4.19 Vestibular 3 Flashcards
What are the 2 eye reflexes we talked about for gaze stabilization?
- vestibulo-ocular reflex (VOR)
- optokinetic reflex
What is gaze stabilization
visual fixation: keeping gaze steady during head movements
What does the VOR do?
- stabilizes visual field during fast head movements
- moves the eyes in the opposite direction to the head
VOR: voluntary or automatic?
automatic
frontal control and VOR
frontal control required to suppress the VOR and move eyes with the head
What happens to the eyes when you move the head quickly
they lag behind
What type of reflex is the VOR considered?
brainstem reflex
VOR is needed to be able to do this
look L & R back and forth (as well as up/down)
Why does nystagmus occur? (VOR)
- excessive VOR stimulation
- pathological damage
VOR can’t keep up with head rotation
VOR normally does this for rotation
compensates for rotation
How can the VOR be triggered normally?
- excessive rotation
- quickly moving objects
What is pathologic nystagmus?
nystagmus with NO excessive rotation
Where is the damage with pathologic nystagmus?
in the semicircular canals or the receptors for the canals
could also be in the vestibulocerebellum or due to a problem with the otoliths
Both the optokinetic and the VOR go through this nucleus
medial vestibular nucleus
function of optokinetic reflex
- stabilizes images during slow head movements
- helps focus on larger objects int he visual field
Where does the optokinetic cut through (as well as the medial vestibular nucleus)
pretectal area
Where does the optokinetic reflex start?
receptors in the retina
Where does the VOR start?
inner ear
3 major eye movement types
- saccades
- smooth pursuits
- eye vergence
What are saccades?
fast eye movements from one object to another
What do saccades allow for?
- allows you to see new object details
- how you follow something in visual field without really realizing it
saccades go through this area
superior colliculus
What is the superior colliculus?
unconscious visual center
smooth pursuits
eye tracking to follow a moving target
smooth pursuits: voluntary or involuntary?
requires conscious effort
eye vergence
purposeful alignment of the eyes on a near target
What is eye vergence similar to? (reflex)
accommodation
How is eye vergence and accommodation reflex different?
eye vergence is purposeful
