Microglia in the optic nerve head and the region of parapapillary chorioretinal atrophy in glaucoma

Background: Microglia, the macrophages and immune surveillance cells of the central nervous system. are quiescent normally but become activated in inj ured neural tissue. We have determined the distribution and potential parti cipation of microglia in glaucomatous optic nerve degeneration. Methods: Microglia were localized by immunohistochemistry on paraffin secti ons of age-matched normal and glaucomatous human eyes obtained within 24 ho urs after death. Monoclonal and polyclonal antibodies that recognize specif ic epitopes on microglia and other cell types were localized by immunoperox idase and immunofluorescence. Results: Stellate cells with thin, ramified processes, positive for HLA-DR and CD45 but negative for glial fibrillary acid protein, were identified as quiescent microglia. These cells were found throughout the normal optic ne rve head in the walls of large blood vessels and surrounding capillaries in glial columns and cribriform plates. In glaucomatous eyes with moderate an d severe optic nerve head damage, microglia were present as clusters of lar ge ameboid, activated cells in the compressed lamina cribrosa and as format ions of concentric circles surrounding blood vessels. In the parapapillary chorioretinal region of glaucomatous optic nerve heads, large, activated mi croglia were present as single cells or clusters on the termination of the Bruch's membrane. In addition, along the optic nerve/choriocapillaris-scler al interface, activated microglia appeared to form linear arrays near the c horiocapillaris vessels. These cells were parenchymal and not in close asso ciation with the vasculature. Conclusions: In glaucoma, microglia in the optic nerve head become activate d and redistributed. Enlarged, activated microglia appear in the parapapill ary chorioretinal region, perhaps due to migration from the disorganized pr elaminar and laminar tissue. Strategically positioned microglia may also se rve a neuroprotective function in relation to a damaged blood-retinal barri er. The activity of microglia in the parapapillary chorioretinal region in glaucoma may be responsible for some of the biomicroscopic and histological changes that are associated with parapapillary chorioretinal atrophy.