Question

The amplitude of the ERG voltage is typically

• A. 50 mV and is a function of the movement of the eye
• B. 5 mV and is a function of the intensity of the light falling on the eye
• C. 500 $\mu$V and is a function of the intensity of the light falling on the eye
• D. 50 $\mu$V and is a function of the movement of the eye

Hint:

The Electroretinogram (ERG) measures the retina's electrical response to light. It operates in the microvolt range ($\approx 500\ \mu$V) and its amplitude depends directly on the intensity of the light stimulus.

Answer 1

The Correct Option is C

Concept: An Electroretinogram (ERG) measures the electrical responses of various cell types in the retina, including photoreceptors (rods and cones), inner retinal cells, and ganglion cells. This biopotential is recorded using a non-invasive electrode placed on the surface of the cornea in response to a visual stimulus.

Step 1: Determining the signal amplitude scale.
Retinal electrical potentials are very small when recorded from the cornea. A typical clean ERG waveform (consisting of the initial negative $a$-wave followed by the positive $b$-wave) has a peak amplitude scale in the microvolt range, typically around 100 $\mu$V to 500 $\mu$V ($0.1\text{ mV}$ to $0.5\text{ mV}$). This rules out large millivolt-scale choices like 5 mV or 50 mV.

Step 2: Identifying the physiological driver.
The ERG is an evoked potential that measures the retina's electrical response to light stimulation. The amplitude of the $b$-wave is directly driven by the intensity of the light stimulus falling on the retina. By contrast, the signal that tracks eye movement is the Electrooculogram (EOG), which measures the permanent metabolic dipole potential between the cornea and the retina as the eye rotates. Therefore, an ERG is characterized by a microvolt-scale amplitude ($\approx 500\ \mu\text{V}$) and varies as a function of light intensity, confirming Option (C).