Myopia or short-sightedness: It is a vision defect in which a person can see nearby objects clearly but cannot see the distant objects clearly beyond a certain point. This defect is common among children.
Cause of myopia: This defect arises due to either of the following two reasons:
(i) The eyeball gets elongated along its axis so that the distance between the eyelens and the retina becomes larger.
(ii) The focal length of the eyelens becomes too short due to the excessive curvature of cornea.
Fig. Myopic and its correction
Numerical: As the focal length is negative, the lens used is concave. The boy is suffering from myopia.
Here, f = - 50 cm = -0.50 m
Power, 
