What are the characteristic ocular findings in myasthenia gravis?

Eye Signs in Myasthenia Gravis

Primary Ocular Manifestations

Ptosis (drooping eyelids) is the most common initial ocular sign, appearing in 50% of myasthenia gravis patients at presentation, and characteristically worsens with prolonged upgaze or sustained effort. 1, 2

Ptosis Characteristics

• Ptosis may be unilateral or bilateral and frequently changes sides between examinations—this variability is a diagnostic hallmark. 2, 3
• Among patients with initially symmetric ptosis, 40% develop asymmetric ptosis at follow-up visits. 4
• Ptosis typically manifests within 30 seconds of sustained upgaze in 58% of patients, with mean time to onset of 27.6 seconds. 4
• The drooping extends beyond the normal 1-2 mm coverage of the upper corneal limbus. 5

Diplopia and Strabismus Patterns

• Diplopia (double vision) from extraocular muscle weakness is highly variable and can mimic any form of pupil-sparing ocular motility disorder. 1, 6
• In 95% of patients with diplopia, double vision contains both vertical and horizontal components simultaneously. 4
• At follow-up examinations, 83% of patients manifest diplopia in different gaze directions than initially observed—this changing pattern is pathognomonic for myasthenia. 4
• Diplopia typically appears within 30 seconds of sustained gaze in 87% of patients, with mean onset at 11.6 seconds. 4
• Variable strabismus that changes during examination is characteristic and can mimic any incomitant strabismus pattern. 1, 2

Extraocular Muscle Involvement

• Slow ocular saccades (rapid eye movements) are a characteristic finding that reflects muscle fatigue. 2
• Extraocular muscles are particularly susceptible because of their twitch fiber composition and fewer acetylcholine receptors compared to other skeletal muscles. 1, 3
• Weakness of orbicularis oculi (eyelid closure) may be present, causing incomplete lid closure. 1

Critical Diagnostic Features

Fatigability and Fluctuation

• The hallmark of myasthenic eye signs is fatigability—symptoms worsen with sustained activity and improve with rest. 2, 3
• Symptoms characteristically worsen as the day progresses or with repetitive use of affected muscles. 2
• Temporary improvement occurs with rest or application of ice to the affected eyelid (ice pack test). 2

Pupillary Sparing

• Pupils are NOT affected in myasthenia gravis—pupillary involvement should immediately redirect you toward alternative diagnoses such as third nerve palsy. 2

Diagnostic Testing for Ocular Signs

Bedside Examination Techniques

• Test ptosis and diplopia in multiple gaze directions for 30-60 seconds during at least two follow-up visits to maximize detection of the characteristic changing patterns. 4
• Sustained upgaze for 60 seconds will provoke or worsen ptosis in most cases. 2, 4
• Systematic examination of extraocular muscle fatigability in two horizontal and four oblique directions for 60 seconds reveals diplopia patterns. 4

Edrophonium (Tensilon) Test

• For adults, inject 0.2 mL (2 mg) intravenously within 15-30 seconds; if no reaction occurs after 45 seconds, inject the remaining 0.8 mL (8 mg). 7
• A positive response shows increased muscle strength with improvement in ptosis and diplopia. 7
• This test is less sensitive for ocular myasthenia than for generalized disease. 6

Clinical Progression and Prognosis

• 50-80% of patients presenting with purely ocular symptoms will develop generalized myasthenia gravis within a few years. 1, 2
• When disease remains limited to ocular muscles, it is classified as MGFA Class I. 2, 8
• Early corticosteroid therapy may reduce the probability of generalization by approximately 75%. 6, 9

Antibody Patterns in Ocular Disease

• Acetylcholine receptor antibodies are present in only 40-77% of patients with ocular myasthenia, compared to nearly all patients with generalized disease. 1, 2
• Changes in ptosis side occur less frequently in seronegative patients (50%) compared to those with acetylcholine receptor antibodies (70%) or MuSK antibodies (69%). 4

Key Clinical Pitfalls

• Failure to recognize that ocular myasthenia is a "great masquerader"—it can mimic any pupil-sparing ocular motility disorder including third nerve palsy, sixth nerve palsy, internuclear ophthalmoplegia, or isolated muscle palsies. 2, 6
• Patients reporting no functional limitations from diplopia typically manifest symptoms only after 30 seconds of sustained gaze, which may be missed on brief examination. 4
• Atypical or inconsistent examination findings should raise suspicion rather than lower it—variability is the disease signature. 2, 4