Oculomotor Function Flashcards
What are three visually guided eye movements? What do they do?
VOR- steady scene against movement
foveal pursuit- bring objects of interest to fovea by following it
convergence- change plane of focus for depth vision
Does the forebrain or the brainstem tell eyes to track an object in foveal pursuit?
forebrain (frontal eye fields)
What is the accomodation reflex?
constriction of pupils when following an object near
What is damaged in internuclear opthalmoplegia (INO)?
mlf
What are the symptoms of INO?
affected eye shows impaired adduction (can’t move past midline), contralateral eye shows abducting nystagmus
What is preserved in INO? why?
convergence, it is driven by CN III nuclei not by mlf
How does the forebrain play into vision?
decision making- decides where and when you look
What drives voluntary saccades? Can you still pursue objects if this structure is damaged?
frontal eye fields, yes you can still pursue if they are damaged
What does the right front eye field do?
turns eyes left
What processes info from V1 related to directing hand/eye to follow an object?
superior parietal cortex
What is oculomotor apraxia? What does this look like in the patient?
when frontal eye fields aren’t working, saccade generator and plants (vestibular nuclei) can drive eyes from below
patient jerks head past point they want to fixate on so VOR compensates to allow them to look at the target
What is the PPRF?
where the horizontal saccade generators are, next to CN VI
receives message from frontal eye fields to activate CN VI and III via mlf
How do the inhibitory bursters affect PPRF function?
makes it easier to turn eyes in the right direction when the antagonist muscles are inhibited too
What is CN VI palsy?
lateral rectus doesnt work in pursuits or saccades
What is oscillopsia?
sense that visual scene is moving
What does a step change in neural activity do to saccade of eye?
with an increase in tonic firing rate, there is a sliding saccade due to inertia of causing the eye to change position, not a fast enough saccade
What does a pulse change in neural activity do to saccade of eye?
with a burst of electrical activity, eye quickly jerks to new position but inertia drags it back
What does a pulse change with a step change in neural activity do to saccade of eye?
burst of activity and increase in tonic firing rate gets it to move fast enough to right position and stay there
What do burst cells do?
pick the burst amplitude and firing rate needed to generate saccade
What does the integrator do?
integrates the burst over time to determine the new firing rate to tell to the tonic cells which maintain the new rate
If the integrator or tonic cells are damaged, what would happen?
eye would reach target but would have trouble holding there
What happens with partial burster loss?
sliding saccade, slow movement to target and problem holding position there
Where is the vertical saccade generator?
midbrain near CN III
Where is the horizontal saccade generator?
pons near CN VI
What happens with cerebellar induced nystagmus?
problem with integrator, can make saccade but can’t hold it so drifts back
What is opsoclonus?
eyes make quick jerking random saccades because of a loss of pause cells
If there is a saccade generator problem, does it affect both eyes?
yes, since it drives both eyes it affects both eyes
