Anatomy-Eye Movements

Question 1

Conjugate eye movements

Answer 1

Eyes move in same direction

Question 2

Vergent eye movements

Answer 2

Eyes move in opposite direction (converge or diverge)

Question 3

Saccadic eye movements

Answer 3

Rapid eye movements, no sensory feedback

Question 4

Requirement for smooth eye movements

Answer 4

Sensory feedback

Question 5

Intorsion

Answer 5

Top of eye rotates medially

Question 6

Extortion

Answer 6

Top of eye rotates laterally

Question 7

Strabismus

Answer 7

Misalignment of eyes

Question 8

Diplopia

Answer 8

Double vision

Question 9

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Answer 9

Esotropia. Bad eye pointed inwards.

Question 10

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Answer 10

Exotropia. Bad eye pointed outwards.

Question 11

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Answer 11

Hypertropia. Bad eye pointed upwards.

Question 12

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Answer 12

Hypotropia. Bad eye pointed downwards.

Question 13

What brainstem nuclei do the lower motor neurons that innervate the extra ocular muscles come from?

Answer 13

Abducens, trochlear & oculomotor nuclei. They are all in the same column as the hypoglossal nucleus.

Question 14

What components are contained in the abducens nucleus shown below?

Answer 14

1) LMNs that form CN VI and innervate lateral rectus 2) Internuclear neurons that pass through the contralateral MLF on their way to the oculomotor nucleus, here they synapse on the neurons that innervate the medial rectus. This system makes sure that the medial & lateral rectus contract simultaneously.

Question 15

What role does the abducens nucleus play in convergence?

Answer 15

None. Stimulation goes straight to the medial rectus muscles to cause convergence when an object is close.

Question 16

List 4 ways you could damage the abducens nerve.

Answer 16

ICA aneurism, increase ICP that compresses it on the petrous temporal bone, AICA aneurism or a stroke of the ventral pons.

Question 17

A patient presents to the ED after a car accident. He has increased intracranial pressure and is complaining of horizontal diplopia. Physical exam reveals an adducted right eye on attempted forward gaze. What other physical exam tests will you do?

Answer 17

This patient likely has a right CN VI injury. You would have the patient attempt to gaze right. The right eye would remain forward and the left eye would go right. On attempted left gaze and convergence everything should be normal because you do not need the lateral rectus to do these things.

Question 18

A patient presents to the ED after a car accident. He has increased intracranial pressure. Physical exam reveals that both eyes deviate left on attempted forward gaze. What other physical exam tests will you do?

Answer 18

This patient has a lesion in the right abducens nucleus. This causes unopposed action of the right medial rectus and left lateral rectus and patients can’t look towards the side of the lesion. When asked to look right, the patient will only be able to look forward. Looking left & convergence will be normal.

Question 19

A patient with MS presents with a left eye that is slightly turned outward. On physical exam, the patient cannot move the left eye past the midline when asked to look right. He also has monocular nystagmus in the right eye. What is your diagnosis?

Answer 19

He has a right MLF lesion affecting the medial rectus movements. Left gaze & convergence will be normal.

Question 20

Where do the structures indicated below course as they exit the brainstem?

Answer 20

These are trochlear nerves. they cross and go around the brainstem to innervate the contralateral superior rectus muscle.

Question 21

Main actions of the superior oblique muscle when looking forward. What happens when CN IV is lesioned?

Answer 21

Intortion and depression. When lesioned the eye will extort and elevate.

Question 22

Main actions of the superior oblique when the eye is adducted. What happens when CN IV is lesioned?

Answer 22

Depress. When lesioned it will present as elevated when adducted.

Question 23

How do children compensate for superior oblique weakness?

Answer 23

When the superior oblique, the eye is extorted and elevated. They will compensate by tilting their head to line up the bad eye’s visual axis and a vestibulocular reflex causes the good eye to intort and match it.

Question 24

Extra ocular muscles innervated by the oculomotor nucleus.

Answer 24

Superior rectus, medial rectus, inferior rectus, inferior oblique, levator palpebrae superioris. The ciliary body and sphincter pupillae also get sympathetic fibers that run with CN III.

Question 25

A patient presents with complete right-sided ptosis. You lift up the eyelid and the eye is abducted and depressed. The pupil is blown. Physical exam reveals no pupillary light reflex in the right eye and inability to accommodate as you move your finger toward his nose. What is causing these symptoms?

Answer 25

CN III lesion. This causes all muscles except the lateral rectus (abduction) and superior oblique (abduct & depress) to be paralyzed, pushing the eye down and out. It also gets the LPS muscle, causing complete ptosis. Destruction of preganglionic sympathetic fibers causes absence of pupillary light reflex in the affected eye.

Question 26

What is the pathway to produce conjugate saccade to the lateral side?

Answer 26

The cortex sends a signal to the horizontal gaze center (near the reticular formation in the pons). The horizontal gaze center sends an excitatory signal to the abducens nucleus. This causes direct firing of the lateral rectus and stimulation of CN III nucleus to fire the contralateral medial rectus.

Question 27

What is the pathway to produce conjugate vertical saccade?

Answer 27

The cortex sends a signal to the vertical gaze center (near the reticular formation in the midbrain). The vertical gaze center sends an excitatory signal to the ipsilateral CN III & IV nuclei and contralateral vertical gaze center via the posterior white commissure.

Question 28

How does movement of your head to the right initiate movement of your eyes to the left?

Answer 28

Firing of the RT vestibular nerve -\> RT vestibular nucleus -\> Left CN VI nucleus -\> left CN VI goes to lateral rectus -\> right CN III nucleus -\> right CN III goes to right medial rectus

Question 29

What if your are turning your head to the right, but you don’t want the vestibulocular reflex to push the eyes to the left?

Answer 29

The cerebellum sends an inhibitory signal to the right vestibular nucleus -\> Inhibits stimulation of the left CN VI nucleus

Question 30

Why does the vestibulocular reflex still work when your horizontal gaze center is lesioned?

Answer 30

The vestibulocular reflex does not use the horizontal gaze center. You just would not be able to make voluntary horizontal gaze movements.

Question 31

What region of the brain is involved in reflex saccades in response to stimuli?

Answer 31

Superior colliculus. It has projections that go to the contralateral horizontal & vertical gaze centers.

Question 32

What cortical region produces contralateral horizontal gaze movements?

Answer 32

The frontal eye field sends projections to the contralateral gaze centers to produce vertical or horizontal voluntary saccades.

Question 33

What cortical region produces saccades in response to trying to focus on a visual target.

Answer 33

Posterior parietal area. It connect to the frontal eye field and gaze centers to produce visually guided saccades.

Question 34

A patient presents to the clinic with an inability to look to his left and a preference to gaze towards his right. What other assessments might you do to determine where his possible lesion is?

Answer 34

The frontal eye field and CN VI both produce lateral gaze movements. A FEF lesion would also come with motor symptoms because it is near the motor cortex. If this patient had a FEF lesion it would be on the right because the fibers cross the the horizontal gaze centers and the patient would not be able to look left.

Question 35

What cortical region conveys information about a visual target to the cerebellum?

Answer 35

V5.