Exodeviations

Symptoms

intermittent or constant outward drift of one eye

symptoms often worse with fatigue, illness, or distance fixation

diplopia (in acquired cases; children commonly suppress)

squinting or eye-closing in bright light (classic for intermittent exotropia)

Clinical Findings

Intermittent exotropia (IXT)

• most common childhood exodeviation
• pathognomonic sign: child closes one eye in bright sunlight to suppress second image
• control grading (newcastle or mayo) is more critical than angle magnitude for management
• good control: phoria-only on cover test; fair control: intermittent tropia
• poor control: constant tropia >50% of waking hours

IXT subtypes (distance–near relationship)

• basic: distance deviation equals near deviation
• true divergence excess: distance deviation significantly greater than near
• simulated divergence excess: distance equals near only after patch test
• convergence insufficiency type: near deviation greater than distance

Constant & sensory types

• infantile exotropia: onset <6 months; large-angle; often linked to neurologic or craniofacial syndromes
• sensory exotropia: results from chronic monocular vision loss; more common than sensory esotropia in adults

Motility patterns

• "v" pattern: greater exodeviation in upgaze (associated with io overaction)
• "a" pattern: greater exodeviation in downgaze (associated with so overaction)
• dissociated vertical deviation (dvd) and amblyopia may be present

Etiology

Primary types

• intermittent exotropia: most common form; triggered by fatigue or distance fixation
• congenital (infantile): rare, large-angle, early onset; associated with neurologic disease

Secondary & acquired

• sensory: chronic monocular vision loss (cataract, retinal disease) disrupting fusion
• cn iii palsy: "down-and-out" eye with ptosis and possible pupil involvement
• consecutive: overcorrection following prior esotropia surgery
• incomitant: duane syndrome type 2 or orbital disease

Red Flags

new-onset exotropia with ptosis or mydriasis (rule out cn iii palsy/aneurysm)

intermittent exotropia progressing to constant tropia (risk of fusion loss)

sensory exotropia secondary to unidentified unilateral vision loss

bilateral exotropia with upgaze limitation (parinaud syndrome; image dorsal midbrain)

Investigations

Clinical exam

• visual acuity with best correction to assess for amblyopia
• ocular motility: check for oblique overactions, a/v patterns, or duane syndrome
• prism and cover test: measure in cardinal fields and at distance/near
• stereopsis and color vision testing

Diagnostic tests

• patch test: monocular occlusion for 30–60 min to reveal full fusion-free angle
• cycloplegic refraction: essential to identify refractive components
• myasthenia workup: ice test or antibodies if deviation is variable/fatigable

Imaging

• mri brain/orbits: if neurologic disease, parinaud syndrome, or new cn iii palsy is suspected

Treatment

Conservative measures

• correct significant refractive errors and treat underlying amblyopia
• alternate daily patching to reduce suppression and improve fusion control
• over-minus lenses to stimulate accommodative convergence
• orthoptic exercises for convergence insufficiency

Surgical intervention

• infantile exotropia: surgery typically performed within 1 year of onset
• intermittent exotropia: indicated for poor control or frequent manifest tropia
• sensory exotropia: surgery for alignment/cosmesis

Special considerations

• sensory cases: mandatory polycarbonate protective lenses for the better-seeing eye
• incomitant types: treat underlying cause (e.g., third nerve palsy)

Differential Diagnosis

• pseudoexotropia
• exophoria
• intermittent exotropia (ixt)
• constant infantile exotropia
• sensory-deprivation exotropia
• consecutive exotropia
• cn iii palsy
• duane syndrome type 2
• isolated convergence insufficiency
• parinaud syndrome
• myasthenia gravis

Related Strabismus Conditions

• Esodeviations
• Strabismus Syndromes