Videonystagmography
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| VNG stands for VIDEONYSTAGMOGRAPHY and it is used to record nystagmus, which is an involuntary eye movement characterized by the eye jerking back and forth. It can be generated by the peripheral vestibular system associated with each ear. What we are recording then is known as the vestibular ocular reflex. The VNG provides a permanent record of eye movements, either with eyes open or closed. The VNG has been around since the early 1940's and is still the basic balance test that physicians will order when treating patients with symptoms of dizziness. |
| The VNG test administered in our facility today consists of computerized recordings which allow the examiner to use a wide sample of informative data for analysis. It utilizes a specialized camera system housed in a lightweight goggle to record the VNG data. |
| The VNG consists of seven basic tests. However, the term VNG is so commonly used to refer to the entire test battery that very few people know the names of the individual subtests which make up the entire VNG test battery. They include: |
- Gaze test: Eye movements are recorded as the patient looks straight ahead, looks to the right, looks to the left, looks up and down, with eyes open and closed. The recording is inspected for the presence of nystagmus under any of these conditions.
- Saccades: The patient's eye movements are recorded as he looks back and forth between two points in a horizontal plane. The recording is inspected for defects of saccadic eye movement.
- Pendular tracking testing: Eye movements are recorded while the patient follows a slowly moving visual target. The recording is inspected for defects of pursuit eye movement.
- Optokinetic test: Eye movements are recorded while the patient watches vertical stripes or a light moving horizontally at several different speeds to the right and then to the left. The recording is inspected to determine whether the nystagmus generated by this stimulus becomes stronger as the stimulus speed increases and whether it is stronger in one direction than in the other.
- Positional test: Eye movements are recorded with the patient's eyes both open and closed, after the patient has been placed in various positions. The recording is inspected for the presence of nystagmus in any position.
- Hallpike maneuver: The patient is moved rapidly from sitting to the head hanging position. The recording is inspected for nystagmus following each movement.
- Caloric test: Each ear is irrigated twice, once with air or water that is above body temperature and once with air that is below body temperature. Each irrigation affects the vestibular receptors of the irrigated ear and provokes a horizontal nystagmus response. The responses of the right ear are compared with those of the left ear to determine whether the sensitivities of the right and left vestibular mechanisms are equal
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| The Positional, Hallpike, and Bithermal Caloric tests are usually the subtests of most interest because they are most likely to indicate whether there is some significant peripheral vestibular dysfunction. The data is a determinant of whether a person's dizziness is caused by the ear or if it is due to some other factor such as the central nervous system. |
| Patients who are referred to our facility for VNG testing must not take certain medications such as anti-dizziness medication, depressants of any kind, antihistamines, etc. for a period of 48 hours prior to administration of the test. The consumption of alcohol is also prohibited. The taking of such can affect the patient's responses on the VNG subtests. Blood pressure and heart medication can be taken without problem. |
| Women should not wear any makeup, as it is removed in preparation for the placement of the VNG electrodes. Patients should be counseled not to eat too heavily before administration of the test. Patients can usually drive themselves home following the test but it is always advisable for an elderly patient to have a family member accompany him at the time of his VNG appointment. |
