**4. Diagnosis**

The diagnosis of the disease is primarily clinical, based on fundus biomicroscopy. In its mildest form, ERM is detected only as a mild glistening light reflex from the inner retina. Fundus examination or fundus photographs with a blue filter may facilitate visualization of very thin membranes [41]. In more advanced cases, wrinkling and/or striae of the retinal surface, as well as retinal vessel distortion may be noticed during examination. Usually, the membrane itself is invisible; nevertheless in advanced cases and particularly in cases of secondary membranes associated with retinal breaks and RD, the ERM can be seen as a grey-whitish membrane that obscures the visualization of the underlying retinal vasculature and retinal surface. Other associated biomicroscopic findings may include PVD, small intraretinal and preretinal haemorrhages, central macular oedema due to retinal vascular leakage, areas of whitening of the inner retina due to axonoplasmic stasis secondary to ischaemia, foveal ectopia due to macular traction and pseudoholes. A pseudohole is a commonly associated clinical finding and is considered to be the result of the formation of a membrane defect accompanied by the displacement of retinal tissue that occurs during the contraction of the ERM [9]. The Watzke-Allen slit beam test is a useful clinical test that can differentiate between a pseudohole and a true full-thickness macular hole [42]. In cases of a positive Watzke-Allen test, the patient will perceive a "break" in the slit beam. The test is negative in the case of a pseudohole.

induce the differentiation of glial cells into myofibroblasts, granting ERMs their contractile properties [30-31]. Increased expression of the vascular endothelial growth factor (VEGF) has also been reported in iERMs, though its exact role in the disease pathogenesis still remains unknown [29, 32-33]. Furthermore, proteins such as apolipoprotein A-1, transthyretin, αantitrypsin, serum albumin and interleukin-6 have also been proposed to participate in the

ERMs tend to remain stable or to present limited progression over time, with most patients experiencing mild or no symptoms following the initial diagnosis, indicating that membrane contraction possibly occurs at an early phase after its original formation and generally stabilizes thereafter. According to the findings of the population based "Blue Mountains Eye Study", epiretinal membrane progression was encountered in 28.6% of cases, stability was noticed in 38.8% of eyes, while 25.7% of cases regressed during a five-year follow-up period [35]. Accordingly, former studies have supported the non-progressive character of the disease [36-37], since only 10 to 25% of eyes seemed to show a significant decrease in visual acuity over time, with variable rates of progression [2, 9]. In fact, previous reports suggest that less than 5% of ERM cases present visual acuity of 20/200 or worse [38-39]. Moreover, rare cases of spontaneous ERM separation from the retina with associated visual improvement have also

ERMs are symptomatic only if the macular or peri-macular area is involved. In its mildest forms, such as in cases of cellophane maculopathy, the disease is usually asymptomatic [38-39]. Symptomatic patients usually complain of decreased visual acuity (VA), metamorphopsia or vague visual disturbances. Other less common symptoms include micropsia and monocular diplopia [38-39]. In general terms, the extent of the visual effect of the disease is determined mainly by the degree of the induced retinal distortion, the position of the membrane in association to the macula, as well as its thickness and transparency. The decrease in VA can generally be attributed to the filtering effect of the ERM that prevents light from reaching the photoreceptors, the distortion of the retinal surface, as well as the macular oedema and the associated vitreoretinal traction due to incomplete PVD, if present. The distortion of the retinal surface due to ERM contraction, which in some cases can involve the entire retinal thickness, is the primary cause for metamorphopsia, which is usually the leading and most disturbing

The diagnosis of the disease is primarily clinical, based on fundus biomicroscopy. In its mildest form, ERM is detected only as a mild glistening light reflex from the inner retina. Fundus examination or fundus photographs with a blue filter may facilitate visualization of very thin

pathogenesis of the disease [27, 34].

118 Advances in Eye Surgery

been documented [9, 40].

symptom of the disease.

**4. Diagnosis**

**3. Natural course and associated symptoms**

Optical coherence tomography (OCT) is the most sophisticated and contemporary imaging modality in the diagnosis of ERMs. In OCT imaging, an ERM is typically demonstrated as a hypereflective band over the retinal surface, while wrinkling of the retina is easily visualized when present. Associated clinical entities, such as vitreomacular traction, macular oedema, loss of the foveal pit and foveal ectopia due to ERM traction are also readily demonstrated using this imaging technique (Figure 1). Moreover, OCT can easily differentiate between a pseudohole and a true macular hole, and can also serve as a very useful tool in ERM preop‐ erative planning and in postoperative follow-up.

**Figure 1.** OCT image of an epiretinal membrane. In addition to the apparent thick membrane, the OCT scan reveals considerable macular thickening and cystoid macular oedema. Notice the prominent vascular tortuosity (left) and the obvious edge in the OCT scan of the membrane (right), which may be used for peeling initiation during surgery.

In addition, fluorescein angiography (FA) is another adjuvant diagnostic test for ERM. Despite the fact that it is usually not necessary to establish the diagnosis of an ERM, FA can be helpful in assessing the extent of vascular distortion and detect the presence of vascular leakage and macular oedema. ERM associated vascular leakage, when present, is typically irregular, asymmetric and within the area of the ERM. It is also useful to exclude other lesions that may share common clinical findings with ERMs, such as choroidal neovascularization and other vascular diseases of the retina.
