Retinal microglia originate flom hemopoietic cells and invade the retina from the retinal margin and the optic disc, most likely via the blood vessels of the ciliary body and iris, and the retinal vasculature. respectively. The microglial precursors that appear in the retina 34-325oJerent microglia popula.prior to vascularization arc major histocompatibilily complex (MHC) class 1-and II-positive and express the CD45 marker, but lack specific macrophage markers. They differentiate into ramified parenchymal microglia in the adult retina. A second category of microglial precursors, which do express specific macrophage markers, migrate into the retina along with vascular precursors. They appear around blood vessels in the adult retina and are similar to macrophages or cells of the mononuclear phagocyte series (MPS). Microglia are distributed in the outer plexiform laver (OPL), outer nuclear laver (ONL), inner plexiform layer (IPL), ganglion cell layer (GCL), and nerve fiber laver (NFL) of the primate retina. The pattern of microglial distribution in the avascular retina of the quail indicates that blood vessels are not responsible for the final location of microglia in the retina. In the human retina, microglia express MHC class l, MHC class II, CD45. CD68, and $22 markers. In the rat and mouse retina. OX41, OX42, OX3, OX6. OX18, ED1, Mac-l, F4/80, 5D4 anti-keralan sulfate, and lectins are used to recognize microglia. Microglial cells play an important role in host defense against invading microorganisms, immunoregulation, and tissue repair. During neurodegeneration, activated microglial cells participate in the phagocytosis ol debris and facilitate regenerative processes. In autoimnmne disease, microglia have dual functions: initialing uveoretinitis, but also limifing subsequent inflame marion. Retinal microglia may he associated wiih vitreoretinopathy, diabetic retinopathy, glaucoma, and age-related macular degeneration. The goal of this article was to review the present knowledge about retinal microglia and the function of retinal microglia in pathological conditions.