An epiretinal membrane (ERM) is a thin sheet of fibrous tissue that can develop on the surface of the macular area of the retina and cause disturbance in vision. An epiretinal membrane can also be called macular pucker, premacular fibrosis, surface wrinkling retinopathy or cellophane maculopathy. Most commonly, macular epiretinal membrane are asymptomatic or causes mild symptoms of metamorphopsia and/or modest decrease in central visual acuity. A minority of these membranes can cause macular distortion or macular edema to induce clinicians to recommend ERM removal via pars plana vitrectomy.
Optical coherence tomography (OCT) has become the most useful, noninvasive ancillary test for the evaluation of epiretinal membranes. OCT may be predictive of visual outcomes with ERM surgery. The hyperreflective line above retinal pigment epithelium (RPE) demonstrates the inner segment/outer segment (IS/OS) junction of photoreceptors. Several studies have demonstrated that an intact continuous IS/OS junction is predictive of better visual outcome at 12 months. (1, 2) OCT also helps in distinguishing macular pseudo holes from full thickness macular hole which is an exclusion criterion for this study. (1) The detection of elevated ERM via enface OCT could assist safer grasping of the ERM and indicate the potential for visual outcome improvement after PPV and ERM peeling.(3)
The multifocal electroretinogram (mfERG) represents a cone generated response of localized retinal function in the central macula, which is useful in establishing the presence of macular dysfunction. (4) Multifocal electroretinography (mfERG), is a noninvasive, objective method to detect regional functional changes in the central retina by measuring electrophysiologic responses, has demonstrated macular function changes in eyes with ERM by several reports. (5, 6) The biphasic first order response of the mfERG includes an initial negative deflection [N1] followed by a positive peak [P1]. Previous studies have found that abnormalities in the P1 latency disorders might reflect dysfunctions of the inner retinal layers and Müller cells.(7)
The mfERG values might be associated with numerous factors. In another study it was demonstrated that there was a significant correlation between P1 implicit time and CMT. MfERG abnormalities appear to demonstrate subtle macular function changes and correlate with visual acuity and central macular thickness in eyes with ERM. In first-order mfERG responses, P1 wave changes may be a sensitive functional measurement for ERM patients.
The goal of membrane peeling is to reduce or eliminate the most common mechanisms of visual loss, including macular distortion, traction macular detachment, foveal ectopia, tissue that covers the fovea, retinal vascular leakage with macular edema, and traction induced obstruction of axoplasmic flow. In general, most patients considered for vitrectomy have significant visual impairment.
ERMs are found most frequently over the age of 50 and several large clinical studies have noted a clinical prevalence lying between 7% and 11.8%. (8, 9) Most of these are asymptomatic, with many being extra foveal in location. There appears to be no significant gender predilection and 20 to 30 % are bilateral. Other eye involvement was reported in the Blue Mountains Eye Study to occur in 13.5% of patients over a 5 years time period. (10) The majority of ERMs are globally adherent to the retinal surface, however, some appear to have focal adhesions.(11) These focal adhesions are more common in eyes with secondary ERMs.
The incidence of symptomatic ERM formation is 4–8% after repair of rhegmatogenous retinal detachment, (12, 13) and 1–2 % after prophylactic treatment of peripheral retinal breaks. (14)
The electroretinography (ERG) is a diagnostic test that measures the electrical activity generated by neural and non-neuronal cells in the retina in response to a light stimulus. The electrical response is a result of a retinal potential generated by light-induced changes in the flux of transretinal ions, primarily sodium and potassium. Most often, ERGs are obtained using electrodes embedded in a corneal contact lens, which measure a summation of retinal electrical activity at the corneal surface. The International Society for Clinical Electrophysiology of Vision (ISCEV) introduced minimum standards for the ERG in 1989. The ERG can provide important diagnostic information on a variety of retinal disorders. Moreover, an ERG can also be used to monitor disease progression.