Purpose/background: Epiretinal membrane (ERM) formation is a common change resulting in disturbance of macular vision and predisposing to rhegmatogenous retinal detachment. Current treatment strategies rely chiefly on surgical removal of the membranes from the surface of the retina, allowing the retina to remodel and reattach. Improved knowledge of the pathological process behind the formation of these membranes, particularly knowledge of the cell types involved in their formation, is likely to increase our understanding of the way this group of diseases behave and to improve treatment.

Methods: We reviewed the histological findings of 109 surgically removed specimens and correlated these to age-related changes seen in a 32 cadaver eyes studied after corneal harvesting. The samples were studied using light microscopy and immunocytochemistry.

Results: In all cases of idiopathic ERMs, including cellophane maculopathy, macular hole, and vitreomacular traction syndrome, laminocytes were the exclusive cell type present. In cases of macular pucker associated with retinal tears, the membranes contain variable cohesive groups of retinal pigment epithelial (RPE) cells in addition to laminocytes. In cases of proliferative diabetic retinopathy, membranes consist almost entirely of capillaries and hyaline stromal tissue, with or without haemosiderin pigment and RPE cells and in which laminocytes and ILM were not identified. In cadaver eyes PVD was seen in 17/32 (53%) of cases, and the vitreous was attached in 14/32 (43.7%) and in one case no vitreous was present. Isolated laminocytes were present on the retinal surface in 12/18 cases with detached vitreous and in 1/14 cases with attached vitreous. In all cases laminocytes were scanty and confined to the optic nerve head, macular or subjacent macular retina. Immunohistochemistry findings indicate that laminocytes are positive for glial fibrillary acidic protein (GFAP), cytokeratin marker AE1/AE3, type II collagen, and type IV collagen. In some cases novel basement membrane formation was seen. There was a tendency for increased positivity of GFAP and AE1/AE3 with increased cellularity, and where novel basement membrane formation was present.

Conclusion: Laminocytes are the fundamental cell type in idiopathic ERMs. These cells are frequently found in small and dispersed numbers in eyes containing a PVD. The presence of retinal pigment cells invariable indicates proliferative retinopathy and is only seen in association with a retinal detachment or tear. Diabetic membranes are composed of neovascular stromal tissue, which is most likely to be a response to retinal hypoxia.