VOR Flashcards
Stabilizes retinal image during head motion
VOR
VOR generates eye movements that are
Same speed as head motion but opposite direction to keep the target on the fovea
If you move a book in front of your eyes the words will be
Blurry. Because of no VOR. Visual info takes 100ms to get to motoneurons
If you keep a book stable but move your head the words will be
Clear - VOR active. Vestibular info takes 7-15 ms to get to motoneurons
Visual into compared to vestibular info
Visual info takes longer than VOR
Since the VOR driver is vestibular and not visual
It is operational in the dark! Unlike visual info
Change in position from side to side , up and down, or for and aft
Translation
Linear acceleration
Change in orientation, left to right, tilt up and down, roll shoulder to shoulder is
Rotational
Angular acceleration
What is the key difference in static and dynamic
Dynamic gets eyes there, while static keeps them there
Compensate for the head remaining still in single tilted or turned position
Static
Compensates for the active process of tilting or rotating the head -> accelerated change
Dynamic
Both: static and dynamic
Change the eye’s positions as the head position is changed
What is the net result of static and dynamic responses?
Eye pointing to the same place in space as before the movement
The goal of an effective VOR eye movement is to
Compensate for head movement (math the velocity)
Gain is the eye/head velocity. Which is ideally
-1.0
Phase is the temporal difference which is ideally
180 degrees
Normal values for horizontal and vertical VOR in the dark
In the dark the VOR gain is -0.9 and phase shift is 0
Worse
Normal values for horizontal and vertical VOR in light
VOR gain is -1.0 and phase shift is 0.
Light may be helped with visual input and OKN
VOR is mainly from ___.
Anterior and posterior canals
Static torsional VOR is mediated by
Otolith (not canals)
If gain is too high/low and there is a phase lead/lag they will cause
Blur and oscillopsia (imbalance )
Ig gain is too high/low there will be
Transient stability of the retinal image
If phase lead or phase lag there will be
Constant instability of the retinal image
Peripheral (labyrinth) lesions cause
Static (nystagmus) and dynamic (abnormal gain/pahse) imbalance
Would it be better to have a shorter or longer time contact (quantifying VOR)
It would be better to have a long time constant because it means you’re accomplishing the task with more time
What is the time constant?
What is the normal?
Time it takes for the GAIN to decrease to 37% of its original value
(Normal; 12-15 second)
What cab decrease time constant (Tc)
Repeated test Newborns (have lower than adults) Amblyopia Diseases ANYTHING THAT DECREASES TC IS BAD FOR YOU
Time constant is when 37% of peak v occurs. You don’t want. To leave peak so quickly meaning
You don’t want a shorter Tc
Otolith organs
Utricle and succulent
Otoliths contain ____ and ____.
Crystals attached to gelatin
And
Hair cells (sterocilia and kinocilia)
When there’s a bend towards kinocilia
Depolarization occurs
Sterocilia and kinocilia are embedded in layer and bend when
Crystals are displaced
Utricle detects
Horizontal acceleration
Saccule detects
Vertical acceleration
Inertia of the otoconia with head movements causes dereliction of the stereocilia and A
Subsequent stimulatory or inhibitory response in sensory nerve fibers within CN
When stereocilia bend away from kinocilium
Hyper polarized vestibular nerve (inhibition)
When stereocilia bend toward kinocilium
AP in vestibular nerve (excitation/depolarization)
If head is tilted right, ___ activated and ___ inhibited.
Resulting in + to___ and - to ___. IPSILATERAL INTORTION
R med utricle activated
R lat utricle inhibited
+ RSO
-RIO
IPSILATERAL INTORTION
What can go wrong with otoliths?
Skew deviation: vertical strabismus cause by supranuclear brainstem or cerebellar lesion. It has been associated with asymmetric otolith ocular inputs
