Hypermetropia and myopia are the most common defects of vision affecting humans. Both these defects can be corrected and perfect vision can be restored with the use of suitable lenses of appropriate focal lengths. Hypermetropia can be corrected by using convex lenses while myopia can be corrected by using concave lenses. The power of prescribed lens for both these defects depends on the focal length of the respective corrective lens. The power, $P$ of the lens is given by
$P=\frac{1}{f (\mathrm{in} \mathrm{metres})} \mathrm{dioptres}$
Now, consider a situation in which the near point of a defective eye is at a distance of $1.0 \mathrm{m}$. Assuming the near point of a normal eye to be $25 \mathrm{cm}$, answer the following question:
What type of lens should be used to correct the vision?