Why do stars twinkle?

$A$ person needs a lens of power $-5.5 \, D$ for correcting his distant vision. For correcting his near vision,he needs a lens of power $+1.5 \, D$. What is the focal length (in $cm$) of the lens required for correcting near vision?

The far point of a myopic person is $80 \,cm$ in front of the eye. What is the nature and power of the lens required to correct the problem?

Why is a normal eye not able to see clearly the objects placed closer than $25 \,cm$?

What is meant by the power of accommodation of the eye?

$A$ 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?