The eye defect known as $Presbyopia$ is corrected by using a $........$ lens.

What is meant by the least distance of distinct vision? How does this vary between the very young and old people?

$A$ near-sighted person can see only nearer objects.

$A$ person is unable to read a book clearly when kept at a distance of $25 \,cm$ from his eye. Name the defect. How can it be corrected? Draw ray diagrams for $(i)$ defective eye $(ii)$ corrected eye and explain them.

For which position of the object does a convex lens form a virtual and erect image? Explain with the help of a ray diagram.

$A$ person suffering from an eye defect uses lenses of power $-1\, D$. Name the defect he is suffering from and the nature of lens used.