Epiretinal membrane (ERM) can be defined as pre-retinal proliferation of myofibroblastic cells associated with extracellular matrix (ECM). Various aetiologies can lead to this final common pathway. Current imaging modalities are excellent at identifying and grading severity of ERMs, but do not yet differentiate histopathological variations which suggest that this is a heterogeneous group of diseases.
The prevalence of epiretinal membrane (ERM) is 7% to 11.8%, with increasing age being the most important risk factor. Although most ERM is idiopathic, common secondary causes include cataract surgery, retinal vascular disease, uveitis and retinal tears. Anti-VEGF injections are identified as a significant risk factor for ERM formation especially in patients with diabetes. The myofibroblastic pre-retinal cells are thought to transdifferentiate from glial and retinal pigment epithelial cells that reach the retinal surface via defects in the internal limiting membrane (ILM) or from the vitreous cavity. Grading schemes have evolved from clinical signs to ocular coherence tomography (OCT) based classification with associated features such as the cotton ball sign. Features predictive of better prognosis include absence of ectopic inner foveal layers, cystoid macular oedema, acquired vitelliform lesions and ellipsoid and cone outer segment termination defects. OCT-angiography shows reduced size of the foveal avascular zone.
The presence of continuous ectopic inner foveal layers was significantly associated with lower visual acuity. ERMs are divided into 4 stages. Stage 1 ERMs are mild and thin and a foveal depression was present. Stage 2 ERMs are associated with widening of the outer nuclear layer and loss of the foveal depression.
Stage 3 ERMs are associated with continuous ectopic inner foveal layers crossing the entire foveal area. In stages 1, 2, and 3 all retinal layers were clearly defined on OCT. Stage 4 ERMs are thick and associated with continuous ectopic inner foveal layers. In addition, retinal layers were disrupted.
Vitrectomy with membrane peeling remains the mainstay of treatment for symptomatic ERMs. Additional ILM peeling reduces recurrence but is associated with anatomical changes including inner retinal dimpling.
