Elimination of paradoxical diplopia following treatment with botulinum toxin and prism

Paradoxical diplopia occurs when binocular visual cerebral cortex projection of diplopic images (the "subjective angle") is not commensurate and identical with angle or direction of strabismus (the "objective angle"). Its presence infers anomalous retinal correspondence and is manifest as heteronymous or crossed diplopia in esotropia and homonymous or uncrossed diplopia in exotropia. When treated, the prognosis for achieving fusion is poor, while the risk for intractable diplopia is reputedly high. We report a patient with paradoxical diplopia that resolved (and some binocular fusion developed) following botulinum toxin injections and prism therapy.

Case report.

A 25 year old man was evaluated for an exotropia. At age 4 years, he had acquired an esotropia due to a traumatic lateral rectus palsy. The esotropia resolved over 3 years. At age 14 years, he developed a consecutive exotropia. The exotropia was eventually treated surgically. There remained a residual exotropia following surgery, and he experienced paradoxical diplopia and projected it homonymously on all sensory tests as if he was esotropic. Treatment with botulinum toxin injections to both lateral rectus muscles along with a small prismatic correction in spectacles eliminated the exotropia and paradoxical diplopia, permitting some binocular fusion.

Botulinum toxin injection and prism therapy can be effective in eradicating paradoxical diplopia.