What is the cause of Duane Syndrome?
Duane syndrome is due to miswiring of the eye muscles. The “mistake” probably happens around the 6th week of pregnancy and is due to poor development of tiny parts of the brain stem that control the eye muscles. In Duane syndrome, the sixth cranial nerve that controls the lateral rectus muscle (the muscle that rotates the eye out towards the ear) does not develop properly. Why the nerve does not develop is not yet understood. Thus, the problem is not primarily with the eye muscle itself, but with the nerve that transmits the electrical impulses to the muscle. There is also irregular innervation of a branch from the third cranial nerve, which controls the medial rectus muscle (the muscle that rotates the eye toward the nose). This is why abnormalities may be found in both left gaze and right gaze.
