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

Name the part of the human eye that helps in changing the focal length of the eye lens.

$A$ 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.

Explain how a normal human eye is able to see distinctly objects placed at a distance as well as those placed at a nearer distance. What is the far point and near point of a normal human eye?

Where is the image formed in an eye suffering from near-sightedness?

Give one cause of near-sightedness (myopia).