19.
Pathogenesis of Epiretinal Membranes
Peter Wiedemann (Leipzig)
Macular surface disorders comprise cellophane maculopathy, surface wrinkling maculopathy
and macular pucker; these entities are also described as idiopathic premacular gliosis. This
disorder is related to premacular secondary fibrosis and vitreomacular traction syndrome.
Primary epiretinal membranes (ERM) are globally adherent to the retina, secondary focally.
Premacular gliosis is seen in up to 8 % of patients and is bilateral in 30 %. Significant bilateral
loss is not common.
ERM are composed of a wide variety of different cell types: glial cells (including microglia,
Müller cells and fibrous astrocytes), epithelial cells originating from the RPE and ciliary body,
blood-derived immune cells (such as macrophages, lymphocytes, and neutrophils), and myofibrocytes.
Within the membranes, glial and RPE cells transdifferentiate into contractile myofibrocytes.
Epiretinal membranes develop at sites where Müller cells proliferate and migrate onto the inner surface of the retina
(probably in response to growth factors present in the vitreous), and where hyperthrophied Müller cell processes extent
into the vitreous cavity. The membranes are focally connected with the retinal tissue via fibers of Müller cells. Enhanced
amounts of growth factors in the vitreous direct the progression of epiretinal membranes. Among these factors, especially
the hepatocyte and platelet-derived growth factors stimulate the scattering, migration, and proliferation of retinal cells such
as glial and RPE cells. The contraction of epiretinal membranes is stimulated by vitreal factors, especially insulin-like and
and platelet-derived growth factors, which are also present in blood serum extravasated into the vitreous. Blood-derived
immune cells within the vitreous are attracted to sites of glial reactivity in the retina after glial expression of inflammatory
factors like monocyte chemoattractant protein-1. The phase of separation in posterior vitreous detachment may be of fundamental
importance in the formation of ERM.
Spontaneous separation of ERM from the retina is seen. Peeling of epiretinal membranes may improve the delivery of oxygen
and glucose from the vitreal fluid to the underlying ischemic retina, and the exchange of ions across the inner retinal
surface which is important, for example, for retinal potassium buffering.