Oculomotor Function

Question 1

What are three visually guided eye movements? What do they do?

Answer 1

VOR- steady scene against movement
foveal pursuit- bring objects of interest to fovea by following it
convergence- change plane of focus for depth vision

Question 2

Does the forebrain or the brainstem tell eyes to track an object in foveal pursuit?

Answer 2

forebrain (frontal eye fields)

Question 3

What is the accomodation reflex?

Answer 3

constriction of pupils when following an object near

Question 4

What is damaged in internuclear opthalmoplegia (INO)?

Answer 4

mlf

Question 5

What are the symptoms of INO?

Answer 5

affected eye shows impaired adduction (can’t move past midline), contralateral eye shows abducting nystagmus

Question 6

What is preserved in INO? why?

Answer 6

convergence, it is driven by CN III nuclei not by mlf

Question 7

How does the forebrain play into vision?

Answer 7

decision making- decides where and when you look

Question 8

What drives voluntary saccades? Can you still pursue objects if this structure is damaged?

Answer 8

frontal eye fields, yes you can still pursue if they are damaged

Question 9

What does the right front eye field do?

Answer 9

turns eyes left

Question 10

What processes info from V1 related to directing hand/eye to follow an object?

Answer 10

superior parietal cortex

Question 11

What is oculomotor apraxia? What does this look like in the patient?

Answer 11

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

Question 12

What is the PPRF?

Answer 12

where the horizontal saccade generators are, next to CN VI

receives message from frontal eye fields to activate CN VI and III via mlf

Question 13

How do the inhibitory bursters affect PPRF function?

Answer 13

makes it easier to turn eyes in the right direction when the antagonist muscles are inhibited too

Question 14

What is CN VI palsy?

Answer 14

lateral rectus doesnt work in pursuits or saccades

Question 15

What is oscillopsia?

Answer 15

sense that visual scene is moving

Question 16

What does a step change in neural activity do to saccade of eye?

Answer 16

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

Question 17

What does a pulse change in neural activity do to saccade of eye?

Answer 17

with a burst of electrical activity, eye quickly jerks to new position but inertia drags it back

Question 18

What does a pulse change with a step change in neural activity do to saccade of eye?

Answer 18

burst of activity and increase in tonic firing rate gets it to move fast enough to right position and stay there

Question 19

What do burst cells do?

Answer 19

pick the burst amplitude and firing rate needed to generate saccade

Question 20

What does the integrator do?

Answer 20

integrates the burst over time to determine the new firing rate to tell to the tonic cells which maintain the new rate

Question 21

If the integrator or tonic cells are damaged, what would happen?

Answer 21

eye would reach target but would have trouble holding there

Question 22

What happens with partial burster loss?

Answer 22

sliding saccade, slow movement to target and problem holding position there

Question 23

Where is the vertical saccade generator?

Answer 23

midbrain near CN III

Question 24

Where is the horizontal saccade generator?

Answer 24

pons near CN VI

Question 25

What happens with cerebellar induced nystagmus?

Answer 25

problem with integrator, can make saccade but can’t hold it so drifts back

Question 26

What is opsoclonus?

Answer 26

eyes make quick jerking random saccades because of a loss of pause cells

Question 27

If there is a saccade generator problem, does it affect both eyes?

Answer 27

yes, since it drives both eyes it affects both eyes