Quick Facts
The radial glial cells are elongated neuroglial cells traversing all the layers of the retina and forming its most important supporting element (Dorland, 2011).
Structure and/or Key Features
Radial glial cells, or Müller cells, are the most common type of glial cell in the retina. Glial cells are specialized to surround, support and insulate neurons. There are approximately 10 million Müller cells in the retina, collectively forming a dense regular pattern around the neurons they support (Remington and Goodwin, 2011; Bringmann et al., 2006).
Spanning almost the entire thickness of the retina, Müller cells make up much of the retinal volume. Extending from a cell body in the inner nuclear layer, two thick fibers runs radially in opposite directions perpendicular to the retinal layers. The outward extending process sends branches into lateral lamellae that further divide among the processes of the outer plexiform layer, while the main trunk extends through the outer nuclear layer and the layer of photoreceptor inner segments. It ends here by making tight junctions with photoreceptors and other Müller glia to form the outer limiting membrane of the retina. The Müller cell processes that extends from the cell body in the opposite direction passes through the inner plexiform, ganglion cell, and optic nerve fiber layers ending as an expanded terminal foot plate, also known as the “endfoot.” These endfeet are connected to each other by tight junctions forming the inner limiting membrane, the retina’s innermost surface (Standring, 2016).
Müller cells make contact with blood vessels, particularly capillaries of the inner nuclear layer. The basal laminae of Müller cells fuse with the basal laminae of vascular endothelial, helping to form the blood-retinal barrier (Standring, 2016).
Anatomical Relations
The cell bodies of Müller cells are located in the inner nuclear layer. The processes of Müller cells, however, span the entire thickness of the retina, with its apex in the layer of rods and cone and its basal aspect at the inner retinal surface.
Function
As the primary glial cell of the retina, Müller cells are largely responsible for maintaining the structural integrity and supporting the functional ability of the neurons. Specifically, Müller cells are integral in retinal glucose metabolism, providing neurons with important nutrients for oxidative metabolism and removing waste products. Müller cells play an additional role in neuronal signaling processes by facilitating the rapid uptake and recycling of neurotransmitters. Further, they play a role in the maintenance of the retinal blood-retinal barrier and in the maintenance of the ion, water, and pH homeostasis of the retinal tissue (Bringmann et al., 2006). Müller cells monitor the oxygen concentration of retinal layers and are the source of signaling via vascular endothelial growth factor (VEGF) whether vascular proliferation should proceed or retract (Alon et al., 1995).
List of Clinical Correlates
- Diabetic retinopathy
- Retinal detachment
- Macular edema
- Proliferative retinopathies
- Retinopathy of Prematurity (also known as retrolental fibroplasia)
References
Alon, T., Hemo, I., Itin, A., Pe'er, J., Stone, J. and Keshet, E. (1995) 'Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity', Nat Med, 1(10), pp. 1024-8.
Bringmann, A., Pannicke, T., Grosche, J., Francke, M., Wiedemann, P., Skatchkov, S. N., Osborne, N. N. and Reichenbach, A. (2006) 'Muller cells in the healthy and diseased retina', Prog Retin Eye Res, 25(4), pp. 397-424.
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Remington, L. A. and Goodwin, D. (2011) Clinical Anatomy of the Visual System E-Book. Elsevier Health Sciences.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41 edn.: Elsevier Limited.
