Internuclear ophthalmoplegia (INO)
 

a. Normal primary position b. Left impaired adductionn on right gaze c. Normal left abduction on left gaze d. Normal convergence Left internuclear ophthalmoplegia

. The most common scenario in the examination is young female with history of multiple sclerosis. However, it can also be  seen in older patients with cerebrovascular accident. The main feature of this condition is impaired adduction. A favourite  question is the site and side of the lesion (see question below). In unilateral case, the affected eye shows failure (or impaired) adduction (failure of conjugate eye movement). The abducting  eye shows jerk nystagmus with the quick phase towards the opposite side (this is called ataxic nystagmus but may not be  obvious and  can be absent). The horizontal saccade is abnormal with the affected eye lagging behind the normal eye. The  vertical saccade and convergence are normal.     Left saccade abnormality. This may be the only sign present in patient  with recovered internuclearophthalmoplegia. In the examination: there may be strabismus in the primary position the internuclear ophthalmoplegia may be bilateral with or without asymmetry if ask for further examination, mention that you would like to examine the patient for signs of demyelination: fundal examination for pale disc (from previous optic neuritis which may be in either eye) afferent pupillary defect (again from previous optic neuritis) cerebellar signs (for example scanning speech, disdianochokinesia, intentional tremor,  past-pointing in finger nose test)

Questions:

1. What is the mechanism of internuclear ophthalmoplegia?

answer
It is due to a lesion in the medial longitudinal fasciculus (MLF) which connects the sixth nerve nuclei to the contralateral medial rectus muscle nucleus. In unilateral case, there is loss of adduction of the ipsilaterall medial rectus on attempted conjugate gaze. There is abducting nystagmus of the ipsilateral eye. The horizontal saccadic, pursuit and vestibuloocular systems are affected but the convergence is usually normal.

2. A patient with internuclear ophthalmoplegia has problem with left adduction, which side is the lesion located?

answer
As explained above, the lesion is ipsilateral to the eye that has problem with adduction. Therefore the lesion is in the left medial longitudinal fasciculus.

3. Is convergence ever affected in lesion of the medial longitudinal fasciculus?

answer
Convergence is usually not affected in lesion of the medial longitudinal fasciculus (MLF) alone. However, if the lesion extends into the mid-brain the convergence may be involved as in Cogan's anterior internuclear ophthalmoplegia in which the patient has bilateral INO and convergence failure.

4. What is the mechanism of one and a half syndrome?

answer
An extensive lesion in the lower part of the pons can affect he horizontal gaze centre and the adjacent MLF. The lesion causes motility problems with both medial recti and one lateral rectus. On examination, there is a pontine gaze palsy to the ipsilateral side together with an INO on gaze to the contralateral side. In a right-sided lesion, there is failure of the eyes to look to the right, and on left gaze only the left eye will abduct with ataxic nystagmus.

5. What is wall eyed syndrome?

answer
 This is the presence of exotropia with bilateral internuclear ophthalmoplegia. It is also called WEBINO which is short for Wall Eyed Bilateral Inter-Nuclear Ophthalmoplegia.

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