Wall-Eyed Internuclear Ophthalmoplegia: History and Hypothesis.

Abstract

Most patients with internuclear ophthalmoplegia (INO) are orthotropic, although a subset is exotropic. When INO is bilateral, this is termed wall-eyed bilateral internuclear ophthalmoplegia (WEBINO). In 1979, Sharpe described his "first case" of wall-eyed monocular internuclear ophthalmoplegia (WEMINO) as "a unique clinical syndrome" characterized by unilateral INO and ipsilateral exotropia. WEMINO was clinically identified in seven patients, with oculographic correlation in six and neuropathological confirmation in one. Oculographic features of exotropic INO patients were compared with those of six orthotropic INO patients using magnetic search coil and infrared oculography. All clinically defined WEMINO patients showed slowed, hypometric ipsilateral saccades by oculography. Six patients had ipsilateral exotropia, and three had ipsilateral hypertropia. Ipsilateral abducting saccades had faster peak velocities for smaller saccades, more so for orthotropic patients. Exotropic patients had normal sinusoidal mean vestibulo-ocular reflex (VOR) gains and phases; orthotropic patients had subnormal mean VOR gains and phase leads. WEMINO is a clinical ocular motor syndrome characterized by unilateral slow, hypometric adducting saccades with exotropia and hypertropia of the ipsilateral eye. We propose that it results from discrete unilateral damage to burst-tonic fibers in the medial longitudinal fasciculus (MLF) with sparing of the adjacent extrafascicular pathways. Paradoxically, orthotropic INO results from more extensive damage to ascending pathways lateral, ventral and caudal to the MLF. Direct injury to the medial rectus subnucleus is not required. This manuscript was in preparation at the time of Dr Sharpe's death in 2013 and is an acknowledgement of his forward-thinking, as his hypotheses have stood the test of time.