Week 5: VNG

Question 1

equipment needed for VNG

Answer 1

• otoscope
• computer to analyze data
• infrared goggles or skin electrodes and Frenzel’s lenses
• patient table
• light bar
• bithermal caloric irrigator (air or water)
• proper lighting (must be able to reduce lighting)

Question 2

two notes about placing electrodes with ENG

Answer 2

• can be interesting, especially with pliable skin

* also be careful to not cause bleeding when scrubbing the skin

Question 3

goggle placement with VNG

Answer 3

very important to keep eye makeup clear, especially mascara and eyeliner

Question 4

ENG or VNG test battery

Answer 4

*calibration
*spontaneous and gaze nystagmus test
*saccades test
*smooth pursuit
*optokinetic
*headshake
*positional tests (positional and positioning)
caloric tests

Question 5

what does VNG stand for

Answer 5

videonystagmography

Question 6

what does ENG stand for

Answer 6

electronystagmography

Question 7

calibration

Answer 7

• dark room so no fixation
• have pt look left and right (should make square wave)
• disorder may be present if square wave cannot be properly formed

Question 8

spontaneous nystagmus: VNG

Answer 8

• examiner instructs pt to sit and stare ahead, record for 30-40 seconds.
• do with fixation and without
• tasking is necessary (anytime fixation is denied, task)
• allows us to see nystagmus that might not be visible with the naked eye
• may be an indication of peripheral lesions if present
• may be an indication of central vestibular disorder

Question 9

gaze nystagmus: VNG

Answer 9

• performed with light bar
• 20 degrees to the right, left, up, and down (with and without fixation)
• if spontaneous nystagmus (with fixation) was present earlier it will probs still be present
• endpoint nystagmus (30-60 degrees is not clinically sig.)
• results:
• –vertical nystagmus= central
• –torsional nystagmus= central
• –if nystagmus increases without fixation, then it is probably acute peripheral lesion

Question 10

Alexander’s law for gaze nystagmus

Answer 10

• the horizontal nystagmus increases in intensity as the patient gazes further in the direction of the fast component of the nystagmus
• –this applies only to horizontal nystagmus
• –usually away from affected ear
• sometime though with irritative lesions there will be a hyperfunction instead of hypo that makes the side of lesion the more active side, so in this case the nystagmus will beat towards the side of lesion and not follow alexander’s law

Question 11

rebound nystagmus in gaze nystagmus testing

Answer 11

• nystagmus is produced beating in the last direction the eye moved as the eye is returned to primary position
• this is normal if only a beat or two occurs, but if it persists, it is a central pathology indicator

Question 12

saccades: VNG

Answer 12

• pt will track a random movement of light
• they should follow the target closely
• instructions should be that the pt follow the light as it moves and does not try to guess where the light will move next
• watch for overshoots, undershoots, and overall poor tracking
• –pt guessing might look like this so re-instruct if needed

Question 13

smooth pursuit: VNG

Answer 13

• like a golf ball on a string, the lights move back and forth
• instructions: please follow the lights as smoothly and accurately as you can
• looking for smooth sine wave to be generated on computer screen
• lack of smooth pursuit can be a central sign
• pursuit test is the 1st to be affected by aging and meds

Question 14

optokinetic: VNG

Answer 14

• you should see nystagmus here
• lights or stripes used
• instructions: watch each light as it crosses the center
• –be careful not to over explain, pt tend to overthink this task
• pt should reflexively follow one (slow phase) and jerk back to catch the next one (fast phase)
• two directions are used, to the right and to the left

Question 15

oculomotor: VNG

Answer 15

• some computers will allow testing at varying speeds
• symmetrical recordings should be obtained for right and left
• central signs include:
• –inability to induce nystagmus during OPK
• –asymmetry
• –low gain

Question 16

Dix-Hallpike (positioning): VNG

Answer 16

• primarily to check for BPPV (check for vertebral artery insufficiency before doing)
• head turned 45 degrees
• pt is seated and lies back quickly as possible with AuDs help
• performed to left and right
• look for dizziness and nystagmus
• may have brief delay in onset (classic of BPPV)
• pts may become distressed

Question 17

summary of dix-hallpike findings

Answer 17

• posterior canal affected: rotary up-beating, torsion to the side involved
• –ipsilateral superior oblique and contralateral inferior rectus
• horizontal canal affected: horizontal; geotrophic-canalithiasis and ageotrophic-cupulothiasis
• –ipsilateral medial rectus and contralateral lateral rectus
• anterior canal affected: rotary down beating, torsion to the side involved
• –ipsilateral superior rectus and contralateral inferior oblique

Question 18

postitional testing: VNG

Answer 18

• placing head and body into various positions to check for positional nystagmus
• –head right, center, and left
• –body right and left
• usually record for at lease 20-30 seconds in each position, if nystagmus is noted continue testing as long as allowed by the computer
• performed with and without fixation, remembering to task when fixation is denied
• be cautious of back and neck problems

Question 19

temperatures to use for calorics (water and air)

Answer 19

air: 51 degrees C for warm and 23 degrees C for cool

* water is +/-7 degrees from body temp (37 degrees) while air is +/- 14 degrees

Question 20

what happens to each temp in each ear with calorics

Answer 20

COWS
*cool in right= left beating
*cool in left= right beating
*warm in right= right beating
*warm in left= left beating
(cool opposite, warm same)

Question 21

bithermal caloric irrigation: VNG (instructions and procedure)

Answer 21

• instructions: I am going to put some air in your ear for 90 seconds. You may feel a sensation of movement, that is normal and it will subside within a few minutes. Your eyes should remain open as much as possible
• do otoscopy 1st and don’t do on surgical ear unless medically cleared and only with air
• pt head elevated 30 degrees
• nystagmus should be seen until a drop in intensity is noted, the allow fixation
• pt opens eyes and stares at light for 10 seconds
• remember to task after removing the air or water
• rest 5-7 minutes between irrigation
• measuring the horizontal SCC

Question 22

bithermal caloric irrigation interpretation

Answer 22

• computer generates a number in degrees per second (eye speed) for each of the 4 irrigations
• figure out how much the right ear and left ear are contributing (should be equal 50/50)
• unilateral weakness: if one ear is contributing significantly less
• –typically sig at 20-25% or greater difference
• –can state “borderline weakness”
• –usually indicates a peripheral weakness
• there may be hypoactive systems, bilaterally, for example with vestibulotoxicity
• directional preponderance: beating in one direction is sig stronger (left or right)
• –greater than 27 degree is sig
• –note if there is spontaneous nystagmus will likely see directional preponderance
• –dir preponderance can indicate a central lesion or nonlocalizing
• other central indications: symmetrical caloric irrigations with central signs seen throughout VNG battery