Internuclear ophthalmoplegia (INO) is a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction.

That is if the right eye is affected the patient will "see double" when looking to the left, seeing two images side-by-side.

[1] The disorder is caused by injury or dysfunction in the medial longitudinal fasciculus (MLF), a heavily myelinated tract that allows conjugate eye movement by connecting the paramedian pontine reticular formation (PPRF)-abducens nucleus complex of the contralateral side to the oculomotor nucleus of the ipsilateral side.

In young patients with bilateral INO, multiple sclerosis is often the cause.

[4] Accompanying symptoms include scanning speech, intention tremor, incontinence, and nystagmus.