The endfoot processes of astrocytes completely envelop all retinal blood vessels ( 12). Morover, astrocytes have an intimate structural relationship with the retinal microvasculature. Astrocytes in the diffusely vascularized retina have been posited to be derived from the optic nerve ( 11). Additionally, the presence and distribution of retinal astrocytes have been shown to possess high consistency with the presence and distribution of retinal blood vessels, while only vascularized retina contain astrocytes ( 10). The arterial wall near the optic disk is composed of five to seven layers of smooth muscle cells. Retinal arteries differ from arteries of the same size in other organs as they have an unusually developed smooth muscle layer and lack an internal elastic lamina. Accordingly, certain structural similarities may indicate that ONH astrocytes play a similar role in the eye. The optic nerve is considered to be a continuation of the central nervous system. Astrocytes, in addition to these supportive roles, may play a central role in many other aspects of brain function, including neuronal signal regulation and cerebrovascular regulation ( 8, 9). These findings indicated the possible involvement of glial cells in the autoregulation of ONH blood flow ( 7). Recent studies have found that the perfusion pressure of ONH decreased significantly when intraocular pressure was artificially elevated in gliotoxic compound treated rabbits, whereas blood flow was maintained in control eyes. Glial cells have been shown to contribute to basal retinal vascular tone and modify the dynamic response of arteries and veins toward changes in perfusion pressure ( 6). Studies have also suggested the presence of paracrine and/or autocrine signaling within the LC( 3– 5). Two distinct cell types are believed to serve the LC: ONH astrocytes and LC cells ( 1, 2). The LC region is composed of glial columns and connective tissue plates. The lamina cribrosa (LC) of the optic nerve head (ONH) serve as the definite site in which the central retinal artery and vein (CRA and CRV) pass through to enter or leave the eye.
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