Duane Syndrome | Symptoms & Causes

What causes Duane syndrome?

Duane syndrome occurs when the sixth cranial nerve—the nerve originating in the brainstem that controls the movements of the lateral rectus muscle — either doesn’t develop at all, or doesn’t work properly.

If there is no nerve to carry the signal from the brain to the muscle:

  • It is like having no wire between the light switch and the light bulb – nothing happens.
  • Instead, the nerve that is supposed to control the opposite muscle, the medial rectus muscle, sends an extra branch to activate the lateral rectus muscle.

But with this jumbled wiring:

  • The lateral rectus muscle tries to pull the eye outward when the brain is telling the medial rectus muscle pull the eye inward.
  • As a result, the two muscles end up in a tug of war that causes the eye to retract partially into the eye socket as the medial rectus muscle overcomes the lateral rectus muscle to pull the eye inward.
  • This is why some people call the condition “Duane retraction syndrome,” and retraction of the eye during attempted inward movement is the hallmark of the diagnosis.

In some people, the lateral rectus muscle overcomes the medial rectus muscle in the tug of war, and the eye can move outward but not inward (Duane syndrome Type II). In other cases, neither the lateral nor the medial rectus muscle dominates, and the eye does not move well either inward or outward (Duane syndrome Type III.) 

Children with Duane syndrome are born with the disorder. However, it might not become readily apparent until the child grows older and starts demonstrating difficulty with vision or an abnormal head turn to the side. Most cases of Duane syndrome are diagnosed by age 10. 

Ninety percent of children with Duane syndrome have no family history of the disorder. About 5 percent of people with Duane syndrome have a parent with Duane syndrome (dominant inheritance). Here at Children's, our research team has discovered the CHN1 mutation in patients with dominantly inherited Duane syndrome. There is currently no test available that can detect a genetic marker for the disorder, except for the CHN1 genetic test when Duane syndrome affects more than one generation in a family. 

What are the symptoms of Duane syndrome?

Although Duane syndrome is congenital (present at birth), it may take as long as several years for it to become noticeable: very young children cannot vocalize the fact that they are having trouble with their vision, while older children may have learned to compensate very well for their visual difficulties. In both cases, the symptoms children show can be quite subtle. Most people with Duane syndrome are diagnosed by age 10. 

When symptoms are noticeable, they usually include:

  • holding the head in an abnormal posture, turned to the right or left
  • crossing or misalignment of the eyes
  • closing one eye to see better 

Older children may be able to describe the problems they are experiencing, such as:

  • double vision
  • neck pain
  • headaches
  • difficulty seeing things on the side of the affected eye 

Since these symptoms can also be caused by other eye disorders, it’s important to obtain an evaluation from a qualified eye doctor as soon as possible.