The rods and cones of the eye retinal layer are modified:

The diameter of the pupils is regulated by the muscle fibres of ...........

In glaucoma,which of the following occurs?

It is an aldehyde of Vitamin $- A$.

Identify the part of the eye concerned with the following two sentences in the given figure. Which alphabet is used to indicate this part?
$1$. It is the coloured visible part of the eye.
$2$. It is a pigmented and opaque structure.

$A$ person suffering from a deficiency of rhodopsin (visual pigment) should consume: