These are the eight VNG tests performed by our system (standard ones):
- Smooth Pursuit
- Head Rotation (HFHS)
What Those VNG Tests Entail
In order to know where the participant’s eyes are fixating on the computer screen, you must first "teach" the computer what the eye looks like when the participant is fixated on known locations on the screen. This is what happens during the calibration and validation procedure. During a calibration session, the participant fixates on 9-13 points on the screen while the eyetracker monitors the eye. After calibration is performed, the computer then “validates” the information by re-presenting the targets and determining whether its estimation of eye position is indeed close to the known position of the targets. If errors are found to be minimal, calibration is indicated as successful.
Saccades VNG Tests
One section of the Oculomotor battery part of a VideoNystagmoGraphy (VNG) exam. Saccades are rapid eye movements made to bring an object of interest into the center of the line of sight (foveal vision). Saccades are voluntary or reflex eye movements that help refix one’s gaze with minimal duration of retinal slip, not necessarily refocus. Articles don’t have to come into focus, they just need to be targeted by the eye. In the saccades VNG test, eye movement is measured for speed and latency. The saccades eye movement goal is to fixate quickly and accurately on a new object.
In the Saccades VNG tests, eye movement that is equal in amplitude to the distance between the former object of interest and the new target is desired. Saccadic velocity is measured as the peak speed of eye movement when refixating gaze from one target to another.
The saccade test is performed much like the calibration procedure. However, true saccadic testing must involve a randomly moving target. Light targets are moved randomly by the VNG software.
VNG Test for Smooth Pursuit
The smooth pursuit tracking VNG tests are also in the oculomotor battery as part of the videonystagmography (VNG) exam. Here balanceback™ tests if the patient can maintain a stable gaze upon objects that are moving within their visual field. We allow the patient to focus upon an object, then blur the background. Smooth pursuit must follow the speeding object (a light in the Smooth Pursuit VNG tests) at the same speed, and disregard the background. Smooth pursuit is evaluated for symmetry (the difference between rightward and leftward scores) and gain (eye velocity versus target velocity).
Gaze Vision Enabled Testing with our iVNG- If gaze nystagmus is observed during the vision-denied condition, the patient performs the same gaze task (which elicited the nystagmus) with a visual stimulus projected onto the viewing surface. For example, if nystagmus is elicited in vision denied, right eccentric gaze testing, then right eccentric gaze testing with vision enabled is performed. In this case, the patient is simply instructed to follow the stimulus with only their eyes while keeping the head still.
Head Rotation (HFHS) Tests
VNG Test for Positionals
The patient is instructed about and assisted into each of the test positions under the vision-denied condition initially. For this portion of testing, the patient is instructed to keep their head still and look center or look straight ahead. The cover is placed over the goggles. The patient is instructed about and assisted into each of the test positions. All patients can be tested in supine, head right, and head left conditions. If nystagmus is present in a given head position, then it is essential to re-test that position with vision enabled. If the patient can not provide enough rotation of the head due to limited range of motion, the examiner uses body right and body left testing instead of head right and head left. If there is no positional nystagmus, the examiner continues to the next subtest (Calories).
Positional Balance Tests – Vision enabled
If nystagmus is observed in the vision-denied condition, the patient is subsequently tested with vision enabled in the provoking position(s). During the conditions with vision, the patient is instructed to stare at the fixation light that come on during the trial. Eye movement is recorded for 20 seconds.
Body Right/Body Left Headshake Balance Testing
This test is performed in the vision denied condition. The patient is instructed to lie on their side. Prior to the test, the patient is instructed that a tone would be presented that will assist them with the appropriate speed to shake their head (2 Hz). In some cases, it is helpful to demonstrate the headshake to the patient. The cover is placed over the goggles. The patient is instructed to look straight ahead until the tone is heard at which time they begin shaking their head side to side synchronized with the tone. When the tone stops at the end of the 20 s, the patient has to keep their eyes open and their head still until the test is complete. If the patient experiences dizziness or nausea it is necessary to allow the patient to recover before proceeding to the next test.
Hallpike VNG Testing
Instructions for Modified Hallpike with iVNG – Each patient is instructed that they might experience dizziness during the test, but if they have BPPV, it would only have a brief duration. The patient is also instructed that their head would be off the table and supported by the examiner. It is necessary that the patient allow the examiner to fully support the head of the patient so that appropriate extension of the neck will be maintained to provoke any BPPV. It was also important for the patient to keep their eyes open during the procedure so that nystagmus can be visualized and recorded. Upon returning to the seated position, the patients are instructed that they may experience dizziness.
Modified Hallpike Procedure – Each patient is seated on the exam table with their back to the examiner and legs resting comfortably on the table. The patient is positioned on the table so when supine, the head was off the table. The patient crosses their arms over their chest and turns their head 45° toward the side to be tested (i.e., right side then left side). The examiner stands behind the patient and supports the head and neck of the seated patient. Slowly and comfortably, the patient is laid down. The examiner moves down with the patient to a seated position. The examiner continues to support the head by holding the neck of the patient. The patient’s neck is hyperextended when the head is off the table. The patient remains in this position for approximately 30 seconds if there is a negative finding, or until the nystagmus or vertigo subsides in conjunction with a positive finding. If the nystagmus and vertigo persists beyond 1 min, the patient is moved out of the provoking position. The patient is asked to return to a seated position and the procedure is repeated for the opposite ear. The examiner always maintains supportive contact with the patient as provocation of symptoms is always possible on return to the seated position.
Instructions for Side-lying Hallpike –
Each patient is instructed that they might experience dizziness during this test, but if symptoms of BPPV are provoked, the duration of the symptoms will be brief. The patient was also instructed to keep their head in the appropriate position (turned to the left when testing the right ear and turned to the right when testing the left ear). The patient is reminded to remain on their side and not to roll to their back. It is also important for the patient to keep their eyes open during the procedure so that nystagmus can be visualized and recorded. Upon returning to the seated position, the patient is told that they may experience dizziness.
Side-lying Halpike Testing with the iVNG– This procedure is used for evaluation of patients with cervical spine, hip, or other issues that would preclude testing using Modified Hallpike. The patient is centered on the side of the exam table in a seated position. To test the right ear, the examiner is positioned to the patient’s right. The patient is instructed to cross their arms over their chest and turn their head away from the test ear (to the left when testing the right ear). The patient is positioned on the right side, swinging their legs onto the table. The examiner prompts the patient’s legs during this maneuver. The patient is then looking up at the ceiling. The patient remains in this position for approximately 30 seconds if there is a negative finding or until the nystagmus or vertigo subsides in conjunction with a positive finding. If the nystagmus and vertigo persists beyond 1 min, the patient is moved out of the provoking position. Then the patient is returned to a seated position. This procedure was repeated for the left ear. The patient was instructed to sit up independently from the Side-lying position while the examiner provides supportive guidance as patients may provoke on return to the seated position. If the patient experiences dizziness or nausea it is sometimes necessary to allow the patient to recover before proceeding to the next test. If a rotary-torsional nystagmus is present, this is indicated appropriately using the iVNG pop up box. If subjective vertigo is reported, this is also indicated appropriately using the pop up box. Vertigo is qualified as transient or persistent when prompted by this iVNG program.