Which optical phenomenon is responsible for the twinkling of stars?

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

What is the lens-like structure present in the eye called?

$A$ child sitting in a classroom is not able to read clearly the writing on the blackboard.
$(a)$ Name the type of defect from which his eye is suffering.
$(b)$ With the help of a ray diagram show how this defect can be remedied.

The focal length of the eye lens increases when eye muscles

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