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Enhanced Pupillary Light Reflex in Infancy Predicts Elevated Autistic Symptoms at Two Years of Age
We recently discovered that ten-month-old siblings of children with autism spectrum disorder (ASD) had stronger pupillary light reflexes compared to low risk control infants (Nyström et al., 2015, Molecular Autism), a result which contrasts sharply with the weak pupillary light reflex typically seen in both children and adults with ASD. This finding raises the possibility that the pupillary light reflex captures early neurodevelopmental processes associated with autism risk. According to one hypothesis, atypicalities in the pupillary light reflex reflect a dysregulation in the cholinergic system, which is disrupted in ASD and plays a key role in the regulation of excitatory-inhibitory balance early in life.
Objectives: We followed up the infants in our previous study to an age when ASD outcome could be assessed. Based on the result of our previous study we predicted that infants who later developed high levels of ASD symptoms would have stronger pupillary light reflexes than other infants.
Methods: The pupillary light reflex was assessed using non-invasive eye tracking and the amplitude and latency was calculated in accordance with Nyström et al. (2015; Molecular Autism). 49 infants were included in the final sample. At 24 month of age, the Autism Diagnostic Observation Schedule, second edition (ADOS-2) was administered. ADOS standardized calibrated severity scores (CSS; range 1-10) were calculated, where scores in the 6-10 range indicate moderate-to-severe concern for ASD (Esler et al, 2015, JADD). We classified individuals in the high risk group with scores in this range as ASD positive (n = 6). Remaining infants were either ASD negative (n = 29) or low risk controls (n = 14).
Results: We found that the amplitude of the pupillary light reflex was larger in 10-month-olds who were classified as ASD positive at 24 months compared to unaffected high risk infant siblings – who in turn had larger amplitudes compared to infants with no family history of ASD (both Ps <.05).
Conclusions: This study indicates that dependent on its magnitude, the pupillary light reflex in infancy signals either sub-threshold ASD risk or full-blown clinical symptoms, and suggests that pupillometry can facilitate risk assessment in human infants.