Eye contact is a very personal and intimate thing. Children with autism are uncomfortable with this and will look at something other than the eyes even when they are looking at a person’s face. Children who don’t like to be hugged or kissed will especially avoid eye contact.
Other children with autism aren’t really avoiding eye contact; they are just too involved in trying to remember every last detail of something they want to tell you, verbatim. Eyes rolling away or looking in another direction are typical actions of non-autistic people who are trying really hard to remember something important. You can see it if you spend time with an elderly relative; they squint, look at the floor or off in the distance, or close their eyes to get closer to what it was they wanted to tell you.
It may also be that the child is a little shy. High functioning children with autism are not immune to shyness. Parents can tell the difference if their child is generally quiet around adults and other children and hides entirely behind Mom or Dad when company comes a-calling.
As to the medical reasons behind it, it’s not entirely certain there is a medical cause. It definitely appears to be more rooted in social and psychological behaviors, which only a trained and licensed psychologist can determine. Family histories and home life are a big factor when the psychologist evaluates the child with autism; more than meets the eye can tell what and/ or why a child with autism might not be willing to make eye contact.
Parents should become thoroughly acquainted with how their child behaves in various situations. Because they already don’t make eye contact, children with autism are less likely to get caught in a lie unless parents and teachers can recognize or already know when and how a child with autism is lying. Of course, this only applies to children who are verbal. Non-verbal children will have very guilty body language when they have done something they are aware is wrong.