Surgical Treatment of Duane Syndrome

The innervational anomalies in Duane syndrome produce a variety of ocular motility disturbances that dictate the proper surgical management. The fundamental abnormality in Duane syndrome remains the aberrant or inappropriate innervation of the lateral rectus muscle by a branch of the oculomotor nerve. The position of the eye at rest; positions of comfortable binocular vision; and relative amounts of abduction, adduction, and retraction depend upon a continuum of the power of cocontraction of the lateral rectus muscle and, to a lesser extent, the amount of contracture that has developed in the lateral rectus muscle.444 The general principles that guide the surgical approach to the child with Duane syndrome include the following:

Esotropia in Duane Syndrome

1. Most children with Duane syndrome who require surgical treatment have an esotropia with a compensatory face turn to fuse. In this setting, unilateral recession of the medial rectus muscle in the involved eye is often sufficient to restore ocular alignment in primary gaze.175 In Duane syndrome, however, the size of the necessary medial rectus recession varies for a given deviation, depending on the amount of cocontraction in primary gaze. Surgical treatment of esotropia in Duane syndrome is fraught with pitfalls because a given deviation may be associated with either mild or severe cocontraction of the lateral rectus muscle.

From a surgical point of view, it is useful to view Duane syndrome with esotropia as existing on a continuum from congenital sixth nerve palsy (i.e., cases with only minimal lateral rectus cocontraction) to cases with severe cocontraction, which tend to manifest with upshoots and downshoots. The most important (and overlooked) step in the preoperative evaluation of Duane syndrome with esotropia is to attempt to assess the amount of cocontraction on the basis of clinical findings. In a child with minimal cocontraction, even a large medial rectus recession (e.g., 7 mm) may be insufficient to restore ocular alignment (as would be the case with a sixth nerve palsy). In a child with marked cocontraction, even a moderate medial rectus recession may unleash the cocontracting lateral rectus muscle and produce postoperative exotropia, limited adduction, and iatrogenic synergistic divergence.

In addition to observing the degree of retraction of the globe in attempted adduction, the amount of lateral rectus cocontraction can be judged by observing the degree of

face turn relative to the degree of esotropia. A large face turn relative to the degree of esotropia (as would be seen in a sixth nerve palsy), suggests that there is minimal lateral rectus cocontraction and that a large medial rectus recession is, therefore, required to realign the eyes.200 A smaller- than-expected face turn in the presence of a large esotropic deviation suggests the presence of marked lateral rectus cocontraction in primary position because even mild adduction produces sufficient cocontraction to realign the eyes. In this circumstance, a large medial rectus muscle recession to improve the primary position alignment of the eye leaves the strongly cocontracting lateral rectus muscle unopposed in primary position, resulting in a consecutive exotropia. In gaze away from the affected eye, the cocontracting lateral rectus muscle, which is now unopposed, may now abduct (rather than adduct) the affected eye, resulting in postoperative synergistic divergence.

If this complication can be anticipated by preoperative examination, it can be avoided by performing only a small recession of the medial rectus of the affected eye (e.g., 3 mm) along with a large (e.g., 8 mm) recession of the medial rectus muscle in the unaffected eye.492 This leads to a mild limitation of adduction of that eye, but serves the purpose of aligning the eye in primary position without allowing the lateral muscle of the affected eye to overwhelm its antagonist when it cocontracts. It also minimizes the risk of postoperative synergistic divergence.195 Marked enophthalmos in the Duane eye also suggests that a large amount of cocontraction is present. The finding of normal saccadic velocities of adducting saccades in Duane syndrome also suggests minimal contraction, while a decreased adducting saccadic velocity suggests significant cocontraction.609 Although isolated medial rectus recession in the normal eye is also efficacious.492 This procedure can produce a prominence of the globe that contrasts sharply with the enophthalmos of the affected eye.

2. Although some have treated Duane syndrome with recess– resect procedures,384 lateral rectus muscle resections are generally to be avoided. The lateral rectus muscle is already short, tight, and innervationally abnormal in Duane syndrome. Resection of this muscle creates the risk of producing disfiguring enophthalmos, severely limiting adduction and producing iatrogenic synergistic divergence.

3. Although transposition procedures of the vertical rectus muscles can increase abduction, vertical rectus muscle transpositions have the benefit of increasing abduction.70,468,530,539,563 They have the potential to induce a vertical deviation and disrupt fusion, especially in patients with marked cocontraction. Many strabismus surgeons, therefore, favor the inherent simplicity of unilateral or bilateral medial rectus recessions.39,306