The evolution of visual systems is constrained by a trade-off between spatial and temporal resolution. In this article we aim at identifying the causes of the trade-off at the retinal level in both artificial and natural visual systems. We start by selecting two factors that limit the values of spatial and temporal resolution. Then we show in two experiments on the evolution of an artificial system that the two factors induce trade-off curves connecting the evolved values of spatial and temporal resolution. A comparison of the experimental results with the resolution evolved in natural visual systems leads us to the conclusion that in natural systems the same factors are responsible for the observed trade-off.