A new study published in Nature Communications suggests infants who are later diagnosed with autism spectrum disorder react more strongly to sudden changes in light. This finding provides support for the view that sensory processing plays an important role in the development of the disorder.

Despite being defined by symptoms in social communication, researchers are increasingly embracing the idea that the earliest signs of autism may reside in more basic processes of brain development. Also, in the latest edition of the diagnostic manual that many countries use to diagnose the condition, sensory symptoms have been included as defining features of autism.

In the new study, the researchers investigated the pupils’ light reflex in 9- to 10-month-old infants — that is, the reflex that controls the amount of light that reaches the retina. The infants who fulfilled criteria for autism at three years of age constricted their pupils more than infants who did not fulfill autism criteria at follow up. Further, the amount of pupil restriction in infancy was associated with the strength of autism symptoms later on.

The study builds on earlier studies of older children with autism, which have found a common light sensitivity among children with ASD, but in an opposing way — a weaker reaction to light by the pupils.

“We believe the findings are important because they point to a very basic function that has not been studied before in infants with later autism diagnosis,” says Terje Falck-Ytter, an associate professor in the department of psychology at Uppsala University and the study’s principal investigator.

The study is a part of the larger project Early Autism Sweden (EASE), which is a collaboration between Uppsala University and the Center of Neurodevelopmental Disorders at Karolinska Institutet (KIND) in Sweden. In this particular experiment, data from Sweden were combined with data from a similar longitudinal study of siblings with an older sibling with autism conducted at Birkbeck, University of London (UK). In total, 147 infants with an older sibling with autism took part in the study, of whom 29 met criteria for autism at follow-up. The study also included a control group consisting of 40 infants from the general population.

Researchers warn it will take time and more research for the finding to be developed into a reliable method of early screening for autism. Still, they are excited at the prospect.

“Currently, autism cannot be reliably diagnosed before two to three years of age, but we hope that with more knowledge about the early development of the condition, reliable diagnosis will be possible earlier, which should facilitate early access to intervention and support for the families,” Falck-Ytter says.

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