ENG and VNG tests
ENG and VNG are objective test methods used to assess the ‘vestibular’ system (the organ of balance or the ‘labyrinth’) as well as pathways to the level of the brainstem. The VNG test is the gold-standard for diagnosis of inner ear disorders. The purpose of the ENG is to determine whether or not dizziness may be due to inner ear disease. These tests evaluate:
- The function of the balance system
- If the right and left labyrinth are working equally, as normal
- Whether one side is under-performing or over-performing compared to the other
- Indicating which ear is affected
ENG and VNG method
During ENG, small electrodes are applied beside each eye and connected via wires to a computer. The equipment can read movements of the eyes via the electrodes.
During VNG, goggles are placed over the eyes and connected to the equipment via wires. The goggles have a camera inside that monitors eye movement. VNG is a more advanced method compared to ENG. During this test
- Numerical data are collected on a computer and later analysed
- An audiologist interprets the results to determine the integrity of the balance system
Both tests are painless and noninvasive.
What does the patient do during these tests?
The patient is required to sit on a comfortable medical bed/couch or adjustable chair, wear goggles (VNG) and keep their eyes open. There are three parts to the test:
Part one: The calibration test evaluates rapid eye movements. The tracking test evaluates movement of the eyes as they follow a visual target. The patient is sitting up while watching a moving light or lights. This assesses some visual pathways to the brain and helps identify whether an opthalmological referral is needed given eye movement abnormalities or whether the eyes give an indication that the ears might be affected. It is important to note that the eyes movements act as a ‘window to our balance system’.
Part two: The positional tests (explained in detail below). measures dizziness associated with positions of the head. the patient is sitting and lying back at the instruction of the audiologist. Eye movements are monitored in different head and body positions. This assesses the effect of position changes on the patient.
Part three: the patient is lying back at an angle. Cool and warm water or air is introduced in and out of the ear for a short period of 30 or 60 seconds each time. This assesses the vestibular system or labyrinths.
How should I prepare for the evaluation?
The patient should prepare for the examination as follows:
– Avoid alcohol at least 48 hours prior to the evaluation as it may interfere with the true readings.
– Not wear eye make-up as it may interfere with the eye recordings.
– Discontinue anti-dizziness medications for up to 48 hours prior to the evaluation. All other medication can be continued, if in doubt please consult your audiologist.
– If possible, ask to be accompanied by a friend or relative to drive them back, in case they feel dizzy after the tests.
When will the results be ready?
The audiologist will analyze the data and write the report. In most cases they can communicate the results on the day, unless further analysis is needed.
What would the patient feel?
These procedures may cause some shortlived dizziness, which can be normal as their inner ear is stimulated to be measured. The patient can ask the clinician to stop the test at any time, should they feel uncomfortable.
The goal of positional testing is first to detect positional nystagmus, and if there is positional nystagmus, to determine if it is due to the ear (usually BPPV), brain (central positional nystagmus), or neck (cervical nystagmus). Neck and back contraindication are assessed prior to the test. The tests are not performed should the patient have had recent (i.e. few months) neck or back surgery.
There are several methods of doing this, but we will only document the methodology that we recommend:
- Dix-Hallpike test
- Horizontal or Roll test
In this test, the patient is brought from sitting to a supine position, with the head turned 45 degrees to one side. Any possible nystagmus (i.e. certain eye movement) is recorded, and then the patient is returned to the upright position and records for 10 seconds or until the nystagmus stops. The test is repeated onto the other side to identify which side is affected. A positive Dix-Hallpike tests consists of a burst of nystagmus (jumping of the eyes). The eyes move upward in a torsional fashion.
If there is horizontal nystagmus during the Dix-Hallpike, the clinician will perform the horizontal positional test.
The Dix Hallpile test is used in the diagnosis of BPPV – benign paroxysmal positional vertigo, which is shortlived dizziness on particular positions, usually on one side. It is very common and affects any age. It constitutes 20% of all vestibular related conditions and it is easy to treat, in most cases in the same day as the test itself.
The Horizontal or Roll Test is also used in the diagnosis of positional disorders affecting the horizontal labyrinth and again can be treated on the same day as the test.