Since autism can be quite difficult to diagnose in the first years of a child's life, researchers have been looking for new ways to spot it.
A recently developed blood test, for instance, may be able to detect the condition with up to 92 percent accuracy, while other researchers have turned to the sensory symptoms of the condition to aid diagnosis.
It is known that autism is sometimes accompanied by either over- or under-sensitiveness to certain stimuli, be they smells, lights, or sounds.
This led some researchers to believe that looking into the more basic blocks of brain development and sensory processing might hold the key to an earlier and more accurate diagnosis of autism.
Terje Falck-Ytter, an associate professor at the Department of Psychology at Uppsala University in Sweden, is one such researcher. He and his team set out to examine if the pupillary light reflex of infants — which controls how much light gets to their retinas — is a valid marker of autism.
Falck-Ytter explains the motivation behind the study, saying, "Earlier studies on older children with autism has suggested a weak pupillary light reflex in this group. These findings motivated us to assess the reflex in infant siblings of children with autism."
The findings were published in the journal Nature Communications.
Stronger reflexes may predict autism
Falck-Ytter and colleagues combined data from a Swedish longitudinal study with analogous data from another study carried out at Birkbeck, University of London in the United Kingdom.
The British-based research examined siblings who had an older brother or sister with autism. The study participants were 9–10 months old at baseline, and they were clinically followed when they turned 3 years of age.
At the beginning of the study, the infants had their pupillary reflexes tested. By the age of 3, they were assessed for autism.
Overall, 147 infants who had an older brother or sister with autism took part in the study. Of these, 29 were diagnosed with autism at age 3.
An additional group of 40 infants from the general, neurotypical population was also recruited for the study.
The study found that children who were diagnosed with autism at follow-up had their pupils more constricted than those who did not receive such a diagnosis.
Additionally, how much the pupils were restricted correlated directly with how strongly the children displayed symptoms of autism at age 3.
Falck-Ytter refers to older infants with autism who have been shown to have a weak pupillary light reflex in previous research, saying, "Most of these infants develop typically, yet the probability of later being diagnosed with autism is considerably higher in this group than in the general population."
He goes on to point out the novelty of his findings compared with those of previous studies, saying, "Surprisingly, we found that in infancy, the group differences were in the opposite direction than in older children: we found stronger reflexes in the infants later diagnosed with autism than in controls."
"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."
"Currently," he notes, "autism cannot be reliably diagnosed before 2–3 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."
But, Falck-Ytter cautions, "[T]he results in this study demonstrated significant group differences only, and it is too early to say whether the method can facilitate early detection in a clinical context."