Ophthalmology – Moebius Syndrome

Basics

Description

Moebius syndrome is a congenital, usually nonprogressive disorder characterized primarily by:

• Unilateral or bilateral facial weakness
• Impaired ocular abduction
• Variable involvement of other cranial nerves
• Possible craniofacial and limb anomalies

The disorder is considered part of the spectrum of congenital cranial dysinnervation disorders (CCDDs).

Epidemiology

Incidence

Approximately 0.0002–0.002% of live births.

Prevalence

Estimated historical figures include:

• About 2,000 affected individuals worldwide
• About 800 affected individuals in the United States

Because the syndrome is rare and variably expressed, its true prevalence is uncertain.

Risk Factors

Possible risk factors include:

• Family history of Moebius syndrome
• Family history of another congenital cranial dysinnervation disorder
• In-utero exposure to certain proposed teratogens or vascular-disruptive events

Reported associations include:

• Maternal hyperthermia
• Chorionic villus sampling
• Electric shock
• Benzodiazepine abuse
• Alcohol
• Cocaine
• Thalidomide
• Misoprostol

Not every exposed pregnancy develops Moebius syndrome, and many cases occur without an identifiable exposure.

Genetics

Most cases are sporadic, but several inheritance patterns have been reported:

• Autosomal dominant
• Autosomal recessive
• X-linked recessive

Expression and penetrance may vary.

Reported loci have included:

• MBS1: 13q12.2–q13
• Proposed MBS2: 3q21–q22
• Proposed MBS3: 10q21.3–q22.1

Multiple chromosomal abnormalities have also been associated with a Moebius-like phenotype.

General Prevention

There is no specific preventive treatment.

General measures include:

• Avoidance of known or suspected teratogens during pregnancy
• Genetic counseling when there is:
• A family history
• A syndromic phenotype
• A known chromosomal abnormality

Pathophysiology

The exact mechanism is incompletely understood.

Moebius syndrome is thought to result from abnormal development of the rhombencephalon/brainstem, affecting predominantly:

• Cranial motor nuclei
• Cranial nerve axons
• Their long central pathways

Developmental disruption is thought to occur very early in embryogenesis, approximately during the 3rd to 5th weeks of gestation.

The classic neurologic involvement affects:

• CN VI — abducens nerve
• CN VII — facial nerve

Other cranial nerves may also be involved.

Etiology

Possible etiologies include:

• Genetic or inherited developmental abnormalities
• Chromosomal abnormalities
• Teratogenic exposure
• Embryonic vascular disruption

In many patients, no single cause is identified.

Commonly Associated Conditions

Cranial Nerve Abnormalities

Other cranial nerve abnormalities may occur.

CN XII Involvement

Hypoglossal nerve involvement may cause:

• Tongue hypoplasia
• Abnormal lateral tongue grooves or crenulations

Craniofacial Abnormalities

Reported features include:

• Epicanthal folds
• Flat nasal bridge
• Micrognathia
• High-arched palate
• External ear abnormalities
• Dental abnormalities
• Hypertelorism

Limb Abnormalities

Extremity malformations are common and may include:

• Syndactyly
• Brachydactyly
• Limb reduction defects
• Clubfoot
• Arthrogryposis

Feeding and Swallowing Problems

These are common and may result from:

• Cranial nerve dysfunction
• Poor oral motor coordination
• Weak facial musculature
• Tongue dysfunction

Other Ocular Motility Disorders

Duane retraction syndrome may coexist.

Poland Syndrome

Some patients have associated Poland syndrome, characterized by:

• Hypoplasia or absence of the pectoral muscle
• Ipsilateral upper-limb abnormalities

Rare Associations

Reported uncommon associations include:

• Congenital heart defects
• Dextrocardia
• Arthrogryposis multiplex congenita
• Urinary tract abnormalities
• Anosmia
• Hypogonadotropic hypogonadism

Diagnosis

Diagnosis is primarily clinical.

The classic combination is:

• Congenital facial weakness
• Congenital limitation of ocular abduction

Other cranial nerve, limb, and craniofacial abnormalities support the diagnosis.

History

Important points include:

• Family history
• Maternal medication or drug exposure
• Possible teratogenic exposure during pregnancy
• Feeding difficulties
• Swallowing difficulties
• Speech delay
• Abnormal facial movement since birth
• Eye movement abnormalities since birth
• Exposure symptoms such as:
• Tearing
• Irritation
• Redness
• Photophobia

Physical Examination

Ocular Examination

A complete ophthalmic examination should include:

• Visual acuity
• Refraction
• Pupils
• Ocular motility
• Alignment
• Anterior segment examination
• Corneal surface assessment
• Fundus examination

Ocular Motility

The most characteristic abnormality is limited abduction due to CN VI dysfunction.

Patients may have:

• Bilateral abduction limitation
• Unilateral abduction limitation
• Esotropia
• Variable primary-position alignment

Some patients may be approximately orthophoric in primary gaze despite significant abduction limitation.

Facial Weakness

CN VII dysfunction may cause:

• Reduced facial expression
• Inability to smile normally
• Weak orbicularis oculi
• Poor eyelid closure
• Lagophthalmos

The characteristic “mask-like” facial appearance is due to congenital facial nerve weakness rather than lack of emotional expression.

Ocular Surface Examination

Because orbicularis weakness may impair blinking and closure, evaluate carefully for:

• Lagophthalmos
• Exposure keratopathy
• Superficial punctate keratitis
• Corneal epithelial defects
• Corneal ulceration

Visual Function

Assess for:

• Refractive error
• Strabismic amblyopia
• Anisometropic amblyopia
• Reduced visual acuity from corneal exposure

Children require particular attention because amblyopia can become permanent.

External Examination

Look for:

• Facial asymmetry
• Mask-like facial appearance
• Micrognathia
• Ear abnormalities
• Dental abnormalities
• Palatal abnormalities
• Limb defects

Systemic Examination

Patients should be evaluated for:

• Limb abnormalities
• Feeding dysfunction
• Swallowing dysfunction
• Speech abnormalities
• Hearing problems
• Respiratory compromise
• Developmental concerns

Diagnostic Tests

Laboratory Testing

Routine laboratory testing is generally unnecessary.

When the phenotype is atypical or no clear environmental cause is identified, consider:

• Chromosomal microarray
• Karyotype in selected patients
• Targeted genetic testing when another congenital cranial dysinnervation disorder is suspected

There is no single universally diagnostic genetic test for classic Moebius syndrome.

Imaging

Routine imaging is not always necessary.

MRI Brain and Brainstem

MRI may be performed to assess:

• Brainstem anatomy
• Cranial nerve nuclei
• Cranial nerve pathways
• Associated central nervous system abnormalities

Imaging findings may be normal despite clinically definite disease.

Special Considerations

If the history of congenital disease is uncertain and ophthalmoplegia is progressive rather than static, consider alternative diagnoses such as:

• Mitochondrial disorders
• Chronic progressive external ophthalmoplegia
• Kearns–Sayre syndrome

A progressive course is not typical of Moebius syndrome.

Differential Diagnosis

Important differential diagnoses include:

• Isolated CN VI palsy
• Congenital esotropia with pseudo-abduction deficit
• Duane retraction syndrome
• Other congenital cranial dysinnervation disorders
• Hanhart syndrome
• Hypoglossia-hypodactyly syndrome
• Oromandibular limb hypogenesis syndromes
• Chronic progressive external ophthalmoplegia
• Mitochondrial disorders
• Thyroid eye disease
• Brainstem lesions

Internuclear ophthalmoplegia is fundamentally different because it is a central supranuclear/internuclear disorder rather than a congenital bilateral abduction deficit.

Treatment

There is no medication that corrects the underlying congenital cranial dysinnervation.

Management focuses on:

• Protecting the cornea
• Treating strabismus
• Preventing amblyopia
• Supporting feeding, speech, and development
• Correcting associated craniofacial or limb abnormalities when appropriate

Ocular Surface Treatment

Lubrication

For ocular surface dryness or exposure:

• Preservative-free artificial tears
• Lubricating gel
• Ophthalmic ointment at bedtime

Eyelid Protection

If lagophthalmos is significant:

• Tape eyelids closed at night
• Use moisture chambers when appropriate
• Increase lubrication

Bandage Contact Lens

A bandage contact lens may be considered for severe exposure-related epithelial disease.

Close monitoring is essential because contact lenses can increase the risk of infectious keratitis.

Amblyopia Treatment

Treat amblyopia when present using:

• Full refractive correction
• Patching of the better eye
• Penalization when appropriate

Early childhood treatment is especially important.

Strabismus Management

Strabismus surgery may be considered when clinically significant esotropia or another alignment abnormality is present.

Goals include:

• Improving primary-position alignment
• Improving binocular function where possible
• Improving abnormal head posture
• Cosmetic improvement

Because the underlying disorder is dysinnervational, normal abduction usually cannot be restored completely.

Exposure Keratopathy Surgery

Tarsorrhaphy

Temporary or permanent tarsorrhaphy may be needed for severe:

• Lagophthalmos
• Exposure keratopathy
• Recurrent epithelial breakdown
• Corneal ulceration

Multidisciplinary Management

Moebius syndrome frequently requires care from multiple specialties.

Possible referrals include:

• Pediatric ophthalmology
• Strabismus specialist
• Oculoplastic specialist
• Clinical genetics
• Pediatrics
• Neurology
• ENT
• Dentistry
• Orthopedics
• Plastic/craniofacial surgery
• Speech-language pathology
• Occupational therapy
• Physical therapy
• Nutrition
• Psychology or neuropsychology

Feeding and Swallowing

Feeding difficulties may require:

• Feeding therapy
• Occupational therapy
• Speech-language pathology
• Nutritional support

Severe bulbar dysfunction may rarely necessitate more intensive airway or feeding support.

Speech

Facial, lingual, and palatal weakness can cause dysarthria.

Speech therapy may improve:

• Articulation
• Oral motor control
• Communication strategies

Complementary and Alternative Therapy

No complementary treatment has been proven to reverse the underlying neurologic abnormalities.

Ongoing Care

Follow-Up Recommendations

Follow-up frequency depends on ocular complications.

Patients with exposure keratopathy may require frequent review.

Children require ongoing surveillance for:

• Refractive error
• Amblyopia
• Strabismus
• Corneal exposure

Patient Monitoring

Monitor:

• Visual acuity
• Refraction
• Ocular alignment
• Corneal integrity
• Lid closure
• Amblyopia treatment response
• School performance
• Feeding and speech development
• Overall developmental progress

Diet

There is no specific Moebius syndrome diet.

Dietary modifications may be needed when swallowing or chewing difficulties are present.

A nutritionist or feeding team may help determine:

• Food consistency
• Caloric requirements
• Aspiration precautions

Patient and Family Education

Families should understand that:

• Moebius syndrome is congenital
• It is generally nonprogressive
• Facial immobility does not indicate lack of emotion or cognitive impairment
• Corneal protection is important
• Amblyopia treatment must be performed early
• Multidisciplinary support may substantially improve function

Genetic counseling should be offered when appropriate.

The Moebius Syndrome Foundation can provide patient and family support.

Prognosis

Moebius syndrome is generally a nonprogressive congenital condition.

With appropriate supportive care:

• Life expectancy is usually normal
• Vision can remain good if:
• Exposure keratopathy is prevented
• Amblyopia is treated
• Significant strabismus is managed

Functional outcome depends largely on the extent of associated cranial nerve and systemic abnormalities.

Complications

Important ophthalmic complications include:

• Exposure keratopathy
• Corneal epithelial breakdown
• Corneal ulceration
• Corneal scarring
• Rare corneal perforation
• Amblyopia
• Strabismus-related visual dysfunction

Other important complications may include:

• Feeding difficulty
• Aspiration
• Speech impairment
• Dental problems
• Psychosocial difficulties related to facial immobility

Ophthalmology Pearls

• The classic Moebius phenotype combines CN VI and CN VII dysfunction.
• Think abduction deficit + congenital facial weakness.
• The ocular motility disorder is developmental and typically nonprogressive.
• Facial weakness can cause lagophthalmos and exposure keratopathy, making corneal protection a major ophthalmic priority.
• Strabismus and refractive error can produce amblyopia, so early pediatric ophthalmic surveillance is important.
• Progressive ophthalmoplegia should prompt reconsideration of the diagnosis and investigation for mitochondrial or acquired neurologic disease.
• A child with Moebius syndrome may appear expressionless, but facial immobility should not be interpreted as impaired emotion or intelligence.