Electroretinography measures the electrical responses of various cell types in the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

, including the photoreceptors ( rods and

cones In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the ''apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines, ...

), inner retinal cells ( bipolar and amacrine cells), and the ganglion cells.

Electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s are placed on the surface of the

cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...

(DTL silver/nylon fiber string or ERG jet) or on the skin beneath the eye (sensor strips) to measure retinal responses.

Retinal pigment epithelium The pigmented layer of retina or retinal pigment epithelium (RPE) is the pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), ...

(RPE) responses are measured with an EOG test with skin-contact electrodes placed near the

canthi The canthus (: canthi, palpebral commissures) is either corner of the eye where the upper and lower eyelids meet. More specifically, the inner and outer canthi are, respectively, the medial and lateral ends/angles of the palpebral fissure. The ...

. During a recording, the patient's eyes are exposed to standardized

stimuli A stimulus is something that causes a physiological response. It may refer to: *Stimulation **Stimulus (physiology), something external that influences an activity **Stimulus (psychology), a concept in behaviorism and perception *Stimulus (economi ...

and the resulting signal is displayed showing the time course of the signal's amplitude (voltage). Signals are very small, and typically are measured in microvolts or nanovolts. The ERG is composed of electrical potentials contributed by different cell types within the retina, and the stimulus conditions (flash or pattern stimulus, whether a background light is present, and the colors of the stimulus and background) can elicit stronger response from certain components. If a dim flash ERG is performed on a dark-adapted eye, the response is primarily from the rod system. Flash ERGs performed on a light adapted eye will reflect the activity of the cone system. Sufficiently bright flashes will elicit ERGs containing an a-wave (initial negative deflection) followed by a b-wave (positive deflection). The leading edge of the a-wave is produced by the photoreceptors, while the remainder of the wave is produced by a mixture of cells including photoreceptors, bipolar, amacrine, and Müller cells or

Müller glia Müller glia, or Müller cells, are a type of retinal glial cells, first recognized and described by Heinrich Müller (physiologist), Heinrich Müller. They are found in the vertebrate retina, where they serve as support cells for the neurons, as ...

. The pattern ERG (PERG), evoked by an alternating checkerboard stimulus, primarily reflects activity of

retinal ganglion cell A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptor cell, photoreceptors via two intermediate neuron types: Bipolar ...

Diagnostics

Clinically used mainly by

ophthalmologists Ophthalmology (, ) is the branch of medicine that deals with the diagnosis, treatment, and surgery of eye diseases and disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a ...

the electroretinogram (ERG) is used for the diagnosis of various retinal diseases. Inherited retinal degenerations in which the ERG can be useful include: *

Retinitis pigmentosa Retinitis pigmentosa (RP) is a member of a group of genetic disorders called inherited retinal dystrophy (IRD) that cause loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visua ...

and related hereditary degenerations * Retinitis punctata albescens *

Leber's congenital amaurosis Leber congenital amaurosis (LCA) is a rare inherited eye disease that appears at birth or in the first few months of life. It affects about 1 in 40,000 newborns. LCA was first described by Theodor Leber in the 19th century. It should not be ...

* Choroideremia * Gyrate atrophy of the retina and choroid * Goldman-Favre syndrome *

Congenital stationary night blindness Congenital stationary night blindness (CSNB) is a rare non-progressive retinal disorder. People with CSNB often have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients may also have reduced visu ...

- ''normal a-wave indicates normal photoreceptors; absent b-wave indicates abnormality in the

bipolar cell A bipolar neuron, or bipolar cell, is a type of neuron characterized by having both an axon and a dendrite extending from the soma (cell body) in opposite directions. These neurons are predominantly found in the retina and olfactory system. The em ...

region.'' * X-linked juvenile

retinoschisis Retinoschisis is an eye disease characterized by the abnormal splitting of the retina's neurosensory layers, usually in the outer plexiform layer. Retinoschisis can be divided into degenerative forms which are very common and almost exclusively i ...

Achromatopsia Achromatopsia, also known as rod monochromacy, is a medical syndrome that exhibits symptoms relating to five conditions, most notably monochromacy. Historically, the name referred to monochromacy in general, but now typically refers only to an aut ...

Cone dystrophy A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision. Presentation The most common symptoms of cone dystrophy are vision loss (age of onset ...

* Disorders mimicking retinitis pigmentosa *

Usher syndrome Usher syndrome, also known as Hallgren syndrome, Usher–Hallgren syndrome, retinitis pigmentosa–dysacusis syndrome or dystrophia retinae dysacusis syndrome, is a rare genetic disorder caused by a mutation in any one of at least 11 genes result ...

Other ocular disorders in which the standard ERG provides useful information include: *

Diabetic retinopathy Diabetic retinopathy (also known as diabetic eye disease) is a medical condition in which damage occurs to the retina due to diabetes. It is a leading cause of blindness in developed countries and one of the lead causes of sight loss in the wor ...

* Other ischemic retinopathies including

central retinal vein occlusion Central retinal vein occlusion, also CRVO, is when the central retinal vein becomes occluded, usually through thrombosis. The central retinal vein is the venous equivalent of the central retinal artery and both may become occluded. Since the cent ...

(CRVO), branch vein occlusion (BVO), and

sickle cell retinopathy Sickle cell retinopathy can be defined as retinal changes due to blood vessel damage in the Human eye, eye of a person with a background of sickle cell disease. It can likely progress to loss of vision in late stages due to vitreous hemorrhage or r ...

* Toxic retinopathies, including those caused by Plaquenil and Vigabatrin. The ERG is also used to monitor retinal toxicity in many drug trials. * Autoimmune retinopathies such as cancer associated retinopathy (CAR), melanoma associated retinopathy (MAR), and acute zonal occult outer retinopathy (AZOOR) *

Retinal detachment Retinal detachment is a condition where the retina pulls away from the tissue underneath it. It may start in a small area, but without quick treatment, it can spread across the entire retina, leading to serious vision loss and possibly blindness. ...

* Assessment of retinal function after trauma, especially in vitreous hemorrhage, dense cataracts, and other conditions where the fundus cannot be visualized. The ERG is also used extensively in eye research, as it provides information about the function of the retina that is not otherwise available. Other ERG tests, such as the photopic negative response (PhNR) and pattern ERG (PERG) may be useful in assessing retinal ganglion cell function in diseases like

glaucoma Glaucoma is a group of eye diseases that can lead to damage of the optic nerve. The optic nerve transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of ...

. The multifocal ERG is used to record separate responses for different retinal locations. The international body concerned with the clinical use and standardization of the ERG, EOG, and VEP is the International Society for the Clinical Electrophysiology of Vision (ISCEV).

Other uses

In addition to its clinical diagnostic purpose, the ERG can be used during the course of

drug development Drug development is the process of bringing a new pharmaceutical drug to the market once a lead compound has been identified through the process of drug discovery. It includes preclinical research on microorganisms and animals, filing for regu ...

and in clinical trials for testing ocular safety and efficacy of new or existing drugs and treatment modalities. A 2013 study by Nasser et al. found that the retinal

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. It is an amine synthesized ...

rgic response to eating a brownie is equivalent in magnitude to the response to a 20 mg dose of

methylphenidate Methylphenidate, sold under the brand names Ritalin ( ) and Concerta ( ) among others, is a central nervous system (CNS) stimulant used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It may be taken Oral adm ...

, which implies that the activity of dopamine neurons in the retina reflects brain dopaminergic activity. The study concludes that, if verified by further research, "ERG could provide the neurotransmitter specificity of

PET A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive/ cute appearances, inte ...

at a much lower cost". The ERG has been shown to differ in people with schizophrenia and may be useful in helping to differentiate schizophrenia and bipolar disorder.

History

ERG was one of the earliest recorded biological potential. The first known ERG was recorded by the Swedish physiologist

Alarik Frithiof Holmgren Alarik Frithiof Holmgren (October 22, 1831 – August 14, 1897) was a Swedish physician, physiologist and professor at Upsala University, most noted for his research of color blindness. He was a vocal opponent of vivisection, and particularly the ...

, who recorded it in 1865 on an

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

retina. However, he failed to understand his findings accurately. He thought the responses he recorded were from the optic nerve instead of the retina. The first human ERG was recorded in 1877 by Scottish chemist and physicist

Sir James Dewar Sir James Dewar ( ; 20 September 1842 – 27 March 1923) was a Scottish chemist and physicist. He is best known for his invention of the vacuum flask, which he used in conjunction with research into the liquefaction of gases. He also studie ...

. James Dewar and

John Gray McKendrick John Gray McKendrick (12 August 1841 – 2 January 1926) was a Scottish physiologist. He served as Regius Professor of Physiology at the University of Glasgow from 1876 to 1906, and was co-founder of the Physiological Society. Early life McKe ...

independently suggested that the biological potential was from retina. In 1908, Einthoven and Jolly divided the ERG response into three components: A-wave, B-wave, and C-wave. In 1941, American psychologist Lorraine Riggs introduced a

contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

electrode for ERG recording. Many of Ragnar Granit's observations became the basis of ERG understanding, for which he was awarded the 1967

Nobel Prize in Physiology and Medicine The Nobel Prize in Physiology or Medicine () is awarded yearly by the Nobel Assembly at the Karolinska Institute, Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single ...

References

{{Authority control Diagnostic ophthalmology Electrodiagnosis

Diagnostics

Other uses

History

See also

References