= due to lesions of the medial longitudinal fasciculus (MLF) dorsomedial pons or midbrain
The side of the internuclear ophtalmoplegia is ipsilateral to the MLF lesion, the same side to have the adduction deficit.
– loss of adduction of the ipsilateral eye
– nystagmus present in the contralateral abducting eye
– ischaemia in older patients
– demyelinating lesions in younger patients