Adaptive Phänomene bei internukleärer Ophthalmoplegie

Abstract

Introduction: Abduction nystagmus and hypermetric abduction saccades are the main abnormalities on the non-paretic eye in internuclear ophthalmoplegia (INO). Their origin is still debated and includes an adaptively increased phasic innervation adjusted to the paretic medial rectus muscle (adaptation hypothesis). This hypothesis predicts a relation between the degree of the adduction paresis and the degree of the abduction overshoot and the occurrence of an abduction nystagmus in opposite eye. The present study investigates these predictions. Material and Methods: Direct-current electro-oculography and analysis of horizontal saccades in 50 consecutive patients with unilateral and 25 with bilateral INO. Results: All patients had overshooting abduction saccades on the eye opposite to the adduction paresis. In patients with unilateral and bilateral INO, linear regression showed negative correlations between adduction saccade velocity on the paretic eye and the degree of abduction overshoot and the duration of the phasic innervation on the other eye (correlation coefficients between r = -0.515 and -0.675). The frequency of abduction nystagmus increased with increasing degree of the adduction paresis. Patients with abduction nystagmus had a significantly higher degree of abduction overshoot and significantly longer duration of the phasic innervation of abduction saccades. Conclusions: These findings add further evidence to the existence of an adaptively increased phasic innervation adjusted to the paretic medial rectus muscle in patients with unilateral and bilateral INO. Such adaptation explains overshooting abduction saccades and abduction nystagmus present in most patients with INO on the non-paretic abducting eye.