Myasthenia gravis appears to be an autoimmune disease caused by an antibody attacking and diminishing the integrity of the body’s components. The autoimmune attack on the neuromuscular junction accounts for the symptoms and signs of ocular and generalized myasthenia gravis. The disease attacks only the voluntary muscles and more frequently the muscles of the eye, the arms, neck and legs. People who have myasthenia gravis appear to produce a blocking antibody which deposits on the receptor muscle membrane and prevents the entry of acetylcholine molecules which are used in the neuromuscular transmission. This results in muscular fatigue.
Ocular myasthenia gravis can be characterized by an abrupt or insidious onset of weakness and fatigue of one or both eye lids or eye muscles. This means that the condition can appear suddenly or develop slowly over time and effect either one or both eyes. People with ocular myasthenia gravis have trouble with their sight because of double vision or drooping eyelids. Their eyes do not often move together in balanced alignment, which causes them to see double images.
These symptoms can range from mild to severe. In fact, eye weakness can change from day to day and over the course of one day. Problems with the eyes are often worse at the end of the day or after the eyes have been used for a prolonged period of time. Individuals who suffer from ocular myasthenia gravis will find that these problems can be temporarily improved if their eyes are rested by closing them for several minutes when the symptoms are troubling.
Individuals who suffer from ocular myasthenia gravis do not have symptoms that involve their necks, swallowing, speaking or breathing. Neither do they complain of symptoms in the arms or legs. Symptoms that do plague them are the previously described a double vision and drooping eyelids. The eyelid will appear to cover the pupil of the eye and vision will become obstructed.
Often times problems with double vision and drooping eyelids are the first symptoms of myasthenia gravis. In most individuals these symptoms will continue to progress and involve voluntary muscles and other parts of the body. Only about one in six or seven people with myasthenia gravis will have only ocular problems, or problems with their eyes. Individuals who have had only eye problems for the first five years of their myasthenia gravis will probably not develop any additional weaknesses.
Unfortunately it is not possible to predict which patients will have only eye weakness and which will have more generalized symptoms. Interestingly, most people who suffer from the congenital form of myasthenia gravis will not have ocular myasthenia gravis and individuals with ocular myasthenia gravis are more likely to have sero negative disease. This means that those with only ocular disease have no measurable acetylcholine receptor antibodies in their bloodstream as compared to people who have generalized illness.
Why the eye muscles are more frequently involved in patients who have both ocular disease and those who are generalized disease is not fully understood. One hypothesis is that these individuals may simply notice eye weakness more often than milder weakness in other muscle groups in the body. Another hypothesis is that the eye and eyelid structures are different from muscles in the trunk and limbs. Eye muscles also contract more rapidly than other muscles and may be more likely to fatigue easier.
Individuals with ocular myasthenia gravis must balance the severity of the symptoms with the risks and benefits of the treatment options currently available. Individuals may have primarily cosmetic problems because of the drooping eyelids or double vision and may consider nonpharmacological treatment such as wearing dark glasses in the bright light which can decrease symptoms or using eyelid tape to assist with drooping eyelids.
Another treatment advises the application of a patch to one eye which permits a patient with double vision to see only one image at a time. It is important to alternate the patch from one eye to the other to avoid permanent vision loss in the eye that is consistently patched.
If the symptoms are severe or disabling then treatment with agents such as Mestinon may be helpful for drooping eyelids but are generally not very useful for double vision. A thymectomy is not considered for individuals who have only ocular myasthenia gravis unless the manifestations are severe or or disabling. Eyelid or eye muscle surgery is also contraindicated in individuals with myasthenia gravis to correct the drooping eyelids or poor control of the eye muscles.
Current Opinion in Ophthalmology: Ocular Myasthenia Gravis
Muscle and Nerve: Ocular Myasthenia Gravis in a Senior Population
Myasthenia Gravis Foundation of America: Ocular Myasthenia Gravis
Myasthenia Gravis Association of Western Pennsylvania: Ocular Myasthenia Gravis
Brigham and Women’s Hospital: Ocular Myasthenia Gravis