Internuclear Ophthalmoplegia

 

The salient features on examination were deficits in adduction of the right eye associated with nystagmus of the abducted left eye, which is suggestive of a right internuclear ophthalmoplegia.

 

Convergence was spared.

 

Aetiology include (deficits to median longitudinal fasciculus):

• Multiple sclerosis

• Cerebrovascular disease (basilar artery or paramedian branches)

 

Differentials include:

• A partial third nerve palsy with prominent medial rectus weakness may be confused with an INO. Distinguishing features include other third nerve deficits (weakness of elevation, ptosis, pupil dilation), impaired convergence, and absence of the contralateral abduction nystagmus, all of which point to a third nerve palsy rather than an INO

 

Note, ‘one and a half syndrome’

• This is a combined internuclear ophthalmoplegia and abducens nerve palsy on the same time

• For example, if it was on the left:

  • The left eye would not be able to make any lateral movements (lateral rectus affected by 6th nerve palsy, and adduction affected by INO)

  • The right eye cannot adduct properly

    • Why would this be? An ipsilateral horizontal gaze palsy (failure of both eyes to deviate in one direction) rather than an isolated abduction deficit occurs with lesions involving the abducens nucleus in the pons because of involvement of the interneurons of the medial longitudinal fasciculus. These interneurons control contralateral medial rectus function (adduction) during attempted ipsilateral horizontal gaze

• Aetiologies - MS, stroke, tumour of dorsal pons