OBJECTIVE: Explored the causation of a case of incomitant vertical strabismus 
accompanied with elevation deficit and globe retraction by surgery.
METHODS: Case report. Orbital imaging study of MRI was used to discover the 
anatomic feature of extraocular muscle. By released the restrictive structure to 
treat strabismus. Histopathologic inspection was used to confirm the origin of 
the abnormal structure.
RESULTS: Abnormal extraocular muscle that located within the cone formed by the 
four recti muscles was the causation of strabismus. It arose at the annulus of 
Zinn, passing forwards between the inferior rectus muscle and lateral rectus 
muscle, and insert directly on the sclera. After Released it from eyeball and 
recession of inferior rectus muscle the strabismus was improved. Elevation 
deficit was not improved. Histopathologic inspection confirmed that the 
structure was muscular in origin.
CONCLUSION: The abnormal structure that found by MRI was the cause of elevation 
deficit and globe retraction. Its histopathologic inspection confirmed the 
muscular origin. The abnormal structure was an accessory extraocular muscle. For 
incomitant vertical strabismus accompanied with elevation deficit and globe 
retraction anomalous orbital structures maybe the causation. Orbital imaging 
studies should be done to explore the origin of disease.