What is the least distance of distinct vision for a normal adult with normal vision?

$A$ person is able to see objects clearly only when these are lying at distances between $50 \text{ cm}$ and $300 \text{ cm}$ from his eye. Identify the kind of defects of vision he is suffering from. Give reason for your answer.

What is the muscular structure located behind the cornea in our eye called?

What is the role of the pupil in a human eye?

$(a)$ State two main causes of a person developing near-sightedness (myopia). With the help of a ray diagram, suggest how this disability can be corrected.
$(b)$ The far point of a myopic person is $150 \ cm$ in front of the eye. Calculate the focal length and power of the lens required to enable him to see distant objects clearly.

What happens to the image distance in the eye when we increase the distance of an object from the eye?