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.
Defect of vision: Myopia or short sightedness or near sightedness
Causes of myopia:
Methods of correction:
By the use of concave lens of suitable power or focal length the defect is corrected.