WHY DOES NYSTAGMUS OCCUR IN THE EYE OF THE NORMAL EYE WHICH ABDUCTS NORMALLY in internuclear ophthalmoplegia

bcz the occulomotor nuclei is trying hard to get the other eye to move so it exerts more action potentials which becaus eit cant get through to the other eye due to the lesion in the MLF it causes nystagmus in the eye that is connected properly

black is lesioned area

when asked to look left which is the side of the lesion the eye with lesion will look left with nystagmus but the signal will not get through to tell the normal side to also look left this lesion results in one eye at a time being able to look horizontally this can cause double vision

• Explain the anatomical reasons behind signs and symptoms associated with brainstem lesions

remember the location of nuclei and the rule of 4 for CNs for location of lesion the 4 Ms for medial and 4 S’s for side lateral lesions

remember what each CN does

and remember that the lesion affects the same side within the brain stem eg face that the rest of the body so there may be loss of sensation on the LHS of the face but RHS body loss of sensation

remember the symptom onset can be related to different causations

fast - slow is shown in the diagram below