Epiretinal membrane contracture associated with macular prolapse. We treated two patients with annular epiretinal membranes that produced unusual macular morphologic characteristics. Contracture of the membranes caused herniation of macular tissue through a hole in the center of the membrane. The membranes were removed surgically, and ultrastructural analysis disclosed cells with properties resembling myofibroblasts and apparent new vitreous collagen. Contracture of the cellular components probably produced tangential traction on the retina, which caused prolapse of the retinal tissue through a central defect in the membrane. 