What Is Ocular Myasthenia Gravis?
Myasthenia gravis is an
autoimmune disease that affects the transmission of signals from nerves to muscles. The name myasthenia gravis comes from Greek and Latin words meaning "grave muscle weakness." However, most cases of myasthenia gravis are not as "grave" as the name implies, and most people with myasthenia gravis can expect to live normal or nearly normal lives.
Ocular myasthenia gravis is a type of myasthenia gravis that only affects the eyes and eyelid movement. The hallmark of ocular myasthenia gravis is eye muscle weakness that increases during activity and improves after rest.
Understanding Nerves and Muscles
Normally when impulses travel down the nerves, the nerve endings release a neurotransmitter substance called acetylcholine. Acetylcholine travels through the neuromuscular junction and binds to acetylcholine receptors, which are activated and generate a muscle
contraction.
What Causes Ocular Myasthenia Gravis?
In ocular myasthenia gravis, antibodies block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction. This prevents the muscle contraction from occurring. Ocular myasthenia gravis is considered an
autoimmune disease, in which the body's immune system mistakenly turns against itself, attacking its own tissues. Research scientists are still trying to understand why the immune system attacks the acetylcholine receptors.
Ocular
myasthenia gravis occurs in men and women of all ethnic groups. Although myasthenia gravis usually affects women under 40 and men over 60, it can occur at any age. Ocular myasthenia gravis is not directly inherited, nor is it contagious.
The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Symptoms of ocular myasthenia gravis affect the muscles that control eye and eyelid movement. Common ocular
myasthenia gravis symptoms include:
- Drooping of one or both eyelids (ptosis)
- Blurred vision due to weakness of the muscles that control eye movements
- Double vision (diplopia) due to weakness of the muscles that control eye movements.
Ocular myasthenia gravis symptoms vary in severity.
Diagnosing Ocular Myasthenia Gravis
Weakness is a common symptom of many disorders, which is why ocular myasthenia gravis is often misdiagnosed in people who experience mild weakness. Therefore, a delay in diagnosis of one or two years is not unusual in cases of ocular myasthenia gravis.
In order to diagnose ocular myasthenia gravis, healthcare providers will:
- Review the patient's medical history
- Review the patient's physical and neurological examinations
- Look for symptoms such as impairment of eye movements.
Tests that are used to confirm an ocular myasthenia diagnosis include the following:
- Blood test
- Edrophonium test
- Nerve conduction study
- Single fiber electromyography (EMG).
(Click Myasthenia Diagnosis for more information on the tests that used to diagnose ocular myasthenia gravis.)
Symptoms of ocular
myasthenia gravis can be controlled. The goals of treatment are to improve symptoms while minimizing side effects and possible risks. Treatment options for ocular myasthenia gravis may include:
- Medications
- Thymectomy
- Assistive devices.
Medications
Medications that are used for the treatment of ocular myasthenia gravis include anticholinesterase agents such as neostigmine and pyridostigmine, which help improve neuromuscular transmission and increase muscle strength. Immunosuppressive drugs such as
prednisone, cyclosporine, and
azathioprine may also be used for the treatment of ocular myasthenia. Ocular myasthenia gravis medications are used as treatment to improve muscle strength by suppressing the production of abnormal antibodies. However, it is important to note that these medications must be used with careful medical follow-up because they may cause major side effects, especially in children.
Thymectomy
Thymectomy is the surgical removal of the thymus gland, which is often abnormal in myasthenia gravis patients. A thymectomy may:
- Improve symptoms
- Cure ocular myasthenia gravis
- Re-balance the immune system.
However, a thymectomy is usually only recommended for patients with severe ocular myasthenia gravis.
Assistive Devices
Doctors may recommend assistive devices for people with mild or moderate symptoms of ocular myasthenia gravis. Assistive devices include:
- Eyelid crutches, which are devices that attach to glasses to keep eyelids open. Eyelid crutches are helpful for patients with significant eyelid droop that does not respond to medicine and for patients who want to avoid surgery.
- Eyelid tape, which mechanically keeps eyelids open. Eyelid tape is helpful for patients with significant eyelid droop that does not respond to medicine and for patients who want to avoid surgery.
- Eyeglass prisms, which are a simple, safe, solution for certain types of double vision. Eyeglass prisms can be extremely helpful for individuals that require binocular vision for their livelihood.
- An eye patch to one eye, which eliminates double vision. An eye patch is a safe way to eliminate double vision for people who do not require binocular vision for their livelihood. People should rotate the eye patch because using it on the same eye can cause reduced vision over time in the uncovered eye.
