PURPOSE: To report an elevation deficit, which was caused by an accessory 
extraocular muscle, in a 6-year-old boy.
METHODS: Computed tomography and magnetic resonance imaging were used to confirm 
an accessory, fusiform, well-defined, solid structure in the retrobulbar space.
RESULTS: A supernumerary intraconal muscle was detected between the annulus of 
Zinn and the posterior part of the left globe.
CONCLUSION: This rare anomaly may represent an atavistic retractor bulbi muscle.