Barry N. Wasserman

BASICS

DESCRIPTION

• Manifest convergent misalignment of the visual axes that varies quantitatively with different fields of gaze.

• Congenital or acquired

EPIDEMIOLOGY

Incidence

Varies depending on underlying cause, but overall strabismus prevalence (including comitant deviations) is 1–4%.

Prevalence

More common in adults

RISK FACTORS

• Brain injury or increased intracranial pressure

– Thyroid eye disease

– Myasthenia gravis

– Family history or genetic predisposition (isolated or syndromic)

– Orbital trauma (medial orbital wall fracture, medial fat and fibrous trauma), tumor or infiltration

– Eye muscle surgery (excessively resected medial rectus muscle or over recessed lateral rectus muscle)

– Craniofacial disorders

Genetics

• See chapter on craniofacial disorders

• Congenital cranial dysinnervation disorders (CCDD):

– See chapters on Duane syndrome, Brown syndrome, Moebius syndrome

– Also Congenital fibrosis of the extraocular muscles (but usually exotropia): CFEOM1 – autosomal dominant, K1F21 A gene (12cen); CFEOM2 – autosomal recessive, ARIX/PHOX2 A (11q13); CFEOM3 – autosomal dominant, TUBB3 (16q24.2–24.3)

– Also horizontal gaze palsy with progressive scoliosis (HGPPS) – autosomal dominant, ROBO3 (11q23–25)

GENERAL PREVENTION

Genetic counseling

PATHOPHYSIOLOGY

Unbalanced functioning of horizontal rectus muscles whether due to structural muscle change, muscle restriction, or muscle innervation dysfunction

ETIOLOGY

• Paresis of cranial nerve VI

– Infiltration of medial recti: Thyroid eye disease, leukemia, pseudotumor

– Myasthenia gravis

– Muscle entrapment/injury/restriction: Orbital trauma (medial orbital wall fracture, medial fat and fibrous trauma, or lateral orbital hemorrhage), infiltration, tumor, or eye muscle surgery

– Congenital/genetic: CCDD, hypoplastic lateral recti, craniofacial disorders with absent/anomalous muscles

COMMONLY ASSOCIATED CONDITIONS

• Brain injury or increased intracranial pressure

– Thyroid eye disease

– Orbital trauma, infiltration, tumor, hemorrhage

– Horizontal rectus muscle surgery

– Craniofacial disorders

DIAGNOSIS

HISTORY

• Binocular, horizontal diplopia that is worse at distance and in lateral gaze

– Orbital trauma

– Prior infections, head trauma, ocular surgeries

– Family history of CCDD or craniofacial disorder

– Hyperthyroidism or myasthenia gravis

PHYSICAL EXAM

• Full ocular examination with emphasis on extraocular muscle functioning and ocular alignment in 9 positions of gaze (up, down, right, left, up right, up left, down right, and down left) as well as near

– Measured esodeviation angle increases in lateral gaze

– Determination of fixation pattern and visual acuity with best correction (cycloplegic refraction)

– Cranial nerve and sensory exam

– Forced-duction testing if necessary to distinguish lateral rectus from medial rectus dysfunction and to distinguish paresis from restriction

– Proptosis and lid retraction may be seen with thyroid eye disease

– Evaluate anomalous head positions, often manifest to maintain binocularity

• Congenital bilateral sixth and seventh cranial nerve palsies may indicate Moebius syndrome. Also assess for other cranial nerve palsies and defects of the neck, tongue, chest, and limbs

– Congenital abduction deficit with an aberrant lateral rectus innervation and globe retraction ion attempted adduction may indicate Duane syndrome.

DIAGNOSTIC TESTS & INTERPRETATION

Lab

Initial lab tests

• Thyroid function tests if thyroid eye disease suspected

• Acetylcholine receptor antibody test if myasthenia gravis suspected

Follow-up & special considerations

Even if initial thyroid function or myasthenia gravis tests are normal, consider repeating at later date if clinical suspicion persists.

Imaging

• If acute-onset or neurological signs and symptoms are present, neuroimaging is necessary to rule out intracranial pathology.

• Consider orbital CT scan with suspected thyroid eye disease, or to rule out orbital mass, fracture, infiltration, or inflammatory lesions.

• Consider CT scan to evaluate for orbital fracture

Diagnostic Procedures/Other

B scan orbital ultrasound may be useful.

Pathological Findings

• CCDDs: Absent cranial nerve nuclei, absent or hypoplastic cranial nerve, fibrotic/hypoplastic extraocular muscle

– See thyroid eye disease and myasthenia gravis chapters

DIFFERENTIAL DIAGNOSIS

• Comitant esotropia (accommodative or non-accommodative)

• Pseudo-abduction defect in infantile large angle esotropia with cross fixation

– Esophoria

– Negative angle kappa

– Hyperopic anisometropia with varying deviation as fixation changes between eyes

TREATMENT

MEDICATION

• Consider systemic steroid for orbital inflammatory disease or ocular myasthenia.

• See also chapters on thyroid eye disease and myasthenia gravis.

• Medical management of increased intracranial pressure/cerebral edema.

ADDITIONAL TREATMENT

General Measures

• Amblyopia treatment as indicated

– Fresnel press-on prisms to correct primary gaze diplopia

– Complete remission usually occurs without intervention in sixth cranial nerve palsies if the palsy is caused by a vascular condition or increased intracranial pressure/cerebral edema.

Issues for Referral

• Neurosurgery consult if intracranial etiology is detected

– Notify primary care physician if thyroid eye disease suspected, consider endocrinology consultation.

– Consider neurology or neuro-ophthalmology if myasthenia gravis

– Consider genetic counseling/geneticist where appropriate

Additional Therapies

• Smoking cessation in thyroid eye disease

• Beyond the amblyogenic age range, occlusion of one eye may be used to eliminate symptomatic diplopia

COMPLEMENTARY & ALTERNATIVE THERAPIES

None proven or indicated

SURGERY/OTHER PROCEDURES

• Surgery for a cranial nerve palsy VI or thyroid eye disease is indicated when spontaneous resolution does not occur after 6 months

– Botox injections into the medial rectus may be useful with traumatic cranial VI paresis (1)

– Muscle transposition is indicated with cranial VI total paralysis

– Rectus muscle recession is the preferred surgery for thyroid eye disease

– Orbital fracture may require liberation of entrapped tissues and fracture repair

– Neurosurgical intervention for intracranial process if indicated

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

• For children in amblyopic age range, frequent follow-ups recommended for close monitoring of visual acuity

– Primary care physician for glucose and blood pressure control if underlying vascular disorder suspected

– Neurosurgery if intracranial pathology is suspected

– Endocrinology if systemic thyroid disease is suspected

• Serial evaluations helpful in cases of variable strabismus including thyroid eye disease and ocular myasthenia

– Stability of strabismus important before pursuing surgical intervention

Patient Monitoring

• Observation for acute neurological changes

– Observe for amblyopia in children

PATIENT EDUCATION

• Strict glucose and blood pressure control if vascular causes of cranial nerve VI palsy are suspected

• Parents of strabismic children should be educated about the child’s risk of developing amblyopia and impaired binocular depth perception

– Diplopia management strategies

PROGNOSIS

• Dependent upon type. Some types can be improved with strabismus surgery

• In CCDDs the primary goal is improved head position and orthophoria in primary gaze

• Cranial VI palsies usually resolve spontaneously, especially if congenital or due to increased intracranial pressure

– About one-third of palsies in older patients are associated with intracranial lesions

– See chapters on thyroid eye disease and myasthenia gravis

COMPLICATIONS

• Amblyopia in children

– Anomalous head posture

– Loss of binocularity

– Diplopia

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