To the Editor.
—The transient, intermittent vertical diplopia and/or shimmering monocular visual distortion seen in superior oblique myokymia (SOM) is by now well recognized by most clinicians dealing with ophthalmologic and neurologic problems.1 The cause of this apparent transient discharge from the trochlear nerve remains unsolved.Several other neurologic phenomena have similarities with SOM, including trigeminal neuralgia,2 hemifacial spasm,3 and Meniere's disease. They have in common transient, intermittent discharges of the nerves associated with these syndromes, namely V, VII, and VIII, respectively. There is now evidence that a substantial proportion of these cases are diagnosed on the basis of compression of the involved nerves by vascular structures in the posterior fossa. Surgical transposition of these nerves frequently resolves the problem.Therefore, SOM may have its origin in a similar nerve compression by vascular structures in the posterior fossa. Unfortunately (or perhaps fortunately), I have not had a