Okay. So considering vision, we could mention that retina is an inner structure in our eyes that allows us to perceive light through the incidence in it of the photonic rays from light sources or from objects which reflect it.
This is possible since the retina has a set of photoreceptors cells called cones (there're three types of them: reds, greens, and blues cones) and rods. These two differ from each other in the fact that the first ones are more abundant, and have no color sensibility, and the second ones are less abundant but have the capability to perceive color.
In the retina, there're other kinds of cells, like the ganglion ones, or the bipolar ones, and what happens in this process is that the ganglion cells receive information from bipolar cells, which are continually sending actions potentials throughout their axons in the vision process.