Atypical Pupillary Light Reflex and Heart Rate Variability in Children with Autism

Background: Atypical pupillary light reflexes (PLR) were previously reported in children with Autism Spectrum Disorder (ASD). A replication study is being conducted in a larger population to further investigate PLR profiles in children with ASD. Heart rate variability (HRV) was also measured simultaneously to explore potential impairments in the autonomic nervous system (ANS) associated with ASD.

Objectives: To study PLR and HRV profiles in children with ASD.

Methods: PLR and HRV were analyzed in 143 children with ASD (age 10.7±3.4 years, 128 males and 15 females) and 109 children of typical development (age 11.0±2.9 years, 80 males and 29 females). PLR induced by a 100ms green light was measured in both light adapted (LA) and dark adapted (DA) conditions using a two channel binocular apparatus. Five basic PLR measurements including resting pupil diameter, relative constriction, latency, constriction velocity and redilation velocity were calculated to quantify PLR. HRV was measured using a remote heart rate device during the entire PLR test.  In addition to time domain HRV parameters, Fourier transform was applied to calculate the high frequency (“HF”) and low frequency (“LF”) components of the RR tachogram power spectrum.

Results: Similar to the previous findings, children with an ASD had significantly longer PLR latency (p < 0.0001) and smaller PLR constriction (p = 0.0034) than the typical controls. In typical controls, the PLR latency decreased significantly from 6 to 8 years old (one way ANOVA p <0.05) and stabilized thereafter. No significant age effect was observed in latency obtained in the ASD group. The average heart rate was significantly higher in children with an ASD (p < 0.05). The control group showed lower normalized HF power (high frequency power divided by total of high frequency and low frequency power) and higher LF/HF ratios (ratio between high frequency power and low frequency power) during the PLR test than during the resting periods (p < 0.05). The same change was also observed in the ASD group, but the magnitude of change was much smaller than that of the controls.  

Conclusions: The atypical PLR profiles found in our preliminary study were confirmed in a larger ASD population in this study. The different age effect on PLR latency suggests that the developmental trajectory associated with PLR pathway may be altered in children with ASD. The observed high average heart rate indicated elevated sympathetic tone in the ASD group. HRV changes during administration of the PLR (higher LF/HF and lower HF power) suggest that children with ASD have an altered ANS response to the PLR.