I will briefly summarise some key aspects of vertebrate retinal processing, mainly from published work on mouse, and then elaborate on some new data from my lab where we looked at retinal processing in zebrafish. In each case I will seek to draw on the animal's visual ecology in an attempt to make sense of the many functional differences observed between these two species, as part of a broader argument aiming to relate the functional architecture of sensory networks to the sensory world for which they evolved to operate.