Question
Wave as “marked by an arrow” shown on photograph of Electroretinogram is due to ?
A. Rods.
B. Cones.
C. Bipolar cells.
D. Pigment epithelium.
Show Answer
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Correct Answer » C Explanation |
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Ans:C. Bipolar cells.
B wave is marked in Electroretinogram.
Electroretinogram (ERG)
- It is a diagnostic test that measures the electrical activity generated by neural and non-neuronal cells in the retina in response to a light stimulus.
- 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 a-wave, sometimes called the “late receptor potential,” reflects the general physiological health of the photoreceptors in the outer retina.
In contrast, the b-wave reflects the health of the inner layers of the retina, including the ON bipolar cells and the Muller cells.
Two other waveforms that are sometimes recorded in the clinic are the c-wave originating in the pigment epithelium and the d-wave indicating activity of the OFF bipolar cells.
Two principal measures of the ERG waveform are taken:
- The amplitude (a) from the baseline to the negative trough of the a-wave, and the amplitude of the b-wave measured from the trough of the a-wave to the following peak of the b-wave; and
- the time (t) from flash onset to the trough of the a-wave and the time (t) from flash onset to the peak of the b-wave .These times are referred to as “implicit times” in electroretinography.
