Disorders of Ocular Motility

Clinical features

Children with infantile esotropia often alternate fixation between eyes and may cross-fixate (i.e., look to the left with the right eye and to the right with the left eye). The misalignment is sufficient that family members see that a problem exists. Some children fixate almost entirely with one eye and are at risk for permanent loss of visual acuity, developmental amblyopia, in the other.

Accommodative esotropia occurs when accommodation compensates for hyperopia. Accommodation more sharply focuses the blurred image. Because convergence accompanies accommodation, one eye turns inward. Some children with accommodative esotropia cross-fixate and use each eye alternatively, while the other maintains fixation. However, if one eye is more hyperopic than the other eye, only the better eye fixates and the unused eye has a considerable potential for amblyopia.

Diagnosis

An ophthalmologist should examine the eyes to determine whether hyperopia is present.

Management

Eyeglasses correct hyperopic errors. The treatment of early onset esotropia, in which only one eye fixates, consists of alternate eye patching to prevent amblyopia. Early corrective surgery is required for persistent esotropia. Esotropia presenting after 6 years of age raises concern for a posterior fossa disorder such as a Chiari malformation.

Clinical features

Exophoria is a relatively common condition that begins before 4 years of age. It is most often evident when the child is fatigued and fixating on a far object or in bright sunlight. The natural history of the condition is unknown. Exotropia may be congenital but poor vision in the outward-turning eye is also a cause.

Diagnosis

Exotropia is an indication to examine the eye for intraocular disease.

Management

In children with intermittent exotropia, the decision to perform corrective surgery depends on the frequency and degree of the abnormality. When exotropia is constant, treatment depends on the underlying cause of visual loss.

Clinical features

Congenital oculomotor nerve palsy usually is unilateral and complete. Pupillary reflex paralysis is variable. Other cranial nerve palsies, especially abducens, may be associated. The palsy is often unrecognized at birth. Most oculomotor nerve palsies are idiopathic, but some are genetic or caused by orbital trauma. The affected eye is exotropic and usually amblyopic. Lid retraction on attempted adduction or downward gaze may be evidence of aberrant regeneration.

Diagnosis

Magnetic resonance imaging (MRI) excludes the possibility of an intracranial mass compressing the nerve. Exophthalmos suggests an orbital tumor. A nonreactive, dilated pupil excludes the diagnosis of myasthenia gravis, but a normal pupil requires testing for myasthenia.

Management

Extraocular muscle surgery may improve the cosmetic appearance but rarely improves ocular motility or visual function.

Clinical features

Congenital superior oblique palsy is usually unilateral. Birth trauma is usually the suspected cause, but the actual cause is rarely established. Most congenital cases are idiopathic. The head tilts away from the paralyzed side to keep the eyes in alignment and avoid diplopia. The major ocular features are hypertropia, greatest in the field of action of the involved superior oblique muscle; underaction of the paretic superior oblique muscle and overaction of the inferior oblique muscle; and increased hypertropia when the head tilts to the paralyzed side (positive Bielschowsky test ).

Diagnosis

Head tilt, or torticollis (see Chapter 14 ), is not a constant feature. Once examination confirms a superior oblique palsy, important etiological considerations other than congenital include trauma, myasthenia gravis, and brainstem glioma.

Management

Prisms are effective for small angle deviations; otherwise patients require surgery.

Clinical features

Congenital abducens nerve palsy may be unilateral or bilateral and is sometimes associated with other cranial nerve palsies. Lateral movement of the affected eye(s) is limited partially or completely. Most infants use cross-fixation and thereby retain vision in both eyes. In the few reported cases of congenital palsy with pathological correlation, the abducens nerve is absent and its nucleus is hypoplastic.

Möbius syndrome is the association of congenital facial diplegia and bilateral abducens nerve palsies (see Chapter 17 ). Duane syndrome is congenital, non-progressive horizontal ophthalmoplegia caused by aplasia of one or both nuclei of the abducens nerve with innervation of the atrophic lateral rectus by fibers of the oculomotor nerve. In most cases, the cause is unknown; however, a minority are caused by heterozygous mutations of the CHN1 gene. The characteristic features are lateral rectus palsy, some limitation of adduction, and narrowing of the palpebral fissure because of globe retraction on attempted adduction. Möbius and Duane syndromes are rhombencephalic maldevelopment syndromes often associated with lingual, palatal, respiratory, or long track motor and coordination deficits.

Diagnosis

MRI excludes the possibility of an intracranial mass lesion and hearing testing is required.

Management

Surgical procedures may be useful to correct head turn and to provide binocular single vision, but they do not restore ocular motility.

Clinical features

Elevation is limited in adduction but is relatively normal in abduction. Passive elevation (forced duction) is also restricted. Other features include widening of the palpebral fissure on adduction and backward head tilt.

Diagnosis

The diagnosis of Brown syndrome requires the exclusion of acquired shortening of the superior oblique muscle. The causes of acquired shortening of the superior oblique muscle include juvenile rheumatoid arthritis, trauma, and inflammatory processes affecting the top of the orbit (see section on Orbital Inflammatory Disease later in this chapter).

Management

Surgical procedures that extend the superior oblique muscle can be useful in congenital cases.

Clinical features

Affected children have congenital bilateral ptosis and restrictive ophthalmoplegia, with their eyes partially or completely fixed in a downward position. CFEOM is a relatively static disorder that is phenotypically homogeneous when completely penetrant. The head is tilted back to allow vision, and diplopia is not associated despite the severe misalignment of the eyes. Identifying the inheritance pattern and associated features such as cognitive impairment, microcephaly, or oligodactyly aids in differentiating various subtypes.

Diagnosis

The clinical findings and the family history are key for diagnosis. Genetic testing is available.

Management

The goal of treatment is improvement of vision by correcting ptosis.

Clinical features

Although transmission of these disorders is by autosomal recessive inheritance, a male-to-female bias of 2:1 exists. Symmetric ptosis and ophthalmoplegia are present at birth or shortly thereafter. Mild facial weakness may be present but is not severe enough to impair feeding. If partial at birth, the ophthalmoplegia becomes complete during infancy or childhood. Generalized weakness sometimes develops. Electrophysiological studies in patients suffering from sudden apnea suggest a defect in acetylcholine resynthesis and ChAT. Refractoriness to anticholinesterase medications and partial or complete absence of AChE from the endplates suggest a mutation in COLQ. Multiple mutations have been identified, including CHRNE (accounting for over 50% of cases), RAPSN , CHAT , COLQ , and DOK7 .

Diagnosis

Suspect the diagnosis in any newborn with bilateral ptosis or limitation of eye movement. Repetitive nerve stimulation of the limbs at a frequency of 3 Hz may evoke a decremental response after 5–10 minute stimulation that is reversible with edrophonium chloride. The 50 Hz repetitive stimulation may also show a 10% decrease in CMAP between the first and fifth stimulation. This suggests that the underlying defect, although producing symptoms only in the eyes, causes generalized weakness at birth. Genetic testing is available.

Management

No evidence of an immunopathy exists and immunosuppressive therapy is not a recommendation. Thymectomy and corticosteroids are ineffective. Anticholinesterases may decrease facial paralysis but have little or no effect on ophthalmoplegia. The weakness, in some children, responds to 3,4-diaminopyridine (DAP), an agent that releases acetylcholine combined with anticholinesterases.

Clinical features

Congenital ptosis is often unnoticed until early childhood or even adult life and then diagnosed as an “acquired” ptosis. Miosis is sometimes an associated feature and suggests the possibility of a Horner syndrome, except that the pupil responds normally to pharmacological agents. Some patients have a synkinesis between the oculomotor and trigeminal nerves; jaw movements produce opening of the eye ( Marcus-Gunn phenomenon ).

Diagnosis

Box 15.1 lists the differential diagnosis of ptosis. Distinguishing congenital ptosis from acquired ptosis is essential. The examination of baby pictures is more cost-effective than MRI to make the distinction. If miosis is present, test the eye with pharmacological agents (Paredrine and cocaine test for denervation) to determine whether denervation rather than sympathetic hypersensitivity is present, indicating a Horner syndrome. Concurrent paralysis of extraocular motility is evidence against congenital ptosis.

Management

Early corrective surgery to elevate the lid improves appearance and vision.

Clinical features

Aneurysms at the junction of the internal carotid and posterior communicating arteries are an important cause of unilateral oculomotor palsy in adults but are a rare cause in children. Compression of the nerve by expansion of the aneurysm causes the palsy. Intense pain in and around the eye is frequently experienced at the time of hemorrhage. Because the parasympathetic fibers are at the periphery of the nerve, mydriasis is an almost constant feature of ophthalmoplegia caused by aneurysms of the posterior communicating artery. However, pupillary involvement may develop several days after onset of an incomplete external ophthalmoplegia. A normal pupil with complete external ophthalmoplegia effectively excludes the possibility of aneurysm.

Sometimes, aneurysms affect the superior branch of the oculomotor nerve earlier and more severely than the inferior branch. Ptosis may precede the development of other signs by hours or days.

Diagnosis

Contrast-enhanced MRI and magnetic resonance angiography (MRA) or computed tomography (CT) angiogram identify most aneurysms.

Management

Surgical clipping is the treatment of choice whenever technically feasible. Oculomotor function often returns to normal after the procedure.

Clinical features

Symptoms begin between 2 and 13 years of age, with a peak between ages 5 and 8 years. The period from onset of symptoms to diagnosis is less than 6 months. Cranial nerve palsies, usually abducens and facial, are the initial features in most cases. Later, contralateral hemiplegia and ataxia, dysphagia, and hoarseness develop. Hemiplegia at onset is associated with a more rapid course. With time, cranial nerve and corticospinal tract involvement may become bilateral. Increased intracranial pressure is not an early feature, but direct irritation of the brainstem emetic center may cause vomiting rather than increased pressure. Intractable hiccup, facial spasm, personality change, and headache are early symptoms in occasional patients.

Brainstem gliomas carry the worst prognosis of any childhood tumor due to their location. The course is one of steady progression, with median survival times of 9–12 months.

Diagnosis

MRI delineates the tumor well and differentiates tumor from inflammatory and vascular disorders ( Fig. 15.1 ).

Management

Radiation therapy is the treatment of choice. Several chemotherapeutic programs are undergoing experimental trials, but none has established benefit.