A range of neuronal mechanisms can enable animals to detect the direction of visual motion. Computational models now indicate that a factor as simple as eye size might explain some of this diversity. See Article p.105 The starburst amacrine cell (SAC) dendrites of the retina play an essential role in the computation of direction selectivity in the detection of moving visual stimuli. Past studies of SAC anatomy have mostly involved the rabbit retina. Now Kevin Briggman and colleagues present a large-scale reconstruction of the mouse retina at single-synapse level, which reveals a striking asymmetry in the distribution of inhibitory and excitatory input synapses onto SAC dendrites. Using computer modelling and further physiological imaging, the authors demonstrate that the mouse-specific retinal circuitry is adapted to its smaller eye size, compared to the rabbit. Without this adaptation, mice would be blind to slowly moving objects.