Under scotopic conditions, which wave is typically the earliest measurable response?

Under scotopic conditions, which wave is typically the earliest measurable response?

• A. A-wave
• B. B-wave
• C. C-wave
• D. D-wave

Answer: (A)

Under low-light (scotopic) conditions, the rod system drives the retina’s initial response. When light hits, rod photoreceptors hyperpolarize right away, producing the earliest deflection in the ERG trace—the negative-going a-wave. This first response reflects the photoreceptors themselves reacting to light. The following wave is the b-wave, arising from inner retinal cells (bipolar and Müller cells) and occurring after the a-wave. So, the a-wave is the earliest measurable response under scotopic conditions; the other waves come later as the downstream retinal cells respond.

Under low-light (scotopic) conditions, the rod system drives the retina’s initial response. When light hits, rod photoreceptors hyperpolarize right away, producing the earliest deflection in the ERG trace—the negative-going a-wave. This first response reflects the photoreceptors themselves reacting to light. The following wave is the b-wave, arising from inner retinal cells (bipolar and Müller cells) and occurring after the a-wave. So, the a-wave is the earliest measurable response under scotopic conditions; the other waves come later as the downstream retinal cells respond.