Control of Eye Movements

Question 1

• What do normal eye movements require?

Answer 1

• Head movements (vestibular information)
• Visual objects
• Proprioceptive info (LMNs)
• Selection of a visual target (brainstem and cortical area)

Question 2

• What are saccades?
• What type of movement are they

Answer 2

• Rapid eye movements
• Bring image of object onto the fovea

Question 3

• What is a smooth pursuit movement?
• What type of movement is this?

Answer 3

• Keeps moving image centered on the fovea
• Conjugate

Question 4

• What is a vestibular-ocular movement?
• What type of movement is this?

Answer 4

• Holds image steady on the fovea during head movements
• Conjugate

Question 5

• What is vergence?
• What type of movement is this?

Answer 5

• Keep image on the fovea when an object is moved near
• Disconjugate (eyes are crossing-not moving in same direction to focus on target)

Question 6

Summary of the types of eye movements and their control mechanisms

Answer 6

Question 7

• What are the three types of neurons that are important in saccadic eye movements?
• Where are these neurons located?

Answer 7

• Excitatory/Burst neurons-move eyes towards target
• Tonic neurons-keep eyes locked on final target
• Pause neurons-inhibit burst neurons so no further movement occurs

Question 8

• Describe the horizontal saccade system

Answer 8

• KEY POINT WITH HORIZONTAL SACCADE: Stimulate right frontal eye field, eyes move to the left (and vice versa)
• Steps
  
  • Frontal eye field stimulated
  • Sends axons to PPRF/Horizontal Gaze Center of CONTRALATERAL Side
  • Axons project to ABDUCENS nuclei on same side of PPRF
    
    • Axons from abducens nuclei can go to
      
      • Lateral rectus m (on same side)
      • OR
      • via MLF to CN III nucleus to innervate medial rectus of opposite side

Question 9

• Describe the vertical saccade system

Answer 9

• Axons from frontal eye field travel to riMLF (Vertical Gaze Center)
• These axons travel to
  
  • CN IV nucleus (Trochlear) to innervate superior oblique m
  • or
  • CN III nucleus (Oculomotor) to innervate inferior oblique m

Question 10

• What will happen if there is a tumor of the superior mudbrain/pineal gland/ or posterior commissure?

Answer 10

• Selective palsies of vertical gaze (can’t look up)

Question 11

• What will happen if there is a tumor in the red nucleus?

Answer 11

• Selective palsies of vertical gaze
• Cant look down

Question 12

• How can you test saccadic eye movements?
• What will happen if there is a pathology of the frontal gaze center
  
  • ​Destructive lesion
  • Seizure activite

Answer 12

• Ask the patient to visually jump from one object to another (Basically ask them to scan the room)
• Destructive lesion-eyes will deviate towards side of lesion (if there is a car accident you’re driving by, your eyes will look towards it)
• Seizure activity/Irritation to the frontal eye field-eyes will deviate away (look away from something if irritated)

Question 13

• Describe the smooth pursuit pathway
• What is different about smooth pursuit and saccadic movements (besides speed?)

Answer 13

• Smooth pursuit pathway-if the parieto-occipital junction is stimulated, the eyes will move to the same side (unlike saccadic movements where if frontal eye field is stimulated and eyes look to contralateral side)
• STEPS
  
  • Parieto-occipital junction is stimulated
  • Axons relayed to pontine nuclei (IPSILATERAL side)
  • Axons from pontine nuclei sent to CONTRALATERAL vestibulocerebellum/flocculonodular lobe
  • Axons from vestibulocerebellum sent to the CONTRALATERAL ABducens nucleus
    
    • Axons sent to Lateral rectus m
    • or
    • via MLF to CN III to innervate medial rectus m

Question 14

• How do you test for smooth pursuit movements?
• Pathology-lesion of parietal lobe causes loss of smooth pursuit movements to which side?

Answer 14

• Test
  
  • H Test
  • Optokinetic . tape
• Pathology
  
  • Lesion of the parietal lobe will cause loss of smooth pursuit movements TOWARDS side of lesion
  • No optokinetic nystagmus when tape is moved toward damaged lobe

Question 15

• Describe the optokinetic reflex

Answer 15

• Holds image of target steady on retina during sustained head rotation
• Smooth pursuit pathway and nuclei of accessory optic system
• Visual target broken when the target reaches the limit of visual field (can’t look any further in that direction)
• Eyes make quick move in opposite direction (optokinetic nystagmus)
• Requires intact parieto-occipital eye fields

Question 16

• Describe the vestibulo-ocular system

Answer 16

• KEY CONCEPT: Head turned to right-eyes go to left (and vice versa, similar to the saccadic eye movements)
• STEPS
  
  • Head turned to right (as an example)
  • Right vestibular portion of CN VIII activated
  • Sends projections to vestibular nuclei (cerebellum) of IPSILATERAL side
  • Vestibular nuclei sends projections to CN VI of CONTRALATERAL side
  • CN VI sends projections to
    
    • Lateral rectus of same side of abducens nuclei
    • OR
    • via MLF to contralateral CN III nuclei to medial rectus m.

Question 17

• How do you test vestibular-ocular movements

Answer 17

• Dolls eye maneuver
  
  • Eyes move in opposite direction of head turning
• Ice water caloric
  
  • COWS mneumonic
  • REMEMBER THAT IF A PATIENT IS UNCONSCIOUS THIS WILL NOT WORK
  • REMEMBER COWS IS NAMED FOR THE DIRECTION OF THE NYSTAGMUS

Question 18

• What will happen to a patient’s vestibular-ocular reflex if there is a lesion at the brainstem

Answer 18

• Absence of ice water caloric and dolls eye reflexes

Question 19

• Internuclear opthalmoplegia (INO)

Answer 19

• Lesion in MLF (pons or midbrain)
• Patient cannot ADduct the affected eye
• ABduction nystagmus of normal eye

EX: Patient’s left MLF is damaged:

• Ask patient to look to the left( fine because the left abducens works fine and right MLF works fine)
• Ask patient to loo to the right (right eye will work fine, but since left MLF is damaged, patient cannot ADduct their left eye (or move it towards the right)
• Convergence is fine (also gives you hint that its INO)

Question 20

• Lesion summary slide

Answer 20

Question 21

• Describe the components and pathway of the near reflex

Answer 21

• Components
  
  • Convergence (so image is on the fovea)
  • Accomodation (lens thickens to focus image)
  • Pupillary constriction (narrow pupil to focus light in)
• Pathway
  
  • Vision pathway with additional axon to visual association cortex
  • Axons sent to superior colliculus/pretectal plate
  • These axons sent to CN III (Medial recti adduct) and Edinger Westphal nucleus (Constriction of pupil)
• note that this pathway does not include MLF (so despite someone having INO, they can still converge their eyes)

Question 22

• How do you test for vergence?

Answer 22

• Move finger close to patient’s face to see if their eyes move to focus

Question 23

• What is indicative of pathology of vergence

Answer 23

• Argyll Roberston pupil (often caused by neurosyphilis)
• Absent light reflex
• Pupil constricts in near reflex testing