The pupil is the window of the eye, and the rays of light which enter the eye must pass through it.
What power has the iris over the pupil?
The iris has the power of making the pupil larger or smaller, according to the amount of light which it receives.
How does a bright light affect the iris?
It causes the iris to contract, so that the pupil becomes smaller.
How does a faint light affect the iris?
It causes the iris to dilate, so that the pupil becomes larger.
Of what advantage is the iris to the eye?
The iris acts like a sentinel to protect the eye from any sudden light.
How does a sudden light affect the eye?