Ocular myasthenia gravis is an autoimmune disorder in which the signal from nerve to eye muscles is disrupted. Because of this, the eyelid may droop and vision may double. A telling feature is that symptoms worsen toward evening or with fatigue and ease after rest.
What ocular myasthenia gravis is
Myasthenia is a disorder of the so-called neuromuscular junction. Normally a nerve releases a substance called acetylcholine, which “switches on” the muscle. In myasthenia the person’s own immune system mistakenly produces antibodies that block the acetylcholine receptors on the muscle. The signal gets through poorly, and the muscle tires and weakens quickly. When only the muscles of the eyes and eyelids are affected, we speak of the ocular form. It may stay isolated for years, or over time it may progress to generalised myasthenia, when weakness spreads to the muscles of the face, neck, arms, swallowing and breathing.
Causes
- An autoimmune malfunction: the body produces antibodies against its own acetylcholine receptors.
- Changes in the thymus gland — its enlargement or a tumour (thymoma).
- An inherited tendency toward autoimmune diseases.
- Triggers may include infections, severe stress, exhaustion, and certain medicines.
- Often the exact cause cannot be named — the disease appears without an obvious reason.
Symptoms
- Drooping eyelid (ptosis) — one or both; less in the morning, more toward evening.
- Double vision (diplopia), especially during prolonged reading or screen time.
- Variable complaints: symptoms build up with fatigue and by the end of the day and lessen after rest or sleep.
- A feeling of “heavy” eyelids and quickly tiring eyes.
- Sometimes it is hard to hold the gaze upward for a long time.
- The hallmark of the disease is precisely this variability, not a constant, unchanging weakness.
Why this is a neuro-ophthalmological condition
Ptosis and double vision are eye symptoms, but their cause lies in the working of nerves and muscles, not in the eye itself. That is why the situation should be assessed by a doctor at the border of neurology and ophthalmology — a neuro-ophthalmologist. This specialist distinguishes myasthenia from other causes of a drooping eyelid (for example, nerve damage, vascular or thyroid problems) and orders the right tests. A wrong diagnosis delays treatment, so the neuro-ophthalmological examination is key.
Diagnosis
- A blood test for antibodies to acetylcholine receptors.
- The rest test: after a few minutes with the eyes closed, the ptosis temporarily improves.
- The ice-pack test: applying cold to the drooping eyelid briefly reduces the ptosis.
- Electroneuromyography (ENMG) — assesses the fatigability of neuromuscular transmission.
- CT or MRI of the chest — to rule out a thymoma (a tumour of the thymus gland).
- An examination by a neuro-ophthalmologist, assessing eye and eyelid movements over time.
Treatment
Treatment is chosen by the doctor individually. Medicines that improve the signal to the muscle are used and, if needed, agents that reduce the excessive activity of the immune system. When a thymoma is found, its removal is considered. The main thing is seeking help early: the sooner the diagnosis is made and treatment begun, the greater the chance of controlling symptoms and preventing progression to the generalised form. A drooping eyelid or double vision should not be written off as “just tiredness”, especially if they come and go during the day.
When to seek urgent help
Seek medical help immediately if the eye symptoms are joined by difficulty swallowing, choking, a change in voice, weakness of the arm or leg muscles, and especially a feeling of shortness of air or laboured breathing. These may be signs that myasthenia is spreading to the breathing muscles — a condition that requires emergency care.
German Eye Clinic, phone 0 800 507 670, the “Neuro-ophthalmologist consultation” service page.
