Ocular myasthenia: causes, symptoms, diagnosis and treatment

By Cristiano Antonino Last updated May 30, 2023

Myasthenia gravis is an autoimmune disorder that presents itself as increased fatigability and muscle weakness throughout the day

It can therefore also affect the muscles of the eyes and eyelids and is specifically referred to as ocular myasthenia.

The causes of ocular myasthenia are different, but this disease can be classified as an autoimmune disease

The body will produce auto-antibodies against the neuromuscular junctions causing difficulty in contracting the eye muscles and symptoms of fatigability.

Usually the presenting symptoms of myasthenia are ocular and may affect the patient’s ability to see: among the most common signs may be heaviness of the eyelid, ptosis, with reduction of the visual field, or if extraocular muscles are affected, there may be strabismus and double vision (diplopia).

Myasthenia gravis is a rather rare disease

Patients suffering from this disease can be of any age. In fact, the groups affected by this condition are women between the ages of 20 and 30 and men between the ages of 50 and 60.

Furthermore, the female-to-male ratio shows that this disease affects mainly the female sex with a 2-to-1 ratio.

Furthermore, of the patients affected by myasthenia gravis, around 15 per cent are diagnosed with ocular myasthenia.

Ocular myasthenia is a special type of myasthenia gravis

The latter term denotes an autoimmune disease that is characterised by impaired transmission of contractile signals.

In this disease, the signals sent from the nerve to the muscle are impaired.

The main symptoms consist of the onset of fatigue, weakness and difficulty in performing even everyday actions due to lack of strength.

These symptoms give the disease its name, which is made up of three words: gravis meaning severe, myo meaning muscle and asthenia meaning weakness.

To understand the mechanism of this pathology, it is therefore crucial to understand the importance of the communication between muscles and nerves.

The abnormal production of these antibodies that affect nerves and muscles means that the patient may experience difficulty in speaking, swallowing and, in the case of the symptoms of ocular myasthenia, have difficulty keeping their eyes open.

Ocular myasthenia can manifest itself with different symptoms, depending on various factors

These can include the patient’s age and the stage of the diagnosed disease.

At certain times, the symptoms of ocular myasthenia may be absent and the patient may be asymptomatic, which makes it more difficult to diagnose the condition in its early stages.

Among the most common symptoms of ocular myasthenia are

weakness of the eye muscles and eyelids
blurred or double vision;
drooping eyelids;
strong weakness of the eye muscles, especially at the end of the day or after straining the eyes.

After using the muscle repetitively, it can become very weak.

This difficulty can manifest itself not only in the eye muscles but, in the case of myasthenia gravis, also in the rest of the body.

Repetitive movements become complex to make, due to increased muscle fatigue.

Ocular myasthenia can also be the first symptom of more complex diseases or of myasthenia gravis in the rest of the body.

About 40 per cent of people suffering from ocular myasthenia will later have myasthenia gravis.

Causes

The cause of ocular myasthenia as already mentioned is the production of antibodies capable of attacking the communication between nerves and muscles.

As in all autoimmune diseases, there is an overreaction of the immune system, which recognises certain components of the body, such as tissues or organs, as foreign and reacts accordingly.

In this way, the immune system tries to defend the body against these elements considered foreign by producing antibodies.

The latter with their action can also lead to changes in the affected components that are considered foreign.

The causes of ocular myasthenia can therefore be reduced to this reaction of the immune system.

The reason why this condition leads the immune system to produce antibodies against muscles and nerves is not certain.

Myasthenia in children

Ocular myasthenia can affect subjects of all ages, including children.

In younger subjects in particular, three forms of the disease are distinguished:

Congenital Myasthenic Syndromes, i.e. a group of genetically transmitted diseases characterised by structural or functional alterations of proteins involved in neuromuscular transmission.
Transient Neonatal Myasthenia, caused by the passage of auto-antibodies directed against the acetylcholine receptor, from the mother with Myasthenia Gravis or Congenital Myasthenic Syndrome, to the foetus. It occurs in about 20% of infants born to affected mothers and causes hypotonia, respiratory distress and feeding difficulties. Symptoms usually appear in the first 4 days after birth and resolve, with appropriate treatment, within 4-6 weeks.
Myasthenia Gravis Juvenile, an autoimmune disease that occurs before the age of 19.

Diagnosing ocular myasthenia is not easy

The large number of eye diseases with symptoms similar to this autoimmune disease makes it very difficult to detect it accurately.

Moreover, as mentioned above, the symptoms of this autoimmune disease can be almost imperceptible at the beginning, while they already become complex in more advanced stages.

Diagnosing myasthenia ocularis in time is crucial for quickly prescribing an appropriate treatment.

A diagnosis made too late can lead to various complications and make it more complex to resolve and live with this disease.

Usually, to diagnose an autoimmune disease, the first step is a visit to one’s general practitioner.

Thanks to this first examination, it is possible to obtain an accurate anamnesis and an objective test of the patient’s symptoms, any cases in the family and the appearance of the first symptoms.

In this way, the doctor can get an initial overview of the patient’s state of health.

The patient can then be referred for a specialist examination and more precise tests including: blood tests, electromyography, the edrophonium test and, where necessary, imaging tests.

These tests can help the doctor not only to diagnose myasthenia ocularis but also to rule out any other related conditions.

Treatments

There are different treatments for ocular myasthenia, depending on the patient’s symptoms and the stage of the pathology.

Therapy is exclusively medical and is aimed at dampening the immune system’s response and decreasing circulating auto-antibodies.

This reduces symptoms and also improves the described ocular symptoms.

Medical therapy can take the form of various drugs:

cholinesterase inhibitor drugs, which aim to block the enzyme responsible for degrading acetylcholine, including pyridostigmine, and improve muscle response;
immunosuppressive treatments that aim to decrease the immune response and make antibodies less aggressive (e.g. methotrexate, azathioprine and cyclosporine);
corticosteroid drugs that have a similar purpose to immunosuppressive drugs, reducing the immune response;
vision aids, such as contact lenses or crutch glasses, to help the drooping eyelid and avoid double vision;
the only surgical approach, which is quite debated, is the surgical removal of the thymus, a central gland in our immune response and which may be hyperfunctioning in myasthenia.

Medications essential for the treatment of ocular myasthenia are aimed at increasing acetylcholine in order to reduce muscle weakness.

These treatments can be modified according to the patient’s needs.

This is why it is essential to obtain a therapy tailored to the stage of the disease, but also to the patient’s needs.

The effectiveness of these treatments may diminish over time or lead to side effects.

One of these can be cholinergic crisis, an excessive muscle weakness that can lead to diplopia and drooping eyelids.

Patient management is therefore complex and must be multidisciplinary, involving several medical figures.

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