Ocular Myasthenia

Ocular myasthenia is a form of myasthenia gravis where muscle weakness affects only the eyes and eyelids, causing symptoms like drooping eyelids and double vision that can vary throughout the day.

Table of contents

• What Is Ocular Myasthenia?
• How Common Is It?
• Symptoms
• The Difference Between Ocular and Generalized Myasthenia Gravis
• What Causes Ocular Myasthenia?
• How Is Ocular Myasthenia Diagnosed?
• Will Ocular Myasthenia Progress?
• Treatment Options

What Is Ocular Myasthenia?

Ocular myasthenia is a form of myasthenia gravis (a neuromuscular disease that causes muscle weakness) in which only the muscles that control the eyes and eyelids are affected^[1][4]. The word “ocular” means related to the eyes.

In this condition, the extraocular muscles (the muscles that move your eyes) and the muscles that lift your eyelids become easily tired and weak^[4]. Unlike generalized myasthenia gravis, which affects muscles throughout the body, people with ocular myasthenia experience weakness only in the eye area^[1].

• Eye muscles (extraocular muscles)
• Eyelid muscles

How Common Is It?

Almost 50% of people with myasthenia gravis first experience only eye-related symptoms when the disease begins^[2]. Eye problems occur in 15 to 50% of all myasthenia cases^[2]. The overall incidence of ocular myasthenia based on population studies is 1.13 per 100,000 people per year^[2].

About 15% to 20% of people with myasthenia gravis have symptoms that remain limited to the eyes even years after diagnosis^[1][2]. If eye symptoms persist alone without other muscle weakness for the first two years, further spread of the disease to other muscles is uncommon^[5].

Symptoms

The main symptoms of ocular myasthenia affect your vision and eyelids^[1][4]:

• Drooping eyelids (called ptosis): One or both eyelids may droop to cover all or part of the eye pupil, blocking your vision^[4][6]. This can affect one or both eyes.
• Double vision (called diplopia): Your eyes do not move together properly, causing you to see two images instead of one^[1][4]. This happens because weakness in the eye muscles leads to misalignment of the eyes^[1].
• Trouble focusing^[1]
• Blurry vision^[3]

Eye weakness often changes from day to day and even during the same day^[4]. Problems with the eyes are typically worse at the end of the day or after the eyes have been used for a long time^[4][6]. The amount of weakness usually gets worse with activity and improves with rest^[1]. You may find that closing your eyes for several minutes when symptoms bother you can temporarily improve the problem^[4].

If you have ocular myasthenia, you will not have difficulty swallowing, speaking, or breathing, and you will not experience weakness in your arms and legs^[4][6]. These symptoms occur only in generalized myasthenia gravis.

The Difference Between Ocular and Generalized Myasthenia Gravis

Ocular myasthenia gravis affects only the muscles that move the eyes and eyelids^[1]. In contrast, generalized myasthenia gravis affects muscles throughout the body. People with generalized myasthenia may experience visual symptoms along with trouble speaking, trouble swallowing, and weakness in the arms, legs, neck, or throat^[1][3].

For about half of patients with myasthenia gravis, the first symptoms are visual. About 15% of these patients will continue to have only visual symptoms, even years after their diagnosis. In the other 85% of patients, however, symptoms of weakness will develop in another part of the body, usually within the next three years. At that time, these patients are considered to have generalized myasthenia gravis^[1].

What Causes Ocular Myasthenia?

Ocular myasthenia is an autoimmune disease, which means the body’s immune system mistakenly attacks its own healthy tissues^[2][5]. Normally, nerves send signals to muscles using a chemical called acetylcholine, which tells the muscles when to move^[1][5].

In people with myasthenia gravis, the immune system produces antibodies (immune system proteins) that mistakenly interfere with the muscles’ receptors for acetylcholine^[1][2]. These antibodies block the acetylcholine receptor sites and prevent signals from reaching the eye muscles to contract^[7]. When these receptors cannot work properly, the affected muscles tire easily^[1].

The eye and eyelid muscles are particularly vulnerable because they are structurally different from muscles in the rest of the body. They have fewer acetylcholine receptors, which is where the defect occurs in autoimmune myasthenia^[4]. Additionally, eye muscles contract much more rapidly than other muscles, so they may be more likely to fatigue regardless of the disease^[4].

In patients with ocular myasthenia gravis (those who have visual symptoms only), the blood test for these antibodies is positive in about 50% of cases^[1][4]. The anti-acetylcholine receptor (AChR) antibodies are the most commonly tested^[2][4].

How Is Ocular Myasthenia Diagnosed?

Diagnosis is made by the neurologist examining your clinical features and the results of tests^[4]. Your doctor will begin by asking about your symptoms and performing a physical examination^[1]. It is important to carefully test the eyelids and eye movements, and to see what happens to the muscles when they are tired and when they have rested^[1].

Your doctor may request additional tests to confirm a diagnosis of myasthenia gravis^[1]:

• Blood test: This checks if the immune system is blocking the signals that travel from the nerves to the muscles by looking for anti-acetylcholine receptor (AChR) antibodies^[1][4]. In patients with ocular myasthenia gravis, this blood test has lower accuracy, so a negative result might require additional testing^[1].
• Ice pack test: Placing an ice pack over the eyelid can temporarily improve drooping, helping to confirm the diagnosis^[5].
• Electromyography (EMG): This is an electrical test that measures the electrical activity of muscles and nerves^[5]. One type of test, called a nerve conduction study, delivers a small electrical stimulation to a nerve, and the responses are measured from a muscle^[1]. Both tests can reveal a pattern of responses that suggests myasthenia gravis.
• Single fiber electromyogram (SFEMG): This is the most accurate test to diagnose myasthenia gravis^[1][2]. It involves very small needles that can measure responses from two nearby muscle fibers.

Many people with ocular myasthenia first consult their optician (eye doctor) about their eye problem. Optometrists are frequently the first medical professionals to suspect myasthenia and will refer you to a neurologist for further tests^[4].

Will Ocular Myasthenia Progress?

Ocular myasthenia gravis can evolve into generalized myasthenia gravis in about 20 to 60% of cases^[2][7]. If a person has had symptoms affecting only their eyes for two years or more, it is unusual for other parts of the body to be affected later on^[6].

According to the Myasthenia Gravis Foundation of America, about half of people who have only eye problems in the first year after a diagnosis go on to develop generalized myasthenia gravis^[18]. People who have only eye-related symptoms for five years or more usually do not develop generalized disease^[18].

Treatment Options

While there is no cure for ocular myasthenia, treatments can effectively manage symptoms and improve quality of life^[5][13]. Treatment plans are individualized and may include medications, supportive measures, and lifestyle adjustments.

Medications

The treatment of ocular myasthenia is primarily through the following medications^[2][4]:

• Pyridostigmine (Mestinon®): This is a cholinesterase inhibitor that is commonly used as the first medication^[1][4][7]. It helps build higher levels of the chemical acetylcholine, which is the signal that tells a muscle to move^[1]. The medication boosts the message from the nerve to the muscle, resulting in easier muscle contraction and movement^[4]. It has to be taken periodically throughout the day for it to take full effect. Side effects can include diarrhea, abdominal cramps, nausea, and vomiting^[1].
• Corticosteroids (such as prednisone or prednisolone): These medications can be very effective at controlling the immune response that causes myasthenia^[1][4]. Steroids are frequently required in cases of eye muscle paralysis^[2]. Prednisolone is often started on a relatively high dose and gradually reduced until the best dosage is achieved. Symptoms usually start to improve 2 to 4 weeks after treatment is started, with maximum benefit usually seen after 6 to 12 months^[4]. Unfortunately, long-term use of steroids is associated with side effects that include weakening of bones (osteoporosis), diabetes, high blood pressure, sleep disturbance, and emotional changes^[1].
• Other immunosuppressive medications: In some cases, other medications can be used to help control the immune system and lower the dosage of prednisone^[1][4]. These include:
  • Azathioprine (Imuran®): Acts slowly and can take up to a year to take full effect^[4]
  • Mycophenolate mofetil (Cellcept®): Can take up to 3 to 6 months to take full effect^[4]
  • Methotrexate: Can take up to 8 to 12 weeks to take full effect^[4]
  • Cyclosporine (ciclosporin): Can take up to 2 to 3 months to take full effect^[1][4]

  All of these medications require regular blood tests for monitoring^[4].

• Intravenous immunoglobulin (IVIg): This medication can be used intermittently and can be very effective^[1]. However, it is typically not utilized for ocular myasthenia, though in rare cases it may be used on a case-by-case basis^[15].

Supportive Measures for Vision

Several approaches can help manage the vision problems caused by ocular myasthenia^[15]:

• Eye patches: Wearing an eye patch over one eye or covering one of the eyeglass lenses with tape can help manage double vision^[4][15]. You can alternate the eye patch from one eye to the other to avoid eye strain^[19].
• Prism glasses: Your eye doctor may be able to reduce your double vision by putting prisms in your eyeglass lenses^[4][19]. However, the difficulty with prisms is that double vision often changes throughout the day and is related to fatigue^[15].
• Eyelid crutches: These can be added to your glasses to help hold your eyelids open^[17].
• Taping eyelids: You can use light-adhesive tape or silk tape to tape up your eyelids to cope with droopy lids^[19].
• Eye drops and gels: Use these to relieve your eyes from becoming dry, especially if your eyes do not close completely during sleep^[14].
• Sunglasses and sun visors: These can help reduce glare^[19]. Wearing sunglasses to protect from bright light may also help^[17].

Lifestyle Adjustments

Managing ocular myasthenia also involves making changes to daily habits^[13][14]:

• Rest your eyes: Close your eyes for several minutes when your symptoms are troubling you^[4]. Symptoms often improve with rest.
• Pace yourself: Learn to recognize tiredness because this is when symptoms are likely to be triggered. Focus activities at your strongest time of the day^[16].
• Avoid temperature extremes: Do not get too hot or too cold, as changes in temperature can have a noticeable effect on muscle function^[16].
• Keep up with eye care: Make sure you wear glasses or contacts if needed and are up to date with your eye prescription. This may help prevent strain and discomfort^[17]. Have your eyes tested regularly, especially if you are taking steroid medication, which can cause glaucoma or cataracts^[19].
• Think carefully before driving: If you have a problem with double vision or droopy lids, consider whether it is safe for you to drive^[19].
• Manage stress: Stress can worsen myasthenia, so try to avoid excess emotional or physical stress^[14][16].
• Eat well and rest well: A well-balanced diet and plenty of rest can really help^[16].

Remember that every person’s experience with ocular myasthenia is unique. Work closely with your neurologist and eye doctor to find the treatment approach that works best for you.