EOG (ElectroOculoGraphy) measures eye movement. It detects movement by placing electrodes near the eye. We distinguish VEOG for vertical eye movement (looking up and down) and HEOG for horizontal eye movement (looking left and right). EOG measurement is noninvasive and sometimes used together when doing EEG measurement or neurofeedback training.
The human eye acts as an electrical dipole: it has a positive charge at the front (cornea) and a negative charge at the back (retina). By placing two electrodes in the electrical field of the eye (either above and beneath the eye or left and right of the eye) the difference in electrical charge is measured. As the eye moves, the EOG measurement detects changes in the electrical charge between the cornea and retina. In this way, eye movement can be deducted.
When using the EOG signal, the frequency of the signal is of less interest. For interpretation of the signal, we look at the shape (morphology) and amplitude of the signal. EOG is usually measured together with EEG. Slow eye movements in the vertical axis (looking up and down) can generate vertical shifts in the EEG signal measured on the scalp. Eye blinks appear as spikes in the VEOG signal.