A case of paradoxical diplopia in large-angle consecutive exotropia

To describe the investigation and subsequent management of paradoxical diplopia in unsightly exotropia. A 32-year-old lady requested surgical correction of a large manifest consecutive exotropia which, on initial correction with any base-in prism, was accompanied by paradoxical diplopia.

Botulinum toxin to the right lateral rectus reduced the deviation to 30 delta over a one-week period. The residual deviation was corrected with base-in Fresnel prisms which the patient wore constantly for another two weeks. Although there was demonstrable diplopia initially, it disappeared after 3-4 days of prism wear. Surgery was carried out comprising right lateral rectus recession (6 mm) and right medial rectus advancement from 12 mm to 6 mm posterior to the limbus.

There was no diplopia following the surgery and the residual exodeviation measured 6 delta for near and 16 delta for distance (fixing OD). The patient remains symptom-free and cosmetically excellent.

A gradual progressive reduction in the deviation using a combination of Botulinum toxin and prisms allowed a more informative conclusion to be made regarding the potential post-operative sensory status in this patient, by allowing her to slowly adjust to an altered ocular alignment. In patients with non-functional strabismus who may be at risk from post-operative diplopia, a trial with prisms over a few weeks with or without the addition of Botulinum toxin is advocated.