Well, Looky Here
Your pupil is your eye’s aperture, an opening at the centre of the iris through which light from the world around us passes before it
focuses onto the retina behind it. Muscles in the iris help to dilate it in low light and constrict it in bright light: At its smallest, the adult pupil may be less than 1 millimetre in diameter, but can increase up to ten times when expanded.
I Can See Clearly Now
Red-eye occurs in photos because our pupils open wide in low light to allow extra light to help us see—when the flash goes off, it bounces off the back of the eye, called the choroid (a place loaded with blood vessels), which make it glow red in images.
Sight for Sore Eyes
The pupil of your eye expands as much as 45 percent when you look at someone you’re attracted to. Pupils also tend to dilate when you feel disgust: Unpleasant odours, dead or decomposing material and even unpleasant stimuli like violence, for example, can all trigger this reaction.
Now You See Me
One of the human body’s first reactions when experiencing pain is to dilate the pupils. Why? When the flight response is activated (AKA, the “running away” part of “fight or flight”), our brains need all our senses functioning at their most prolific. Our vision needs to be 100 percent pin-sharp to identify any further danger in the vicinity, and your pupils are there to make sure you get it right.