A student is unable to see clearly the words written on the black board

A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it. 

Answer

Defect of vision - Myopia or short sightedness or near sightedness

Causes of myopia:

1. Excessive curvature of eye lens/eye lens becomes more converging
2. Elongation of eye ball

Methods of correction: By the use of concave lens of suitable power or focal length the defect is corrected.