Müller cells are glial in origin and form a supporting element in the neural retina extending from the inner segments of the photoreceptors to the internal limiting membrane (ILM), which is formed by their end feet. They buffer the ionic concentrations in the extracellular space, enclose the subretinal space by helping form the external limiting membrane (ELM), and may play a role in vitamin A metabolism of cones.
The other nonneural, or neuroglial, cells of the retina are macroglia (mainly astrocytes) and microglia. Macroglia
provide physical support to neuronal and vascular cells
regulate the ionic and chemical composition of the extracellular milieu
participate in the blood–retina barrier
form the myelin sheath of the optic nerve (This function is performed by oligoden-drocytes, which are macroglia that are similar to Schwann cells in the peripheral nervous system. Because the myelination does not usually extend into the retina, these glial cells are not found in the retina.)
guide neuronal migration during development
exchange metabolites with neurons
Microglia are related to tissue macrophages and are activated when retinal homeostasis is disturbed. These cells mediate immune responses in the central nervous system.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.