Reciprocity between light intensity and rhodopsin concentration across the rat retina.

1. If a purpose of photostasis - absorption of a constant number of photons by the retina, regardless of incident light levels - is to maintain rods at saturation during the light period, then in retinal regions where light intensity is low, rhodopsin concentration should be high, and vice versa. 2. Our ocular transmission photometric measurements revealed that the distribution of light intensity across the rat retina was not as simple as had been thought and, furthermore, that the local concentration of rhodopsin had a high negative correlation with the light intensity. 3. The reciprocity between these two parameters leads to nearly uniform rates of photon absorption in rods across the retina.