Tasks

As described above, the cone receptors serve for daytime vision. Through the three types of cones (blue, red and green) and a process of additive color mixing, the colors we see can be seen. This process is different from physical, subtractive color mixing, which is the case, for example, when mixing painter’s colors.

In addition, the cones, especially in the visual pit – the place of sharpest vision, also serve for sharp vision with a high resolution. This is due in particular to their neural circuitry. Fewer cones conduct to a respective ganglion neuron than in the rods; the resolution is therefore better than in the rods.

In the fovea centralis there is even a 1:1 conduction. The rods, on the other hand, have an absorption maximum of 500 nm, which is located quite centrally in the visible light range. They therefore react to light from a broad spectrum.

However, since they only contain rhodopsin, they cannot separate light of different wavelengths. Their great advantage, however, is that they are more sensitive than the cones. Even much lower light incidence is sufficient to reach the reaction threshold for the rods.

They are therefore used for vision in the dark when the human eye is color blind. On the other hand, the resolution is much worse than with the cones. More rods lead converging, i.e. converging, to a ganglion neuron.

This means that regardless of which rod is excited from the cone, the ganglion neuron is activated. Thus, no such good spatial separation as with the cones is possible. It is interesting to note that the rod assemblies are also the sensors for the so-called magnocellular system, which is responsible for the perception of movement and contours.

In addition, some of you may have noticed that at night stars are not visible in the focus of the field of view, but rather at the edge. This is due to the fact that the focus projects onto the visual fossa, which does not have rods. The rods are located around them, so you can see the stars around the focus of the field of view.