Congenital cranial dysinnervation disorders (CCDDs) are a group of strabismus entities that have in common a developmental defect of one or more cranial nerves. There can be nuclear hypoplasia, nerve misdirection, and/or or absence of the nerves themselves. These anomalies lead to various patterns of abnormal innervation of the eye muscles that often result in secondary abnormal structural changes to the affected muscles, usually stiffening or contracture. Onset of the innervation anomalies can be as early as the first trimester in utero. Included in this group are Duane retraction syndrome, congenital fibrosis of the extraocular muscles, Möbius syndrome, and some cases of congenital fourth nerve palsy (see Chapter 11). In recent work, congenital Brown syndrome has been postulated to be a form of CCDD.
Duane Retraction Syndrome
Duane retraction syndrome is a spectrum of ocular motility disorders characterized by anomalous co-contraction of the medial and lateral rectus muscles on actual or attempted adduction of the involved eye or eyes; this co-contraction causes the globe to retract. Horizontal eye movement can be limited to various degrees in both abduction and adduction. An upshoot or downshoot often occurs when the affected eye is innervated to adduct; vertical slippage of a tight lateral rectus muscle by 1–2 mm, which has been demonstrated by magnetic resonance imaging (MRI) studies, is the typical cause. Less commonly, anomalous vertical rectus muscle activity is responsible for upshoots and downshoots.
Although most affected patients have Duane retraction syndrome alone, many associated systemic defects have been noted, such as Goldenhar syndrome (hemifacial microsomia, ocular dermoids, ear anomalies, preauricular skin tags, and eyelid colobomas) and Wildervanck syndrome (sensorineural hearing loss and Klippel-Feil anomaly with fused cervical vertebrae). Studies of patients with Duane retraction syndrome related to prenatal thalidomide exposure show that the underlying defect in development occurs between the fourth and sixth weeks of gestation.
Most cases of Duane retraction syndrome are sporadic, but approximately 5%–10% show autosomal dominant inheritance. Instances of links to more generalized disorders have been reported. Discordance in monozygotic twins raises the possibility that the intrauterine environment may play a role in the development of this syndrome. A higher prevalence in females is reported in most series, and there is a predilection for the left eye.
In most anatomical and imaging studies, the nucleus of the sixth cranial nerve is absent or hypoplastic and an aberrant branch of the third cranial nerve innervates the lateral rectus muscle. Results of electromyographic studies have been consistent with this finding. Although Duane retraction syndrome is considered an innervational anomaly, tight and broadly inserted medial rectus muscles and fibrotic lateral rectus muscles, with corresponding forced duction abnormalities, are often encountered during surgery.
The most widely used classification of Duane retraction syndrome defines 3 types, but they may represent differences only in the severity of horizontal rotation limitations. Type 1 refers to poor abduction, frequently with esotropia in primary position (Fig 12-1); type 2 refers to poor adduction and exotropia (Fig 12-2); and type 3 refers to poor abduction and adduction, with esotropia, exotropia, or no primary position deviation (Fig 12-3). Approximately 15% of cases are bilateral; the type may differ between the 2 eyes. The spectrum of dysinnervation among cases means that classification of patients based on these categories can be arbitrary in some situations, especially in deciding between type 1 and type 3. Synergistic divergence is a rare and bizarre motility disturbance that is often classified as a fourth type of Duane syndrome. There is usually exotropia, and when the affected eye looks in the direction that should result in adduction, it actually abducts even further—a finding colorfully described as “the ocular splits.” Synergistic divergence can be unilateral or bilateral and can be due to biallelic COL25A1 mutations.
Figure 12-1 Type 1 Duane retraction syndrome with esotropia, left eye, showing limitation of abduction, almost full adduction, and retraction of the globe on adduction. Far right, Compensatory left head turn.
(Courtesy of Edward L. Raab, MD.)
Figure 12-2 Type 2 Duane retraction syndrome, left eye. Top row, Full abduction and marked limitation of adduction. Bottom row, Variable upshoot and downshoot of the left eye with extreme right-gaze effort. The typical primary position exotropia is not present in this patient.
(Courtesy of Edward L. Raab, MD.)
Figure 12-3 Type 3 Duane retraction syndrome, right eye. Severe limitation of abduction and adduction, with palpebral fissure narrowing even though adduction cannot be accomplished. There is no deviation in primary position.
(Courtesy of Edward L. Raab, MD.)
Type 1 (with esotropia and limited abduction) is the most common form of Duane retraction syndrome, accounting for 50%–80% of cases in several series. Affected individuals or their caregivers often incorrectly believe that the normal eye is turning in excessively, not realizing that the involved eye is failing to abduct. Observation of globe retraction on adduction obviates the need for neurologic investigation for sixth nerve palsy, from which it must be differentiated; however, retraction can be difficult to appreciate in an infant. Another indicator that the condition is not sixth nerve palsy is the relatively small esotropia in primary position (usually <30 prism diopters [Δ]) in the setting of a severe abduction deficit. A further point of differentiation is that even in esotropic Duane retraction syndrome, a small-angle exotropia is sometimes present on gaze to the side opposite that of the affected eye, a finding that does not occur in lateral rectus muscle paralysis. Finally, examination at the slit lamp can help confirm the diagnosis in mild cases: if the vertical slit-lamp beam cast from the cornea onto the lower eyelid is disrupted by globe retraction when the eye adducts, Duane retraction syndrome is present.
No surgical approach will normalize rotations. Surgery is reserved for cases with a primary position deviation, a head turn, marked globe retraction, or large upshoots or downshoots. Because Duane retraction syndrome is a spectrum of motility disorders, the surgical plan must be individualized for the patient. In many patients with this syndrome, the eyes are properly aligned in at least 1 position of gaze, allowing the development of binocular vision. The main goal of surgery is to centralize this field of single binocular vision to eliminate the need for a head turn. Expansion of the field of single binocular vision, while laudable, is more relevant in patients with sixth nerve palsy than in those with Duane syndrome, who rarely report diplopia in ipsilateral gaze.
For unilateral type 1 Duane retraction syndrome, recession of the medial rectus muscle on the involved side has been the procedure most often used to correct the primary position deviation and eliminate the head turn. Adding recession of the opposite medial rectus (bilateral surgery) has been advocated by some surgeons, but the rationale is unclear, as this does not increase innervation to the lateral rectus muscle (as it would in sixth nerve paresis) and any decrease in medial rectus innervation is offset by a decrease in anomalous innervation to the lateral rectus muscle of the involved eye. These operations do not usually improve abduction significantly. Primary position overcorrection can occur due to excessive medial rectus recession, and the resulting exotropia will worsen in the field of gaze in which the involved eye is adducted. Recession of the lateral rectus muscle of the uninvolved eye can offset this effect to some extent.
Because of concern that lateral rectus muscle resection will exacerbate globe retraction, most surgeons do not favor this approach. Occasionally, however, there are patients with minimal co-contraction in whom a small resection (<3–4 mm) can produce dramatic improvement in abduction. Partial or full lateral transposition of both vertical rectus muscles or the superior rectus alone, usually with medial rectus recession, with or without posterior scleral fixation (myopexy), has been shown to improve abduction in some patients.
The most commonly recommended surgery for type 2 Duane retraction syndrome is recession of the lateral rectus muscle on the involved side; resection of the medial rectus muscle is avoided. Some surgeons recess both lateral rectus muscles if a large-angle exotropia is present, but when a fixating unaffected eye is operated on, the effect of increased contralateral medial rectus innervation (and associated lateral rectus anomalous innervation) must be considered.
Patients with type 3 Duane retraction syndrome often have straight eyes near the primary position and do not require surgical treatment for their minimal head turn or horizontal strabismus. Globe retraction may be severe enough to warrant treatment and can be lessened by recession of both the medial and the lateral rectus muscles, which may also reduce any upshoot or downshoot in adduction. This is also an option for treating retraction in type 1 and type 2 Duane retraction syndrome. The lateral recession must be large to improve the retraction. Other procedures to address an upshoot or downshoot include splitting of the lateral rectus muscle in a Y configuration, retroequatorial fixation of the lateral rectus muscle and, more recently, deactivation of the lateral rectus muscle, such as by disinsertion and reattachment to the lateral periosteum of the orbit with a subsequent transposition procedure.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.