Control of eye movements

Question 1

Main function, Control Mechanism, and Effect: Vestibuloocular reflex

Answer 1

Holds images steady on the fovea during brief head rotations

Semicircular canals and the vestibular nuclei

Conjugate deviation of eyes opposite to direction of the head

Question 2

Main function, Control Mechanism, and Effect: Smooth pursuit

Answer 2

Holds image of a moving target on the fovea

Visual pathway and parietooccipital cortex
Vestibulocerebellum

Conjugate deviation toward direction of movement of object (ipsilateral to parietooccipital cortex)

Question 3

Main function, Control Mechanism, and Effect: Optokinetic

Answer 3

Holds image of the target steady on the retina during sustained head rotation

Visual pathway
Parietooccipital cortex
vestibulocerebellum
vestibular nuclei

Maitains deviation of eyes initiated by the VOR

Question 4

Main function, Control Mechanism, and Effect: Saccade

Answer 4

Brings the image of an object of interest onto the fovea

Frontal eye fields
superior colliculus
Pontine paramedian reticular formation

Rapid conjugate deviation toward opposite side

Question 5

Main function, Control Mechanism, and Effect: Nystagmus quick phase

Answer 5

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

Cortical

Quick deviation toward stimulated labyrinth
quick deviation toward inhibited cerebellum

Question 6

Main function, Control Mechanism, and Effect: Vergence

Answer 6

moves the eyes in opposite directions (disconjugate) so that images of single object are placed on both fovea

Unknown direct input to oculomotor neurons

Accommodtion to near targets

Question 7

Horizontal saccadic system

Answer 7

Voluntary: Frontal eye fields
Reflex: Superior colliculus

Frontal eye field goes to contralateral Paramedian pontine reticular formation

then goes to ipsilateral (to PPRF) and contralateral oculomotor (via the MLF)

causes both eyes to turn away from the stimulated Frontal eye field or to the same side of the PPRF

Question 8

Vertical Saccdic system

Answer 8

Frontal Eye fields and the superior colliculus

Rostralintersitial Nucleus of the medial Longitudinal fasciculus: also called the vertical gaze center
-issues in midbrain lead to damage with the inabillity to look up

Intersitital nucleus of cajal damgae usually have trouble with saccads downward

both play a factor on CN 4 (look down)
CN 3 (Look up)

Question 9

What cortexs play a factor in the voluntary and reflex saccadic eye movements

Answer 9

Supplementary and parietal eye fields: voluntary

super colliculus: reflex saccade eye movements

Question 10

What are the three types of neurons that play a factor with saccades

Answer 10

Excitatory burst neurons: burst or pulse movement of eyes towrd the target

Tonic neurons: locking on and fixing on the target

Pause neurons: Inhibit burst neurons once the target is fixed upon

Question 11

Burst cells innervation in horizontal and vertical movements

Answer 11

Horizontal: Pontine paramedian reticular formation

Vertical: Rostral interstitial nucleus of MLF

Question 12

Tonic Cells innervation in horizontal and vertical movements

Answer 12

Horizontal: Nucleus prepositus hypoglossi

vertical: Intersitial nucleus of Cajal

Question 13

Pause cells innervation in horizontal and vertical movements

Answer 13

Omnipause cells of Raphe nuclei for both vertical and horizontal

Question 14

Destructive lesion of the frontal gaze center

Answer 14

Stroke i.e.

transient conjugate eye deviation toward the side of the lesion, difficulty looking away from the lesion

Question 15

Irritating lesion of the frontal eye gaze

Answer 15

seizure i.e.

eyes deviate away from the firing gaze center

Question 16

Smooth pursuit

Answer 16

Parieto-occipital junction (brodmanns area 19)
then travels to the ipsilateral pontine nuclei
then decussates to the vestibulocerebellum
then to the ipsilateral vestibular nuclei
then to the contralateral abducens
and to the contralateral oculomotor via the MLF from the abducens nuclei

causes the eyes to slowly move in the direction of the cortical excitement

Horizontal; CN 6 and 3
Vertical: CN 3 and 4

Question 17

Optokinetic

Answer 17

Holds images of the target steady on the retina during sustained head rotation

smooth pursuit pathway and nuclei of the accessory optic system

visual target is broken when the target reaches the limit of the visual field

Eyes make a quick move in the opposite direction (optokinetic nystagmus)

Requires intact parietooccipital eye field

goes from the retina to the lateral genticulate ganglion to the primary visual cortex
to the visual association cortex
to the nuclei of the accessory optic system
to the pons
to the vestibulocerebellum
to the vestibular nuclei
to the eye nuclei
also goes to the inferior olive for corrective error movements

Question 18

How to test smooth pursuit movements and to tell if their is a lesion

Answer 18

patient visually tracks slow moving object
-optokinetic tape

lesion of the parietal lobe will cause loss of smooth pursuit movements towards the side of the lesion

also no optokinetic nystagmus when tape is moved toward the damaged lobe

Question 19

Internuclear Ophthalmoplegia (INO)

Answer 19

Characterized by impaired horizontal eye movements

• weak adduction of the affected eye
• abduction nystagmus of the contralateral eye when attempting to adduct the other eye

Resulting from a lesion in the medial longitudinal fasciculus

convergence is normal

abducens eye is good

oculomotor eye is bad when looking ADducting

Question 20

What happens if I cant look both eyes one direction

Answer 20

issue with the ipsilateral abducens nucleus

Question 21

What is the pathway of the near reflex

Answer 21

also called the accomadation reflex or vergence

visual pathway
visual association complex
to the superior colliculus or the pretectal area
then to oculomotor area and the edinger westphal nucleus

Convergence - Adduct both eyes
Accommodation: lens thickens for near sight
pupillary constriction: better optical performance

Process bypasses MLF

Question 22

Argyll Robertson pupil

Answer 22

absent light reflex but pupil constricts in near reflex testing