Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder that causes muscle weakness. Patients often first notice weakness in the muscles that control the movement of their eyes and eyelids, with many later developing muscle weakness elsewhere.
For 10–40% of MG patients, the muscles controlling eye and eyelid movements remain the only ones affected. In these cases, the condition is known as ocular MG. Studies have indicated that people having only symptoms of ocular MG for two to three years are unlikely to develop weakness elsewhere.
Nerve cells send signals to muscle cells by releasing a signaling chemical called acetylcholine, which binds to acetylcholine receptors on muscle cells. In MG, the body’s immune system mistakenly attacks these acetylcholine receptors, disrupting nerve-muscle communication and causing muscle weakness.
There are several possible explanations for why MG affects eye muscles as it does. Among the reasons suggested is that the eye muscles contain fewer acetylcholine receptors, rendering them more sensitive to their loss or damage, which takes place over the course of the disease.
Eye muscles are also structurally different from limb or trunk muscles and contract more frequently, so they might be more prone to fatigue. Another possibility is that eye muscles have a specific gene signature associated with the body’s immune response that may render them more sensitive to the disease’s immune attacks.
Common symptoms of ocular MG include double vision (diplopia), and drooping in one or both eyelids, a condition called ptosis. To confirm these symptoms are related to MG, a diagnostic exam called ice pack test can be performed. During this test, an ice pack is placed over a patient’s closed eyelid for several minutes. If the ice pack temporarily relieves eyelid droopiness, it is an indication of ocular MG.
Muscle weakness in ocular MG often affects upward eye movement first, and tends to worsen with continuous eye muscle use. For this reason, it is typically more severe toward the end of the day.
Treatment and prognosis
Double vision may be alleviated by applying a patch over an eye or wearing a single opaque contact lens. This should be alternated between each eye to reduce eye strain. Special prism glasses may also help to correct double vision in some patients.
Specialized eyelid tape can be used to prevent eyelid droopiness, although it is recommended that one eyelid be taped at a time and alternated. Glasses can also be equipped with thin wires, called eyelid crutches, to help people with ptosis.
Ocular MG in general has a good prognosis in patients whose symptoms are kept under control with treatment.
Last updated: Nov. 5, 2021
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