Vestibular Foundations - Session 7 - VHIT

and objective efficient means of testing the vestibular system that provides immediate results regarding side specific vestibular dysfunction

1 -subjective results as it’s the examiners opinion whether or not an abnormal eye movement has occurred in response to head movement

-the human eye can only detect the more obvious eye movements that occur after head movements (known as Overt Saccades)

3- the human eye isn’t capable to detecting eye movements that occur within the head movement (known as Covert Saccades)

1 - vHIT using EyeSeeCam allows the professional to accurately and objectively assess the dizzy patients for vestibular dysfunction on the 1st office visit without the time and expense of ENG saving the patient and healthcare professional time and money

2- the EyeSeCam is objective, portable and reliable and easy to use making vHIt ad obvious choice as a starting point for Vestibular Assessment

vHIt is a measure of the VOR in response to head movement

-a patient with a healthy vestibular system should be able to keep their eyes focused on a object even when head is in motion

VOR, remember shaking the paper vs shaking your head

in patients, with vestibular dysfunction, when the head moves, the eyes will move with the head, requiring a corrective movement back to the target = inability to remain focus

-vHIT captures this abnormal eye movemnt, analyses and puts it into a digital graph which is easily read and understood

dedicated goggles made of 2 major components:

1- Inertial Measurement Unit (IMU)= is a combined Gyroscope and Accelerometer that measures head movement WHILE

2- Infrared Camera captures records eye movement

1- secure goggles

2-perform brief calibraton of eye movement

3- exmainer asks patient to maintain eye focus on a stationary object

4-the examiner manipulates the pateint head with quick precisie head movements

the goggles must be fitted securely to avoid slippage

the entire process should take less than 10 mins to perform and provides immediate side specific results

-its designed to perform intricate and repeatable calculations of the relationship between head and eye movements to determine whether there is a weakness in 1 or both vestibular systems

shows an analysis of instantaneous gain. specifically at 40, 60 and 80milli seconds

the software provides and analysis of velocity regression meaning a calculation is derived form a comparison of eye and head velocity in the time range of 0-100 milli seconds after impulse onset, to give a quick estimate of symmetry of symmetry between vestibular systems

-as tracings which clearly show the presence of overt and covert saccades

to differentiate between no vestibular dysfunction and peripheral vestibular dysfunction and central vestibular dysfunction

normal horizontal semi-circular vestibular dysfunction at high velocity head movements between -4 Hz

referral for more advance testing such as:

- Video Nystagmography

- Electrocohleography

Quick, side specific information regarding vestibular function

-Portable equipment allows for bedside testing for non ambulatory patients. Further recommendation for care can be made based on vHIT results

easily tolerated by most patients as its quick test that utilises natural head movements

-utilises natural head movements that emulate normal, daily activities particularly in 1-4 H range (such high frequency info can only be attained by vHIT

-accurate data interpretation and storage allows for objective reporting ad comparsions of vestibular nerve function to measure vestbular compenstation over time to see effectiveness of vestibular therapies

can be used as a pre-operative and post operative evaluation of vestibuar function

(those who are those with cervical issues with the neck or spine

those who cannot relax enough for quick head movements required

patients who are visually impaired as they won’t be able to see the target

1- Lightweight goggles with built-in laser calibration.

2- Switchable left/right camera with ball-and-socket design.

3- Instantaneous gain plots at 40, 60, and 80ms for detailed data analysis.

4- Velocity regression analysis for frequency range assessment.

5- USB-driven for easy plug-and-play setup.

6- Generates PDF reports for quick review.

neither

vHIT is a quick, well tolerated test

vHIT yields side specific information

vHIT guides further recommendations and treatments

vHIT increases your efficiency by saving both time and money

Head movement activates semicircular canals: Detects rotational motion.

Signals travel via vestibular nerve: Superior/inferior branches send signals to the brainstem.

Central processing: Vestibular nucleus complex and cerebellum integrate signals with visual and proprioceptive input.

Reflex output: Activates pathways like the vestibulo-ocular reflex (VOR) for stable vision and vestibulospinal reflex (VSR) for balance.

its described as the bedside test of semi-circular canal function

it examines the ability to maintain fixation on a target without the generation of abnormal eye movements during an extremely fast angular acceleration of the head

Angular acceleration (thrusting head) is applied during head movements.

Asymmetry occurs between inhibitory and excitatory neural firing patterns in the vestibular system. - excitation on the side you’re thrusting the head to and inhibits the other side to 0 (no neural activity).

The angular reflex (a component of the VOR), controlled by the semicircular canals, compensates for head rotation to maintain stable vision.

It only tests for VOR because its too fast for other tests like optokinetic.

both sides

Sensitivity and Specificity: Mean sensitivity is 46%, specificity is 94%.

Subjectivity: Relies on the examiner’s ability to interpret and detect overt saccades, leading to variability based on technique and experience.

Covert Saccades: Difficult to detect covert saccades that occur during head movement.

Lack of Feedback: Provides no feedback on the quality or frequency of head impulses.

easy to miss people with small vestibular abnormalities

Sensitivity and Specificity: vHIT has high sensitivity and specificity, validated against scleral coils with comparable specificity.

*Reasons for Accuracy:

High-speed camera captures precise eye movements.

Gyroscopes measure head movement accurately.

Sophisticated software provides detailed analysis.

*vHIT is a simple test.

*Procedure:

Involves passive, unpredictable, and abrupt head turns.

Uses angular acceleration to reach peak head velocity, followed by immediate deceleration.

*Normal Response: In a healthy subject, both eyes move to compensate for head movement, maintaining stable vision.

RALP (Right Anterior Left Posterior): Assessed by head tilts stimulating the right anterior and left posterior canals. (diagonal tilting)

Lateral Canals: Assessed by lateral head movements (side-to-side). (horizontal movement)

LARP (Left Anterior Right Posterior): Assessed by head tilts stimulating the left anterior and right posterior canals. (diagonal in opposite plane)

Displacement: 10°–20°ensuring appropriate stimulation without excessive motion. (this isnt a of of movement)

Peak Head Velocity: 100°/s – 250°/s high enough for VOR stimulation but not too rapid for patient safety.

Peak Head Acceleration: 1000°/s² – 2500°/s² providing sufficient angular acceleration to activate the lateral canals effectively.

*The head is tilted 35°–45°, and the patient maintains gaze at a fixation point during small, abrupt head movements.

Amplitude: 10°–15°.

Velocity: 100°–150°/s.

*Movements:

Downward stimulates the anterior canal.

Backward stimulates the posterior canal.

patient with any neck injury ar unsuitable

patients who are visually impaired cant do it because they cant wear glasses because of goggles and have to see the target

Each impulse: Represents a separate measure of vestibular function. so you should be able to see a abnormality of the first impulse

Repetition: Improves confidence in results.

Recommendation: 20–30 impulses are suggested by some manufacturers.

Key Focus: Prioritize quality of impulses over quantity.

Goggle Slippage: Movement of the goggles can affect accuracy.

Predictable Head Movements: Reduces test reliability as the patient may anticipate the motion. (non rhythmic like an audiogram)

Patient Positioning: Sitting too close to the target can distort results as eyes can cross over due to the target being too close.

Focus on more than just saccades or gain.

Both are complementary indicators of vestibular loss and should be interpreted together for accurate assessment.

they are both abnormal and mean there is a vestibular abnormality.
its has some diagnostic properties as it can tell us about any compensation strategies, how long ago someone had a vestibular episode? whether they started to compensate for that? it can indicate management plans?

The absence of saccades in a patient with impaired VOR could indicate a severe abnormality in the vestibular system, central nervous system, or visual pathways.

Overt Saccades: Occur after head movement.

Covert Saccades: Occur during head movement.- they are harder than to spot than the overt as by the time the head movement stops, the eyes will be on the target.

-the blue is the head movement

the green is the eye movement

if the green movement is after the blue, its and overt sacade

no, they are random deviation eye movements, saccades would be lots of them, constant (around the same time), clustered

Presence or Absence: Check if saccades are present or absent.

Latency: Measure the time delay before the saccades occur.

Consistency: Evaluate how consistent the saccades are across impulses.

the difference between the head movements and the eye movements (ideally 1:1 ratio so should be 1 but this is not always the case due to things like visual acuity)

*lateral Canals:

Normal: >0.8 – <1.2

Abnormal ->Unilateral Loss: 0.1 – 0.8

Abnormal - Bilateral Loss: <0.1

*Vertical Canals:

Normal: >0.7 – <1.2

Abnormal - Unilateral Loss: 0.1 – 0.7

Abnormal - Bilateral Loss: <0.1

the eye wasn't keeping up with the head movement and the saccade is the corrective mechanism that is implemented to get the eyes back onto the target

so it tells us the gain.

if the line is reaching the outside line then the gain is 1

the inside line is 0.5

if its marked in green, its a normal gain and has fallen within the normal parameters

e.g. caloric give info about ONLY the lateral SCC and the nerves that supply it and takes 1 hour

BUT

vHIT assesses all 6 SCC and their afferent pathways in around 15 mins

can be used when other tests cant be done like calorics cant be done with middle ear abnormalities

non evasive, paediatrics

we use it early on to give us info on whether their history matches up with the vHIT and gives indication on what further testing we need to do -MDT with MDT