Is the a-wave positive or negative in an ERG?

Is the a-wave positive or negative in an ERG?

• A. Positive
• B. Negative
• C. Neutral
• D. Cannot be determined

Answer: (B)

The initial part of an ERG waveform is driven by photoreceptor activity. When light hits the retina, photoreceptors hyperpolarize, which reduces the dark current. With a typical corneal electrode setup, this change appears as a downward, or negative, deflection right after the light stimulus—the a-wave. The next positive deflection that follows is the b-wave, produced mainly by ON-bipolar cells and Müller cells. So, in standard recordings, the a-wave is negative. The other options don’t fit the usual pattern: there is a definite deflection, and its polarity is defined by the photoreceptor response, not neutral or indeterminate.

The initial part of an ERG waveform is driven by photoreceptor activity. When light hits the retina, photoreceptors hyperpolarize, which reduces the dark current. With a typical corneal electrode setup, this change appears as a downward, or negative, deflection right after the light stimulus—the a-wave. The next positive deflection that follows is the b-wave, produced mainly by ON-bipolar cells and Müller cells. So, in standard recordings, the a-wave is negative. The other options don’t fit the usual pattern: there is a definite deflection, and its polarity is defined by the photoreceptor response, not neutral or indeterminate.