Washington DC, Feb. 23 -- Researchers have discovered a fundamental mechanism that affects pupil size: breathing. The study shows that the pupil is smallest during inhalation and largest during exhalation, which could affect vision.

Researchers at Karolinska Institutet in Sweden have discovered a fundamental mechanism. The study was published in The Journal of Physiology.

Like the aperture in a camera, the pupil controls how much light reaches the eye. Therefore, it is fundamental to vision and how we perceive our surroundings.

Over a century ago, three mechanisms that can change the size of the pupil were known: the amount of light, focus distance, and cognitive factors such as emotion or mental effort.

Now, scientists have discovere...