How to Perform Videonystagmography (VNG)

15 February 2022
10 - 30 mins
Reading

Expected outcomes

  • Site of lesion localization: Determine which sensory input, motor output, and/or neural pathways may be responsible for the patient’s reported symptoms
  • Functional ability: Assess patient’s functional ability to use the system inputs in an integrated fashion
  • Vestibular rehabilitation: Determine if patient is an appropriate candidate for vestibular rehabilitation

 

Prior to testing

  • Prior to testing, review basic points of the VNG test procedure with the patient
  • Ensure that the patient has followed the VNG pre- test instructions, including use of contraindicated medications for 48-72 hours prior to testing. (Note that discontinuation of some medications may not be appropriate)
  • Obtain a case history from the patient. Question the patient about visual function and history of neck and/ or back problems, or medical conditions that may contraindicate certain test
  • Perform an eye movement exam to check for conjugate eye movement prior to placing the goggles

 

Testing guidelines

Prior to a VNG evaluation, the following procedures are recommended:

  • Current audiogram. Audiometric testing should be performed on all patients who are referred for a Without audiometric assessment, there will be limitations in interpretation of results.
  • An otoscopic examination must be performed routinely on all patients undergoing a VNG to ensure there are no contraindications to performing certain portions of the test battery, such as calorics.
  • Tympanometry, Acoustic Reflexes and Reflex Decay should also be performed routinely prior to VNG.

 

Test preparation

 

1. Apply goggles

Use the focus knobs on the goggles to adjust focus of eye images. Use the centering feature in the VNG software (top-mount cameras) or the adjustment knobs (side-mount cameras) to center the patient’s eyes in the viewing window. Pupil tracking is automatic and, in most cases, requires minimal or no adjustments. However, should minor adjustments be needed to ensure that the crosshairs stay centered on the pupils, adjust the threshold sliders in the software until crosshairs are stable and centered on each pupil. For situations in which one eye cannot be recorded, use the disable left or right eye feature in the VNG software to discontinue recordings for that eye.

 

2. Calibrate eye movements

Use this icon Button with an encircled, dotted crosshair and the word 'calibration'. to initiate the calibration procedure. When calibration is started, the stimulus on the secondary monitor will move to five distinct positions to accomplish both horizontal and vertical calibration in a single procedure. Ask the patient to focus on the stimulus target and follow its movement with his/her eyes, while keeping the head still. Repeat and reinstruct the patient as necessary. In situations where a good calibration cannot be obtained, it is optional to select and use default calibration as an alternative.

 

Test procedures

  • During all tests, procedures with a fixation target should be completed with goggles uncovered and eyes open. Procedures without fixation should be completed with goggles covered, eyes open and with verbal alerting tasks.
  • For oculomotor testing, the patient should be directed to keep the head still (in a neutral position) and follow the stimulus target on the secondary monitor with the eyes only.
  • Note that in all tests, particularly oculomotor tests, repeat testing with reinstruction may be required to elicit the patient’s best response.

 

Spontaneous test

  1. Record for 20- 30 seconds with the goggles Alert the patient.
  2. Keeping the goggles covered, turn on the fixation light and record for an additional 20- 30 seconds. No alerting is needed during the fixation portion of the spontaneous

 

Gaze test

  1. With the patient sitting and facing the secondary monitor with head in a neutral position, direct the patient to gaze at the stimulus target with goggles uncovered.
  2. Record for 10- 20 seconds in each target position.
  3. The following target positions are recommended: center, right 30⁰, left 30⁰, up 20⁰, and down 20⁰.

 

Smooth pursuit test

  1. Instruct the patient to keep his/her head still and to follow the stimulus target smoothly with the eyes as it moves back and forth across the screen.
  2. The target speed will gradually increase from 0.1 Hz to 0.5 Hz. A minimum of two complete cycles for each speed should be completed.

 

Saccade test

  1. Instruct the patient to keep his/her head still and to follow the stimulus target with the eyes as it moves randomly to different areas on the screen.
  2. Optionally, randomize the targets to mix horizontal and vertical saccades together in the protocol manager.
  3. Perform at least 30 saccades to obtain sufficient data for analysis.

 

Optokinetic test (OPK)

  1. Inform the patient that multiple stimuli will move quickly across the Instruct patient to look at the screen (but not stare at or follow) as the stimuli cross the field of vision.
  2. Initiate testing at the 20⁰/sec target velocity and record for 15 - 30 seconds with stimuli moving in the rightward direction and repeat for leftward-moving stimuli.
  3. Initiate testing at the 40⁰/sec target velocity and record for 15 - 30 seconds with stimuli moving in the rightward direction and repeat for leftward-moving stimuli.
  4. Optionally, record at 30⁰/sec. Always perform at least two speeds and look for the patient’s best performance.

 

Dix-Hallpike maneuver (positioning)

  1. Confirm that patient has no pre- existing neck or back conditions and/ or concerns for vertebrobasilar insufficiency that would contraindicate Dix- Hallpike testing.
  2. Prepare test chair or table by lowering to a flat position and lowering head rest support to allow the patient’s head to hang to a 30⁰ angle.
  3. Support the patient’s head and neck.
  4. Begin the recording in the VNG software prior to positioning the patient.
  5. Direct the patient to turn his/her head 45 degrees to the right and then lie down until the head is in the desired 30⁰ head-hanging Hold this position for 30- 40 seconds, or until the nystagmus completely subsides if a positive BPPV response is present.
  6. Observe the video recording for abnormal eye movements.
  7. After at least 30 seconds, bring patient back to the sitting position. The return-to-sit position will be marked in the software when the forward button on the remote or the enter key on the keyboard is Direct the patient to look straight ahead with eyes open. Record for at least another 10 seconds in the sitting position while observing video for a change in the direction of nystagmus (if present).
  8. After the procedure, question the patient about symptoms (if any) observed during the procedure.
  9. If nystagmus is noted, repeat the procedure to determine fatigability.
  10. Repeat entire procedure for the head-hanging left 45⁰ position.

 

Positional testing

  1. Record for approximately 30 seconds with the goggles covered in each of the following positions:
    • Supine with head in neutral position.
    • Supine with head turned to the right.
    • Supine with head turned to the left.
  2. If nystagmus is noted in any of the first three positions continue to the following positions:
    • Body right side.
    • Body left side.
  3. Optionally, bow and lean positions can also be completed from a sitting position to help differentiate the involved ear when lateral canal BPPV is suspected.
  4. When nystagmus is present with vision-denied in any position, the fixation light can be turned on to ensure that the patient is able to suppress the nystagmus with fixation.
  5. It is not uncommon to need additional recording time beyond 30 seconds when nystagmus is Additional time can be added to any individual position subtest by pressing this button in the left menu panel Button with a plus sign and the words 'add time'.
  6. In each position, instruct the patient to keep eyes open and perform alerting tasks.
  7. Specific positions may be contraindicated when the patient has a history of back and neck pain, concern about circulatory issues (particularly in the head hanging position), or limited mobility.
  8. Precautions should be taken to prevent the patient from falling off table while shifting from one position to another.

 

Caloric test

  1. Water irrigation is contraindicated in patients with tympanic membrane perforation, pressure- equalization (PE) tubes, or middle ear abnormality.
  2. Test settings are as follows:
    Table with two main columns: air irrigation and water irrigation. For air irrigation, the duration of irrigation is 60 seconds, the volume of stimulus is 8L, the warm stimulus temperature is 48 degrees centegrade, and the cool stimulus temperature is 24 degrees centegrade. For water irrigation, the duration of irrigation is 30 seconds, the volume of stimulus is 250ml, the warm stimulus temperature is 44 degrees centegrade, and the cool stimulus temperature is 30 degrees centegrade.
  3. Describe the procedure and expected response to the patient.
  4. Place the patient in a supine position with the head elevated to a 30⁰ incline.
  5. Prepare the patient and place the cover on the goggles.
  6. Perform a warm irrigation in the right ear first, using the appropriate stimulus type (air or water).
  7. Initiate verbal alerting tasks following the end of irrigation.
  8. After peak slow-phase velocity (SPV) has been obtained, check for fixation suppression. The VNG software has an automated procedure in the caloric test, allowing the fixation light to initiate at the appropriate time following peak SPV. Alternatively, the fixation light can be manually turned on by the examiner
  9. Remove the goggles cover and wait a minimum of 5 minutes between If a large response is noted, a longer interval may be required to allow the patient to completely suppress the response.
  10. Repeat the warm irrigation for the left ear, then complete the cool irrigations in the left and right ears, respectively.
  11. Note that each caloric test should last approximately 2-3 minutes. Make sure that all four irrigations are of the same duration.
  12. Inspect tracings to ensure the adequacy of the Repeat any suspect irrigations.

 

Interpretation of caloric results

  1. 25% asymmetry or greater is significant for a unilateral weakness.
  2. 30% or greater is significant for directional preponderance.
  3. < 24⁰/second total caloric response is significant for bilateral weakness.
  4. > 140⁰ total left ear (or right) response is considered a hyperactive response.

McCaslin DL. Electronystagmography and Videonystagmography ENG/VNG. San Diego: Plural Publishing; 2012.

 

Monothermal warm caloric screening test (MWST)

While not considered best practice, monothermal caloric screening can be administered as an alternative to the traditional bithermal caloric test in certain instances. Monothermal warm irrigations may be completed when the following criteria are met:

  • The warm monothermal caloric asymmetry must be less than 15%.
  • The warm SPV results must be greater than 8⁰/sec on each side.
  • There must be no evidence of a potential directional preponderance or spontaneous nystagmus.

Lightfoot, G., Barker, F., Belcher, K., Kennedy, V., Nassar, G. and Tweedy, F. The Derivation of Optimum Criteria for Use in the Monothermal Caloric Screening Test. Ear & Hearing. 2009; 30(1): 54-62.

Zapala, DA., Olsholt, KF., Lundy, LB. A comparison of Air and Water Caloric Responses and Their Ability To Distinguish Between Patients With Normal and Impaired Ears. Ear & Hearing. 2008; 29(4): 585-600.

 

Ice water caloric test

  1. Ice caloric testing is appropriate if no caloric response is noted in one or both ears (considering any previously measured spontaneous nystagmus or supine positional nystagmus).
  2. Prepare the patient as appropriate for testing without fixation.
  3. Turn the head so the ear to be tested is uppermost.
  4. Fill the ear with 2 cc of ice water (4-10⁰ C); keep water in the ear canal for 20 seconds.
  5. Direct the patient to turn his/her head to neutral position (draining the water) and begin verbal alerting tasks.
  6. If any nystagmus is present during the ice caloric procedure, then after 30 seconds of verbal alerting, direct the patient to sit upright quickly and dip head downward to check for reversal of nystagmus.

 

Interpretation of Ice water caloric results

Measurable nystagmus of greater degree than any pre- existing spontaneous or supine positional nystagmus must be present to be considered a true caloric response. When it is unclear whether the response is from spontaneous nystagmus, then move the patient to a prone position with head hanging down 30⁰. The response must reverse direction in the prone position to be considered a true caloric response.

McCaslin DL. Electronystagmography and Videonystagmography ENG/VNG. San Diego: Plural Publishing; 2012.

 

Active headshake

  1. An additional spontaneous test can be added to the VNG protocol and renamed for performing active headshake or a variety of other tests that may be desired.
  2. In protocol manager, set the test duration to 60 seconds and change fixation light to manual.
  3. Active headshake is performed with the cover on the goggles and no fixation.
  4. Have the patient drop his/her chin downward slightly (30⁰) to place the lateral semicircular canals in a true lateral position.
  5. To perform the test, always obtain a 5-10 baseline recording to verify presence of any pre-stimulus nystagmus.
  6. Continue recording and have the patient begin shaking his/her head quickly (2 Hz) from side to side in a horizontal sinusoidal pattern for 15-20 seconds.
  7. Instruct the patient to stop shaking his/her head and continue recording for a minimum of 20 seconds to watch for any post-headshake nystagmus.

Asawavichiangianda, S., Fujimoto, M., Mai, M., Desroches, H., Rutka, J. Significance of Head-shaking Nystagmus in the Evaluation of the Dizzy Patient. Acta Otolaryngol. 1999; Suppl 540: 27-33.


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