Electro-Oculogram (EOG)
Electrooculography (EOG) is a technique for measuring the corneo-retinal standing potential that exists between the front and the back of the human eye. Other areas of the visual pathway can be investigated by specific electrical tests. The electro-oculogram (EOG) investigates abnormalities of the outermost layer of the retina, the retinal pigment epithelium, allowing the early diagnosis of some inherited macular diseases such as Best disease.
The EOG is used to assess the function of the pigment epithelium. During dark adaptation, resting potential decreases slightly and reaches a minimum ("dark trough") after several minutes. When light is switched on, a substantial increase of the resting potential occurs ("light peak"), which drops off after a few minutes when the retina adapts to the light. The ratio of the voltages (i.e. light peak divided by dark trough) is known as the Arden ratio. In practice, the measurement is similar to eye movement recordings. The patient is asked to switch eye position repeatedly between two points (alternating looking from center to the left and from center to the right). Since these positions are constant, a change in the recorded potential originates from a change in the resting potential.
Ophthalmic Electro-Diagnostic Test
Test Name | Area Tested | Time Taken | Dilating Drops |
| Flash ERG | Global Retina(rods and cones) | 60 minutes | Yes |
| Pattern ERG | Macular (central retinal) function | 30 minutes | No |
| EOG | Retinal Pigment epithelium | 30 minutes | No |
| Cortical VEP | Visual pathway (optic nerve to visual center in brain | 45 minutes | No |
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