What nerve palsies cause diplopia?

Nerve Palsies That Cause Diplopia

The primary nerve palsies that cause diplopia are third (oculomotor), fourth (trochlear), and sixth (abducens) cranial nerve palsies, each affecting different extraocular muscles and producing characteristic patterns of double vision. 1

Third Nerve (Oculomotor) Palsy

Clinical Presentation

• Affects multiple muscles: superior rectus, inferior rectus, medial rectus, and inferior oblique
• Presents with ptosis (drooping eyelid) due to levator dysfunction
• Eye typically positioned in "down and out" position (abducted and infraducted)
• Diplopia has both horizontal and vertical components
• May have pupillary involvement (dilated pupil) depending on etiology
• Accommodative deficiency may cause reading difficulties 1

Etiology

• Annual incidence: approximately 4 per 100,000 1
• Common causes:
  • Microvascular (diabetes, hypertension, hyperlipidemia)
  • Aneurysm (especially posterior communicating artery)
  • Trauma
  • Compression (tumor)
  • Giant cell arteritis (in elderly)

Key Diagnostic Considerations

• Pupil involvement is critical - pupil-involving palsy requires urgent neuroimaging to rule out aneurysm 2
• Pupil-sparing with vascular risk factors suggests microvascular etiology
• Partial involvement requires neuroimaging regardless of pupil status 2

Fourth Nerve (Trochlear) Palsy

Clinical Presentation

• Affects superior oblique muscle
• Vertical diplopia, worse on looking down and toward the nose
• Characteristic head tilt away from the affected side
• Patients may present with compensatory head position
• Associated with fundus torsion (excyclotorsion) 3

Etiology

• Most common cause of vertical diplopia 4
• Causes include:
  • Trauma (most common)
  • Microvascular ischemia
  • Intracranial mass
  • Idiopathic

Key Diagnostic Considerations

• Severe oculomotor limitation, large fundus torsion, and intracranial mass indicate higher risk of incomplete recovery 3
• Approximately 65.7% achieve complete recovery, typically within 3-4 months 3

Sixth Nerve (Abducens) Palsy

Clinical Presentation

• Affects lateral rectus muscle
• Horizontal diplopia, worse at distance and when looking toward the affected side
• Compensatory head turn toward the affected side
• Esotropia (inward deviation) of the affected eye 1

Etiology

• Annual incidence: approximately 11 per 100,000 1
• Common causes:
  • Microvascular (diabetes, hypertension)
  • Trauma
  • Neoplasm (most common cause in young adults 20-50 years) 5
  • Increased intracranial pressure
  • Demyelinating disease

Key Diagnostic Considerations

• Most vasculopathic palsies resolve within 6 months (about one-third within 8 weeks)
• Lack of recovery after 6 months suggests serious underlying pathology in about 40% of cases 1

Diagnostic Approach

1. Detailed history:

   • Onset (acute vs. chronic)
   • Pattern of diplopia (horizontal, vertical, or both)
   • Associated symptoms (pain, ptosis, other neurological symptoms)
   • Risk factors (diabetes, hypertension, trauma)

2. Comprehensive examination:

   • Ocular alignment in all gaze positions
   • Pupillary function
   • Presence of ptosis
   • Compensatory head position
   • Fundus examination for torsion

3. Neuroimaging considerations:

   • Required for:
     • All third nerve palsies with pupil involvement
     • Young patients (<50 years)
     • Multiple cranial nerve involvement
     • Progressive symptoms
     • Lack of improvement after 3 months for presumed microvascular causes 2

Management Approach

Acute Phase

• Occlusion therapy (eye patch, occlusive contact lens) for bothersome diplopia 2
• Observation for 3-6 months in cases of presumed microvascular etiology
• Treatment of underlying cause when identified

Intermediate Phase

• Prism therapy for residual diplopia following partial recovery
• Botulinum toxin injection to antagonist muscles while awaiting recovery 2

Chronic Phase (>6 months without recovery)

• Surgical intervention based on specific nerve involvement:
  • For third nerve: Recession of lateral rectus + resection of medial rectus, with possible superior oblique weakening 2
  • For fourth nerve: Superior oblique tendon procedures
  • For sixth nerve: Transposition procedures, medial rectus recession 1

Prognosis

• Microvascular causes: Generally good prognosis with recovery within 3-6 months
• Traumatic causes: Variable recovery, often incomplete
• Compressive lesions: Dependent on successful treatment of underlying cause
• Fourth nerve palsy: 65.7% achieve complete recovery 3
• Sixth nerve palsy: Most recover within 6 months if vasculopathic 1

Important Caveats

• Never assume a microvascular etiology without appropriate workup, especially in younger patients
• Pupil-involving third nerve palsy requires urgent evaluation for aneurysm
• Patients should be advised that the goal of treatment is to eliminate diplopia in primary position, but they may continue to have diplopia in extreme gaze positions 1
• Recent studies show that in young adults (20-50 years), a substantial proportion of ocular motor nerve palsies have pathologies other than presumed microvascular causes 5