It has become evident in the past two decades that different tissue compartments of the eye, including the cornea, uveal tract, and retina, contain heterogeneous populations of cells of myeloid lineage, namely dendritic cells (DCs) and macrophages, including microglia.
1 –7 Hyalocytes were first described as a discrete group of cells by Hannover in the 1840s,
8 and, though their origin and function were unclear until recently, Schwalbe,
9 as early as 1887, suspected they had leukocyte origin. They were more fully defined by Balazs et al.
10,11 as a unique population in many species. In the healthy adult mammalian eye, hyalocytes are now considered the resident macrophages of the vitreous body. They are embedded in a scattered fashion along the vitreous cortex close to the inner limiting membrane of the retina.
12,13 Hyalocytes exhibit many phenotypic characteristics of macrophages and have a well-described phagocytic function that likely aids in maintaining vitreal transparency through the clearance of cellular and extracellular debris.
8,14 They are also known to produce antiangiogenic agents thought to inhibit vessel growth and to ensure the vitreous remains in an avascular state.
15 Their ability to respond to different experimental conditions, such as laser photocoagulation,
16 experimental vitreous hemorrhage,
17 and intraocular delivery of bacteria and carbon particles,
14 suggests that hyalocytes play an active role in immunologic and repair processes. Their lineage and relationship to the retinal parenchymal microglia and other ocular myeloid cells are, however, still unclear.