Epiretinal Membrane: NBEO & OKAP Guide
Master epiretinal membrane staging, OCT findings, and surgical indications for NBEO and OKAP with this focused board review.
Which posterior segment finding is often noted in eyes with idiopathic epiretinal membrane and supports its pathophysiology?
Epiretinal Membrane in 30 Seconds
An epiretinal membrane is a fibrocellular membrane that forms on the inner retinal surface along the internal limiting membrane, distorting the macula. Most cases are idiopathic and asymptomatic, found incidentally on exam or OCT. Board exams test whether you can distinguish ERM from macular hole and vitreomacular traction, and whether you know when surgery is indicated.
How an Epiretinal Membrane Forms
Posterior vitreous detachment is thought to create microscopic defects in the internal limiting membrane that permit migration of glial cells, hyalocytes and retinal pigment epithelial cells onto the retinal surface, where they proliferate and contract. Idiopathic ERM accounts for approximately 80 to 90 percent of cases. Secondary ERM follows retinal tears, uveitis, diabetic retinopathy, retinal vein occlusion, trauma, or prior retinal surgery or laser, where inflammatory mediators drive additional fibrocellular growth.
Staging and Classification
- Stage 1: preserved foveal contour, no ectopic inner foveal layers on OCT, mild or no visual complaints.
- Stage 2: foveal contour flattened, ectopic inner foveal layers begin to appear, mild metamorphopsia possible.
- Stage 3: continuous ectopic inner foveal layers across the fovea, outer retinal layers generally preserved, more symptomatic.
- Stage 4: ectopic inner foveal layers plus disruption of outer retinal architecture, associated with worse preoperative vision and generally poorer postoperative visual recovery.
4 Facts Exams Always Ask
- The hallmark of advanced ERM (Govetto Stage 3 to 4) is the presence of ectopic inner foveal layers: inner retinal tissue displaced into the outer foveal region, replacing the normal foveal pit.
- Metamorphopsia results primarily from tangential traction and distortion of the retinal architecture.
- The Amsler grid is the classic bedside tool for detecting and monitoring metamorphopsia in ERM patients.
- Pars plana vitrectomy with ERM and internal limiting membrane peel is considered for patients with bothersome metamorphopsia, progressive visual decline, or vision-limiting ERM, not for asymptomatic ERM regardless of OCT stage.
The Classic Trap
A common board exam pitfall is confusing ERM with macular hole or vitreomacular traction based on symptoms alone. All three can cause metamorphopsia and reduced acuity, but OCT differentiates them: ERM shows a hyperreflective band on the inner retina without a full thickness defect, macular hole shows a full thickness neurosensory defect, and vitreomacular traction shows persistent vitreous attachment pulling on the fovea without a separate membrane. A second trap is recommending surgery for an incidental, asymptomatic ERM found on routine OCT. Since most ERMs are asymptomatic and management is driven by visual complaints rather than OCT appearance, the correct answer is observation.
Clinical Pearl
Always check the fellow eye. ERM is bilateral in approximately 10 to 20 percent of patients at presentation, with additional patients developing involvement of the fellow eye over time. Mild ERMs may cause excellent Snellen acuity despite significant metamorphopsia, so symptoms should not be judged by visual acuity alone. This detail turns a straightforward ERM question into a "what do you examine next" question, which is a favorite exam pivot.
Checkpoint 1
An epiretinal membrane is located on the surface of the:
Checkpoint 2
Surgery for symptomatic epiretinal membrane typically consists of:
A 68-year-old presents for a routine exam. Fundus exam shows a subtle sheen over the macula. She denies any visual complaints and reads 20/20 without difficulty. OCT confirms a thin hyperreflective band on the inner retina with a preserved foveal contour.
What is the standard medical therapy for idiopathic epiretinal membrane?
Sources & Reviewer Info
Diagram created with AI image generation, clinically reviewed for accuracy.
References
- AAO EyeWiki, Epiretinal Membrane
- AAO BCSC Section 12, Retina and Vitreous
- Ryan's Retina
- Govetto R, et al. The Govetto OCT staging system (EIFL classification). Ophthalmology. 2017.
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