Electroretinography

Electroretinography

Electroretinography (ERG) is a technique employed to measure the electrical responses of various cell types within the retina, encompassing photoreceptors (rods and cones), inner retinal cells (bipolar and amacrine cells), and ganglion cells. Electrodes are typically positioned on the cornea and adjacent skin areas near the eye, although ERG can also be recorded from skin electrodes. During the procedure, standardized stimuli are presented to the patient's eyes, and the resultant signal displays the amplitude (voltage) over time.

The signals obtained are exceedingly minute, usually quantified in microvolts or nanovolts. The ERG waveform comprises electrical potentials contributed by diverse retinal cell types, and variations in stimulus conditions (such as flash or pattern stimuli, presence of background light, and stimulus/background colors) can evoke stronger responses from specific components.

In a flash ERG conducted on a dark-adapted eye, the response primarily arises from the rod system. Conversely, flash ERGs performed on light-adapted eyes reflect cone system activity. Intense flashes can elicit ERGs characterized by an initial negative deflection (a-wave) followed by a positive deflection (b-wave). The a-wave's leading edge originates from photoreceptors, while the remaining portion results from a combination of cells including photoreceptors, bipolar, amacrine, and Muller cells or glia. Pattern ERGs, evoked by alternating checkerboard stimuli, predominantly mirror the activity of retinal ganglion cells.

Primarily utilized by ophthalmologists and optometrists in clinical settings, ERG aids in diagnosing various retinal ailments.

Inherited retinal degenerations for which ERG is valuable include:

 • Retinitis pigmentosa and related hereditary degenerations
 • Retinitis punctata albescens
 • Leber's congenital amaurosis
 • Choroideremia
 • Gyrate atrophy of the retina and choroid
 • Goldman-Favre syndrome
 • Congenital stationary night blindness (CSNB) - normal a-wave signifies intact photoreceptors; absent b-wave suggests bipolar cell region abnormality.
 • X-linked juvenile retinoschisis
 • Achromatopsia
 • Cone dystrophy
 • Disorders mimicking retinitis pigmentosa
 • Usher Syndrome

Other ocular conditions where standard ERG provides valuable insights include:

 • Diabetic retinopathy
 • Ischemic retinopathies like central retinal vein occlusion (CRVO), branch vein occlusion (BVO), and sickle cell retinopathy
 • Toxic retinopathies induced by medications like Plaquenil and Vigabatrin, and also utilized in monitoring retinal toxicity in drug trials.
 • Autoimmune retinopathies such as Cancer Associated Retinopathy (CAR), Melanoma Associated Retinopathy (MAR), and Acute Zonal Occult Outer Retinopathy (AZOOR)
 • Retinal detachment
 • Evaluation of retinal function post-trauma, especially in conditions like vitreous hemorrhage where fundus visualization is challenging.

ERG also serves as a crucial tool in eye research, furnishing insights into retinal function not accessible through other means.

Additional ERG tests like Photopic Negative Response (PhNR) and pattern ERG (PERG) are valuable in assessing retinal ganglion cell function, particularly in conditions like glaucoma.

Multifocal ERG enables recording of distinct responses for various retinal locations.

The International Society for the Clinical Electrophysiology of Vision is the international body overseeing the clinical application and standardization of ERG, EOG, and VEP.