Control of eye movements Flashcards
Main function, Control Mechanism, and Effect: Vestibuloocular reflex
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
Main function, Control Mechanism, and Effect: Smooth pursuit
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)
Main function, Control Mechanism, and Effect: Optokinetic
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
Main function, Control Mechanism, and Effect: Saccade
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
Main function, Control Mechanism, and Effect: Nystagmus quick phase
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
Main function, Control Mechanism, and Effect: Vergence
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
Horizontal saccadic system
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
Vertical Saccdic system
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)
What cortexs play a factor in the voluntary and reflex saccadic eye movements
Supplementary and parietal eye fields: voluntary
super colliculus: reflex saccade eye movements
What are the three types of neurons that play a factor with saccades
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
Burst cells innervation in horizontal and vertical movements
Horizontal: Pontine paramedian reticular formation
Vertical: Rostral interstitial nucleus of MLF
Tonic Cells innervation in horizontal and vertical movements
Horizontal: Nucleus prepositus hypoglossi
vertical: Intersitial nucleus of Cajal
Pause cells innervation in horizontal and vertical movements
Omnipause cells of Raphe nuclei for both vertical and horizontal
Destructive lesion of the frontal gaze center
Stroke i.e.
transient conjugate eye deviation toward the side of the lesion, difficulty looking away from the lesion
Irritating lesion of the frontal eye gaze
seizure i.e.
eyes deviate away from the firing gaze center
Smooth pursuit
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
Optokinetic
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
How to test smooth pursuit movements and to tell if their is a lesion
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
Internuclear Ophthalmoplegia (INO)
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
What happens if I cant look both eyes one direction
issue with the ipsilateral abducens nucleus
What is the pathway of the near reflex
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
Argyll Robertson pupil
absent light reflex but pupil constricts in near reflex testing
