CHAPTER 12
Special Forms of Strabismus
The BCSC Master Index and BCSC Section 5, Neuro-Ophthalmology, should be consulted for additional discussion of several entities covered in this chapter. See Chapter 14 for discussion of some of the surgical procedures mentioned in this chapter.
Congenital Cranial Dysinnervation Disorders
Congenital cranial dysinnervation disorders (CCDDs) are a group of strabismus entities that have in common a developmental defect of one or more cranial nerve nuclei and, as a result, hypoplasia or absence of the nerves themselves. These anomalies lead to various patterns of abnormal innervation of the eye muscles, which often result in secondary abnormal structural changes to the affected muscles, usually stiffening or contractures. 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 (CFEOM), Möbius syndrome, and some cases of congenital fourth nerve palsy (see Chapter 11). Recent work suggests that congenital Brown syndrome may also be a form of CCDD.
Engle EC. The genetic basis of complex strabismus. Pediatr Res. 2006;59(3):343–348.
Engle EC. Oculomotility disorders arising from disruptions in brainstem motor neuron development. Arch Neurol. 2007;64(5):633–637.
Traboulsi EI. Congenital cranial dysinnervation disorders and more. J AAPOS. 2007;11(3):215–217.
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, has been proposed as the cause. An alternative theory is that anomalous vertical rectus muscle activity is responsible for upshoots and downshoots, but this is less common.
Although most affected patients have Duane retraction syndrome alone, many associated systemic defects have been observed, 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). A defect in development occurring between the fourth and sixth weeks of gestation appears to be the cause of Duane retraction syndrome, according to studies of patients prenatally exposed to thalidomide.
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 be important 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.
Clinical features
The most widely used classification of Duane retraction syndrome defines 3 groups, but they may represent differences only in the severity of horizontal rotation limitations: type 1 refers to poor abduction, frequently with primary position esotropia (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.
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.
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 Duane retraction syndrome (with esotropia and limited abduction) is the most common form, 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 lack of correspondence between the absent or typically modest primary position esotropia (usually <30Δ) and the usually profound abduction deficit (a comparison useful in ruling out paralysis in other entities as well). A further point of differentiation is that even in esotropic Duane retraction syndrome, a small-angle exotropia is frequently present on gaze to the side opposite the affected eye, a finding not present 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.
Management
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. Since Duane retraction syndrome is a spectrum of motility disorders, the surgical plan has to 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 goals of surgery are to centralize and expand the field of single binocular vision.
For 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 recommended for deviations larger than 20Δ in primary position. These operations do not usually improve abduction significantly. Primary position overcorrection due to excessive medial rectus recession can occur, and the resulting exotropia will worsen when the involved eye is adducted. Recession of the lateral rectus muscle of the uninvolved eye can offset this effect.
Because of the likelihood that globe retraction will worsen, most surgeons do not favor resection of the lateral rectus muscle for type 1 Duane retraction syndrome, but there are occasional exceptions. Partial or full lateral transposition of both of the vertical rectus muscles or the superior rectus alone, with or without posterior scleral fixation (myopexy) has been found to improve abduction.
The most commonly recommended surgery for type 2 Duane retraction syndrome is recession of the lateral rectus muscle on the involved side in proportion to the size of the exotropia; resection of the medial rectus muscle is avoided. Some surgeons recess both lateral rectus muscles if a large-
angle exotropia is present.
Patients with type 3 Duane syndrome often have straight eyes in or near the primary position and little, if any, head turn. Severe globe retraction may be lessened by recession of both the medial and the lateral rectus muscles, which also may benefit the induced anomalous vertical movements. This is also an option for treating retraction in type 1 and type 2 Duane retraction syndrome. The lateral recession must be very large to improve the retraction. Procedures to address the upshoot or downshoot include large lateral rectus recession, splitting of the lateral rectus muscle in a Y configuration, retroequatorial fixation of the lateral rectus muscle, and, more recently, disinsertion of the lateral rectus muscle and reattachment to the lateral periosteum of the orbit.
Rosenbaum AL. Costenbader lecture. The efficacy of rectus muscle transposition surgery in esotropic Duane syndrome and VI nerve palsy. J AAPOS. 2004;8(5):409–419.
Congenital Fibrosis of the Extraocular Muscles
Congenital fibrosis of the extraocular muscles (CFEOM), or congenital fibrosis syndrome, is a group of rare congenital disorders in which extraocular muscle (EOM) restriction is present and fibrous tissue replaces these muscles. Some forms have been noted to be inherited, usually as an autosomal dominant trait but occasionally in an autosomal recessive fashion. Cases of CFEOM involve developmental defects of cranial nerve nuclei and of the nerves themselves, resulting in dysinnervation and abnormal structure of the EOMs.
Heidary G, Engle EC, Hunter DG. Congenital fibrosis of the extraocular muscles. Semin Ophthalmol. 2008;23(1):3–8.
Clinical features
There are several variations of CFEOM. Generalized fibrosis is the most severe form, affecting all the EOMs of both eyes, including the levator palpebrae superioris. Congenital unilateral fibrosis is nonfamilial.
A variant that involves the inferior rectus muscle alone may be unilateral or bilateral and sporadic or familial. This condition is commonly inherited as an autosomal dominant trait.
Strabismus fixus involves the horizontal rectus muscles, usually the medial rectus muscles, causing severe esotropia. The condition is usually sporadic and can be acquired late.
Vertical retraction syndrome affects the superior rectus muscle and causes inability to depress the eye.
Diagnosis of CFEOM depends on finding limited voluntary motion with restriction, which is usually severe and can be confirmed with forced-duction testing. The congenital onset is important in distinguishing the syndrome from thyroid eye disease.
Management
Surgery for CFEOM is difficult and requires release of the restricted muscles (ie, weakening procedures). Fibrosis of the adjacent tissues may be present as well. A good surgical result aligns the eyes in primary position, but full ocular rotations cannot be restored and the outcome is unpredictable.
Yazdani A, Traboulsi EI. Classification and surgical management of patients with familial and sporadic forms of congenital fibrosis of the extraocular muscles. Ophthalmology. 2004;111(5):1035–1042.
Möbius Syndrome
Clinical features
Möbius syndrome (or “sequence”; see Chapter 15) is a rare condition characterized by the association
of both sixth and seventh nerve palsies, the latter causing masklike facies. Patients may also manifest gaze palsies that can be attributed to abnormalities in the paramedian pontine reticular formation or the sixth cranial nerve nucleus. Many patients also have limb, chest, and tongue defects, and some geneticists think that Möbius syndrome is one of a family of syndromes in which hypoplastic limb anomalies may be associated with orofacial and cranial nerve defects. Poland syndrome (absent pectoralis muscle) is another variant.
Patients with Möbius syndrome exhibit 1 of 3 patterns of motility involvement, probably related to the severity and timing of the in utero insult:
1.Orthotropia in primary position with marked deficits in abduction and adduction (Fig 12-4) (40% of cases)
2.Esotropia with cross-fixation and sparing of convergence and adduction (50% of cases)
3.Large exotropia with absence of convergence (10% of cases)
Some patients appear to have palpebral fissure changes on adduction or vertical EOM involvement.
Figure 12-4 Möbius syndrome. A, Straight eyes in primary position. B, The patient cannot smile because of bilateral seventh nerve palsy. C, Bilaterally absent adduction and severely limited abduction. D, Vertical movements are not affected. (Courtesy
of Edward L. Raab, MD.)
Management
Medial rectus muscle recession has been advocated for patients with large-angle esotropia, but caution should be exercised in the presence of a significant limitation of adduction. Some surgeons have undertaken to improve abduction by performing vertical rectus muscle transposition procedures after medial rectus muscle restriction has been relieved.
Carta A, Mora P, Neri A, Favilla S, Sadun AA. Ophthalmologic and systemic features in Möbius syndrome: an Italian case