8.1 Features
Epiretinal membranes (ERMs) are essentially cellular proliferations on the surface of the macula and often appear after posterior vitreous detachment (PVD). They may be asymptomatic and are discovered incidentally or due to presenting symptoms of metamorphopsia and visual acuity impairment. Epiretinal membranes may result in anatomic distortion of the retinal tissue and foveal architecture. These distortions can result in retinal dysfunction and subsequent visual symptoms. Fundus examination and optical coherence tomography (OCT) facilitate diagnosis and evaluation of anatomic changes.
8.1.1 Common Symptoms
Commonly asymptomatic and discovered incidentally during a fundus examination or imaging (often OCT) performed for other reasons. Patients may discover symptomatic change when they close the fellow eye. Patients can complain of various visual symptoms predominantly progressive vision loss, blurred vision, aniseikonia (macropsia), metamorphopsia, and much less frequently monocular diplopia. Moderate foveal displacement due to the ERM can explain vision loss and metamorphopsia. Metamorphopsia is also assumed to be related to inner nuclear layer changes. Macropsia is assumed to be due to central photoreceptor contraction in a smaller area and may be responsible for aniseikonia.
8.1.2 Exam Findings
Cellophane glistening reflex of ERM on fundus biomicroscopy is the main examination finding. A careful examination may also notice a thickening of the macula or in some cases cystic changes. Contraction of the ERM may also result in a “macular pseudohole” appearance (a round reddish foveal image that looks like a hole but is not a full thickness macular hole) in about 15% of cases. In some cases, ERM contraction is so severe that it results in deep retinal folds, resulting in an impairment of the axoplasmic transport, appearing as long cotton wool spots. In addition, centripetal contraction of the membrane results in an elevation of central photoreceptors and subsequently a subfoveal yellow spot on funduscopy. In the majority of cases, ERMs are related to PVD which can be noted. Rarely, ERMs complicate the course of other diseases, including diabetic retinopathy, posterior and intermediate uveitis, and retinal detachment. A careful fundus examination should exclude any of these causal diseases.
8.2 Key Diagnostic Tests and Findings
8.2.1 Optical Coherence Tomography
OCT is the gold standard diagnostic test for ERM. It can show the presence of the ERM as a hyperreflective structure of variable thickness lining the inner retinal surface, more visible when it bridges inner retinal folds. The coronal scans (C-scans) segmented at the vitreoretinal interface provide very suggestive images of the ERM and induced retinal folds. OCT also has the advantage of showing and quantifying the macular thickening induced by ERM contraction. Another common finding caused by the constriction of the ERM is the disappearance of the foveal depression. The anterior profile of the macula may be flat, irregular, or often convex (▶ Fig. 8.1). Conversely, in other cases OCT may show an atypical foveal profile of macular pseudohole with a steepened foveal pit combined with thickened foveal edges and a small foveal pit diameter (▶ Fig. 8.2). Sometimes some degree of intraretinal stretching or cleavage in the foveal edge is also associated (▶ Fig. 8.3). Cystic changes can also be noted on OCT (▶ Fig. 8.4). A subfoveal hyperreflective deposit can be found in about 20% of cases on OCT.
Fig. 8.1 (a,b) Typical appearance of an epiretinal membrane (ERM) on a horizontal optical coherence tomography scan of a right eye. The ERM appears as a hyperreflective line on the surface of the retina. The macula is thickened. The scan passes through the foveal center as confirmed by the thickening of the outer nuclear hyporeflective zone due to the elevation of the foveal pit and disappearance of foveal depression.
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