Just like a camera’s aperture (the opening that controls how much light enters), the pupil regulates light reaching the eye—making it critical for clear vision. For over a century, three factors were known to change pupil size: light levels, focus distance, and cognitive states (like emotion or mental effort). Now, a landmark study from Sweden’s Karolinska Institutet reveals a fourth: breathing directly affects vision by altering pupil size. Published in The Journal of Physiology, the research uncovers a never-before-seen pattern that could rewrite our understanding of how breath and sight connect.
“What makes this mechanism unique is that it’s periodic, constant, and doesn’t require external triggers,” explained study leader Artin Arshamian, an associate professor in the Department of Clinical Neuroscience at Karolinska Institutet. “Since breathing influences brain activity and attention, this finding helps us unlock how vision and focus are regulated by our most automatic bodily function.”
To test how breathing impacts pupil size, researchers conducted five experiments with over 200 participants. They systematically varied variables like breathing speed (fast vs. slow), breathing method (nose vs. mouth), lighting (bright vs. dim), gaze distance (near vs. far), task type (resting vs. visual work), and even brain structure (participants with or without an olfactory bulb—a brain region for processing smells). The goal? To confirm if the breathing-pupil link held across real-world conditions.
The results were unequivocal: pupils are smallest during inhalation (breathing in) and largest during exhalation (breathing out). This pattern persisted no matter the scenario—proving it’s an automatic, breath-driven response. The team named this the pupillary respiratory phase response (PRP)—a fundamental biological link between breathing and vision.
Why does this matter for your eyes? Previous research shows smaller pupils enhance detail vision (e.g., reading small text or threading a needle), while larger pupils improve faint object detection (e.g., spotting an animal in low light or a distant sign). The new study suggests your vision shifts within every breath:
- Inhalation: Smaller pupils prioritize sharp, close-up details.
- Exhalation: Larger pupils help you detect faint or distant stimuli.
“Our results mean that during a single breathing cycle—in and out—your vision switches between two modes: precision for fine work and awareness for broader surroundings,” said first author Martin Schaefer, a postdoctoral researcher at Karolinska Institutet. “It’s like your eyes use breathing as a timer to optimize what you see.”
Beyond curiosity, the PRP has major real-world implications. Impaired pupil function is an early warning sign for neurological disorders like Parkinson’s disease—where the brain’s ability to regulate pupil size breaks down. “One day, we could use the PRP to diagnose these conditions earlier or develop targeted treatments,” Arshamian noted. “That’s a key direction for our future work.”
For everyday life, the findings offer a new lens on how our bodies sync: your breath isn’t just for oxygen—it’s a silent regulator of how you perceive the world. Whether you’re reading a book, driving at night, or searching for a lost key, your breathing cycle may be quietly shaping what you notice.
This study isn’t just about pupils—it’s about uncovering how two of our most basic functions—breathing and seeing—are deeply connected. As researchers explore the PRP further, we may soon understand how to harness this link to boost focus, improve vision, or even treat disease.
Study reference: Schaefer et al. (2024). "The pupillary respiratory phase response: A periodic, stimulus-independent link between breathing and pupil size." The Journal of Physiology.}
