The Study of Normal Intraorbital Positions of The Rectus Muscles

Purpose: In order to propose reference values useful for in diagnosing the strabismus related to the abnormal intraorbital pathway of rectus muscles, we evaluated the intraorbital positions and angles of each rectus muscle in normal subjects. Methods: Using previously scanned orbital MRI and orbital CT of patients who did not show any strabismus or organic disease in the orbit, we calculated the angles of each rectus muscle in the orbit, and compared the results with those of a patient with large angle exotropia. Results: Using orbital MRI and orbital CT, the normal angles of each rectus muscles 10 mm posterior to the globe center were -5.13.4 and -1.56.0 degrees in the medial rectus, 185.88.1 and 180.86.9 degrees in the lateral rectus, 98.16.03 and 87.96.7 degrees in the superior rectus, and -79.76.1 and -83.111.7 degrees in the inferior rectus, respectively. In the patient with large angle exotropia, each rectus muscle showed orbital pathways similar to the normal patients. Conclusions: We evaluated the normal positions and angles of each rectus muscle in the orbit. The results may be useful in diagnosing the strabismus related to an abnormal orbital pathway of rectus muscles.