Internuclear Ophthalmoplegia

Internuclear ophthalmoplegia is characterized by an ipsilateral adduction deficit that can be overcome with convergence. It is caused by a lesion affecting the medial longitudinal fasciculus in the brainstem tegmentum. In this chapter, we begin by reviewing the clinical features of internuclear ophthalmoplegia. We next list the common causes of internuclear ophthalmoplegia, which include demyelination, stroke, tumors, and congenital hindbrain anomalies. We then discuss other potential causes of an adduction deficit that can mimic internuclear ophthalmoplegia, which include ocular myasthenia and chronic progressive external ophthalmoplegia, and describe strategies to help diagnose these at the bedside. Lastly, we briefly discuss the treatment approach for internuclear ophthalmoplegia.