Why do our pupils change size?
Pupil is the round opening in the centre of the eye, which looks like a black circle. The amount of light entering our eye is regulated by the pupil.
Two muscles around the pupil automatically adjust the size of pupil to the level of the light.
The dilator muscle enlarges the pupil in dim light so that a higher level of light enters the eye. In bright light, the sphincter muscle makes the pupil smaller to let lesser amount of light enter the eye. When a look at a nearby object, the pupil again becomes smaller to bring the image into sharp focus.