Any of the cells in the vertebrate retina that support the visual sensory cells, notably the rods and cones. These glial cells (known collectively as Müller glia), named after German anatomist Heinrich Müller (1820–64), span the full thickness of the retina, filling the spaces between the retinal neurons. Besides giving physical support to the other cell types, they also regulate the concentrations of certain physiologically important substances within the retina, such as potassium ions, glutamate, and gamma-aminobutyric acid, thereby affecting the activity of other cells. In certain animal groups, such as fish, amphibians, and birds, Müller cells can dedifferentiate following injury and act as stem cells to provide a source of new photoreceptive cells.