01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Myasthenia gravis is an autoimmune disorder of neuromuscular transmission. The muscles controlling the eyelids and eye movements are often affected early, producing ptosis and diplopia that can vary across the day or during a single examination. The weakness may imitate an isolated cranial nerve palsy on one occasion and a different pattern later, so fluctuation and fatigability are important diagnostic clues.
An ocular presentation does not establish that disease will remain confined to the eyes. Assessment must actively seek bulbar, respiratory, neck and limb involvement, and the patient needs clear instructions about deterioration. Treatment can improve symptoms and suppress the immune process, but both the underlying disorder and the medicines require ongoing review. Current UK specialist guidance provides a gradual approach to pyridostigmine and daily prednisolone rather than a single high starting dose for every patient.
Key points
- Ocular myasthenia commonly causes fluctuating ptosis and binocular diplopia that worsen with sustained use and improve with rest.
- Pupils, sensation and visual acuity are usually unaffected; pain, a pupil abnormality or true visual loss warrants investigation for another or additional disorder.
- A negative antibody test does not exclude ocular myasthenia; specialist neurophysiology may be required.
- Ask about chewing, swallowing, speech, neck, limb and respiratory weakness at every assessment.
- ABN 2025 guidance uses daily prednisolone for ocular disease rather than importing an older alternate-day schedule.
- Pyridostigmine is introduced gradually with attention to cardiac and respiratory comorbidity; requirements above 300 mg daily should prompt timely reassessment.
- Treatment, driving advice and monitoring should be coordinated between neuromuscular and ophthalmic services.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Autoimmune neuromuscular disease
Antibodies interfere with proteins involved in transmission between motor nerves and skeletal muscle. The resulting weakness is acquired and fluctuating, with ocular muscles often affected early in the clinical course.
Thymic association
Thymic abnormalities occur in a proportion of people with myasthenia, including thymoma in some cases. Identifying a tumour has implications for management, but thymic enlargement and tumour are not interchangeable diagnoses.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Reduced transmission safety margin
Impaired postsynaptic signalling makes repeated nerve impulses less reliably trigger muscle contraction. Sustained activity can therefore expose weakness that is less evident after rest or during a brief initial examination.
- 2Ocular muscle vulnerability
The eyelid elevators and extraocular muscles perform frequent precise movements. Disturbed neuromuscular transmission can cause ptosis and changing misalignment without damaging the retina, optic nerve or pupillary autonomic pathways.
- 3Generalisation beyond the eyes
The same transmission disorder can involve limb, neck, bulbar and respiratory muscles. Swallowing and ventilatory weakness are especially important because they threaten airway protection and breathing rather than only visual comfort.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Ask whether one or both lids droop after reading, working or later in the day, and whether rest improves them. Compare the beginning and end of sustained upgaze, looking for increased drooping without turning the manoeuvre into a prolonged exhausting test.
Confirm that covering either eye removes the double image. The alignment may vary with fatigue and need not remain within one cranial-nerve distribution. Document the observed pattern while keeping other causes of acute diplopia in the differential.
Ask about tiring while chewing, nasal or slurred speech, coughing during drinks, difficulty swallowing tablets, breathlessness and a weak cough. Look for neck weakness and inability to manage secretions. New significant symptoms demand urgent hospital evaluation even if ocular signs were previously mild.
Explore reading, computer work, stairs, driving and the need to close one eye. Review recent infections, surgery and medication changes. Symptoms often fluctuate, so a reassuring brief morning examination may not represent the patient's usual burden.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Clinical assessment and urgent assessment of generalised weaknessFirst step - Why
- Establish the pattern and detect bulbar or respiratory compromise requiring hospital care.
- Interpretation and limitations
- Examine eyelids, eye movements, pupils and relevant limb, neck and bulbar function. Respiratory concerns require specialist physiological assessment and serial clinical review; a normal oxygen-saturation reading alone is not an adequate assessment of neuromuscular ventilation.
- 02
Acetylcholine-receptor antibodies and directed additional testing - Why
- Seek serological support for autoimmune neuromuscular junction disease.
- Interpretation and limitations
- A positive compatible antibody result supports the diagnosis, but ocular disease may be seronegative. AChR testing is generally followed by MuSK testing; persistent suspicion after negative routine serology warrants specialist assessment, potentially including a more sensitive cell-based panel and neurophysiology.
- 03
Specialist neurophysiology - Why
- Assess neuromuscular transmission when diagnosis remains uncertain or antibodies are negative.
- Interpretation and limitations
- ABN recommends experienced neurophysiology when MG is suspected but antibodies remain undetectable. Repetitive nerve stimulation is the initial test; single-fibre electromyography may be considered where expertise is available. Test symptomatic muscles and interpret results with the clinical picture, because abnormal transmission can also occur in other disorders.
- 04
Bedside rest or ice testing and thymic imaging - Why
- Provide supporting clinical evidence and assess associated thymic disease after specialist evaluation.
- Interpretation and limitations
- Improvement of ptosis after rest or a carefully performed ice test supports suspicion but is not a complete diagnostic pathway. ABN recommends thymic CT or MRI in all suspected myasthenia, including ocular and seronegative presentations; a chest radiograph is insufficient to exclude thymoma.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Ocular motor nerve palsy
A fixed deficit following one nerve distribution suggests a cranial neuropathy, although myasthenia can mimic it. Acute third-nerve palsy still requires urgent investigation for compression regardless of a normal pupil.
Thyroid eye disease
Orbital muscle disease may produce restrictive diplopia with proptosis or lid changes. The examination and appropriate thyroid or orbital assessment help distinguish restriction from fluctuating neuromuscular weakness.
Mechanical or longstanding ptosis
Age-related lid changes and congenital ptosis can cause a drooping lid without fatigable ocular weakness. A stable history and lid examination help assessment, but accompanying variable diplopia warrants further investigation.
Additional chapter-specific clues
A fixed enlarged pupil, painful eye movements, sensory loss, reduced colour perception or a true acuity deficit is not explained by uncomplicated ocular myasthenia. Such findings require assessment for aneurysm, optic neuropathy, orbital disease or another neurological process.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01EmergencyPossible generalisation or crisisFirst stepAn ocular presentation is accompanied by significant swallowing, breathing or rapidly progressive generalised weakness.+
- 1Arrange immediate hospital assessment and communicate the suspected neuromuscular diagnosis and current medicines.
- 2Assess airway protection, ventilation and swallowing, involving neurology and critical care early when deterioration is significant.
- 3Review recent infection, new medicines and any corticosteroid initiation as possible contributors without delaying stabilisation.
- 4Use specialist rescue treatment when indicated rather than advising unsupervised extra pyridostigmine doses at home.
02DiagnosisStable suspected ocular myastheniaFluctuating ptosis or binocular diplopia suggests neuromuscular junction dysfunction without emergency features.+
- 1Refer for neurology and ophthalmic assessment, documenting fatigability, pupil findings and any symptoms outside the eyes.
- 2Arrange antibody testing and experienced neurophysiology for persistent antibody-negative suspicion, without dismissing a convincing fluctuating clinical pattern after negative initial serology.
- 3Assess the thymus and relevant comorbidity as part of the specialist work-up.
- 4Provide practical advice about visual symptoms, driving and the specific bulbar or respiratory changes that require urgent help.
03TreatmentIntroduce and review ocular therapyThe diagnosis has been assessed and symptoms warrant treatment through the specialist plan.+
- 1Introduce pyridostigmine gradually after reviewing cardiac history, asthma and a baseline ECG, and assess benefit against cholinergic adverse effects.
- 2EscalationIf ocular symptoms remain troublesome, consider specialist-initiated daily prednisolone with cautious escalation under the current ABN regimen.
- 3Warn about possible early steroid-related worsening and agree who will review deterioration promptly.
- 4Review persistent disability and treatment toxicity before adding immunosuppression or considering selected surgical options.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Pyridostigmine for ocular symptoms
ABN 2025 starts 30 mg orally three or four times daily with gradual clinician-directed titration; if needed, treatment may reach 60 mg four times daily over five to ten days. Up to 360 mg daily in divided doses may be used, but requirements above 300 mg daily prompt early specialist review.Obtain a baseline ECG and consider cardiac conduction disease and asthma. Monitor diarrhoea, abdominal cramps, sweating, salivation and bradycardia. Worsening weakness or respiratory symptoms requires assessment rather than blind dose escalation; continue and review according to benefit.
Daily prednisolone for ocular myasthenia
ABN 2025 starts 5–10 mg orally daily, increasing by 5 mg every three to five days according to response towards an initial ocular target of 20 mg daily. Further specialist titration may reach 0.5 mg/kg daily, capped at 30 mg daily; subsequent maintenance and taper follow disease control.Initiation can temporarily worsen weakness, especially when bulbar or respiratory involvement is present. Use specialist supervision and an escalation plan, with glucose, blood pressure, infection, bone and adrenal-risk monitoring. Do not substitute an old alternate-day schedule or stop abruptly.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Bulbar dysfunction and aspiration
Weakness of swallowing and airway-protective muscles can cause choking and aspiration. New difficulty with liquids, tablets or secretions should prompt urgent reassessment rather than being accepted as an extension of mild ocular symptoms.
Respiratory crisis
Respiratory muscle weakness can impair ventilation and progress rapidly. Clinical deterioration requires hospital assessment, serial physiological monitoring and potentially critical-care support, even before pulse oximetry becomes abnormal.
Treatment-related harm
Pyridostigmine can produce cholinergic adverse effects, while corticosteroids can initially worsen weakness and later cause systemic toxicity. Gradual introduction, clear escalation advice and ongoing specialist review reduce avoidable complications.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Review both ocular function and symptoms beyond the eyes, specifically chewing, swallowing, speech, neck strength and breathing, at each contact.
- Record treatment response in practical terms such as reading endurance and frequency of diplopia, alongside the examination and patient-reported daily variability.
- Check pyridostigmine adverse effects and total dose, arranging prompt reassessment when requirements rise above 300 mg daily or benefit remains poor.
- During prednisolone escalation and maintenance, monitor for early weakness worsening and later metabolic, infection, bone, mood and adrenal complications.
- With diplopia, advise stopping driving and notifying DVLA in Great Britain or DVA in Northern Ireland; symptom improvement does not itself complete the relevant licensing process.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Seronegative does not mean absent disease
Antibodies are less consistently detected in ocular presentations than in some generalised forms. A convincing clinical pattern should therefore lead to specialist reassessment and appropriately selected neurophysiology, not dismissal after a single negative result.
Normal pupils have a limited meaning
Preserved pupil function fits ocular myasthenia, but other disorders can also spare the pupil. An acute fixed third-nerve pattern still requires its own urgent imaging assessment; a normal pupil is not permission to bypass aneurysm exclusion.
Medication review is part of disease control
Some antibiotics, cardiovascular medicines and other agents can worsen neuromuscular weakness. Check a current specialist interaction resource before new prescribing, balance necessary treatment against risk, and ensure anaesthetic teams know the diagnosis before procedures.
Thymectomy is an individual decision
A thymoma requires specialist assessment, while the role of thymectomy in other presentations depends on disease type and patient factors. An ocular presentation alone is not a reason to recommend surgery automatically to every patient.
11Common pitfallsFrequent interpretation and management errors.
- 01
Assuming variable ptosis is benign because the examination improves after a short rest.
- 02
Excluding ocular myasthenia after one negative antibody result despite a convincing fluctuating pattern.
- 03
Escalating pyridostigmine repeatedly when new bulbar or respiratory weakness actually needs hospital assessment.
- 04
Starting a high corticosteroid dose without warning about early worsening or arranging specialist follow-up.