Abduction nystagmus in internuclear ophthalmoplegia

Abstract

Direct current electro-oculography revealed abduction nystagmus with hypermetric abduction saccades in 35 of 64 patients with unilateral and 55 of 66 patients with bilateral internuclear ophthalmoplegia. Slowing of abduction saccades occurred in 27 unilateral cases, mainly ipsilateral to the paretic eye, and in 36 bilateral cases. Abduction nystagmus with hypermetric abduction saccades of normal velocity is explained by an increased phasic innervation adjusted to adduction paresis. Slowed abduction saccades are attributed to impaired inhibition of the medial rectus muscle. Superposition of impaired medial rectus inhibition and increased phasic innervation best explains abduction nystagmus with slowed hypermetric (6 unilateral and 23 bilateral cases) or normometric abduction saccades (9 unilateral and 5 bilateral cases).

Comments on “Bilateral medial rectus palsy due to midbrain infarction following concussion head injury”

“…[ 2 ] Abducting nystagmus and retained convergence are not sine qua non for INO though are characteristically present, the former may be subtle, missed clinically and may need laboratory evaluation. [ 3 ] The medial longitudinal fasciculus (MLF) carries otolithic pathways along with fibers controlling horizontal and vertical gazes. Abduction nystagmus with hypermetric abduction is due to increased phasic innervations adjusted to adduction paresis.…”

“…Slowed abduction saccades are attributed to impaired inhibition of the MR muscle in the fellow eye. [ 3 ]…”