VOR Flashcards
VOR Purpose and tests
What is VOR?
Vestibular Ocular Reflex.
what is the purpose of VOR testing?
To obtain obtain objective measures to support our hypothesis diagnosis. vestibular assessment will also help us with seperating peripheral and central pathologies, or disease progression and affects.
Explain the vestibulo-ocular reflex (VOR) and its purpose.
The VOR’s primary purpose is to ensure visual stability, especially during rapid or unexpected head movements to prevent blurriness and vertigo.
When the head moves, sensory receptors in the semicircular canals of the inner ear detect this movement. These receptors send signals to the brain, which then quickly sends commands to the eye muscles, instructing them to move in the opposite direction of the head movement. This coordinated response happens almost instantaneously, allowing us to retain a clear, stable image on the retina.
vestibular ocular reflex:
helps maintain stable vision. This is by producing movements which are equal and opposite in velocity and direction to any fast head movements. (about 15m/s due to short neural connections).
When do we not use the VOR and instead use the optokinetic head movements:
This is when the head movements are consist velocity or consistent motion, we use out optikinetic system to maintain these images.
Normal vestibular function results:
the eye is able to make an equal and opposite eye movement to the direction of our head moving. (1:1 relationship)
vestibular abnormality results:
information is not being placed in the input correctly, this means that it is processed in correctly. output is the VOR would not work how we expected.
how can we test VOR?
using vestibular tests such as VNG and VHIT.
Why is VOR important?
- Impaired VOR can cause retinal slip, which can cause blurred vision and postural instability and vision problems.
- the integrity of vestibular organs can be assessed through functional measurements of the VOR.
muscles involved in VOR Reflex:
These include four recti muscles, two oblique muscles, and levator palpebrae superioris. The four recti include the superior, inferior, medial, and lateral rectus. The two oblique muscles include the superior oblique and inferior oblique. These six muscles are responsible for the movement of eyes into different gazes.
Describe changes in vestibular system caused by head rotation to the left: 9 marks
- The semicircular canals are activated. Yea re looking horizontally, so the horizontal SCC detect the rotation.
- When leftward head rotation occurs, the endolymph in the left SSC lags behind due to inertia, causing the cupula to deflect towards the kinocilluim of hair cells in left canal.
- Deflection of cupula causes endolymph to move away causing hyper polarisation of hair cells and reducing firing rate in right side.
- This activity processed by vestibular nuclei In brainstem.
- we perceive left head rotation.
- The VOR is instated, to stabilise gaze during rotation.
The brainstem signal sot the ocular muscles to move right, opposite to head rotation to maintain stable vision. - Projections from vestibular nuclei to spinal cord via vestibulospinal tract to help maintain balance and postural stability during movement.
Describe changes in vestibular system caused by head rotation to the right:
- The semicircular canals are activated. You are looking horizontally, so the horizontal SCC detect the rotation.
- When leftward head rotation occurs, the endolymph in the left SSC lags behind due to inertia, causing the cupula to deflect towards the kinocilluim of hair cells in right canal.
- Deflection of cupula causes endolymph to move away causing hyper polarisation of hair cells and reducing firing rate in left side.
- This activity processed by vestibular nuclei In brainstem.
- we perceive right head rotation.
- The VOR is instated, to stabilise gaze during rotation.
The brainstem signal sot the ocular muscles to move right, opposite to head rotation to maintain stable vision. - Projections from vestibular nuclei to spinal cord via vestibulospinal tract to help maintain balance and postural stability during movement.
