Atypical restrictive strabismus secondary to an anomalous orbital structure: differential diagnosis.

Anomalous orbital structures are very rare causes of restrictive strabismus. Of the 3 types described in the literature, one involves accessory muscle fibers that are innervated by the III and/or VI cranial nerves originating in the posterior orbit and inserting on the globe, optic nerve, or extraocular muscles. Although these structures do not cause specific symptoms that enable us to make a diagnosis, we must take them into account in patients with atypical restrictive strabismus. Computed tomography and, particularly, orbital magnetic resonance imaging are essential for correct diagnosis and treatment, as the only other way to diagnose this condition is through casual findings during surgery to correct strabismus. Our patient was a child who were initially diagnosed as Duane syndrome. Magnetic resonance imaging revealed an anomalous unilateral orbital structure that limited all ocular movements except adduction, and possibly contributed to globe retraction. Surgery for strabismus did not resolve the problem: the posterior location of the orbital structure rendered surgery impossible.