Joseph Brzezinski, Research Fellow, Department of Internal Medicine, University of Michigan Medical School

The retina of a transgenic laboratory mouse showing groups of cone photoreceptors stained in purple. These neurons were labeled as part of a genetic experiment to learn how specialized cell types develop from a common pool of precursors. These cells are framed at the top by the choroid (black) and retinal pigment epithelial (brown) layers, and below by the inner plexiform layer (purple). Each mouse eye contains 500,000 cone and 15 million rod photoreceptors. They are the light-sensing units of the visual system.