Videonystagmography
Videonystagmography records eye movements with infrared video goggles to test the balance system, the brainstem, and the cerebellum. Because the cameras work in darkness, eye movements can be recorded without the suppressive effect of visual fixation, which hides many peripheral vestibular signs. It is a group of tests that includes ocular motor tests, positional and positioning tests, and sometimes caloric testing.
The patient wears lightweight goggles with an infrared camera for each eye, connected to a computer that tracks the pupil position and plots eye movement against time. The test has three parts. Ocular motor tests (calibration, saccades, smooth pursuit, optokinetic nystagmus, and gaze testing) assess the central connections of the eye movement system.
Positional tests (sitting, supine, head right, head left, and lying on each side) look for nystagmus in static head positions, and positioning tests (such as the manoeuvre to provoke benign positional vertigo) look for nystagmus triggered by moving the head.
Caloric irrigation (with its own article) completes the series. The test takes 45 to 90 minutes. Abnormalities are found in about 60 to 70% of patients with a vestibular complaint. Central abnormalities of saccades and pursuit point to the brainstem or cerebellum, while spontaneous or positional nystagmus that is suppressed by fixation points to the inner ear.
Indications.
- Dizziness, vertigo, imbalance, or oscillopsia, to separate peripheral from central causes.
- Suspected benign paroxysmal positional vertigo, to show the canal involved by the direction and character of nystagmus.
- Unilateral vestibular loss (vestibular neuritis, labyrinthitis) with spontaneous nystagmus.
- Suspected central disease: stroke, tumour, multiple sclerosis, degenerative ataxia, and medication effects.
- Head injury or whiplash with dizziness, and concussion follow-up.
- Unexplained falls and imbalance in older adults.
- Preoperative and postoperative assessment of ear and skull base surgery.
- Monitoring of drug effects (anticonvulsants, sedatives, aminoglycosides) on eye movements. Not a test of hearing, and a normal test does not exclude vestibular disease that is between attacks.
Contraindications and precautions.
- Neck or spine injury, severe cervical disease, or unstable spine: head and body positioning can cause harm, and positioning tests are modified or omitted.
- Severe carotid or vertebrobasilar disease, recent stroke, or unstable heart disease: caution with head extension and rotation.
- Severe vertigo, vomiting, or fear: the patient is warned, a basin is ready, and the test can be stopped.
- Eye problems that prevent tracking: severe ptosis, blindness, eye surgery, or nystagmus from eye disease. Heavy eye make-up, contact lenses, and very dark irises can affect tracking.
- Drugs that suppress the vestibular system (benzodiazepines, antihistamines, anticonvulsants, alcohol) are held for 24 to 48 hours when it is safe.
- Caffeine and nicotine are avoided for several hours, and the patient should not be fasting excessively.
- Patients with epilepsy sensitive to flashing lights: the light bar stimuli are used with care.
Preparation and technique.
The history is taken and the ear canals are examined. The goggles are fitted and calibrated by asking the patient to follow targets. Ocular motor tests follow: saccades (jump between two targets), smooth pursuit (following a slowly moving target), optokinetic nystagmus (following moving stripes), and gaze tests (looking centre, right, left, up, and down).
The patient is then placed in several positions in darkness: sitting, supine, head turned right and left, and lying on each side, with each position held for 30 to 60 seconds. Positioning tests are done with rapid head-hanging movements, observing for the delay, direction, duration, and fatigability of nystagmus. Spontaneous nystagmus is measured with and without fixation. Recordings are reviewed by the operator and analysed by the system.
