What does the pupil and iris do?
The pupil is the black part of your eye. Actually it is not black, but transparent, but appears as black because most light is absorbed by the tissues inside your eye. The pupil is responsible for controlling the amount of light reaching your retina, which is where images are formed. This is done by having the iris enlarge or reduce the size of the pupil. An enlarged pupil will allow more light to enter your eye, while a constricted pupil will allow less. Enlarged pupils are common during night time and constricted pupil are common during the day.
