Post-Operative Diplopia After Strabismus Surgery in an Adult
A 34-year-old woman with a long-standing, untreated right esotropia of 28 prism diopters (PD) undergoes bilateral medial rectus recession of 5.0 mm each. Pre-operatively she had no diplopia and demonstrated dense suppression on the Worth 4-dot at near and distance. On post-operative day 1 she reports constant, intolerable horizontal diplopia at both distance and near. Alternate cover test measures a 6 PD right esotropia at distance with a 4 PD right hypertropia, and 2 PD esotropia at near. Visual acuity is 20/20 each eye. She is a commercial driver and asks whether she can return to work next week.
1. Explain the mechanism of her new diplopia and why the pre-operative suppression no longer protects her.
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Pre-operatively, long-standing esotropia allowed the visual system to develop dense suppression of the deviating eye, so she was diplopia-free. Surgery has reduced the angle from 28 PD to a small residual (6 PD esotropia / 4 PD hypertropia at distance). Small-angle deviations are harder to suppress because the images fall close to corresponding retinal areas and the suppression scotoma developed for a 28 PD deviation no longer covers the new image location. The result is intractable diplopia until the system adapts (builds a new suppression pattern or develops anomalous correspondence) or the residual is corrected. The hypertropia component also creates a vertical mismatch that suppression does not readily handle.
2. Outline a management plan over the next 4-6 weeks, including what you would tell her about driving.
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- Reassure that early post-operative diplopia is common and frequently resolves as the motor angle stabilizes and sensory adaptation occurs; do not rush to re-operate. 2) Measure the deviation serially at each visit (cover test at distance and near, with and without correction) to track stability. 3) Consider Fresnel prism temporarily if the residual is stable and symptomatic, but recognize that a 4 PD vertical component plus horizontal may be hard to fully neutralize and prism may interfere with adaptation. 4) Consider a brief trial of monocular occlusion (patching one eye) for symptomatic relief, especially for driving, while adaptation proceeds. 5) For driving: advise she should not drive while experiencing constant diplopia that impairs depth perception and fusion; she may drive with one eye occluded only after confirming monocular acuity and visual field meet licensing standards in her jurisdiction. Document the advice and defer return-to-work clearance until symptoms are controlled.
3. If the diplopia persists unchanged at 8 weeks with a stable 6 PD esotropia and 4 PD hypertropia, what are the options and how would you counsel her?
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At 8 weeks with a stable angle, the deviation is unlikely to resolve spontaneously. Options: (a) prisms ground into spectacles to neutralize the residual (may be limited by the vertical component and by prism-induced distortion); (b) further surgery to address the residual esotropia and hypertropia; (c) occlusion or a fogging lens if fusion cannot be restored and the patient prefers single vision over binocularity. Counsel that restoring binocular single vision is not guaranteed and that the goal may be comfortable single vision rather than perfect alignment. Discuss risks of additional surgery, including overcorrection and persistent diplopia, and involve the patient in shared decision-making. Document the discussion.