Which part of the eye controls the amount of light entering the eye?

$A$ person needs a lens of power $-2.5 \ D$ for correcting his vision. Name the defect of vision he is suffering from. Which lens will he be using for the correction? Also,find the focal length of the lens.

$A$ person with a myopic eye cannot see objects beyond $1.2\, m$ distinctly. What should be the type of the corrective lens used to restore proper vision?

What is the range of clear vision for a person with normal vision?

Accommodation means the adjustment of light going into the eye for image formation.

Draw a neat labelled diagram of the structure of the human eye and mention the functions of any four parts.