It was previously believed that our pupil size was only affected by three things: light, focusing on nearby objects and cognitive effects.

The Newly Discovered “Pupillary Respiratory Phase Response” Now, researchers have confirmed a fourth factor influencing pupil size: breathing. In a newly identified phenomenon called pupillary ...

The pupils, those small black circles at the center of our eyes, could well become a key to understanding sleep. A team of ...

Researchers at Karolinska Institutet in Sweden have discovered a fundamental mechanism that affects the size of the pupil, namely our breathing. The study, published in The Journal of Physiology ...

More information: Martin Schaefer et al, The pupillary respiratory‐phase response: pupil size is smallest around inhalation onset and largest during exhalation, The Journal of Physiology (2025).

For the first time, researchers have been able to observe how the pupils react during sleep over a period of several hours. A ...