Electrooculography

The electrooculography or -graphy (EOG ) is a measurement method in which either eye movements or changes in the resting potential of the retina are measured. In both cases, the electric voltage is discharged, which occurs between two electrodes, which are the left and right (or above and below ) of the eye applied to the skin. The rest potential is a constant electrical potential difference existing between the front and back of the retina, which results in the cornea of the eyeball and the back positive are negatively charged.

Eye movement measurement

The procedure employed in this case is also called electronystagmography. If it is assumed in the measurement, a constant resting potential of the retina. By eye movements to the front of the eye of an electrode approaches, while the back is approaching the other electrode. This results in a voltage difference between the electrodes is measured. This voltage difference is approximately proportional to the angle.

Since eye movements are not only arbitrary, but also controlled by the equilibrium system, the method is not only used for the diagnosis of nystagmus, but also of the equilibrium system. When polysomnography the EOG channel of the recording of the REM phases used. Unlike other eye movement measurements, an EOG can be recorded even with closed eyes, for example, to measure whether a subject responds to sounds with eye movements.

Measurement of changes of the resting potential

For this measurement, the patient is asked to look regularly between two fixed points back and forth. With a constant resting potential of the same voltage change would be measured at each viewing direction. However, changes the lighting situation, so changes the resting potential and thus the size of the measured with the view direction changes voltage change. In a typical clinical examination is first examined how the resting potential after switching off the lighting changes ( dark adaptation ). Usually you can find here a slight decrease in resting potential over several minutes. Then the patient is once again exposed to a light, which usually results in a temporary sharp increase of the resting potential, which also takes a few minutes. Changes from this typical profile are an indication of a disease of the pigment epithelium of the retina.