Table 1 Some differences between EOG and VOG
ELECTRO-oculography (EOG) | VIDEO-oculography (VOG) | |
|---|---|---|
Entity measured | Corneo-retinal electrical potential | Digitized position of a black circle presumed to be the pupil |
Drift | Shift of baseline if DC recording used. | Theoretically no shift |
Variable if AC recording | ||
Artifact | Eye blinks and muscle contraction are the most frequent artifacts | Dark features such as mascara, closed eyes, eye brows “fool” the system momentarily. |
Eye blinks, difficulty detecting the pupil causes large artifacts | ||
Sampling rates | While most commercial units sample calorics at 30 Hz, much higher sampling rates are feasible. This is critical for accurate measurement of quick phases | Video sampling rates are usually 30–60 Hz. Sampling rates of 100 Hz requires specialized equipment. |
Ease of use | Sticky electrodes are required with possible impedance problems, electrical drift and small signal | The patient wears goggles to mount the camera to, which limits eye displacement to approximately 20° |
Determination of maximum slow phase velocity (SPEV) | Maximum average SPEV of the three greatest consecutive beats | Maximum average SPEV for a 10 s window of recording |