What are the variants of internuclear ophthalmoplegia (INO) in multiple sclerosis (MS)?

Updated: Feb 21, 2019
  • Author: Fiona Costello, MD, FRCP; Chief Editor: Hampton Roy, Sr, MD  more...
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Wall-eyed internuclear ophthalmoplegia

Patients with unilateral INO do not typically have significant exotropia (outwardly deviating eye) in primary gaze because convergence tone is intact. [40] In contrast, bilateral MLF lesions can cause exotropia in wall-eyed bilateral INO (WEBINO) syndrome. WEBINO syndrome differs from paralytic pontine exotropia of one-and-a-half syndrome, which is characterized by a unilateral horizontal gaze palsy and INO due to a pontine lesion involving the paramedian pontine reticular formation and MLF. [47]

One-and-a-half syndrome

One-and-a-half syndrome is a clinical disorder characterized by a conjugate horizontal gaze palsy in one direction with an associated INO. The syndrome usually results from a single unilateral lesion of the paramedian pontine reticular formation or the abducens nucleus on one side (causing the conjugate gaze palsy), with interruption of internuclear fibers of the ipsilateral MLF (causing failure of adduction of the ipsilateral eye). Consequently, the single preserved horizontal eye movement is the abducting eye contralateral to the MLF lesion. [40, 48]

Skew deviation

Skew deviation refers to a vertical ocular misalignment caused by supranuclear lesions disrupting inputs to the ocular motor nuclei. [48] Skew deviation may cause vertical diplopia or misalignment in patients with INO because the MLF contains utricular pathways that maintain vertical eye position in addition to interneurons from the abducens nucleus to the medial rectus subnucleus. [40]

In skew deviation caused by a pontine lesion, the ipsilateral eye is lower, whereas, with a midbrain lesion, the ipsilateral eye is higher. [40]

Ocular tilt reaction

Ocular tilt reaction consists of skew deviation, ocular torsion, head tilt, and deviation of the subjective visual vertical, which are all tilted toward the lower or hypotropic eye. [49] The side of the tilt is named for the lower eye. [49] Static ocular tilt reactions from hypofunction are ipsiversive (lower eye on the side of the lesion) with peripheral vestibular and pontomedullary lesions and contraversive with pontomesencephalic lesions. [49] Paroxysmal ocular tilt reaction is rare but has been described in MS. [49]

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