Astigmatism (for a human eye) can be removed by using

For the myopic eye,the defect is cured by

Myopia is due to

Myopia can be corrected with the help of a/an ...

$A$ student can distinctly see objects up to a distance of $15 \, cm$. He wants to see the blackboard at a distance of $3 \, m$. The focal length and power of the lens used,respectively,will be:

$A$ man suffering from myopia can read a book placed at $10 \ cm$ distance. For reading the book at a distance of $60 \ cm$ with relaxed vision,the focal length of the lens required will be ...... $cm$.