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Young boy experiences drifting eyes since birth
When the boy was 3 years old, a left exotropia of 35 ∆D was measured.
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An otherwise healthy 13-week-old infant was initially referred to our clinic in 2009 for drifting eyes since birth. He was also noted to have a preference for a right head turn. There was a positive family history of strabismus.
Examination
On examination, the patient had a tendency to turn his head toward the right. A left exotropia of 18 ∆D was measured on primary gaze. During extraocular motility testing, the patient was unable to adduct the left eye past midline, but instead had a left downshoot. While no ptosis was seen, mild palpebral fissure change was noted when the child attempted to adduct. No nystagmus was seen. Best corrected binocular visual acuity was 20/200 by visual evoked potential and preferential looking cards testing. Cycloplegic refraction was +0.75 +2.00 × 90 in the right eye and +1.00 +2.00 × 90 in the left eye. Pupils were equally reactive with no afferent pupillary defect. Palpated IOPs were normal.
Two months later, the child was noted to have divergence of the eyes on attempted right gaze. Follow-up exam 1 year later was unchanged.
During re-examination at age 3 years, the child continued to have a tendency to turn his head to the right, which was measured at 30°. At primary gaze, a left exotropia of 35 ∆D was measured. A left downshoot on attempted adduction with the inability to adduct the left eye was again seen. Divergence of both eyes was seen on attempted right gaze (Figure 1). There was a possibility of change in the palpebral fissure. No ptosis or pupillary abnormalities were detected.
Figure 1. A left exotropia is seen on primary gaze, and synergistic divergence is seen as the left eye attempts to adduct.
Image: Vuong LN, Strominger MB
What is your diagnosis?
Left exotropia
Given the child’s presentation, two potential diagnoses were considered: a third nerve palsy or Duane’s syndrome.
Diagnosis
Although no ptosis or pupillary involvement was seen, the degree of aberrant innervation to the lateral rectus muscle, absence of obvious globe retraction and palpebral fissure narrowing on the left were concerning for a third nerve palsy. An MRI did not show changes to the third nerve.
The diagnosis of Duane’s syndrome type 2 with synergistic divergence was then made.
Discussion and treatment
In Duane’s syndrome, there is an anomalous co-contraction of the medial and lateral rectus muscles producing globe retraction on adduction. Histological examination reveals the absence of the sixth nerve nucleus with aberrant innervation of the third nerve. Direct examination of the muscles reveal tight and broadly inserted medial rectus muscles with fibrotic-looking lateral rectus muscles.
There are three types of Duane’s syndrome: In type 1, which is the most common (78%), there is limitation of abduction in the affected eye; in type 2, the second most common type (15%), there is limitation of adduction; and in type 3 (7%), there is limitation of both adduction and abduction.
An upshoot or downshoot of the affected eye can be seen and is thought to be the result of side slip of horizontal recti from weakening of horizontal muscle due to chronic contraction vs. anomalous innervation of vertically acting muscles.
Synergistic divergence, in which abduction occurs on attempted adduction, leads to simultaneous abduction of both eyes on lateral gaze in the direction of the affected eye. Synergistic divergence can occur as an extreme form of Duane’s syndrome, in which oculomotor nerve branch fibers originally directed to the medial rectus muscle innervated the lateral rectus muscle.
Patients with Duane’s syndrome seldom have diplopia because they use a head turn to fuse the images. Approximately 10% of patients have amblyopia. There is a 3:2 female predominance, and 60% to 72% of the time the left eye is the involved eye. The majority of Duane’s syndrome cases are sporadic, but 5% to 10% are autosomal dominant with linkage studies to 2q31 and 8q13.
A third nerve palsy can often be ruled out because of the presence of globe retraction and the absence of ptosis and pupillary defect. A sixth nerve palsy can be ruled out because of the presence of globe retraction, normal primary gaze or modest esotropia, and profound abduction deficit seen in Duane’s syndrome. Even in esotropic Duane’s syndrome, small-angle exotropia frequently is present in the gaze to the side opposite the affected eye.
Management of patients with Duane’s syndrome is usually conservative, correcting for refractive errors, treating amblyopia and using prisms to correct head turns.
When surgical intervention is undertaken, it is for primary position deviation, head turns, marked globe retraction or large upshoot/downshoot. In type 1, the medial rectus is recessed on the involved side. Contralateral medial rectus recession is performed for deviation over 20 ∆D. In type 2, the lateral rectus is recessed on the involved side. Contralateral lateral rectus recession is performed for large deviation. In type 3, recession of both horizontal muscles is performed. For upshoot/downshoot, splitting the lateral rectus muscle in a Y configuration, posterior fixation of the lateral rectus muscle, or disinsertion and reattachment to the lateral wall of the orbit can be performed.
In the case of our patient, given the amount of head turn, surgical management will include a left lateral rectus recession.
Summary
Duane’s syndrome is the result of anomalous co-contraction of the medial and lateral rectus muscles producing globe retraction on adduction. Patients in general do not experience diplopia. The syndrome can be categorized into three types: limitation of abduction (type 1), limitation of adduction (type 2), or limitation of both abduction and adduction (type 3). In Duane’s syndrome type 2, synergistic divergence can occur, although a third nerve palsy can be suspected and should be ruled out with an MRI. Most patients are treated conservatively, but surgical intervention can be pursued to correct the ocular alignment at primary gaze, head turns, marked globe retraction or large upshoot/downshoot.