Evaluation of the Pupillary Light Reflex As a Potential Biomarker in Children with Autism Spectrum Disorder

Background:  

Previous studies have found differences in autonomic nervous system (ANS) functioning between children with ASD and typically developing (TD) children. The pupillary light reflex (PLR) is one measure of autonomic functioning that has revealed a longer latency, faster constriction velocity, and lower constriction amplitude for individuals with ASD compared to those with TD between 7 and 20 years of age (Daluwatte et al., 2012; Fan et al., 2009). Evaluation of the PLR in a younger age group could provide insight into the early development of the ANS in ASD and be useful in discovering potential early biomarkers of ASD.

Objectives:  

This study investigated PLR parameters in younger ASD and TD children than have been studied previously, using a simplified paradigm. The goal of the study was to examine differences in the PLR between groups of ASD and TD children between the ages of 3 and 10 years, and to develop a simple testing procedure that could be used for young, pre-verbal children. 

Methods:  

Children with ASD (n= 34, male=28; M_age= 5.79 years) and TD children (n= 33, male=21; M_age= 6.06 years) participated in two testing sessions. Each session lasted under 5 minutes and included four to six 21-second-long trials. The visual stimuli were large black and white circles, presented on a uniform gray background, and alternating every second. A standard LCD monitor (Vizio SV420M), calibrated with a spectroradiometer (PR 650), was used to present the stimuli. Pupil size was measured by an infrared-based eye tracker (Tobii X120). The PLR parameters, measured from the white circle onset, included the means of baseline pupil size (pupil size prior to the presentation of the stimulus, in millimeters), PLR latency (time point when the change in the pupil size over the change in time is maximum, in milliseconds), and dilation time (time point at the maximum pupil size, in milliseconds). 

Results:  

Children with ASD (M=3.83, SD=.38) had significantly larger average baseline pupil size than controls (M=3.59, SD=.31), F(1)=8.22, p < .01,  and had significantly longer mean PLR latency (M=402.88, SD=37.64) than controls (M=382.48, SD=27.10), F(1)=6.10, p=.016. In addition, children with ASD (M=260.44, SD=20.58) had marginally significantly longer mean dilation time than controls (M=250.76, SD=18.16), F(1)=3.91, p=.052.

 A similar pattern was present in the youngest, previously untested age group (ages 3 to 6). The ASD group (n= 23, M=262.96, SD=21.64) had significantly longer mean dilation time than controls (n= 18, M=251.28, SD=11.73), F(1)=4.25, p=.046 and had significantly longer mean PLR latency (M=410.00, SD=40.40) than controls (M=385.00, SD=23.81), F(1)=5.40, p=.025.

Conclusions:  

There were significant differences in PLR parameters between children with ASD and TD in an age group that was younger than previously studied. The results are consistent with previous findings in older children, which suggest that PLR measures could be extended to younger ages and potentially serve as an early biomarker for ASD.