Book 10, Question 77
Why Do Pupils Change Size?
Pupils change size because they are like little doors that control how much light enters your eyes. In dim light they open wide to let more light in. In bright light they shrink to protect the delicate parts inside.
More fun facts
- Your pupil changes size to control how much light enters your eye.
- The colored part around the pupil, called the iris, adjusts the pupil's size, like a camera opening.
- In bright light, a nerve signal from the back of the eye makes iris muscles shrink the pupil.
- Pupils can also change size when you are scared, angry, in pain or in love.
- Pupil changes from thinking and feelings are tiny, usually less than half a millimeter.
- Scientists film pupils with infrared cameras to study things like mental effort and sleepiness.
Sources: Exploratorium, Scientific American, Scientific American
Questions kids ask
How can I watch my pupils change?
Look in a mirror while you or a partner shine a light toward and away from your eye.