21. Control of Eye Movement Flashcards
what does normal eye movement require
head movement (vestibular info)
visual objects (vision)
eye movement & position (proprio)
selection of a visual target (br.stem & cortical areas)
what are supranuclear gaze control systems
saccadic
smooth pursuit
vestibular-ocular
vergence
how does the saccadic system horizontal work
rapid eye movement that brings image of object onto the fovea
starts in frontal eye fields –> cross to opposite PPRF –> CN 6 (some fibers from CN 6 use MLF fibers to innervate contralat CN 3
==> right frontal eye field stimulated –> both eyes look left
How does the saccadic system vertical work
rapid eye movement that brings image of object onto the fovea
frontal eye field –> riMLF –> CN 4, CN 3
==> vertical gaze
what contributes to the reflex saccadic eye movement
supplementary & parietal eye fields & superior colliculus
what are the 3 neurons needed for saccades movement
burst neuron: firing to move eyes toward target
tonic neuons: firing for final locking on and fixing on the target
pause neurons: inhibit burst neurons –> no further movement (prevent jump back to original state
*seperate controls for vertical/horizontal movements*
what is the pathology of the frontal gaze center (saccadic movements)
ask the pt to visually jump from 1 object to next
destructive lesion (stroke): transient conjugate eye deviation towards the side of the lesion, difficulty looking away
seizure activity: eye deviates away from firing gaze center
how does smooth pursuit work
keeps moving objects centered on the fovea
parieto-occipital jxn (brodmann’s area 19) to pontine nuclei –> cross to other side –> to vestibulocerebellum –> to vestibular nuclei –>cross back to CN 6 nuclei –> supply ipsi eye & also use MLF to synapse at the contralat CN3 to contralat eye
==> right region stimulated –> eyes move right
How does optokinetics work
hold images of the target steady on the retina during sustained head rotation (both eyes & head are moving
normal path (retina –> LGN –> V1 –> THEN –> visual association cortex –> nuceli of accessory optic system & nucleus of optic tract –> pons –> vestibulocerebellum –> vestibular nuclei –> CN 3, 4, 6
visual target broken –> when at limit eyes move back quickly (optokinetic nystagmus)
*require parietooccipital eye field
what is the pathology associated with smooth pursuit movements
test: tape or track slow moving object
lesion of parietal lobe causes loss of smooth pursuit movement toward the side of the lesion
no optokinetic nystagmus
how does the vestibular-ocular system work
holds images steady on fovea during head movement
turn head –> activiate ipsi labyrinth –> use CN8 to vestibular nuclei –> cross & synapse at CN 6 –> send fiber to contralat eye & use MLF to cross back and synapse at CN 3 –> CN3 3 innervate ipsi eye
eyes move opposite to head
how do you test vestibular-ocular movements
doll’s eye maneuver : eyes move opp of head
ice water caloric: eyes deviate toward iirgated ear w/ normal nystagmus (must be conscious) cold - opp & warm same side
-in comatose pts w/ dysfxn at the level of br.st- these will be absent
what occurs in internuclear opthalmoplegia (INO)
characterized by impared horizontal eye movements -
- weak adduction of affected eye (eye stays facing forward)
- abduction nystagmus of contralat eye (eye that does move has nystamgus)
bc of lesion of MLF (pons or midbrain)
what is the pathology assocaited with vergence
test- pt focuses on near object –> lead to near reflex
pathology argyll-robertson pupil (neurosyphilis)
-absent light reflex but pupil constricts in near reflex testing
what happens if you have a lesion by the riMLF
common lesion = pineal tumor
= probs with vertial saccades
