Definition

Ophthalmoplegia secondary to lesion in the medial longitudinal fasciculus (MLF).

Double vision, blurry vision, or vague visual complaints.

(See Figures 10.13.1 and 10.13.2. See Video: Internuclear Ophthalmoplegia.)

Figure 10.13.1: Left internuclear ophthalmoplegia: Left gaze showing full abduction.

Figure 10.13.2: Left internuclear ophthalmoplegia: Right gaze with severe adduction deficit.

Critical

Weakness or paralysis of adduction, with horizontal jerk nystagmus of the abducting eye.

NOTE INO is localized to the side with the weak adduction.

Other

May be unilateral or bilateral (“wall-eyed” bilateral INO [WEBINO]). Upbeat nystagmus on upgaze may occur when INO is unilateral or bilateral. The involved eye can sometimes turn in when attempting to read (intact convergence). A skew deviation (relatively comitant vertical deviation not caused by neuromuscular junction disease or intraorbital pathology) may be present; brainstem and posterior fossa pathology should be ruled out. With skew deviation, the three-step test cannot isolate a specific muscle. See 10.7, Isolated Fourth Cranial Nerve Palsy. In addition, presence of other neurologic signs, including gaze-evoked nystagmus, gaze palsy, dysarthria, ataxia, and hemiplegia, favors skew deviation rather than fourth cranial nerve palsy. 

Differential Diagnosis of Attenuated Adduction

• Myasthenia gravis: May closely mimic INO; however, ptosis and orbicularis oculi weakness are common. Nystagmus of INO is faster; myasthenia gravis is more gaze paretic. Symptoms vary throughout the day.

• Orbital disease (e.g., tumor, thyroid disease, idiopathic orbital inflammatory syndrome): Proptosis, globe displacement, or pain may be present. Nystagmus is usually not present. See 7.1, Orbital Disease.

• One-and-a-half syndrome: Pontine lesion that includes the ipsilateral MLF and horizontal gaze center (sixth cranial nerve nucleus). The only preserved horizontal movement is abduction of the eye contralateral to the lesion. This is because of an ipsilateral adduction deficit (from the MLF lesion) and a horizontal gaze paresis in the direction of the lesion (from the horizontal gaze center lesion). Causes include stroke and pontine neoplasia.

• MS: More common in young patients, usually bilateral.

• Brainstem stroke: More common in elderly patients, usually unilateral.

• Brainstem mass lesion.

• Rare causes: CNS cryptococcosis, tuberculosis granuloma, pyoderma gangrenosum (all shown to cause WEBINO).

1. History: Age? Are symptoms constant or only toward the end of the day with fatigue? Prior optic neuritis, urinary incontinence, numbness or paralysis of an extremity, or another unexplained neurologic event (concerning for MS)?

2. Complete evaluation of eye movements to rule out other disorders (e.g., sixth cranial nerve palsy, skew deviation).

   NOTE Ocular motility can appear to be full, but a muscular weakness can be detected by observing slower saccadic eye movement in the involved eye compared with the contralateral eye. The adducting saccade is assessed by having the patient fix on the examiner’s finger held laterally and then asking the patient to make a rapid eye movement from lateral to primary gaze. If an INO is present, the involved eye will show a slower adducting saccade than the uninvolved eye. The contralateral eye may be tested in a similar fashion.

3. Ice test, rest test, or edrophonium chloride test when the diagnosis of myasthenia gravis cannot be ruled out.

4. MRI of the brainstem and midbrain.

Treatment/Follow-Up

1. If an acute stroke is diagnosed, admit to the hospital for neurologic evaluation and observation.

2. If concern for demyelinating disease, consider treatment recommendations described in 10.14, Optic Neuritis.

3. Patients are managed by physicians familiar with the underlying disease.