DrMKZ

There is an abnormality when the patient gazes to the right, in which the right eye abducted with an incomplete adduction of the left eye.

This video shows that when patient gazes to the his right the left eye lags behind as compared to the right eye.

The right eye which is the normal eye may have horizontal nystagmus.

This is called dissociation of conjugate eye movements.

The adduction of the affected eye can become normal when the comtralateral eye is covered.

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Lesion are located at in the medial longitudinal fasiculus of the affected eye, in this video is the left eye.

Saccadic eye movement will be abnormal, pursuit saccadic eye movement.

Therefore have to check properly for the cerebellar abnormality

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 Updated 1.7.2017
From OST page 226

The mlf starta below the commisure and ends in the upper cervical spinal cord. 
In simplistic term connects ipsilateral III with the contralateral VI and involves in the conjugate eye movement.
Lesion will involve in the ipsilateral adduction. 
Key features

1. weakness of ipsilateral adduction of the affected eye.
2. Nystagmus in the abducting eye may or maynot be present

Differentials

Ms

Brainstem lesion affecting the Cr3- infarction tumor aneurysm

Wernicke encephalopathy

Sle

Miller fisher 

Drug overdoae phehytoin tca antidepreassant