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Clinical research: Pupil size may signal autism

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Jessica Wright
5 March 2013

Light response: Clinicians may be able to use a pupil’s reaction to light as an indicator of autism risk.

The pupils of children with autism react to light more slowly and less efficiently than those of controls, according to a study published 18 December in the Journal of Autism and Developmental Disorders1.

This sort of autonomic response — which reflects basic biological functions such as heart rate, and is easy to measure — may signal risk of autism and related disorders. The researchers see a similar effect in children with other neurological disorders. 

Autism is diagnosed using behavioral measures, but people with the disorder also show physiological differences from controls. Researchers hope that some of these differences may become biomarkers, assisting with diagnosis and serving as endpoints for treatments.

Although many biomarker studies focus on brain function, alterations in the autonomic nervous system are also promising. Children with autism may have an elevated heart rate and larger pupils, and may react to stress more readily than controls do2. A 2009 study found that their pupils are slower to constrict when exposed to light than are those of controls3.

The new study looked at pupillary reflex in 152 children with autism, 116 controls and 36 children with other neurological disorders, such as Down syndrome and fragile X syndrome. The researchers also measured heart rate to test whether alterations in pupil size match up with other measures of the autonomic nervous system.

Children with autism and those with other neurological disorders are all slower to constrict their pupils than controls are. They also constrict their pupils less and do so for a shorter period of time.

Children with autism have a faster heart rate than controls do, and the rate for those with other neurological disorders is faster still. For children with autism, but not the other two groups, a faster heart rate accompanies slower pupil contraction. Medication use has no statistically significant effect on the pupillary reflex, the study found.

Typically developing children speed up their pupillary reflex between 6 and 8 years of age, the study found. The researchers did not see the same trend for children with autism, suggesting differences in brain development.

Children with other developmental disabilities also did not show a noticeable improvement in the reflex with age, but the small number of participants makes this result inconclusive, the researchers say.

News and Opinion articles on SFARI.org are editorially independent of the Simons Foundation.


1: Daluwatte C. et al. J. Autism Dev. Disord. Epub ahead of print (2012) PubMed

2: Ming X. et al. Brain Dev. 27, 509-516 (2005) PubMed

3: Fan X. et al. J. Autism Dev. Disord. 39, 1499-1508 (2009) PubMed


Name: Ray
5 March 2013 - 4:12PM

I dont think the research path set by Eric Fombonne and al will be successfull to any siginifacnt discoveries into autism.

Name: Christa Anderson
11 March 2013 - 2:34PM

I think that it is exciting that the finding of an enlarged resting pupil size initially found by our lab group launched these replications and extensions by other lab groups. Our lab group, specifically, has now replicated this finding in 4 independent samples of children with ASD (2 - 12 years of age) and we are continuing to replicate and extend this finding (see Anderson, Colombo, & Unruh, 2012; Anderson & Colombo, 2009; both published in the Developmental Psychobiology). Therefore, I disagree with the previous comment from Ray that this research path will not lead to any significant discoveries in ASD. A sensitive biomarker with this replicability, strong effect size, and sensitivity to ASD classsification is exactly what is needed in this field. In addition, resting and reflex pupil responses are incredibly simple measures to obtain in infancy and are more likely to be used by pediatricians due to familiarity and ease of use, than subjective early behavioral measures that typically require extensive training and time and produce a high rate of false negatives.

Name: La
20 November 2013 - 3:56PM

Very interesting, and definitely true for me!

Name: Lou
5 February 2015 - 11:02AM

Extremely interesting, my daughter diagnosed with autism late at 12 years. She is 15 now and I have often wondered why she has such large dialated pupils (hers hardly ever go small in fact I've never seen them small) she has a sister who doesn't have autism and had normally dialating pupils.
I typed in large dialated pupils and autism and this article came up. It would be a great way of flagging up children to check for autism earlier in life.

Name: Christen
9 February 2015 - 11:42PM

Our son has ASD and is non-verball. He' was diagnosed at age 3....we knew before then. His pupils stay large and are slow to react to light. When they do, the diameter doesn't decrease very much. Interesting research! Keep going!

Name: Lyn
4 March 2015 - 11:37PM

I was concerned as I had been noticing my daughters pupils are often really large and did a search on autism and large pupils and came to this article. Very interesting!!

Name: debbie
26 August 2015 - 7:07AM

My severely autistic son has huge pupils and I have often wondered why.

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