Your pupil changes size to control how much light enters your eye. You can watch the pupil of your eye change size in response to changes in lighting. You can also experiment to determine how light shining in one eye affects the size of the pupil in your other eye.
Use a mirror to look at your eye and the size of your pupil. If you go into a darker room what happens to the size of your pupil? How about if you go into a bright room and shine a torch near your eye? Please be careful not to shine the light into your eye and damage it.
Follow this link to find experiments to demonstrate the blind spot.