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Pupillary light reflex in infants may be able to identify autism early, research from Sweden and the U.K. suggests.

Babies who were diagnosed later with autism spectrum disorder reacted more strongly to sudden changes in light, reported Terje Falck-Ytter, PhD, of Uppsala University in Sweden, and co-authors in

"This is the first time the pupillary light reflex has been linked to the early development of autism," Falck-Ytter told 番茄社区app.

Not only do these infants have stronger pupillary light reflexes, but the amount of pupillary constriction correlates with the strength of autism symptoms. "This indicates that early atypicalities in sensory processing may play an important role in autism spectrum disorder."

Autism can be difficult to diagnose easily in infants, though researchers have found that MRI scans and heart rates can help predict autism early in high-risk families.

For this study, Falck-Ytter and colleagues combined data from a Swedish longitudinal study with data from another cohort of babies in Birkbeck, University of London, and recruited an additional 40 infants from the general population as controls. The babies were 9 to 10 months old when their pupillary light reflexes were examined and were followed until age 3.

Overall, 147 infants who had an older brother or sister with autism participated in the study; of these, 29 were diagnosed with autism at age 3.

Comparisons showed that infants who were diagnosed with autism at follow-up had more constricted pupils than those without that diagnosis. The amount of pupil constriction correlated directly with how strongly children displayed symptoms of autism when they were 3.

Pupillometry may be a promising addition in the toolbox of developmental researchers, but it's too early to assess its use, Falck-Ytter noted. "Others need to replicate the basic findings, and the method needs to be improved for it to be of clinical value."

Asked for his perspective, Scott Murray, PhD, of the University of Washington in Seattle, who was not involved in the study, said that since measuring the pupillary light reflex is a relatively simple, objective measure of physiological function, one could imagine that with further testing it could be included in a battery of infancy tests for individuals at higher risk for autism spectrum disorder.

"This could facilitate early intervention efforts," he told 番茄社区app.

But it's not clear how specific pupillary light reflex changes are to autism versus other developmental disorders: "While there are statistically significant differences between groups in the pupillary light reflex measure, there is more similarity and overlap between groups than differences," he said. "So, by itself, measurements of the pupillary light reflex will likely have limited diagnostic potential."

Nonetheless, the pupil may offer a previously unrecognized window into the neural development of human infants, Falck-Ytter observed: "The findings may help narrow down the search for biological mechanisms in autism, as the neural pathway underlying the reflex is relatively simple."

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