Electroretinography
Encyclopedia
Electroretinography measures the electrical responses of various cell types in the retina
, including the photoreceptors (rods
and cones
), inner retinal cells (bipolar
and amacrine
cells), and the ganglion cell
s. Electrode
s are usually placed on the cornea
and the skin near the eye
, although it is possible to record the ERG from skin electrodes. During a recording, the patient's eyes are exposed to standardized stimuli
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 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 Muller cells or Muller glia
. The pattern ERG, evoked by an alternating checkerboard stimulus, primarily reflects activity of retinal ganglion cells.
Clinically used mainly by ophthalmologists
and optometrists, the electroretinogram (ERG) is used for the diagnosis of various retinal diseases.
Inherited retinal degenerations in which the ERG can be useful include:
Other ocular disorders in which the standard ERG provides useful information include:
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
.
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
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, including the photoreceptors (rods
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
and cones
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
), inner retinal cells (bipolar
Bipolar cell
As a part of the retina, the bipolar cell exists between photoreceptors and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.-Overview:...
and amacrine
Amacrine cell
Amacrine cells are interneurons in the retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.-Overview:...
cells), and the ganglion cell
Ganglion cell
A retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...
s. Electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s are usually placed on the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
and the skin near the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
, although it is possible to record the ERG from skin electrodes. During a recording, the patient's eyes are exposed to standardized stimuli
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
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 flash ERG is performed on a dark-adapted eye, the response is primarily from the rod system
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
. Flash ERGs performed on a light adapted eye will reflect the activity of the cone system
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
. 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
Bipolar cell
As a part of the retina, the bipolar cell exists between photoreceptors and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.-Overview:...
, amacrine
Amacrine cell
Amacrine cells are interneurons in the retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.-Overview:...
, and Muller cells or Muller glia
Muller glia
Müller glia, or Müller cells, are glial cells found in the vertebrate retina, which normally serve the functions of any normal glial cells. However, following injury to the retina, it has been seen that Müller glia undergo dedifferentiation into multipotent progenitor cells...
. The pattern ERG, evoked by an alternating checkerboard stimulus, primarily reflects activity of retinal ganglion cells.
Clinically used mainly by ophthalmologists
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
and optometrists, the electroretinogram (ERG) is used for the diagnosis of various retinal diseases.
Inherited retinal degenerations in which the ERG can be useful include:
- Retinitis pigmentosaRetinitis pigmentosaRetinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...
and related hereditary degenerations - Retinitis punctata albescens
- Leber's congenital amaurosisLeber's congenital amaurosisLeber's congenital amaurosis is a rare inherited eye disease that appears at birth or in the first few months of life, and affects around 1 in 80,000 of the population.It was first described by Theodor Leber in the 19th century...
- ChoroideremiaChoroideremiaChoroideremia is an X-linked recessive retinal degenerative disease that leads to the degeneration of the choriocapillaris, the retinal pigment epithelium, and the photoreceptor of the eye....
- Gyrate atrophy of the retina and choroid
- Goldman-Favre syndrome
- Congenital stationary night blindnessNyctalopiaNyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition...
- normal a-wave indicates normal photoreceptors; absent b-wave indicates abnormality in the bipolar cellBipolar cellAs a part of the retina, the bipolar cell exists between photoreceptors and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.-Overview:...
region. - X-linked juvenile retinoschisisRetinoschisisRetinoschisis is an eye disease characterized by the abnormal splitting of the retina's neurosensory layers, usually in the outer plexiform layer, resulting in a loss of vision in the corresponding visual field in some rarer forms...
- AchromatopsiaAchromatopsiaAchromatopsia , is a medical syndrome that exhibits symptoms relating to at least five separate individual disorders. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to an autosomal recessive congenital color vision disorder,...
- Cone dystrophyCone dystrophyA cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision....
- Disorders mimicking retinitis pigmentosa
- Usher SyndromeUsher syndromeUsher syndrome is a relatively rare genetic disorder that is a leading cause of deafblindness and that is associated with a mutation in any one of 10 genes. Other names for Usher syndrome include Hallgren syndrome, Usher-Hallgren syndrome, rp-dysacusis syndrome and dystrophia retinae dysacusis...
Other ocular disorders in which the standard ERG provides useful information include:
- Diabetic retinopathyDiabetic retinopathyDiabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....
- Other ischemic retinopathies including central retinal vein occlusionCentral retinal vein occlusionThe central retinal vein is the venous equivalent of the central retinal artery, and like that blood vessel can suffer from occlusion , similar to that seen in ocular ischemic syndrome...
(CRVO), branch vein occlusion (BVO), and sickle cell retinopathy - Toxic retinopathies, including those caused by Plaquenil and VigabatrinVigabatrinVigabatrin is an antiepileptic drug that inhibits the catabolism of gamma-aminobutyric acid by irreversibly inhibiting GABA transaminase. It is an analog of GABA, but it is not a receptor agonist...
. 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
- Assessment of retinal function after trauma, especially in vitreous hemorrhage 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
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...
.
The multifocal
Multifocal technique
Multifocal techniques are used in electroretinogram and visual evoked potential recordings to separate the responses originating from the stimulation of different locations in the visual field ....
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
See also
- ElectrooculographyElectrooculographyElectrooculography is a technique for measuring the resting potential of the retina. The resulting signal is called the electrooculogram. The main applications are in ophthalmological diagnosis and in recording eye movements...
- Visual evoked potential