Myasthenia gravis (MG) comes in 2 main types, generalized and ocular. Ocular MG is much less common, affecting only 15 percent of people with myasthenia gravis.1-2
Ocular MG
Ocular means "of the eye or vision." So, ocular myasthenia gravis affects the muscles that move the eyes and eyelids. The most common symptoms of ocular MG are:1,3
- Droopy eyelid (ptosis)
- Double vision (diplopia)
- Trouble focusing or blurred vision
Double vision (seeing 2 objects where there is 1) and trouble focusing occur because the muscles that keep the eyes aligned become weak.
Eyelid droop most often happens to 1 eye only or is more severe in 1 eye than the other. This is called asymmetrical. If the eyelid covers the pupil, then the person will have trouble seeing. Sometimes double vision and eyelid droop happen at the same time. These symptoms can be mild to severe, and change from day to day.2
Most people with ocular MG find their eyes get more tired at the end of the day or after long periods of intense use, like staring at a computer screen. The symptoms often get better after a few minutes of resting the eyes.4
While droopy eyelids and double vision are common early signs of all forms of myasthenia gravis, people with ocular MG never go on to develop muscle weakness in their face, neck, arms, or legs.
Antibodies and ocular MG
Only half of people with ocular MG test positive for the antibodies that cause MG. People with no detectable antibodies are referred to as seronegative. For those that do have detectable antibodies, AChR (acetylcholine receptor) antibodies are the most common. LRP4 antibodies are the next most common.2
Titin and ryanodine or MuSK antibodies are very rare in someone with ocular MG. In fact, people with MuSK MG may not have any eye muscle weakness.1,2
Treatment
An acetylcholinesterase inhibitor may be the only drug needed to control mild to moderate ocular myasthenia gravis. Steroids or another immunosuppressant drug may be added if symptoms are not controlled or flares become frequent or serious. Since MG can change over time, sometimes more or less treatment may be needed.5
Some people with double vision may wear an eye patch or cover 1 lens in their eyeglasses to help correct their vision. Others find that wearing dark glasses in bright light helps. Older treatments include eyelid crutches for droopy eyelids and eyeglass prisms for double vision.3,4
Thymectomy, or surgery to remove the thymus, is controversial for people with ocular MG. Some research shows that it does not improve symptoms for ocular MG. However, thymectomy may be considered if drug treatments do not work, if the person has AChR antibodies, or shows signs of developing generalized MG.2
Progression of the condition
In most people with MG, symptoms of muscle weakness often begin in the eye and gradually spread to other muscle groups. When this happens it is called generalized MG. The muscles in the face and arms or legs are the areas most often affected. Sometimes muscle weakness begins in these muscles and not in the eyes.
If symptoms remain only in the eyes for 2 years, 90 percent will never develop generalized MG, or MG that affects muscles other than the eyes.1
Some studies seem to suggest that prednisolone treatment (a steroid) reduces the risk of ocular MG progressing. to generalized MG However, this has not been confirmed.2
If someone’s myasthenia gravis does not respond well to treatment, it may be called refractory MG. Only 15 percent of people with MG have refractory myasthenia gravis.6
Other things to know
People with ocular MG are more likely to have other autoimmune disorders, especially thyroiditis.
Ocular MG can begin at any age, and the thymus gland is only sometimes problematic. This compares to generalized MG, where the thymus gland is often enlarged, overactive, or has tumors. Ocular MG is more common in East Asia and in people of Asian descent.1,2