Internuclear ophthalmoplegia

Question 1

What is the role of the medial longitudinal fasciculus (MLF)?

Answer 1

It is a pair of tracts that allows for crosstalk between CN6 and CN 3 nuclei. It coordinates both eyes to move in the same horizontal direction. This tract is highly myelinated to allow for quick communication

Question 2

Are lesion of the medial longitudinal fasciculus unilateral, bilateral, or both?

Answer 2

Lesions may be unilateral or bilateral. Bilateral lesions are classically seen in patients with multiple sclerosis.

Question 3

How does the MLF work?

Answer 3

When looking left, the left nucleus of CN 6 fires, which contracts the left lateral rectus and stimulates the contralateral (right) nucleus of CN 3 via the MLF to contract the right medial rectus.

Question 4

What occurs if there is a lesion to the MLF?

Answer 4

Internuclear ophthalmoplegia (INO), a conjugate horizontal gaze palsy

Question 5

What is internuclear ophthalmoplegia?

Answer 5

INO is when there is lack of communication via the MLF such that when the CN 6 nucleus activates the ipsilateral rectus, contralateral CN 3 nucleus does not stimulate medial rectus firing.

Question 6

What happens to the abducting eye?

Answer 6

The abducting eye gets nystagmus due to overfiring of the CN 6 in an attempt to stimulate the contralateral CN 3.