Which ERG wave is characterized as negative?

The A wave of the electroretinogram (ERG) is characterized as negative because it represents the electrical activity primarily generated by the photoreceptors, specifically the phototransduction process of the rods. When light hits the photoreceptors, it causes hyperpolarization of these cells, which leads to the negative deflection observed in the ERG recording.

The A wave occurs first in response to light stimulation and indicates the response from the outer retina, particularly from the photoreceptors and the bipolar cells that are involved in the phototransduction pathway. This wave reflects a decrease in electrical potential due to the hyperpolarization of photoreceptors and has a negative amplitude on the ERG trace.

The other waves in the ERG, such as the B wave, are characterized by positive deflections, as they arise from the inner retinal layers, including the bipolar and ganglion cells, which produce a depolarizing response following the initial hyperpolarization of the photoreceptors. Understanding these distinctions helps clarify the nature of the retinal responses being recorded during an ERG examination.