Informational Differentiating Between Monocular and Binocular Diplopia

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http://youtube.com/watch?v=YoGK45Ot9tQ

A 66-year-old woman with a history of a pituitary macroadenoma had intermittent diplopia after repeatedly changing the direction of her gaze, and she noted mild right ptosis. This video demonstrates her eye motility exam, with marked restriction of elevation, depression, and abduction in the right eye after eccentric gaze (after 00:24). The development of marked restriction in elevation and depression could be consistent with myasthenia or ocular neuromyotonia, but the development of a marked abduction deficit immediately after adduction suggests ocular neuromyotonia as the correct diagnosis. Ocular neuromyotonia involves tonic overaction of the extraocular muscles innervated by any ocular motor nerve with impaired relaxation following activation. The increasingly severe motility deficits seen with continued testing reflect the inability of the third nerve–innervated muscles to relax after their initial activation. Thus, the inability to abduct the eye immediately after adduction provides the critical clue to the diagnosis. • Ocular neuromyotonia may be seen as a delayed complication of radiation treatment, tumors, thyroid eye disease, or vascular irritation. The mechanism by which ocular neuromyotonia occurs is unclear but may relate to ephaptic stimulation of the affected cranial nerve, whereby axons are depolarized via nonsynaptic stimulation. • For a full case discussion and review, see http://ja.ma/2nfUNbq

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