How should diplopia associated with an epiretinal membrane be evaluated and managed?

Management of Diplopia Associated with Epiretinal Membrane

Fogging the affected eye with Bangerter foils or Scotch Satin tape is the most effective first-line treatment for diplopia caused by epiretinal membrane, as this eliminates the central-peripheral fusion conflict that causes the double vision. 1

Understanding the Mechanism

Diplopia from epiretinal membrane (ERM) develops through a unique mechanism called central-peripheral rivalry or "dragged-fovea diplopia syndrome." The ERM distorts the foveal image in the affected eye, making it too dissimilar from the fellow eye to fuse centrally. However, peripheral fusion remains intact and actually works against you—it forces peripheral retinal alignment while leaving the foveas misaligned, causing persistent diplopia 1, 2.

This typically develops within days to weeks of worsening maculopathy and rarely improves spontaneously 1. Between 16-37% of patients with ERM develop this type of diplopia 2.

Diagnostic Evaluation

Key History Elements

• Onset timing relative to macular disease progression
• Frequency and circumstances of diplopia (distance vs reading)
• History of retinal disease affecting the macula 1

Essential Examination Components

Perform a full orthoptic examination because some patients have concurrent treatable strabismus alongside their macular diplopia 1:

• Prism and alternate cover testing: Usually shows either no deviation or small vertical strabismus 1
• Lights on/off test (pathognomonic): Show a small white-on-black letter in complete darkness—the patient sees it single. Turn room lights on—peripheral fusion takes over and diplopia returns 1, 2
• Optotype-frame test (alternative if you can't darken the room completely): Patient fixates an isolated letter on an illuminated monitor. If the letter is single but the monitor frame is double, or maintaining a single frame causes the letter to double, this confirms central-peripheral rivalry 1, 2
• Amsler grid and M-Charts: Quantify metamorphopsia 1
• Awaya test: Quantify aniseikonia 1

Critical Pitfall

Do not assume all diplopia in ERM patients is from macular disease. In one study, 28% of diplopic ERM patients had strabismus as the primary cause, and 8% had mixed causes 3. Missing concurrent strabismus means missing a treatable cause.

Treatment Algorithm

Step 1: Observation

Monitor if symptoms are mild or occasional, or patient declines treatment 1.

Step 2: Nonsurgical Management (First-Line)

Fogging is most successful 1, 2:

• Bangerter foils or Scotch Satin tape on spectacle lens (better tolerated than surgical tape) 1, 2
• Occlusive contact lenses 1
• Mechanism: Creates central scotoma, eliminating the foveal conflict 1, 2

Prism correction may provide transient relief in rare patients, though usually not curative since it doesn't resolve the macular image mismatch 1, 2. Success rate: 57% in one series 4. Consider combining small prism with Bangerter foil for difficult cases 1.

Novel approach: Multifocal center-distance contact lens (+2.50 bifocal power) on affected eye improved diplopia in 59% of patients by functionally masking periphery while maintaining central vision 5.

Step 3: Surgical Considerations

ERM peeling has mixed outcomes and represents a "double-edged sword" 1, 2:

• Resolution of diplopia: 33-44% of diplopic patients improve after peeling 6, 4
• New-onset diplopia: 19% of non-diplopic patients develop diplopia post-operatively 6
• Better postoperative visual acuity and greater aniseikonia appear associated with new-onset diplopia risk 6

When to consider ERM peeling for diplopia:

• Patient has decreased visual acuity, metamorphopsia, or difficulty using eyes together (primary indications per retina guidelines) 7, 8
• Diplopia is incompletely addressed by fogging/optical correction 1
• Superimposition of foveal images by synoptophore diminishes subjective diplopia 1

Strabismus surgery is unlikely successful if synoptophore or prism superimposition doesn't resolve diplopia, since it doesn't address the macular image mismatch 1. May consider if it reduces symptoms incompletely addressed by other methods 1.

Step 4: Counseling

Set realistic expectations 1:

• This condition usually does not improve spontaneously and may worsen
• Fogging may be the most suitable long-term solution
• ERM peeling improves diplopia in only a proportion of patients
• Even successful anatomic repair may not restore fusion due to limited cortical adaptation 9

Referral Pathway

Coordinate care between retina specialist (managing underlying ERM) and strabismus specialist/orthoptist/neuro-ophthalmologist (managing diplopia) 1. The strabismus specialist should discuss potential benefits of membrane peeling with the retina team, while not overlooking value of prism, refractive correction, or strabismus surgery in select cases 1.