Eye Disorders: Ocular Myasthenia Gravis

Myasthenia Gravis causes muscle weakness. The most commonly affected muscles are in the head and neck region, especially the muscles that open the eye (the levator), the muscles that move the eyeball (the recti), and those that control swallowing. When weakness is confined to the eyelids and recti, it is termed "ocular" myasthenia. When other muscles of the face and trunk are affected, it is "generalized."

What causes Myasthenia?
The cause of the weakness is a short-circuit of sorts between the nerve ending and the muscle. Specifically, an autoimmune process (the body's immune system attacking itself) leads to destruction of the acetylcholine receptors on the muscles, so the muscle can't "hear" the chemical signal from the nerve ending.

What are the common symptoms?
Common symptoms of ocular myasthenia include a droopy eyelid and double vision. The generalized form will affect other muscles in the body that may cause difficulty swallowing, combing hair, climbing stairs, or performing other repetitive tasks. If the chest muscles are involved, potentially serious breathing difficulty can result. Any difficulty breathing should prompt a trip to the emergency room.

How is myasthenia diagnosed?
Often a blood test can confirm the presence of antibodies to the acetylcholine receptors. Another test, called an electromyogram (EMG) can confirm the short-circuit between nerves and muscles. Another test is an injection of an "acetycholinesterase inhibitor", which will temporally reverse muscle weakness if myasthenia is present. Other neurological conditions can cause the same symptoms as myasthenia, so an accurate diagnosis is important and sometimes difficult.

What treatments are available?
Treatment is tailored to the specific individual and symptoms. Treatment often consists of immunosuppressive medications, like Prednisone, to halt the autoimmune process. Another medication, called Mestinon, can help the nerves "talk louder" to the muscles. For diplopia, prisms in glasses and patching are options. Occasionally a tumor in the chest called a thymoma may be present and needs to be removed.

The North American Neuro-Ophthalmology Society publishes a web site with good patient information on this condition