What Structure Regulates the Amount of Light That Passes to the Photoreceptors

Question

What structure regulates the amount of light that passes to the photoreceptors of the eye?
A) vitreous body
B) cornea
C) ciliary muscle
D) iris
E) lens

Accepted Answer

The iris is a muscular structure that controls the size of the pupil, which regulates the amount of light that enters the eye and passes to the photoreceptors (rods and cones) in the retina. When the iris contracts, the pupil becomes smaller, allowing in less light, and when it dilates, the pupil becomes larger, allowing in more light.