What happens to the eyes when you breathe?

A team of researchers in Sweden and the Netherlands found that pupil sizes change during breathing.

Some research suggests that the pupil of the eye changes with each inhalation and exhalation during breathing, while a 2022 review found that there is “no conclusive evidence” for this phenomenon.

In this regard, neuroscientist Martin Schäfer of the Karolinska Institute in Sweden and his colleagues set out to review the limitations of previous studies.

In a series of experiments, the research team used a special camera to measure the pupil sizes of more than 100 volunteers, both at rest and while performing a visual task.

The report stated: “The pupil size reaches its minimum at the beginning of inhalation and reaches its maximum during exhalation.”

The researchers saw the same pattern when volunteers performed a simple visual task, or while staring only in one place.

The results contradict previous research that claims that pupil size is smaller when exhaling.

Some previous studies have shown that smaller pupils are better at distinguishing visual details, while larger pupils better detect dim stimuli.

Pupil size also changes depending on emotional state (such as dilation in fear), during physical arousal, and in response to medications (such as dilation in response to antidepressants).

Doctors can use the pupil to measure levels of consciousness and detect mental health conditions, so it is very important to understand more about its behavior.

The study was published on bioRxiv.