Eye Movements I and II Flashcards
What are saccades?
Conjugate eye movements that can be generated reflexively or voluntarily; they are ballistic meaning they cannot respond to subsequent changes in the position of a target during the course of eye movement
What is smooth pursuit?
Slower, conjugate movements that keep a moving stimulus on the fovea.
What are optokinetic reflexes?
Reflexive eye movements to a slow-moving broad visual field. Does NOT require processing of visual signals by visual cortex
What is optokinetic nystagmus?
Normal reflexive response of eyes to large-scale movements (occurs in both smooth pursuit and optokinetic responses)
What is the vestibulo-ocular reflex?
The vestibular system triggers reflexive eye movements in the opposite direction during head movement. Comparison of the eye velocity/head velocity is referred to as the gain which is near 1.
What is gaze?
The additional movement of the head combined with the movement of the eyes.
What would happen if the vestibulo-ocular reflex were not suppressed during saccades?
During a combined head movement, it would be counter-productive if the vestibulo-ocular reflex were not suppressed. Becomes active again once the fovea reaches the target, allowing eyes to be fixed on a target
What causes overshoot dysmetria?
Patients with vestibular lesions, since they don’t make the reverse eye movements when the fovea reaches the target
At what degree difference does gaze need to occur in order to find a target (as opposed to moving the eyes alone)
about 20 degrees
When there is a head movement to the LEFT, which medial vestibular nucleus is activated? Which side abducens nucleus is activated and which is inhibited?
Head movement to LEFT activates the LEFT medial vestibular nucleus. The LEFT abducens nucleus is inhibited (and thus the right oculomotor is inhibited via MLF) and the RIGHT abducens nucleus is activated (and thus the left oculomotor is activated via MLF)
What structure mediates horizontal saccades? What structure mediates vertical and torsional saccades?
Paramedian pontine reticular formation (PPRF) mediates horizontal saccades
Mesencephalic reticular formation (MRF) mediates vertical saccades
If the RIGHT frontal eye field is activated, which PPRF is activated? Which abducens nuclei is activated as a result?
Right frontal eye field via the superior colliculus activates the left PPRF.
Left PPRF activates the left abducens and inhibits the right abducens.
Activation of the left abducens also activates the right medial rectus via MLF.
What nucleus integrates the ‘burst signal’ from the PPRF and transforms it into a step signal?
The prepositus nucleus
What structure participates in eliciting gaze movements?
The tectospinal tract, originating from the superior colliculus
If there is lesion to the right frontal eye field, where will the eyes gaze?
To the RIGHT (side of the lesion)
What provides inputs to the frontal eye field?
Region near the intraparietal sulcus (near area 7). So the parietal sulcus plays a role in choosing the targets of interest
Damage to what area causes a limited deficit in generating smooth pursuit?
Middle and superior temporal visual areas
What is strabismus?
When movement of one eye is defective, so the expected movement of the eye does not occur
What is exotropia and esotropia?
Exotropia = abnormal lateral deviation (abduction) of the wandering eye. Esotropia = abnormal medial deviation (adduction) of the wandering eye
What is it called when children with strabismus that is not corrected?
Amblyopia, or a lack of visual perception from one eye. The brain ignores input from the ‘lazy eye’
What is the most common cause of strabismus, and what is the inciting agent?
Most common cause is a 6th nerve palsy, due to damage by ICP increase or head trauma
Does damage to the right abducens nerve cause right eye esotropia or exotropia?
Esotropia (the eye deviates inward, in the direction of the medial rectus muscle since the lateral rectus is no longer working)
What is the most common cause of compression of CN 3?
Posterior communicating artery berry aneurysm
If you have a lesion of the RIGHT abducens nucleus, what will be the resulting deficit in the eye?
Both eyes are impacted. The right lateral rectus will not be functioning, nor will the left medial rectus, thus rightward eye movements are impacted. Leftward eye movements are relatively normal. Some esotropia may be present in the right eye because the right LR isn’t working
If there is a lesion of the right PPRF, what is impacted?
Prevents rightward saccade movements. Left eye movements are normal, but neither eye moves rightward when attempted.
What is the deficit in eye movement if the left MLF is affected?
The control of the lateral recti muscles is intact, but the right abducens cannot communicate with the left oculomotor. Thus, moving right results in the right eye moving normally (because of the intact right abducens) but the left eye will not move (because of the disrupted connection to the left oculomotor and left medial rectus). Right eye shows nystagmus with downward gaze
