What is the function of Iris and Pupil?

Iris automatically adjusts the size of Pupil according to the intensity of light.

Hence, the iris controls the amount of light entering the eye by adjusting the size of pupil.

Example

If light is bright, it reduces the size of Pupil,so that less light can enter the eyes

If light is dim, it increases the size of the pupil so that more light can enter our eyes

Note

Adjustment of the size of pupil takes time

If we come from sunlight into a dark room,we are not able to see anything for some time