What is meant by the least distance of distinct vision?

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?

List four common defects of vision that can be corrected with the use of spectacles.

An old person is unable to see clearly nearby objects as well as distant objects. $(i)$ What defect of vision is he suffering from? $(ii)$ What kind of lens will be required to see clearly the nearby as well as distant objects? Give reasons.

When one enters a dim-lit room from bright light,one is unable to see the objects in the room for some time. Explain why.

Explain the structure and functioning of the human eye. How are we able to see nearby as well as distant objects?