Scientists Tracked Children’s Pupils and Found a Subtle Flickr of ADHD

Children with ADHD showed more erratic pupil responses, a pattern that shifted with medication.

May I have your attention, please!

A simple enough request. But for someone with ADHD, paying attention is not necessarily the hard part—keeping attention from slipping in and out is.

Scientists now think that flicker may show up in an unexpected place: the pupils.

In a new study, researchers tracked the eyes of children as they worked through the same memory challenge again and again. The pupils of children with ADHD responded more erratically from one round to the next.

A statistical model estimated that unmedicated children with ADHD showed about 23% more trial-to-trial variation than children without the condition.

The result supports a growing view of ADHD as a condition marked by unusually unstable cognitive control—periods of effective focus interspersed with lapses. The study also had a second intriguing finding: when some of the same children took methylphenidate, a common ADHD medication, their pupil responses became less variable and, in several respects, more closely resembled those of the control group.

Watching Attention Waver

The study, led by researchers at the Indraprastha Institute of Information Technology Delhi, reanalyzed data collected from children ages 10 to 12 in Santiago, Chile. Twenty-eight had ADHD and 22 did not. Seventeen of the children with ADHD completed the experiment both after temporarily stopping methylphenidate and while taking their regular medication.

The children performed 160 rounds of a visuospatial memory task. They watched dots appear on a grid, held their locations in memory through a distraction and then decided whether a new dot appeared somewhere they had seen before. An eye tracker recorded their pupils 1,000 times per second.

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Pupils do more than react to light. They also subtly widen and narrow as the brain works. The researchers wanted to know whether those changes were just different in children with ADHD, or simply less consistent from one task to the next.

“Looking at how pupil responses vary from trial to trial may provide information that is missed when we only look at average pupil size or behavioral performance,” Saumya Yadav, the study’s first author, told ScienceAlert.

Previously, a 2017 Scientific Reports study using the same Chilean dataset found that unmedicated children with ADHD had weaker pupil responses during the task and that pupil size tracked performance and reaction-time variability. The new analysis turns the question sideways: How much does the response change from one trial to another?

The pattern was a little more complicated than simply “more variability.” From one round of the task to the next, children with ADHD had less consistent pupil responses. But during any single round, their pupils were actually somewhat less variable than the researchers expected.

There was also an important statistical caveat. When the researchers compared children one by one, the difference only narrowly missed the usual threshold for significance after accounting for multiple tests. The stronger 23% estimate came from a model that pooled information across thousands of individual trials.

That makes the finding intriguing and worth investigating further rather than definitive.

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Still, the physiological differences lined up with behavior. Among unmedicated children with ADHD, greater trial-to-trial pupil variability was associated with poorer accuracy.

Did Medication Do Anything?

The study tested 17 children both with and without methylphenidate. While medicated, they showed a stronger pupil response during the decision-making portion of the task. More importantly for the new hypothesis, their responses became less variable between trials. The overall shape of their pupil response also moved closer to the pattern seen in children without ADHD.

But that does not prove methylphenidate made their attention “normal.”

“We would not interpret this as evidence that medication ‘normalized’ attention,” Yadav explained. “We could not completely separate these pharmacological effects from cognitive effects.”

Methylphenidate itself affects dopamine and norepinephrine systems that can influence pupil physiology. The researchers also lacked information about each child’s dose, and the two sessions occurred roughly six months apart on average, leaving for other changes.

May I Have Your Attention, Please!

Scientists have increasingly looked to the eyes for objective signals of ADHD.

A 2025 PLOS Mental Health study in adults, for example, found that combining pupil diameter with eye movements improved an experimental ADHD classification. But the field is still working to establish whether these measures are reliable enough for clinical use.

That remains an important distinction because, as CDC guidance on ADHD diagnosis explains, there is no single diagnostic test for ADHD. Clinicians instead draw on symptoms, medical history, examinations, and behavior across different settings.

For now, pupils cannot diagnose ADHD.

The study was published in the journal Scientific Reports.