ELECTRORETINOGRAM BASICS PDF

The electrical basis of ERG recordings. ERG responses are recorded with an active extracellular electrode positioned either on the cornea, in the vitreous or at different levels inside the retina. Extracellular recording of electrical activity of living tissue is rendered possible when electrical currents spread along an extracellular matrix with electrical resistance. Similarly, extracellular currents from all retinal cell types will sum up only if they are directed radially. In contrast, lateral currents will cancel each other since the retinal lateral arrangement is completely symmetrical.

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What is electroretinography? An electroretinography ERG test, also known as an electroretinogram, measures the electrical response of the light-sensitive cells in your eyes. These cells are known as rods and cones. They form part of the back of the eye known as the retina. There are around million rods in the human eye and six to seven million cones. Your doctor may perform an ERG to determine if you have an inherited or acquired disorder of the retina, such as: retinitis pigmentosa, which is a genetic disease causing loss of peripheral and night vision macular degeneration, which is a loss of vision due to the death of cells in the macula retinoblastoma, which is a cancer of the retina retinal separation, which is a detachment of the retina from the back of the eyeball cone rod dystrophy CRD , which is vision loss due to impaired cone and rod cells An ERG may also help your doctor assess your need for retinal surgery or other types of eye surgery, such as the removal of cataracts.

The following occurs during an ERG: Your doctor will ask you to lie down or sit in a comfortable position. If your doctor is placing an electrode directly on the eye, they will place anesthetic drops in your eyes, which will make them numb.

This will enable them to carefully place a small electrode on each eye. One type of electrode is about the size of a contact lens. Another type is a fine thread placed on the cornea.

Your doctor will attach another electrode to your skin so that it functions as a ground for the faint electrical signals made by the retina. Depending on what your doctor is looking for, they may only place electrodes on the skin around the eye instead of in the eye. Your doctor will conduct the test in normal light and in a darkened room. The information from the electrodes transfers to a monitor.

The monitor displays and records the information. It appears as a-waves and b-waves. It represents the initial negative deflection of a flash of light measuring rods and cones. The b-wave, or positive deflection, follows. What do the results mean? Abnormal Results Abnormal results may indicate any of the following conditions: arteriosclerosis damage to the retina congenital retinoschisis, which is a splitting of layers in the retina congenital night blindness.

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The Electroretinogram and Electro-oculogram: Clinical Applications by Donnell J. Creel

What is electroretinography? An electroretinography ERG test, also known as an electroretinogram, measures the electrical response of the light-sensitive cells in your eyes. These cells are known as rods and cones. They form part of the back of the eye known as the retina. There are around million rods in the human eye and six to seven million cones. Your doctor may perform an ERG to determine if you have an inherited or acquired disorder of the retina, such as: retinitis pigmentosa, which is a genetic disease causing loss of peripheral and night vision macular degeneration, which is a loss of vision due to the death of cells in the macula retinoblastoma, which is a cancer of the retina retinal separation, which is a detachment of the retina from the back of the eyeball cone rod dystrophy CRD , which is vision loss due to impaired cone and rod cells An ERG may also help your doctor assess your need for retinal surgery or other types of eye surgery, such as the removal of cataracts.

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Electroretinogram

Nijora They replaced the vitreous humor of cats with heavy oil to abolish current flow from the retina to distant sites and thereby ensured large potential recordings of local ERG from the retinal surface. Amplitude and Implicit Time Measurements The most common ERG response from a human, which is elicited with a full-field Ganzfeld flash of light, contains the a-wave and the b-wave as shown in Fig. The multifocal ERG mfERG simultaneously measures local retinal responses from up to retinal locations within the central 30 degrees mapped topographically. Such analysis can also be used to compare ERG data between laboratories as shown in Fig.

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The Electroretinogram: ERG by Ido Perlman

The electrical response is a result of a retinal potential generated by light-induced changes in the flux of transretinal ions, primarily sodium and potassium. Most often, ERGs are obtained using electrodes embedded in a corneal contact lens, which measure a summation of retinal electrical activity at the corneal surface. The ERG can provide important diagnostic information on a variety of retinal disorders including, but not limited to congenital stationary night blindness, Leber congenital amaurosis, and cancer-associated retinopathy. Moreover, an ERG can also be used to monitor disease progression or evaluating for retinal toxicity with various drugs or from a retained intraocular foreign body.

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ELECTRORETINOGRAM BASICS PDF

Rod phototransduction in retinitis pigmentosa: It is clear from Fig. Scotopic threshold response STR of the human electroretinogram. The elcetroretinogram of the b-wave is measured from the trough of the a-wave to the peak more Signal transmission along retinal rods and the origin of the electroretinographic a-wave. Furthermore, the temporal properties of P-II are of value to the clinician. The ERG originates from extracellular currents that are generated in response to a light stimulus.

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