An epiretinal membrane (ERM) is a thin layer of fibrocellular scar tissue that forms directly on the surface of the retina. This condition is common, especially in older adults, and is often discovered during routine eye examinations. The membrane develops over the macula, the small central area of the retina responsible for sharp, detailed central vision. While many cases remain mild and cause no symptoms, the progression of this tissue can lead to distortion and a decline in sight. Up to 34 percent of those over 60 have some form of ERM.
Defining the Epiretinal Membrane
The retina is the light-sensitive tissue lining the back of the eye, and the macula is its functional center. An ERM is a proliferation of various cell types, including glial cells and retinal pigment epithelial cells, which create a sheet-like structure on the retina’s inner surface. This formation is frequently described as resembling a piece of cellophane wrap.
The membrane possesses contractile properties, meaning it gradually tightens and shrinks over time. This contraction exerts a pulling force, or traction, on the underlying retinal surface, causing it to wrinkle and pucker. This mechanical distortion of the macula leads to the characteristic visual symptoms.
Epiretinal membranes are categorized as either idiopathic or secondary. Idiopathic ERMs, which are the most common, develop without an identifiable cause but are strongly associated with a posterior vitreous detachment (PVD). PVD is a natural aging process that occurs when the vitreous gel pulls away from the retina.
Secondary ERMs form as a result of other eye conditions, such as diabetic retinopathy, retinal tears, chronic inflammation, or following certain eye surgeries. The initiating event causes microscopic damage to the retina’s surface, allowing cells to migrate and begin forming the scar tissue.
The Clinical Staging System
The severity and progression of an epiretinal membrane are classified using a system based on high-resolution imaging from an Optical Coherence Tomography (OCT) scan. This diagnostic tool provides cross-sectional images of the retina, allowing specialists to visualize the anatomical changes caused by the membrane’s traction. Current classification systems use four stages to describe the membrane’s impact on the fovea, the center of the macula.
Stage 1 membranes are the mildest, characterized by a thin membrane with minimal pulling, where the natural contour of the fovea, known as the foveal pit, is still present. In this stage, all retinal layers remain defined and undistorted. Progression to Stage 2 involves increased traction, leading to the complete loss of the foveal pit, though the retinal layers remain distinct.
Stage 3 is defined by the appearance of continuous ectopic inner foveal layers (EIFLs) that bridge across the foveal area. These layers signify significant traction-induced reorganization of the inner retinal structure. The presence of EIFLs is a prognostic marker, often correlating with a poorer visual outcome.
The most advanced classification is Stage 4, where the membrane is typically thick and has caused significant macular thickening and anatomical disruption. In this stage, continuous ectopic inner foveal layers are present, and the normal structure of the outer retinal layers has become disorganized or disrupted. Progression through these stages is linked to a decline in central visual acuity.
Visual Impact and Patient Experience
The anatomical changes seen on an OCT scan translate into the patient’s visual experience, which worsens as the ERM progresses. In the mildest cases, particularly Stage 1, a person is often asymptomatic, and the membrane is an incidental finding. Initial symptoms may be subtle, presenting as a minor blurring of central vision or a slight difficulty with fine detail tasks like reading small print.
As the membrane contracts and retinal wrinkling increases, metamorphopsia becomes prominent. This distortion causes straight lines to appear wavy, bent, or irregular. Patients may first notice this effect when looking at door frames, tile patterns, or using the Amsler Grid.
Patients with moderate to advanced stages may also experience micropsia (objects appearing smaller) or macropsia (objects appearing larger). The central blurring and distortion become more pronounced, significantly impacting the ability to read, drive, or recognize faces. This visual impairment is confined to the central field, as the ERM does not affect peripheral vision.
Management Based on Stage
The treatment strategy for an epiretinal membrane is determined by its stage and the resulting visual impact on the patient. For early-stage ERMs, such as Stage 1 or mild Stage 2 cases with good visual acuity and minimal symptoms, the standard approach is watchful waiting. This involves routine monitoring with OCT scans and vision checks, as the risks of intervention typically outweigh the benefits of removing a minimally symptomatic membrane.
Surgical intervention is reserved for advanced stages where the membrane causes significant visual impairment, typically when best-corrected visual acuity drops below 20/30 or when the patient experiences moderate to intense metamorphopsia. The procedure is a pars plana vitrectomy, where the surgeon removes the vitreous gel and peels the membrane off the retinal surface.
The goal of this surgery is to relieve the traction on the macula, allowing the wrinkled retina to flatten and restore its normal contour. While the procedure carries a small risk of complications, such as cataract formation or retinal detachment, it is successful at stabilizing vision and reducing distortion. Patients often experience a gradual improvement in visual acuity and a reduction in metamorphopsia over several months.