Overview of the EOG

An EOG (electro-oculogram) records the electrical difference in biopotentials produced between the cornea and the retina. By placing electrodes outside of the left and right eye outer canthi (region formed by junction of eyelids), above and below the left eye, and on the forehead we will be able to record an individual’s eye movements up to 30 degrees in any direction (7). 

Figure 5: Placement of the electrodes on the face (7)

We will be taking the original signal, which is about 5-20µV for every degree that the eye rotates, and amplifying it by 2000 in order to view it on the screen.  When the subject is looking straight ahead, the corneal-retinal potential has an EOG output of zero. That is because the potentials between the two electrodes are symmetric and cancel each other out. Likewise, when the subject looks left, the cornea moves closer to the left lateral electrode resulting in a positive EOG reading. When the subject looks right, the cornea is closer to the right lateral electrode and will result in a negative EOG output. The same holds true for up and down movements, with up being positive and down being negative. The greater the degree of movement of the subject’s eye, the greater the electrical signal on the monitor will be as shown in the picture below (7).

Figure 6: The movement of the eye in the left and right direction, and resulting EOG signal on monitor (7)