POSTERIOR INTERNUCLEAR OPHTHALMOPLEGIA - CLINICAL AND ELECTROPHYSIOLOGICAL EVIDENCE FOR THE EXISTENCE OF A PRENUCLEAR ABDUCTION PARESIS

In five patients with unilateral and six with bilateral asymmetrical a bduction paresis, electrophysiological testing of masseter and blink r eflexes indicated an ipsilateral rostral pontine or mesencephalic lesi on, and excluded a lesion of the infranuclear abducens nerve. Abductio n paresis was explained by impaired inhibition of the tonic resting ac tivity of the antagonistic medial rectus muscle. The prenuclear origin of the disorder is based on neurophysiological and morphological evid ence of an uncrossed inhibitory connection between the pontine reticul ar formation and the oculomotor nucleus running in close proximity but separeted from the medial longitudinal fasciculus.