Before elective strabismus surgery in a 35-year-old man who has had a constant left esotropia since childhood, the surgeon places prisms equal to the planned correction before his eyes. He reports diplopia that he finds intolerable and cannot suppress. The correct interpretation is:

• A Surgery should proceed, as diplopia always disappears within weeks
• B The test indicates dense amblyopia requiring occlusion first
• C The test confirms anomalous retinal correspondence
• D He is at high risk of intractable postoperative diplopia, and surgery should be reconsidered ✓

Explanation

This is the postoperative diplopia test. Prisms simulate the alignment surgery will create, unmasking whether the brain can fuse or suppress the newly presented image. An adult with long-standing strabismus may have never developed suppression, so restoring alignment can leave intolerable double vision that no further surgery reliably abolishes. A positive test demands careful counselling or abandonment of surgery, not reassurance.

Reference: Khurana Comprehensive Ophthalmology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.