusing power required for forming the image on the retina.

Presbyopia:

With age, the power of accommodation decreases. For most people, the near point gradually recedes farther away. This defect is called presbyopia.

It arises due to gradual weakening of the ciliary muscles and reducing flexibility of the eye lens.