Ocular myasthenia gravis (MG) is a disease of the neuromuscular junction resulting in hallmark variability in muscle weakness and fatigability.
MG is an autoimmune disease where anomalous antibodies are produced against the naturally occurring acetylcholine receptors in voluntary muscles.
Although these blocking antibodies may be confined to one of the larger muscles responsible for moving the face or appendages or for breathing, about 90% of MG patients eventually have eye involvement.
[citation needed] Aside from asymmetric ptosis (which becomes worse with fatigue, sustained upgaze, and at the end of the day) and variable limitation of extraocular muscles/diplopia, other clinical signs of ocular MG include gaze-evoked nystagmus (rapid, involuntary, oscillatory motion of the eyeball) and Cogan’s lid twitch (upper lid twitch present when patient looks straight ahead after looking down for 10–15 seconds).
Eyes may also be less able to adapt to variable weakness, because extraocular muscles use visual rather than proprioceptive (body position-sensing) cues for fine-tuning.
In brief, the diagnosis of MG relies mostly on the patient's history and physical findings, with particular attention to neurologic, eye motility, and eyelid exams.
A tensilon (edrophonium chloride) test can be used, which temporarily blocks the breakdown of acetylcholine, and briefly relieves weakness; however, false-negative results are common.
MG is characteristically variable in course, with the frequency of diplopia and ptosis affected by environmental, emotional and physical factors such as bright sunlight, stress, viral illness, menstruation, pregnancy, etc.
Patients with mild-to-moderate ocular myasthenia are usually treated initially with oral anticholinesterase agents, Mestinon (pyridostigmine) being the most commonly employed.