electro-oculogram (EOG)

The electro-oculogram (EOG) records the standing potential between the electrically positive cornea and the electrically negative back of the eye. The potential reflects the activity of the retinal pigment epithelium (RPE) and the photoreceptors.¹

Electrodes on the skin at the inner and outer canthi pick up the potential as the patient looks alternately to extreme left and extreme right gaze.² The potential is smaller in the dark and larger in the light, and the test reports the ratio of the light peak to the dark trough.^1,2 Normal EOG amplitude varies widely from person to person, and the ratio, long called the Arden ratio, removes that variation.^1,2

The EOG is most useful in diagnosing Best disease and in separating it from adult-onset vitelliform macular dystrophy and pattern dystrophy.³ Only diffuse or widespread RPE disease changes the response much, but widespread photoreceptor dysfunction always makes the EOG abnormal.¹ The voltage between the electrodes also changes as the eye rotates, so the same recording can measure eye position.⁴