What is electroretinography (ERG)?

Electroretinography is an electrophysiological test of the retina, the layer of the eye which detects light. The electroretinogram (ERG) is to the retina what the electrocardiogram (ECG) is to the heart. Just as an ECG is crucial to diagnosing illness and monitoring the heart’s function, ERG plays a critical role in the care of the eye, and is instrumental in the early detection of retinal dysfunction.

Why does ERG matter?

Electroretinography provides a wealth of objective, vital information about retinal function and health. ERG plays a vital role in the diagnosis of acquired and inherited eye diseases, as well as fuel research into the factors that affect the health of the retina or the visual pathways.

How VEP works

A light stimulus provided by a computer monitor or ganzfeld bowl is received by the retinal cells of the eye. The electric potential travels from the retina to the visual cortex of the brain. Electrodes placed on the occipital lobe record the resulting electrical activity within the visual cortex.

What VEP tells us

Abnormalities in the VEP indicate potential distruptions in the visual pathway. VEP can help to detect the causitive mechanism of visual deficits.

• It is useful as a test of the visual pathway as a whole.

• Normal VEP indicates that visual information is successfully transmitted to the brain’s visual cortex for interpretation.

• Abnormalities may indicate issues with the transmission from the eye to the visual cortex.

What do electro-oculogram (EOG) tests measure?

The Electro-Oculogram (EOG) provides a measure of retinal function that depends upon the integrity of the retinal pigment epithelial layer. When this layer is healthy, a standing potential is established between the front and the back of the eye that responds to changes in background illumination. The standing potential in the eye is estimated by measuring the voltage induced across a pair of electrodes as the eye looks from side to side. This potential declines during dark adaptation to a minimum value and rises during light adaptation to a maximum value before returning to a steady equilibrium value. The ratio of the maximum amplitude under light adapted conditions divided by the minimum amplitude under dark adapted conditions is called the Arden ratio. The Arden ratio is the standard diagnostic measure of the EOG.

Fast-Oscillation (FO) EOG

In FO, a minimum of six light/dark cycles are used. Each light or dark period lasts between 60 and 80 seconds and the rest period associated with standard EOG is eliminated to avoid missing peaks.

An effort is being made to standardize FO protocols for corollary purposes. Initial testing suggests that FO is an equally reliable measure to standard EOG.

Related Conditions

• Best’s Disease

• Inherited Retinal Disorders

• Stationary Night Blindness

• Pigment Epithelial Dystrophies