Strabismus syndromes

Special types of strabismus have unusual clinical features. Most of these disorders are caused by structural anomalies of the extraocular muscles, adjacent tissues, or neurologic development. Most strabismus syndromes produce incomitant misalignments.

Duane’s syndrome

Duane’s syndrome is a congenital motility disorder that is characterized by limited ocular movement and retraction of the globe on adduction. There are several forms of Duane’s syndrome based upon the specific limitation of movement that is seen.

ETIOLOGY

The cause of Duane’s syndrome is thought to be an absence of the 6th nerve nucleus and anomalous innervation of the lateral rectus muscle. This results in cocontraction of the medial and lateral rectus muscles on attempted adduction of the affected eye, which leads to the observed retraction of the globe.

CLINICAL PRESENTATION

Within the spectrum of Duane’s syndrome, patients may exhibit impairment of abduction, impairment of adduction, or a limitation of both abduction and adduction (60–62). An upshoot or downshoot of the involved eye on adduction occurs in some cases. They may have esotropia, exotropia, or relatively straight eyes. The majority of patients with Duane’s syndrome exhibit a compensatory head posture to maintain single vision. Amblyopia is uncommon. Duane’s syndrome usually occurs sporadically. It is sometimes inherited as an autosomal dominant trait. It usually occurs as an

isolated condition but may occur in association with various other ocular and systemic anomalies.

DIFFERENTIAL DIAGNOSIS

The diagnosis of Duane’s syndrome may be difficult to make in a young child where the limitation of movement of the eye may be difficult to see. Patients with esotropia that is noted shortly after birth may have Duane’s syndrome. In contrast to those patients with congenital esotropia, the deviation in Duane’s syndrome is usually relatively small. Patients with congenital esotropia have full ocular rotations. The most important disorder with which Duane’s syndrome can be confused is 6th nerve palsy. The need to distinguish between these entities is vital in order to eliminate an unnecessary neurologic work-up in a patient with Duane’s syndrome, or not to miss the need for one in a patient with a 6th nerve palsy. Patients with Duane’s syndrome have a relatively small crossing of their eyes given their large abduction deficit. The presence of globe retraction can also be helpful.

MANAGEMENT/TREATMENT

Surgery is indicated to treat a large compensatory face turn, a noticeable upshoot or downshoot, or significant globe retraction. While surgery to improve alignment or to reduce a noticeable face turn can be helpful, surgery cannot significantly improve the movement of the eye.

PROGNOSIS

Most patients with Duane’s syndrome do not require surgery and remain stable for life. They adjust to the lack of movement of their eye by moving their head to look to the affected side.

Brown’s syndrome

ETIOLOGY

Most cases of Brown’s syndrome are congenital, but acquired Brown’s syndrome may follow trauma to the orbit involving the region of the trochlea or after sinus surgery. It may also occur with inflammatory processes, particularly sinusitis and juvenile rheumatoid arthritis. Some cases have been attributed to structural abnormalities such as a tight superior oblique tendon, congenital shortening or thickening of the superior oblique tendon sheath, or connective tissue trabeculae between the superior oblique tendon and the trochlea.

CLINICAL PRESENTATION

In Brown’s syndrome, elevation of the eye in the adducted position is restricted (63, 64). An associated downward deviation of the affected eye in adduction may also occur. A compensatory head posture may be present to move the eye away from the adducted position. Parents often notice the ‘abnormal’ movement of the other eye; that it elevates higher than the actual affected eye. This apparent ‘overelevation’ is a result of normal movement compared to the limited elevation of the involved side.

DIAGNOSIS

in eliminating a torticollis or significant ocular deviation, it does carry the risk of producing an iatrogenic 4th nerve palsy.

Monocular elevation deficiency (MED)

ETIOLOGY

Monocular elevation deficiency (MED), also called double elevator palsy, describes a monocular elevation deficit in both abduction and adduction. When an affected child fixates with the nonparetic eye, the paretic eye is low and the ipsilateral upper eyelid may appear ptotic. Fixation with the paretic eye causes a hypertropia of the nonparetic eye and a disappearance of the ptosis (65–67). MED may represent a paresis of both elevators, the superior rectus and inferior oblique muscles, or a possible restriction to elevation from a fibrotic inferior rectus muscle (a limited form of a more generalized fibrosis syndrome).

CLINICAL PRESENTATION

Patients may present because of the pseudoptosis and the vertical misalignment may not be noted. A compensatory chin up head posture may be present to allow for binocular vision.

Although the clinical characteristics of Brown’s syndrome usually allow a diagnosis to be made, a definitive diagnosis requires a positive forced duction test. In children, this is often done at the time of surgery. Forceps are placed on the eye and an attempt is made to manually rotate the globe toward the nose while it is being elevated. An inability to move the globe into this position confirms the diagnosis of Brown’s syndrome.

MANAGEMENT/TREATMENT

Surgical intervention may be warranted for cases that involve a compensatory head posture, a large downshoot in adduction, or a vertical strabismus in straight-ahead gaze. Surgery consists of weakening the involved superior oblique. Treatment is not indicated for the lack of elevation in adduction.

PROGNOSIS

Most patients with Brown’s syndrome do not require surgery. While surgery is often successful

DIFFERENTIAL DIAGNOSIS

MED may mimic Brown’s syndrome. Both produce a limitation of elevation in adduction. Severe cases of Brown’s syndrome may display some degree of limitation in abduction as well. Attempted movement of the eye at the time of surgery (forced duction testing) is useful to differentiate these disorders. It is also important to distinguish the type of MED (restrictive versus paralytic) as the treatments are different.

MANAGEMENT/TREATMENT

Treatment for MED is indicated when a deviation exists in straight-ahead gaze or when a compensatory head posture exists. Treatment consists of weakening of the inferior rectus muscle if its restriction is the cause of the deviation, and transposition eye muscle surgery for the paretic form of the disease. Because the apparent ptosis is actually secondary to the strabismus, correction of the hypotropia treats the pseudoptosis.

Möbius syndrome

ETIOLOGY

The cause of Möbius syndrome is unknown. Whether the primary defect is maldevelopment of cranial nerve nuclei, hypoplasia of the muscles, or a combination of central and peripheral factors is unclear. Some familial cases have been reported.

DIFFERENTIAL DIAGNOSIS

Because of the early onset, Möbius syndrome may present as a congenital esotropia. The abduction deficit(s) may lead to a diagnosis of 6th nerve palsy. However, the presence of facial palsy and swallowing difficulties generally makes this diagnosis distinguishable from other forms of strabismus.

MANAGEMENT/TREATMENT

CLINICAL PRESENTATION

The distinctive features of Möbius syndrome are congenital facial paresis and abduction weakness. The facial palsy is commonly bilateral, frequently asymmetric, and often incomplete, tending to spare the lower face and platysma. The abduction defect may be unilateral or bilateral. Esotropia is common although some children will have relative straight eyes (68). Associated developmental defects may include ptosis, palatal and lingual palsy, hearing loss, pectoral and lingual muscle defects, micrognathia, syndactyly, supernumerary digits, or the absence of hands, feet, fingers, or toes.

Surgical correction of the esotropia is indicated and any attendant amblyopia should be treated. As with other cases of 6th nerve palsy, abduction may not improve following successful alignment surgery.