NB9-1 - Eye Movements and DLAs

Question 1

List the extraocular muscles, what they do, and their innervations.

Answer 1

• Medial rectus - adduction - CN-III
• Lateral rectus - abduction - CN-VI
• Superior rectus - elevation, incyclotorsion, adduction - CN-III
• Inferior rectus - depression, excyclotorsion, adduction - CN-III
• Superior oblique - incyclotorsion, depression, abduction - CN-IV
• Inferior oblique - excyclotorsion, elevation, abduction - CN-III

Question 2

What are the cortical control units in the brain? Give the brodman area if relevant and describe their locations.

Answer 2

Frontal Eye Fields - located around the intersection of the middle frontal gyrus with the precentral gyrus, consisting of a frontal and parietal portion. Brodman area 8

Parieto-occipital eye field - located around the parieto-occipital junction and consists of a parietal and occipital portion

Question 3

What neural tracts are most important for left/right conjugate lateral gazes to occur?

Answer 3

To look left/right the left eye needs to abduct/adduct and the right eye needs to adduct/abduct. For this to occur you need synchronous use of the the left abducens/oculomotor and the right oculomotor/abducens. The abducens and oculomotor nerves are located in the pons and midbrain respectively.

The medial longitudinal fasciculus (MLF) is a tract that connects the left abducens nucleus to the right oculomotor nucleus (for left lateral gaze) and the right abducens nucleus to the left oculomotor nucleus (for right lateral gaze). The MLF is crucial for synchronous movement.

Question 4

Draw out (our picture in your head) where the MLF is located in the brainstem.

Answer 4

Question 5

What are saccadic eye movements and what controls them? Does vision persist throughout the movement?

Answer 5

Saccadic eye movements are extremely fast shifts in the direction of gaze from one visual targe to another. It is voluntarily controlled through the frontal eye fields. Vision is switched off during this movement.

Question 6

Is the MLF responsible for carrying information from CN III to CN VI or the other way around? Expain why this is.

Answer 6

The frontal eye field controls saccadic eye movement and it initiates this by sending information to the paramedian pontine reticular formation (PPRF) which is located adjacent to and synapses on the abducens nucleus.

Because of this, the MLF carries signals from CN VI to CN III.

Question 7

Answer 7

D

Question 8

What is the technical term for double vision?

Answer 8

Diplopia

Question 9

Answer 9

B

You’re looking at the dot so its centered in your visual field

Question 10

Answer 10

A

Question 11

Answer 11

A

Question 12

Answer 12

B

Question 13

What is internuclear ohthalmoplegia and what usually causes it?

Answer 13

A disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction. Typically causes by an MLF lesion

Question 14

How would a lesion to the right MLF affect eye movements?

Answer 14

It would prevent adduction of the right eye

Question 15

How would a lesion to the right PPRF affect eye movements?

Answer 15

It would prevent conjugate gave of both eyes to the right

Question 16

What is one and a half syndrome and what causes it?

Answer 16

One and a half syndrome is causes by a lesion to both a PPRF and the contralateral MLF. This leads to prevention of conjugate gaze of both eyes to the right and prevents adduction of the right eye.

Question 17

Answer 17

B