Eye Movements Flashcards
What are the functions of the vestibulo-ocular and optokinetic reflexes?
Keep the eyes still while the head moves
What is the function of saccades?
Change what we’re looking at
What is the function of pursuit and fixation?
Keep an object’s image focused on the fovea
What is the function of vergence?
To change the plane of an object
What direction of eye movements is the riMLF responsible for?
Vertical
What direction of eye movements is the PPRF responsible for?
Horizontal
What are the two pathways of the vestibulo-ocular reflex?
Direct: CN VIII nucleus–> CN VI contralateral
CN VI–> lateral rectus of contralateral eye
CN VI–> CN III
CN III–> Medial rectus of ipsilateral eye
Indirect: CN VIII –> Nucleus propostius hypoglossi (NPH)
What is the function of the indirect vestibulo-ocular pathway (through the NPH)?
Low energy steady firing of the nerves to keep the eyes in position
What is the optokinetic reflex based on?
Visual input (vs. vestibular input in vestibulo-ocular)
What is the purpose of the optokinetic reflex?
Stabilize vision during slow or constant velocity head movement
What are the two components of the optokinetic reflex movement?
Quick pursuit
Slow saccade
Which of the following is constant and which is variable in saccades? Velocity, amplitude, direction
Velocity is constant
Amplitude and direction are variable
What kind of stimuli triggers saccades?
Visual, auditory, or any other kind (tap on the shoulder)
What is the function of frontal eye field (FEF)?
Directs brain stem to move eyes
What is the function of supplementary eye field (SEF)?
Has learned sequences of saccades
What’s the function of the prefrontal cortex?
The dorsolateral prefrontal cortex contains memories of objets and decision making about whether to look or not
What’s the pathway of saccades starting from the FEF?
FEF–> internal capsule–> superior culliculus–> contralateral PPRF–> contralateral abducen nucleus
MLF carries signal to ipsilateral CNIII nucleus–> medial rectus
What is the function of pause neuron in saccades?
Inhibits the PPRF from making a saccade
What is the function of the inhibitory neuron?
Inhibits the pause neuron but also sends signal to ipsilateral (to frontal cortex) CNVI nucleus not to hold up the eye movement.
What is the function of the parietal occipitotemporal area?
Provides velocity information to the FEF in pursuit movements
What is the difference in relationship between FEF and the abducen nucleus in pursuit vs. saccades?
In saccades, the FEF sends information to the contralateral abducen nucleus, while in pursuit, it sends info to the ipsilateral nucleus
What would be the effect of a cortical lesion on saccades?
Eyes would point towards the lesion (away from the hemiperesis)
What would be the effect of pontine lesion on saccades (affecting the abducen nucleus)?
Eyes would point away from the lesion
What would be the effect of a unilateral lesion affecting the MLF on saccades?
The ipsilateral eye would not be able to adduct during saccades or pursuit
It would be able to adduct during vergence
