Daniel Kerschensteiner1,2,3 and Marla B. Feller4,5 1Department of Ophthalmology and Visual Sciences 2Department of Neuroscience 3Department of Biomedical Engineering, Washington University School of Medicine, St. Louis, Missouri 63110, USA 4Department of Molecular and Cell Biology 5Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California 94720, USA Correspondence: mfellerberkeley.edu; kerschensteinerdwustl.edu

Vision begins in the retina, which extracts salient features from the environment and encodes them in the spike trains of retinal ganglion cells (RGCs), the output neurons of the eye. RGC axons innervate diverse brain areas (>50 in mice) to support perception, guide behavior, and mediate influences of light on physiology and internal states. In recent years, complete lists of RGC types (∼45 in mice) have been compiled, detailed maps of their dendritic connections drawn, and their light responses surveyed at scale. We know less about the RGCs’ axonal projection patterns, which map retinal information onto the brain. However, some organizing principles have emerged. Here, we review the strategies and mechanisms that govern developing RGC axons and organize their innervation of retinorecipient brain areas.