An electrooculogram, or EOG, is a recording of the resting potential of the retina. The main applications are in ophthalmological diagnosis and in recording eye movements. As opposed to the electroretinogram, the EOG does not represent the response to individual visual stimuli.
Usually, pairs of electrodes are placed either above and below the eye or to the left and right of the eye. If the eye is moved from the center position towards one electrode, this electrode “sees” the positive side of the retina and the opposite electrode “sees” the negative side of the retina. Consequently, a potential difference occurs between the electrodes. Assuming that the resting potential is constant, the recorded potential is a measure for the eye position.