A scotopic (b-wave) component of the human electroretinogram which results from small (1° to 12°) area stimulation has previously been shown, by the writer and others, to arise almost entirely from stray light in the eye which weakly illuminates large peripheral areas where the rods predominate. It is now indicated that for intermediate (45°) areas, a double-peaked b-wave is elicited which is believed to reflect activity aroused separately by image and stray light stimulus components. When extremely large (over 100°) stimulus areas are used, a unimodal response can be elicited using very weak luminances of stimulation. Since the large area response is mainly attributable to direct retinal stimulation, a basis is provided for comparing the effects of stray light (small area) and direct (very large area) stimulation. From such comparisons, it is concluded that (1) over four times as much luminous flux is required for a small stimulus to elicit a given b-wave as for a very large one to do so, (2) one of the stray light components is Rayleigh (small particle) scatter, and (3) large-particle scatter and reflection from the fundus are also involved.
ROBERT M. BOYNTON, "Stray Light and the Human Electroretinogram," J. Opt. Soc. Am. 43, 442-449 (1953)