Operative indications for orbital blow-out fracture (OBF) remain controversial. One of the major sources of this controversy is that an accurate diagnosis of ocular movement disturbances can not be made by conventional procedures such as the Hess screen test, traction test, or CT scan.
Disturbances in ocular movement resulting from OBF can occur not only with entrapment of the extraocular muscle but also with intraorbital bleeding, edema, and/or a variety of other unclear factors.
To obtain a more accurate diagnosis and to assist in the choice of treatment, ocular movement was examined using orbital “tine mode” MR imaging. MR images were obtained in multiple phases of vertical and horizontal ocular movements by using the “fast SE” capabilities of the SIERRA, GEYMS MR scanner (1.5 Tesla, superconductive).
The fixed eye method was applied to two normal volunteers and to patients with “pure” OBF. Five marks for binocular fixation were affixed to the inner wall of the gantry : one at the primary position and four at secondary positions. While keeping the subject's eye focused on each of these marks for about 30 sec, MR images (head coil) of the axial view and bilateral oblique sagittal view along the optic nerve were carried out.
In the normal volunteers, a good demonstration of smooth movement of the eye ball, extraocular muscles, and the optic nerve could be obtained. In the OBF patients, it was clearly observed that the disturbance in ocular movement was caused by poor extension of the external ocular muscles, specifically the inferior rectus muscle in the orbital floor fracture, and the internal rectus muscle in the medial wall fracture.
These observations suggested that dynamic orbital imaging with MR would be extremely valuable in the assessment of disturbances of ocular movement in OBF.
