ELECTRONYSTAGMOGRAPH (ENG)

Typical Number in Hospital: 2

Cost Bands: 4

References:

Nystagmus is an involuntary eye movement which occurs during an attack of dizziness or vertigo. The electronystagmograph can be used to record spontaneous or induced nystagmus by placing surface electrodes (usually EEG-type silver/silver chloride fluid column electrodes) at either side of the patient's eyes. The small voltages so recorded are derived from the corneo-retinal potential of the eyeball. The electronystagmograph consists of an amplifier with filters (typically 0.1 Hz to 30 Hz) connected to a chart recorder with a paper speed of 1 cm/s. Single channel machines are most common and record the lateral eye movement of both eyes although multichannel machines allow the separate analysis of each eye in horizontal and vertical planes. This is sometimes called an electro-oculograph (EOG).

Electronystagmographs are normally found in audiology departments and are used in conjunction with caloric apparatus and an optokinetic drum to induce nystagmus. Many of the tests are conducted in total darkness since the patient's observed environment has a large effect upon his eye movements (nystagmus usually disappears if the patient is able to fix his gaze on something he can see). The infrared viewer and Frenzel glasses are other devices to enable eye movement to be assessed without the patient being able to fix his gaze.