Hyalocytes are mononuclear phagocytes that reside within the cortical vitreous, 50 - 75 uM anterior to the retina where they act as sentinel cells of the reticuloendothelial system of the body. Following posterior vitreous detachment (PVD), hyalocytes are displaced far from the retina and can no longer play their important physiologic role(s), with possible untoward influences on retinal health. Anomalous PVD with vitreoschisis more than 75 uM from the retina leaves hyalocytes attached to the fundus where they play an important role in proliferative vitreo-retinopathies, most notably macular pucker but also proliferative vitreo-retinopathy following retinal detachment.

Human hyalocytes represent a unique and distinct innate immune cell population specialized and adapted for the tissue-specific needs in the human vitreous. Vitreal hyalocytes are characterized by a strong expression of genes related to antigen processing and presentation as well as immune modulation. Thus, hyalocytes may represent an underestimated mediator in vitreoretinal disease and for the immune privilege of the eye.
 

The complexity of the eye consisting of distinct compartments inhabited by a diverse range of cell types is also reflected by the heterogeneity of ocular macrophages. The nature of these innate immune cells remains poorly understood, in particular from a developmental point of view. Recent advancements in murine transgenic fate mapping models now open the possibility to investigate the origin and turnover of resident ocular tissue macrophages, like hyalocytes.
 

Next generation RNA sequencing reveals considerable differences in the expression profile of hyalocytes isolated from diabetic and control patients. Hyalocytes from patients with proliferative diabetic retinopathy seem to not only eliminate blood constituents in aging vitreous bleeding, but also undergo transdifferentiation to myofibroblasts. Hyalocytes may represent a so far underestimated target for future clinical assessment in proliferative diabetic retinopathy.