EOG- determines function of outer retina and RPE.The standing potential may be determined in 2 ways: TEP is the difference of membrane potential of basolateral and apical membranes of RPE. Standing potential indirectly measures the transepithelial potential (TEP) of the retinal pigment epithelium (RPE). The difference of electrical potential of the anterior and posterior part of the eyeball is called the standing potential. Four recording skin electrodes (silver-silver chloride or gold-disk) are placed at the medial and lateral canthi of both eyes, and the grounding electrode is placed on the forehead. The patient is told to remain still other than moving his/her eyes back and forth. Strong retinal illumination including retinal imaging (fluorescein angiogram, fundus photography and others) and indirect ophthalmoscopy should be avoided during this period.

The patient should be in stable indoor lighting for at least 30 min before the test. Thus the pupillary diameter may change the needed luminance for the same effect on the retina. The amount of light passing through the pupils is measured in a unit called Trolands (the product of luminance (cd/m2) and pupil area (mm 2)). Clinical applications were described first by Geoffrey Arden in 1962, who realized that the most valuable information was the comparison of the amplitudes under light and dark-adapted states (the Arden ratio). The EOG was described and named by Elwin Marg in 1951. The mean transepithelial voltage of bovine Retinal pigment epithelium is 6 millivolts (mV).

The electroocoulogram (EOG) is an elecrophysiologic test that measures the existing resting electrical potential between the cornea and Bruch's membrane.

6.2.4 Conditions that increased systemic standing potential.

6.2.3 Drugs that reduce systemic standing potential.

Winscan eog