Causes of Ptosis
Ptosis results from dysfunction of the eyelid-elevating muscles (levator palpebrae superioris or Müller's muscle) or their innervation, and can be classified into five major etiologic categories: aponeurotic (most common in adults), myogenic, neurogenic, traumatic, and mechanical/pseudoptosis. 1, 2
Etiologic Classification
The most practical approach to understanding ptosis etiology is based on the anatomic mechanism rather than simply congenital versus acquired timing 3:
1. Aponeurotic Ptosis (35-82% of acquired cases)
- Most common cause in adults, particularly elderly patients 4, 3
- Results from dehiscence or disinsertion of the levator aponeurosis
- Typically bilateral, affects females more than males (2:1 ratio) 4
- Age-related involutional changes are the primary mechanism
- Characterized by good levator function (>10mm) with high eyelid crease
2. Myogenic Ptosis (5.7-42% of cases)
Myasthenia Gravis - Critical to recognize due to mortality risk:
- 50% of myasthenia patients present with isolated ocular symptoms (ptosis and diplopia) 5
- 50-80% progress to life-threatening generalized myasthenia within a few years 5
- Variable ptosis that worsens with fatigue (prolonged upgaze)
- Associated Cogan lid-twitch sign
- Contralateral ptosis worsens when manually elevating the more affected lid
- Ice pack test: 2mm improvement after 2 minutes is highly specific 5
- Requires urgent neurology referral and workup for thymoma
Other Myogenic Causes:
- Chronic progressive external ophthalmoplegia
- Oculopharyngeal muscular dystrophy
- Myotonic dystrophy
- Levator palpebrae superioris myositis (rare inflammatory cause) 6
3. Neurogenic Ptosis (6.8-9.6% of cases)
Third Nerve Palsy:
- Pupillary involvement should alert to this diagnosis (unlike myasthenia) 5
- May indicate life-threatening aneurysm or other intracranial pathology
- Poor levator function
Horner Syndrome:
- Mild ptosis (1-2mm) from Müller's muscle dysfunction
- Associated miosis and anhidrosis
- Anisocoria >1mm warrants investigation 7
Other causes:
- Marcus Gunn jaw-winking syndrome
- Aberrant third nerve regeneration
4. Traumatic Ptosis (2.3% of cases)
- Direct injury to levator muscle or aponeurosis
- Orbital or eyelid trauma
- Iatrogenic from prior surgery 4
5. Mechanical/Pseudoptosis
- Thyroid eye disease with extraocular muscle enlargement 5
- Eyelid tumors creating weight
- Dermatochalasis (excess skin, not true ptosis)
- Enophthalmos making lid appear low
- Hypotropia (globe malposition) 3
Critical Diagnostic Pitfalls
Do not miss myasthenia gravis - The variable nature and fatiguability distinguish it from other causes. Perform ice pack testing in any patient with variable ptosis. The 50-80% progression rate to generalized disease with respiratory failure risk makes early recognition life-saving 5.
Pupillary involvement changes everything - Pupil-involving ptosis suggests third nerve palsy requiring urgent neuroimaging, not myasthenia 5.
Bilateral presentation is common - 77% of acquired ptosis cases are bilateral, with aponeurotic being the predominant type 4. Don't assume bilateral means congenital.