Duane syndrome, also called Duane retraction syndrome (DRS), is a congenital and non-progressive type of strabismus. It is characterized by difficulty rotating one or both eyes outward (abduction) or inward (adduction). There may also be changes of eyelid position on attempted movement of the eyes.
Duane syndrome is due to miswiring of the eye muscles. This disturbance probably happens around the 6th week of pregnancy and is due to abnormal development of the nerves 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 abnormal innervation of a branch from the third cranial nerve, which normally 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.
The vast majority of cases occur spontaneously and most often only affect one eye. Around 20% of Duane syndrome patients have both eyes affected. For reasons unknown, the left eye is more often involved than the right eye. Duane syndrome affects girls more often than boys. No particular race or ethnic group is more likely to be affected. 30% of cases are associated with other congenital anomalies.
• Strabismus-the eyes may be misaligned and point in different directions some or all of the time
• Head position-patients often maintain a head posture or head turn to keep the eyes straight
• Amblyopia (reduced vision in the affected eye) – occurs in 10% of patients.
• Eyelid narrowing-the affected eye may appear smaller than the other eye
• Upshoot or downshoot-with certain eye movements, the eye may occasionally deviate upward or downward
Duane retraction syndrome is present from birth, even if it is not recognized during infancy. An abnormal head posture and strabismus are often visible in old photographs taken in early childhood.
In 90% of cases, the patient has no family history of Duane syndrome. Ten percent of patients will have an affected family member and these tend to be cases where both eyes are involved.
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). Type I is the most common form of Duane syndrome. and affected patients will characteristically have a head turn towards the involved side, and will appear esotropic (crossing inward) in straight ahead gaze.
The problem with the 6th cranial nerve is usually an isolated condition and the child is usually otherwise completely normal. With careful follow-up, the long-term prognosis for good vision is usually excellent.
Occasionally, Duane syndrome may be found in association with other eye problems, including disorders of other cranial nerves, nystagmus (an involuntary back-and-forth movement of the eyeball), cataract, optic nerve abnormalities, microphthalmos (abnormally small eye), and crocodile tears.
Not usually, however, some patients with Duane syndrome have other problems, such as hearing impairment, Goldenhar syndrome, spinal and vertebral abnormalities. There is also an increased frequency of Duane syndrome in patients with thalidomide exposure.
For the majority of patients, Duane syndrome does not require surgical treatment. Surgery for Duane syndrome is indicated for one of four reasons:
• To reduce a significant deviation in normal straight-ahead position
• To eliminate a significant abnormal head position
• To eliminate a significant upshoot or downshoot.
• To eliminate disfiguring abnormal eyelid position
The goal of treatment is to restore satisfactory eye alignment in the straight-ahead position, eliminate an abnormal head posture and to prevent amblyopia. Eye muscle surgery is not always required. Because the function of the affected nerve and muscle cannot be restored, the other eye muscles are adjusted to compensate and allow for better eye alignment.
Surgery cannot actually fix the problem of nerves that are miswired, but can move muscles to compensate for the miswiring. Because surgery cannot fix the problem of the abnormal nerves, surgery cannot restore normal eye movement. However, surgery can (and usually does) substantially improve the situation. The full effect of the surgery may take some weeks to become apparent.
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