Control of Eye Movements

Question 1

What are the important players in terms of controlling eye position?

Answer 1

MLF (medial longitudinal fasciculus, reflexes and cerebral centers)

Question 2

What is saccadic movement? How about smooth pursuit?

Answer 2

Chopped up focus/rapid eye movements trying to focus an image on the fovea (scanning the room)
Smooth pursuit keeps a moving image centered on the fovea when head isn’t moving

Question 3

What is vestibulo-ocular eye movement? How about vergence?

Answer 3

Holds image steady on fovea while head is moving

Keeps image steady on fovea when trying to see near and far

Question 4

What is optokinetic eye movement?

Answer 4

keep image on retina while following a target

Question 5

What are the major players involved in saccadic movement?

Answer 5

Frontal eye field (voluntary) and superior colliculus (reflexive)

Question 6

What is the relay center for horizontal saccades and which part of the brainstem is it located? Which CNs are important for this?
What about vertical saccades?

Answer 6

Contralateral paramedian pontine reticular formation (PPRF/horizontal gaze center) in pons. CN III and VI
Rostral interstitial nucleus of the MLF (riMLF)/vertical gaze center in midbrain. CN IV and VI

Question 7

Draw the pathway for horizontal saccades

Answer 7

Ok

Question 8

Which frontal eye field and PPRF are active when eyes are turning left?
Lesion in the PPRF results in?

Answer 8

Right frontal eye field and left PPRF (and vice versa)

Both eyes cannot look to the side of the lesion

Question 9

What happens when you have a pineal tumor?

Answer 9

Compression of the superior colliculus and posterior commissure = problems with vertical saccades

Question 10

Damage to the nucleus of Cajal and red nucleus results in?

Answer 10

Problems with downward saccades since the circuit passes through this general area (medial midbrain)

Question 11

What are the major players involved for reflexive saccades?

Answer 11

Supplementary and parietal eye fields and superior colliculus

Question 12

Explain the mechanism for enabling saccadic control

Answer 12

Excitatory burst that moves eye towards the target > tonic neuron firing which locks the target on the fovea > pause neurons to hold the image still

Question 13

What are the burst, tonic and pause cells for horizontal saccades?

Answer 13

Burst: PPRF
Tonic: Nucleus prepositus hypoglossi
Pause: omnipause cells of Raphe nuclei

Question 14

What are the burst, tonic and pause cells for vertical saccades?

Answer 14

Burst: riMLF
Tonic: Interstitial nucleus of Cajal
Pause: Omnipause cells of raphe nuclei

Question 15

How do you test saccadic movement?

Answer 15

Visually jump from one object to another

Question 16

Saccades:
Destructive lesion to the frontal gaze center means?
Seizure (irritating) activity to the frontal gaze center means?

Answer 16

Eyes are deviated toward the lesioned eye field (that guy whose eyes are stuck to the left)
Eyes are deviated away from the lesioned eye field

Question 17

What are the major players of the smooth pursuit pathway?

Answer 17

Parieto-occipital junction (area 19)
Vestibulocerebellum
Medial vestibular nuclei
MLF

Question 18

Draw the smooth pursuit pathway

Answer 18

Ok

Question 19

Smooth pursuit: If we are moving eyes left, which hemisphere is stimulated?

Answer 19

Left hemisphere (and vice versa)

Question 20

Draw the optokinetic pathway

Answer 20

Ok

Question 21

How would you test smooth pursuit movements?

Answer 21

Visually track slow moving object (using optokinetic tape) and see optokinetic nystagmus

Question 22

When is optokinetic movement lost?

Answer 22

Lesions of parietal lobe equals loss of smooth pursuit towards side of lesion. No Optokinetic nystagmus when tape is moved towards side of damaged lobe

Question 23

Draw the vestibulo-occular reflex pathway again

Answer 23

OK

Question 24

How do you test vestibulo-ocular movements?

When are these tests absent?

Answer 24

Doll’s eye maneuver and ice water caloric

These will be absent in patient with brainstem level lesion

Question 25

What are doll’s eye maneuver and ice water caloric tests?

Answer 25

Doll’s eye - eyes move in opposite direction of head turning

Ice water caloric - nystagmus to irrigated ear

Question 26

Internuclear Ophtalmoplegia (INO)
Cause
Clinical

Answer 26

• MLF lesion (ipsilateral to eye that cannot abduct)

- Weak adduction in affected eye and abduction nystagmus of contralateral eye

Question 27

Draw out the differences between INO (MLF lesion), CN VI nucleus lesion and CN VI palsy

Answer 27

Ok

Question 28

Compare and contrast INO, CN VI nucleus lesion and CN VI palsy

Answer 28

INO: affected eye cannot adduct, other eye has nystagmus
CN VI nucleus: both eyes cannot move to the side of lesion from central position
CN VI palsy: cannot laterally move affected eye

Question 29

What is needed to have the near reflex?

Answer 29

Convegence so image is on fovea (MLF is bypassed)
Pupillary constriction for better optical performance
Accommodation to thicken lens so image is focused on fovea

Question 30

Describe the pathway of the Near reflex

Answer 30

Normal visual pathway > visual association cortex > superior colliculus, pretectal area or both > CN III (adduction of MR) and EWN (pupillary constriction)

Question 31

How would you test vergence?

Answer 31

Make patient focus on a near object and you should see vergence

Question 32

Argyll Robertson pupil

Answer 32

Absent light reflex, but pupil constricts during near reflex testing
Associated wit heurosyphilis