An epiretinal membrane (ERM) is a layer of scar tissue that forms on the surface of the retina, specifically over the macula, the central part responsible for sharp, detailed vision. Also known as macular pucker or cellophane maculopathy due to its wrinkled appearance, ERM is diagnosed and monitored using Optical Coherence Tomography (OCT). This non-invasive, high-resolution imaging technology provides a cross-sectional view of the retina, allowing doctors to visualize the membrane and assess its effect on the underlying tissue.
Understanding Epiretinal Membrane
An ERM begins as a thin, semi-transparent layer of fibrocellular material growing across the inner surface of the retina. The most common cause is the natural aging process, where the vitreous gel slowly separates from the retina. This separation, known as posterior vitreous detachment (PVD), can microscopically damage the retinal surface, allowing glial cells to migrate and multiply, forming the scar tissue.
When the membrane is thin, it is often asymptomatic and discovered incidentally during routine examination. Over time, this tissue can contract, causing the retina underneath to wrinkle or pucker. This physical distortion of the macula leads to typical ERM symptoms, including blurred vision and metamorphopsia (straight lines appear wavy or crooked).
Most ERMs are idiopathic, developing without a clear underlying cause other than age. A smaller number are secondary, developing after other eye conditions or events, such as retinal detachment, trauma, intraocular inflammation (uveitis), or retinal vascular diseases like diabetic retinopathy. Symptom severity relates directly to the amount of traction and distortion the membrane places on the central macula.
Optical Coherence Tomography Explained
Optical Coherence Tomography (OCT) is a sophisticated imaging method that has revolutionized the care of retinal diseases. The technology uses low-coherence, near-infrared light to capture high-resolution images of the eye’s internal structures. It functions like an optical analog of ultrasound, using light waves instead of sound waves to create a detailed cross-sectional picture of the tissue.
During the non-contact procedure, the patient sits in front of the machine and focuses on a target light; the scan takes only a few seconds per eye. The light beam is split, with one part directed at the retina and the other acting as a reference. By analyzing the echoes of light backscattered from the different retinal layers, the OCT machine precisely maps the depth and structure of the retina.
The result is a two-dimensional, color-coded image that clearly delineates the distinct retinal layers, allowing for an “optical biopsy” without tissue removal. This makes OCT the standard tool for visualizing, mapping, and measuring retinal layer thickness. Establishing a baseline measurement allows doctors to quantitatively monitor changes over time using subsequent scans.
Interpreting ERM on an OCT Scan
The OCT scan shows how the scar tissue affects the retina’s structure. On the cross-sectional image, the ERM appears as a thin, highly reflective layer situated directly on the inner retinal surface. The reflectivity of this layer indicates its density and fibrous nature.
The scan reveals the effect of the membrane’s contraction on the underlying neurosensory retina. This traction manifests as a loss of the normal concave foveal depression, the natural dip at the macula’s center. The pulling force also causes the retinal surface to wrinkle, visible on the OCT as an uneven, undulating contour known as macular pucker.
The scan identifies retinal thickening, or edema, particularly at the fovea, measured as Central Foveal Thickness (CFT). Severe traction can lead to intraretinal fluid pockets, visible as dark, cyst-like spaces called cystoid macular edema. The OCT also helps differentiate between a pseudohole, caused by the membrane pulling the retina inward, and a true full-thickness macular hole.
Using OCT to Guide Management and Treatment
OCT data is essential for ERM management decisions. For patients with a thin, non-contracting membrane showing minimal retinal distortion and good visual acuity, the standard approach is watchful observation. The initial OCT scan establishes a baseline of central macular thickness and retinal layer integrity.
Progressive retinal thickening, increasing vitreomacular traction, or the development of cystoid macular edema suggest the condition is worsening. When these findings correlate with a significant reduction in visual acuity or increased visual distortion (metamorphopsia), surgical intervention is considered. The main surgical treatment is a pars plana vitrectomy with membrane peeling.
OCT findings guide the surgeon by identifying the thickest part or an elevated edge of the membrane, which is the ideal starting point for the surgical peel. Post-operatively, OCT monitors anatomical success, looking for reduced central foveal thickness and gradual restoration of the foveal depression, which correlates with improved vision.