The macular epiretinal membrane (MEM) involves the growth of a tissue on the surface of the retina in the macular area, which can contract resulting in decreased vision and deformation of the images.

It occurs because cells that normally come from the retina are deposited on the macula, but that can come from the layers that lie under the retina, such as the pigment epithelium.

These cells secrete collagen and form a mesh, and then have the ability to pull on collagen. Because this tissue is attached to the retina, when it contracts, it also contracts the retina and deforms it.