GLIAL CELLS AND COLLAGENS IN EPIRETINAL MEMBRANES ASSOCIATED WITH IDIOPATHIC MACULAR HOLES

Purpose: To investigate the identity of collagens and cellular components in the epiretinal membrane (ERM) associated with full-thickness idiopathic macular hole and their clinical relevance.

Methods: Pars plana vitrectomy with the peeling of internal limiting membrane and ERM was performed by 2 surgeons in 40 eyes with idiopathic macular holes. The clinical data were reviewed and the surgical specimens were processed for flat-mount and immunohistochemical analysis.

Results: Epiretinal membrane is a GFAP-positive gliotic and fibrotic scar which contains newly formed Type I, III, and V collagens. Type VI collagen was not observed. Colocalization studies found cells coexpressing GFAP/CRALBP, GFAP/alpha-SMA, and alpha-SMA/CRALBP, which are consistent with transdifferentiation of Muller cells into fibroblasts and myofibroblasts. The clinically significant ERMs can be divided into two groups according to the amount of cells in ERM: sparse cellular proliferation and dense cellular proliferation. The latter group is associated with a higher chance of surgical difficulty during internal limiting membrane peeling (P = 0.006). Preoperative and postoperative visual function were not affected by the density of the cellular proliferation.

Conclusion: Retinal glial cells, probably transdifferentiated Muller cells, are involved in the formation of full-thickness macular hole-associated ERMs by a gliotic and fibrotic process. Such ERMs contain newly formed Type I, III, and V collagen depositions. The cell density of ERM affects its biomechanical properties and determines the difficulty of ERM peeling.