RESTRICTIVE LIMITATION OF SURSUMDUCTION CAUSED BY AN ANOMALOUS MUSCULAR STRUCTURE

We report a peculiar case of congenitally restricted sursumduction cau sed by an anomalous band-like structure within the right orbit which w as completely distinct from the extraocular muscles. Imaging (static a nd dynamic ultrasound studies of the orbit and globe, CT and MRI) reve aled the origin of the anomalous structure in Zinn's ring, its intraco nal course and bulbar insertion. The ultrasound characteristics were s imilar to those of the extraocular muscles and optic nerve, and contra ctile activity appeared to occur during eye movements. The seemingly m uscular nature of this structure and its total autonomy with respect t o the normal extraocular muscles distinguish this case from previously reported cases of congenital restrictive strabismus.