Medicine – Ptosis

Ptosis means drooping of the upper eyelid due to weakness or dysfunction of the structures responsible for elevating the lid, especially the levator palpebrae superioris muscle and the sympathetically supplied Müller muscle.

Ptosis may be unilateral or bilateral, congenital or acquired, and the associated neurological or ocular findings often point toward the underlying cause.

1. Unilateral Ptosis

Unilateral ptosis has a broad differential diagnosis. Important causes include congenital ptosis, third cranial nerve palsy, Horner syndrome, myasthenia gravis, eyelid masses, and idiopathic or aponeurotic causes.

2. Congenital Ptosis

Congenital ptosis is usually caused by abnormal development or dysgenesis of the levator palpebrae superioris muscle.

It is often present from birth and may affect one or both eyes, although unilateral disease is common.

If severe, the drooping eyelid can obstruct the visual axis and cause amblyopia, so children with significant ptosis require ophthalmological assessment.

3. Idiopathic or Aponeurotic Ptosis

Some patients develop ptosis without a major neurological disorder.

A common acquired mechanism is aponeurotic ptosis, in which the levator aponeurosis becomes stretched or detached, particularly with increasing age.

The eyelid crease may be elevated, and levator muscle function itself may remain relatively preserved.

4. Third Nerve Palsy

A third cranial nerve palsy can cause marked unilateral ptosis because the oculomotor nerve supplies the levator palpebrae superioris.

Associated eye movement abnormalities are usually present because the third nerve also supplies most extraocular muscles.

The classic pattern is:

Ptosis + eye positioned “down and out” + diplopia.

If parasympathetic fibres are involved, the pupil may become dilated and poorly reactive.

5. Important Third Nerve Warning Sign

A painful third nerve palsy with a dilated pupil is particularly concerning for a compressive lesion such as a posterior communicating artery aneurysm.

This requires urgent neurological assessment.

By contrast, some microvascular third nerve palsies, such as those associated with diabetes, may spare the pupil.

6. Horner Syndrome

Horner syndrome results from disruption of the sympathetic pathway supplying the eye and face.

The classic features are:

Ptosis + miosis + anhidrosis.

The ptosis is usually mild because it results from weakness of Müller muscle rather than complete levator paralysis.

The affected pupil is small because sympathetic dilator fibres are interrupted.

7. Horner Syndrome and Anisocoria

In Horner syndrome, the abnormal pupil is the smaller pupil, and the difference between the pupils is usually more obvious in the dark because the affected pupil cannot dilate normally.

This is an important distinction from third nerve palsy, in which the abnormal pupil may be dilated.

8. Myasthenia Gravis

Myasthenia gravis is an autoimmune disorder of the neuromuscular junction and is an important cause of fluctuating ptosis.

Ptosis may be unilateral or bilateral and often varies during the day.

A characteristic feature is fatigability:

Ptosis worsens with prolonged upward gaze or later in the day and improves with rest.

Diplopia may also occur because extraocular muscles are commonly involved.

9. Lid Tumour

An eyelid tumour or other mass can mechanically weigh down the upper lid and produce mechanical ptosis.

The degree of ptosis depends on the size and location of the lesion.

Examination may reveal a visible or palpable eyelid mass.

10. Bilateral Ptosis

Bilateral ptosis suggests disorders affecting the neuromuscular junction, muscles, or occasionally bilateral sympathetic pathways.

Important causes include myasthenia gravis, myotonic dystrophy, chronic progressive external ophthalmoplegia or other ocular myopathies, and rare bilateral Horner syndrome.

11. Myasthenia Gravis

Myasthenia gravis is one of the most important causes of bilateral fluctuating ptosis.

The ptosis is typically variable and fatigable and may alternate between the two eyes.

Patients may also have:

Diplopia.

Bulbar weakness.

Dysarthria or dysphagia.

Generalised limb weakness.

However, some patients have disease restricted mainly to the ocular muscles.

12. Myotonic Dystrophy

Myotonic dystrophy can cause bilateral ptosis due to progressive muscle weakness.

Other features may include:

Myotonia.

Facial weakness.

Distal muscle weakness.

Early cataracts.

Cardiac conduction abnormalities.

The overall clinical picture usually makes the diagnosis more apparent.

13. Ocular Myopathy

Primary muscle disorders can cause bilateral ptosis together with ophthalmoplegia.

An important example is chronic progressive external ophthalmoplegia, often related to mitochondrial disease.

Patients typically develop slowly progressive:

Bilateral ptosis + limitation of extraocular movements.

Unlike myasthenia gravis, the weakness is usually persistent rather than markedly fluctuating.

14. Bilateral Horner Syndrome

Bilateral Horner syndrome is rare.

It may occur in conditions affecting sympathetic pathways on both sides, including certain spinal cord lesions.

Older teaching links bilateral Horner syndrome with syringomyelia, but this is uncommon and should not be considered a typical cause of bilateral ptosis.

Syringomyelia more classically produces segmental sensory loss and can interrupt sympathetic pathways if sufficiently extensive.

15. Ptosis – Note Form

Unilateral Ptosis

Congenital ptosis: abnormal levator development, usually present from birth.

Aponeurotic/idiopathic ptosis: age-related or acquired stretching of the levator aponeurosis.

Third nerve palsy: marked ptosis with ophthalmoplegia; eye may lie “down and out.”

Third nerve pupil: may be dilated if parasympathetic fibres are involved.

Horner syndrome: mild ptosis with miosis ± anhidrosis.

Myasthenia gravis: fluctuating, fatigable ptosis that improves with rest.

Lid tumour: mechanical ptosis caused by an eyelid mass.

16. Bilateral Ptosis – Note Form

Myasthenia gravis: fluctuating and fatigable bilateral ptosis, often with diplopia.

Myotonic dystrophy: bilateral ptosis with myotonia and other muscle-system features.

Ocular myopathy: persistent bilateral ptosis with progressive ophthalmoplegia.

Bilateral Horner syndrome: rare; may occur with bilateral sympathetic pathway lesions.

17. Useful Clinical Distinctions

Third nerve palsy → ptosis + “down and out” eye ± dilated pupil.

Horner syndrome → mild ptosis + small pupil.

Myasthenia gravis → variable ptosis + fatigability + normal pupils.

Mechanical ptosis → eyelid mass or structural abnormality.

Key Clinical Pattern

When assessing ptosis, first look at the pupil and eye movements.

Ptosis + dilated pupil + ophthalmoplegia → think third nerve palsy.

Ptosis + constricted pupil → think Horner syndrome.

Fluctuating ptosis with normal pupils → think myasthenia gravis.

Bilateral slowly progressive ptosis with ophthalmoplegia → think ocular myopathy.

A particularly important emergency association is:

Painful ptosis + third nerve palsy + dilated pupil → urgently exclude a compressive intracranial aneurysm.