electrooculogram

The electrooculogram, often abbreviated as EOG, is a non-invasive diagnostic test that measures the resting electrical potential of the eye. This potential is generated by the retinal pigment epithelium and is influenced by light. The EOG records the difference in electrical potential between electrodes placed on the skin around the eye as the eye moves in different directions.

To perform an EOG, several electrodes are typically attached to the skin surrounding the eyes, usually at the inner and outer canthi. The patient is then asked to move their eyes horizontally between two illuminated targets positioned at the extremes of their visual field. This movement causes a change in the electrical potential, which is detected by the electrodes and recorded by an electrophysiological device. The amplitude of the potential difference varies depending on the position of the eye relative to the electrodes.

The EOG is primarily used to assess the function of the retinal pigment epithelium (RPE) and the integrity of the outer retina. It is particularly useful in diagnosing and monitoring conditions such as Best disease, a form of inherited macular degeneration, and other retinal dystrophies where RPE function is impaired. The test is also employed in research studies investigating visual function and retinal diseases. The results are typically expressed as a ratio of the light-peak potential to the dark-trough potential, known as the Arden ratio, which provides a quantitative measure of RPE function. A normal Arden ratio indicates healthy RPE function, while a reduced ratio suggests a defect.