Goldfish retina: Dorsal versus ventral areas

Abstract

The dorsal and ventral portions of the goldfish retina were examined functionally and histologically under various background conditions. Dorsal retina was more sensitive than ventral retina in the scotopic range. Ventral retina was slightly more sensitive in the photopic range. The difference in sensitivity between dorsal and ventral retina increased as a function of decreasing background intensity, the sensitivity of dorsal retina being 2.1 times greater than ventral retina at the lowest back-ground tested. Normalized dorsal and ventral spectral sensitivity curves were similar for the majority of the backgrounds tested. The Weber fraction obtained for the intact eye could be accurately represented by a power function: ΔL/L = aL b ( b = −0.75). The major histological differences observed between dorsal and ventral retina were: (1) the presence of a retinal tapetum lucidum (TL) in dorsal retina—the percent reflectance of the TL increased as a function of decreasing background levels, and (2) a greater cone density and decreased cone diameter in ventral retina. The differences in sensitivity between dorsal and ventral retina as a function of decreasing background levels are accounted for in the discussion by the presence of a TL in dorsal retina and a non-linear Weber function. The greater sensitivity of ventral retina under photopic conditions may be accounted for by the greater cone density in ventral retina and the effective shielding of dorsal TL by PE pigment granules.