Eye Movements I and II

Question 1

What are saccades?

Answer 1

Conjugate eye movements that can be generated reflexively or voluntarily; they are ballistic meaning they cannot respond to subsequent changes in the position of a target during the course of eye movement

Question 2

What is smooth pursuit?

Answer 2

Slower, conjugate movements that keep a moving stimulus on the fovea.

Question 3

What are optokinetic reflexes?

Answer 3

Reflexive eye movements to a slow-moving broad visual field. Does NOT require processing of visual signals by visual cortex

Question 4

What is optokinetic nystagmus?

Answer 4

Normal reflexive response of eyes to large-scale movements (occurs in both smooth pursuit and optokinetic responses)

Question 5

What is the vestibulo-ocular reflex?

Answer 5

The vestibular system triggers reflexive eye movements in the opposite direction during head movement. Comparison of the eye velocity/head velocity is referred to as the gain which is near 1.

Question 6

What is gaze?

Answer 6

The additional movement of the head combined with the movement of the eyes.

Question 7

What would happen if the vestibulo-ocular reflex were not suppressed during saccades?

Answer 7

During a combined head movement, it would be counter-productive if the vestibulo-ocular reflex were not suppressed. Becomes active again once the fovea reaches the target, allowing eyes to be fixed on a target

Question 8

What causes overshoot dysmetria?

Answer 8

Patients with vestibular lesions, since they don’t make the reverse eye movements when the fovea reaches the target

Question 9

At what degree difference does gaze need to occur in order to find a target (as opposed to moving the eyes alone)

Answer 9

about 20 degrees

Question 10

When there is a head movement to the LEFT, which medial vestibular nucleus is activated? Which side abducens nucleus is activated and which is inhibited?

Answer 10

Head movement to LEFT activates the LEFT medial vestibular nucleus. The LEFT abducens nucleus is inhibited (and thus the right oculomotor is inhibited via MLF) and the RIGHT abducens nucleus is activated (and thus the left oculomotor is activated via MLF)

Question 11

What structure mediates horizontal saccades? What structure mediates vertical and torsional saccades?

Answer 11

Paramedian pontine reticular formation (PPRF) mediates horizontal saccades
Mesencephalic reticular formation (MRF) mediates vertical saccades

Question 12

If the RIGHT frontal eye field is activated, which PPRF is activated? Which abducens nuclei is activated as a result?

Answer 12

Right frontal eye field via the superior colliculus activates the left PPRF.
Left PPRF activates the left abducens and inhibits the right abducens.
Activation of the left abducens also activates the right medial rectus via MLF.

Question 13

What nucleus integrates the ‘burst signal’ from the PPRF and transforms it into a step signal?

Answer 13

The prepositus nucleus

Question 14

What structure participates in eliciting gaze movements?

Answer 14

The tectospinal tract, originating from the superior colliculus

Question 15

If there is lesion to the right frontal eye field, where will the eyes gaze?

Answer 15

To the RIGHT (side of the lesion)

Question 16

What provides inputs to the frontal eye field?

Answer 16

Region near the intraparietal sulcus (near area 7). So the parietal sulcus plays a role in choosing the targets of interest

Question 17

Damage to what area causes a limited deficit in generating smooth pursuit?

Answer 17

Middle and superior temporal visual areas

Question 18

What is strabismus?

Answer 18

When movement of one eye is defective, so the expected movement of the eye does not occur

Question 19

What is exotropia and esotropia?

Answer 19

Exotropia = abnormal lateral deviation (abduction) of the wandering eye.
Esotropia = abnormal medial deviation (adduction) of the wandering eye

Question 20

What is it called when children with strabismus that is not corrected?

Answer 20

Amblyopia, or a lack of visual perception from one eye. The brain ignores input from the ‘lazy eye’

Question 21

What is the most common cause of strabismus, and what is the inciting agent?

Answer 21

Most common cause is a 6th nerve palsy, due to damage by ICP increase or head trauma

Question 22

Does damage to the right abducens nerve cause right eye esotropia or exotropia?

Answer 22

Esotropia (the eye deviates inward, in the direction of the medial rectus muscle since the lateral rectus is no longer working)

Question 23

What is the most common cause of compression of CN 3?

Answer 23

Posterior communicating artery berry aneurysm

Question 24

If you have a lesion of the RIGHT abducens nucleus, what will be the resulting deficit in the eye?

Answer 24

Both eyes are impacted. The right lateral rectus will not be functioning, nor will the left medial rectus, thus rightward eye movements are impacted. Leftward eye movements are relatively normal. Some esotropia may be present in the right eye because the right LR isn’t working

Question 25

If there is a lesion of the right PPRF, what is impacted?

Answer 25

Prevents rightward saccade movements. Left eye movements are normal, but neither eye moves rightward when attempted.

Question 26

What is the deficit in eye movement if the left MLF is affected?

Answer 26

The control of the lateral recti muscles is intact, but the right abducens cannot communicate with the left oculomotor. Thus, moving right results in the right eye moving normally (because of the intact right abducens) but the left eye will not move (because of the disrupted connection to the left oculomotor and left medial rectus). Right eye shows nystagmus with downward gaze