Control of Eye Movements

Question 1

What do normal eye movements require?

Answer 1

Head movements = vestibular info

Visual objects = vision

Eye movement and position = proprioceptive info (LMN)

Selection of visual target = brainstem and cortical areas

Question 2

What do you need to control eye position?

Answer 2

Medial longitudinal fasiculus

Reflexes

Cerebral centers

Question 3

Describe saccadic.

Answer 3

Rapid eye movements that bring image of object onto fovea

Jumpy

Question 4

Describe Smooth Pursuit.

Answer 4

Keeps moving image centered on fovea.

Question 5

Describe Vestibular-ocular. Control systems?

Answer 5

Holds image steady on fovea during head movement.

Control systems:
Semicircular canals
Vestibular nuclei

Question 6

Describe Vergence. Control systems?

Answer 6

Keeps image on fovea when object is moved near

Control systems:
Unknown direct input to oculomotor neurons, likely through interneurons

Question 7

Name the conjugate movements.

Answer 7

Saccadic

Smooth pursuit

Vestibular-ocular

Question 8

Name the disconjugate movements.

Answer 8

Vergence

Question 9

Describe Optokinetic movement. What happens at the end?

Answer 9

Smooth pursuit + head movement
Smooth pursuit + nuclei of accessory optic system

Hold image of target steady on retina during sustained head rotation

Requires intact parietooccipital eye field

At the end:
Visual target is broken when target reaches limit of visual field
Eyes make quick move in the opposite direction = optokinetic nystagmus

Question 10

Describe Nystagmus quick phase. Control mechanism?

Answer 10

Directs fovea toward oncoming visual scene during self-rotation; resets eyes during prolonged rotation.

Control mechanism:
Cortical

Question 11

What are the control mechanisms of horizontal saccadic system?

Answer 11

Frontal eye fields - voluntary saccades

Superior colliculus - reflexes

Pontine paramedial RF (PPRF) - horizontal gaze center

CN 6 + CN 3

Question 12

What are the control mechanisms of vertical saccadic system?

Answer 12

Frontal eye fields

Superior colliculus

Rostral Interstitial Nucleus of Medial Longitudinal Fasiculus (riMLF) - vertical gaze center

CN 4 + CN 3

Question 13

Where is the riMLF found?

Answer 13

Near the superior colliculus and posterior commissure

Question 14

What does a tumor of the pineal gland compress?

Answer 14

Superior midbrain leading to selective palsies of vertical gaze

Question 15

What does a lesion near the red nucleus lead to?

Answer 15

Selective palsies where you cannot look down

Question 16

How does horizontal saccadic eye movement occur? What is the ultimate effect?

Answer 16

Input sent to the contralateral abducens nuclei at the PPRF. (Input = frontal eye fields)

There abducens nerve fibers will run to the contralateral lateral rectus muscle.

Or send nerve fibers to the ipsilateral oculomotor nucleus using the medial longitudinal fasciculus.

Never fibers synapse there and CN 3 nerve fibers leave to innervate the ipsilateral medial rectus muscle.

Ultimate effect = rapid conjugate deviation toward OPPOSITE SIDE

(ipsilateral and contralateral in relation side “activated” - so right frontal field activation will lead to activation of the right medial rectus and the left lateral rectus are activated. Right frontal field = left movement of eye)

Question 17

What contributes to reflexive saccadic eye movements?

Answer 17

Supplementary and Parietal eye fields

Superior colliculus

Question 18

What needs to happen for a saccadic movement to occur?

Answer 18

1) BURST of neuronal firing = excitatory burst neurons
To move eyes toward target

2) TONIC neuronal firing = tonic neurons
For locking and fixing on target

3) PAUSE neurons = inhibit burst neurons once target is fixed so no further movement occurs

Question 19

Control centers for saccadic movement is different for horizontal and vertical movements. What are the control centers for HORIZONTAL MOVEMENT?

Answer 19

Burst cells = PPRF

Tonic cells = Nucleus prepositus hypoglossi

Pause cells = Omnipause cells of Raphe nuclei

Question 20

What are the control centers for VERTICAL MOVEMENT?

Answer 20

Burst cells = Rostral interstitial nucleus of MLF

Tonic cells = Interstitial nucleus of Cajal

Pause cells = Omnipause cells of Raphe nuclei

Question 21

Where on the brainstem are vertical and horizontal gaze center found?

Answer 21

Vertical = midbrain region

Horizontal = PONS, upper medulla

Question 22

What happens if you have a destructive lesion at the frontal gaze center?

Answer 22

Eye deviates TOWARD side of lesion

Difficulty looking away from lesion

Question 23

What happens if you have seizure activity at the frontal gaze center?

Answer 23

Eyes deviates AWAY from firing gaze center

Question 24

What are the control mechanisms for smooth pursuit?

Answer 24

Parietooccipital cortex (Brodmann’s area 19)

Vestibulocerebellum

Pons

Medial vestibular nuclei (horizontal - CN 6+3, vertical - CN 4+3)

Question 25

Describe the pathway through which smooth pursuit occurs. What is the ultimate effect?

Answer 25

Ultimate effect = conjugate deviation TOWARD direction of movement of object -- ipsilateral to Parietooccipital cortex Suppose the RIGHT Parietooccipital cortex is activated. It will send fibers to the RIGHT pontine nuclei --> LEFT vestibulocerebellum --> LEFT Vestibular nuclei The contralateral vestibular nuclei will send fibers to the ipsilateral (RIGHT) Abducens nuclei. CN 6 fibers will then go to the ipsilateral (RIGHT) lateral rectus. Other fibers from the Abducens nuclei --> contralateral (LEFT) oculomotor nuclei --> LEFT medial rectus Right activation = right movement of eyes

Question 26

What are the control systems of the Optokinetic eye movements?

Answer 26

Visual pathway and parietooccipital cortex Vestibulocerebellum Vestibular nuclei

Question 27

What would you ask a patient to do to test saccadic movement?

Answer 27

Ask them to jump from one object to the next.

Question 28

What would you ask a patient to do to test smooth pursuit?

Answer 28

Have them visually track a slow moving object Look at an Optokinetic tape

Question 29

If a patient had a lesion at the parietal lobe, what would be affected in regards to eye movement?

Answer 29

There will be a loss of smooth pursuit movement toward side of lesion. No optokinetic nystagmus when tape is moved toward damaged lobe.

Question 30

Describe the pathway through which vestibular-ocular system occurs. What is the ultimate effect?

Answer 30

Ultimate effect = movement of eye OPPOSITE to head rotation So suppose the head turns to the RIGHT: it activates the RIGHT labyrinth CN 8 will travel from RIGHT labyrinth --> RIGHT vestibular nuclei --> Fibers to contralateral (LEFT) abducens nuclei --> Abducens nuclei --> contralateral (LEFT) lateral rectus Abducens nuclei --> MLF --> ipsilateral (RIGHT) oculomotor nucleus --> ipsilateral (RIGHT) medial rectus

Question 31

What is internuclear ophthalmoplegia (INO)? What causes it?

Answer 31

Impaired horizontal eye movements Weak adduction of affected eye Abduction nystagmus of contralateral eye Cause = lesion in MLF

Question 32

What needs to happen for the near reflex to occur?

Answer 32

Convergence = image on the fovea Accommodation = lens thickens to image focused on fovea Pupillary constriction = better optical performance

Question 33

Describe the pathway for the near reflex or vergence?

Answer 33

First - normal visual pathway synapsing at LGN and then primary visual cortex Then - PVC sends fibers to Visual association cortex Visual association cortex --> superior colliculus or pretectal plate or both --> Oculomotor n. and Edinger-westphal nucleus Oculomotor n. to make the eyes converge and EWN for pupillary constriction

Question 34

How would you test a patient's vestibular-ocular movements?

Answer 34

Doll's eye maneuver = eyes move in opposite direction of head turning Ice water caloric = COWS

Question 35

When would you see a deficiency in vestibular-ocular movements?

Answer 35

In a comatose patient with dysfunction at the level of the brainstem Doll's yes and Ice water caloric will be absent

Question 36

How would you test vergence?

Answer 36

Have patient focus on near object and see if near reflex occurs

Question 37

What is Argyll-Robertson pupil?

Answer 37

Occurs from neurosyphilis | Absent light reflex but pupil constricts in near reflex testing