What are the causes of ptosis in the eye?

Causes of Ptosis in the Eye

Ptosis can be caused by numerous conditions including myasthenia gravis, third nerve palsy, Horner syndrome, aponeurotic weakness, and mechanical factors, with each requiring specific evaluation to prevent potentially life-threatening complications. 1

Classification of Ptosis

Ptosis can be classified based on the affected part of the motor unit:

1. Neurogenic Causes

• Third Nerve Palsy

  • Caused by lesions affecting the oculomotor nerve (CN III)
  • May be pupil-involving (concerning for aneurysm) or pupil-sparing (often microvascular) 2
  • Locations of lesions:
    • Nuclear (brainstem)
    • Subarachnoid space (aneurysms, especially posterior communicating artery)
    • Cavernous sinus (often with CN IV and VI involvement)
    • Orbital (divisional palsy) 2
  • Associated conditions: aneurysms, tumors, trauma, subarachnoid hemorrhage 2

• Horner Syndrome

  • Due to sympathetic pathway interruption
  • Characterized by ptosis, miosis, and anhidrosis
  • Lesions can occur anywhere from diencephalon to superior orbital fissure 3

2. Myogenic Causes

• Congenital ptosis

  • Present at birth due to levator muscle dysgenesis
  • May lead to amblyopia if not corrected 4

• Muscular dystrophies

  • Chronic progressive ocular muscle dystrophy
  • Part of systemic myopathies 5

• Senile (age-related) ptosis

  • Due to aponeurotic weakness with aging 5

3. Synaptogenic Causes

• Myasthenia Gravis

  • 50% of patients present with ocular symptoms initially
  • 50-80% develop generalized myasthenia within years
  • Associated with autoimmune thyroid disease and thymoma 1
  • Can progress to life-threatening respiratory failure 1

• Botulism

  • Toxin blocks acetylcholine release at neuromuscular junction 5

4. Mechanical Causes

• Eyelid masses/tumors
• Edema
• Inflammation
• Trauma 4

Severity Classification

• Minimal: 1-2 mm drooping
• Moderate: 3-4 mm drooping
• Severe: >4 mm drooping (may cover pupil entirely) 4

Evaluation Approach

1. Assess for emergency causes

   • Pupil-involving third nerve palsy requires urgent neuroimaging to rule out aneurysm 1
   • Even pupil-sparing third nerve palsy with incomplete ptosis may be due to compressive lesion 1

2. Determine onset and progression

   • Congenital vs. acquired
   • Acute vs. gradual onset
   • Fluctuating (suggests myasthenia gravis) vs. stable

3. Evaluate associated symptoms

   • Diplopia, anisocoria, other neurological symptoms (ataxia, tremor, hemiplegia)
   • Systemic symptoms suggesting myasthenia or other disorders 2

4. Physical examination

   • Measure ptosis severity and levator function
   • Check pupils in bright and dim illumination
   • Perform comprehensive eye examination including fundus to evaluate for papilledema or optic atrophy 2

Important Clinical Pearls

• Never dismiss persistent ptosis as merely stress-related without proper evaluation, as it may be the first sign of a life-threatening condition 1

• For third nerve palsy: Classic pupil-sparing third nerve palsy (normal pupil, complete ptosis, complete motility dysfunction) suggests microvascular etiology (diabetes, hypertension, hyperlipidemia) 2

• Warning sign: Partial third nerve involvement with incomplete ptosis may still indicate a compressive lesion even if the pupil is spared 1

• For myasthenia gravis: Ocular symptoms may precede generalized disease that can lead to respiratory failure 1

• Diagnostic tests for specific causes:

  • Myasthenia gravis: Anti-acetylcholine receptor antibodies, anti-MuSK antibodies, single-fiber electromyography, Tensilon test 1
  • Third nerve palsy: MRI with gadolinium, MRA or CTA; catheter angiogram if high suspicion despite normal imaging 2

By systematically evaluating ptosis using this approach, clinicians can identify the underlying cause and implement appropriate management to prevent potential complications affecting morbidity, mortality, and quality of life.