Cover legend: Glial cells envelop blood vessels and regulate blood flow in the retina. Both astrocytes (green) and Müller glial cells (red) extend endfoot processes which surround vessels. Increases in calcium levels within Müller cells mediate dilation of capillaries but not arterioles. Image by Elizabeth MacDonald, Kyle Biesecker, and Eric Newman. For more information, see the article by Biesecker et al. (pages 9435–9445).