VNG is a test to evaluate the possible etiology of a person’s dizziness. Through testing, we are able to determine potential causes of your symptoms and plan a course of treatment. This test takes approximately one hour. During the VNG, the patient wears a set of goggles containing infrared cameras, which record the movement of their eyes. During portions of the test, the goggles will be closed and they will be in the dark.
The VNG is divided into the following three parts:
- Oculomotor Evaluation: This portion of the test evaluates the eye muscles and central nervous system. The patient is asked to follow a red light with their eyes to perform a series of tasks. This portion of the testing lasts approximately 10-15 minutes.
- Positional Evaluation: This portion of the test evaluates both the central nervous system, as well as the balance organs of the inner ear. The patient is asked to sit, lie on their back, turn their head in both directions, and lie on their sides. During part of this portion of the test, the patient is asked to change positions rapidly from sitting to laying. This portion of the test is performed with the goggles closed and lasts approximately 10 minutes.
- Caloric Evaluation: This portion of the test evaluates the function of the balance organ of the inner ear. During this test, the patient lies on their back with the goggles closed. Cool and warm air will be introduced into each ear canal separately. The air will be in the ear for approximately 60 seconds. This change in temperature to the ear canal will induce some dizziness. After approximately 90 seconds, you will be asked to look at a light inside of the goggles. During this period, the dizziness will subside. The patient will be allowed to rest for approximately 3-5 minutes between each part of this portion of the evaluation. Some dizziness does occur during this portion of the test. However, it generally subsides once the ear is back to normal temperature.
Electrocochleography (ECOG) is a diagnostic test that examines the function of the inner ear. This test measures the electrical potentials generated in the inner ear in response to sound. The ECOG is most often used to determine if the inner ear has an excessive amount of fluid pressure, which can cause symptoms such as hearing loss, aural fullness, dizziness, and/or tinnitus. These symptoms are sometimes indicative of certain ear pathologies such as Meniere’s disease or endolymphatic hydrops. The forehead is scrubbed clean and small electrodes will be taped to the skin. The ear canals are scrubbed clean and foam electrodes will be placed in each ear canal. The patient lies still with their eyes closed, while listening to a series of fairly loud clicks. There is not any discomfort during the test. Any tension or muscle movement can slow down the testing process, thus it is very important to be relaxed during this test. A computer will record several responses from the ear. The audiologist will identify a large waveform, which directly results from providing sound stimulation to the inner ear. This waveform contains two components, the summating potential (SP) and the action potential (AP). An enlarged ratio between these two components (SP/AP ratio) can indicate excessive fluid pressure in the ear. This test takes approximately one hour. The audiologist will analyze the results and then give the report to the referring physician.