Example of Duane s Syndrome affecting the right eye. The right eye has difficulty turning outwards and the lid aperture narrows. Duane’s syndrome is an unusual eye muscle problem. It is a type of strabismus a term that describes eyes that are not properly aligned or do not move normally. With Duane’s the eyes do not always move together because the affected eye has limited movement in one direction (usually outward). Children with Duane’s syndrome are otherwise healthy and usually have normal vision. The condition is congenital and is nearly always limited to one eye although both eyes are involved in about 20% of cases.
Eye Movement Limitations Duane’s syndrome is classified into three types depending on the direction of the muscle restriction. In the most common type of Duane’s the affected eye has restricted horizontal movement outwards (toward the ear). Let’s say the left eye is affected. There is limited movement when looking left. There is usually normal movement to the right but often the affected eye may retract slightly into the eye orbit and the eyelids partly close. Another feature is that the left eye may suddenly move upward (called “upshoot”) or downward (“downshoot”) when looking to the right.
In the least common type of Duane’s the movement limitation is in the opposite direction. So an affected left eye does not move or has restricted movement when looking to the right (towards the nose). In the third type of Duane’s there is limited movement outwards and inwards.
Eye Alignment In most people with Duane’s there are some directions of gaze in which the eyes are perfectly aligned. If there is good alignment in the straight-ahead position (this is most common) the condition is not very apparent. To look to the side one merely turns his or her head instead of the eyes. This avoids double vision and maintains a more normal appearance.
Those people whose eyes are not aligned when looking straight ahead need to turn their face to avoid double vision in the forward direction. This is called a compensatory face turn. If the necessary amount of face turn is far off-centre the head tends to be held in a position that does not look normal. Fortunately this can often be corrected.
What Causes the Problem? Nerves from the brainstem act like wires carrying an electrical message to the muscles that move the eyes. With Duane’s some of the nerves are connected to the wrong muscles so when the brain directs the eyes to move in a certain direction only one eye receives the right message. The other eye gets improper signals which prevent it from moving normally. Over time some of the muscles of the affected eye become tight adding to the eye movement problems.
Treatment In most cases treatment is unnecessary. If there is an especially noticeable face turn the involved eye muscles can be surgically corrected to allow looking at things straight on without having to turn the head. The surgery however is only to improve the head position; it will not improve the eye’s limited range of motion.
As one gets older the eye movement problem will not change for better or worse. But it’s still important to have routine eye examinations to guard against the development of amblyopia (lazy eye) a condition that can sometimes occur with any type of strabismus.