Duane Syndrome includes a group of congenital pathologies of extraocular muscles that cause abnormal eye movements. Patients with Duane Syndrome usually have difficulty turning their eyes outward (abduction) or inward (adduction). It is part of the congenital anomalies syndrome. The ocular movements of each eye are controlled by 6 extraocular muscles attached to the outer eye wall. In each eye, two muscles perform horizontal movements. The lateral rectus muscle rotates the eye outward and the medial rectus muscle rotates the eye inward (towards the nose). There are four other muscles that rotate the eye up or down or twist. Each muscle receives commands from the brain through the cranial nerves. In 90% of cases, the patient has no family history of Duane Syndrome. 10% of patients will have an affected family member and these tend to be cases where both eyes are involved. There are currently no clinical tests to determine the hereditary form.
Causes of Duane Syndrome
Duane Syndrome is characterized by the presence of co-contraction of the medial and lateral recti that allows the globe to slip up or down under the tight lateral rectus producing the up and down shoots characteristic of the condition. The head may be turned to the side of the affected eye to compensate for the movement limitations of the eye(s) and to maintain binocular vision.
Duane Syndrome is due to an abnormal innervation of extraocular muscles that is caused by the improper development of the cranial nerve end and/or the nucleus. The abnormality occurs at around the 6th week of pregnancy but the cause, at the moment, remains unknown. The 6th cranial nerve that controls the lateral rectus muscle does not develop properly and does not correctly transmit impulses to the muscle.
There are also abnormal innervations of a branch of the 3rd cranial nerve that innervates the medial rectus muscle. These are compensatory innervations that are peripheral, in orbit, divided by innervating both the medial and lateral rectus muscles. The result is an abnormal eye movement in the right and left gaze.
Duane syndrome is often characterized by whether the primary abnormality is a reduced ability to turn the affected eye(s) outward (type I), inward (type II), or both (type III).
Duane Syndrome: Cure
In Duane Syndrome, surgery is indicated in the presence of obvious strabismus, unacceptable abnormal head position, and alterations such as narrowing of the eyelid of the affected eye that may make the eye appear smaller than the other. The aim of the surgical treatment is to provide a satisfactory alignment in the straight-ahead position, to eliminate or reduce abnormal head position, and to prevent amblyopia. Surgery does not eliminate the cause of the problem, which is caused by the miswiring of the nerves. Surgery cannot restore normal eye movement in all directions. However, surgery is helpful in improving the clinical condition. The full effect of the surgery can take several months to be completely visible.