Simplified diagram of the normal pathway of horizontal eye movement involving the medial longitudinal fasciculus as well as diagrams of internuclear ophthalmoplegia and one-and-a-half syndrome.
Note: one-and-a-half syndrome may occur due to a lesion in either the paramedian pontine reticular formation or CNVI nucleus separately, or a lesion affecting a combination of both. The ipsilateral medial longitudinal fasciculus must have a defect.