Retinal ganglion cell loss does not abolish the scotopic threshold response (STR) of the cat and human ERG

The scotopic threshold response (STR) is a negative wave in the electroretinogram (ERG) elicited by very dim stimuli near visual threshold. Previous work demonstrated that it originates postsynaptic to the photoreceptors and is not the a-wave. Current source density (CSD) analysis had suggested an origin proximal in the retina. To learn whether ganglion cells generate the STR, we cut one optic nerve of three cats. The STR of these eyes was unchanged in amplitude compared with control eyes at 6, 10 and 21 months after optic nerve section. Retinal histology showed a loss of ganglion cells and thinning of the nerve fiber layer in the experimental eyes. We also recorded the ERG from a patient with unilateral, complete optic atrophy from traumatic optic nerve section 22 yr previously. The VECP was absent but the STR was still present on the affected side. We concluded that ganglion cells are not primarily responsible for STR generation.