The multiphasic character of the vertabrate ERG is a well-recognized and generally accepted concept. By convention the initial negative deflection from the resting potential is called the a-wave, the second, corneal positive deflection, the b-wave; another slow positive deflection, the c-wave; and finally, a variably present, negative deflection, the d-wave, associated with the offeffect.
The principal portion of the ERG, comprising the a- and b-waves, has been the subject of extensive investigation for many years. The c-wave, especially as it is present in the human, has received considerably less attention. This may be due, in part, to the fact that no associated potential exists in the optic nerve. In the absence of such a potential, the c-wave is thought to be unrelated to the act of vision.
The literature concerning the nature and origin of the c-wave is confusing. Hartline1 suggested that the c-wave of the human ERG might
PEARLMAN JT. The C-Wave of the Human ERGIts Intensity Dependence and Pupillociliary Origin. Arch Ophthalmol. 1962;68(6):823-830. doi:10.1001/archopht.1962.00960030827018