Anomalous orbital structures resulting in unusual strabismus.

Anomalous orbital structures are a rare cause of strabismus. These structures attach to the globe and produce a mechanical restriction, resulting in incommitant motility disorders. Three types of anomalous structures have been described. The first arise from the extraocular muscles themselves and insert in abnormal locations. The second are fibrous bands located beneath the rectus muscles. The third are discrete anomalous muscles that originate in the posterior orbit and insert in abnormal locations on the globe. These structures have been associated with unusual patterns of strabismus. Clinical findings that suggest the presence of anomalous orbital structures include globe retraction not associated with Duane retraction syndrome, very large vertical strabismus, and an elevation deficit that is worse in abduction. When looking for anomalous orbital structures in patients with atypical strabismus, imaging studies should be considered.