$A$ person is advised to wear spectacles with concave lenses. What type of defect of vision is he suffering from?

$A$ 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.

Which liquid fills the space between the eye lens and the retina?

What is meant by accommodation of the eye?

Why is the colour of the clear sky blue?

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