Figure 2.

T2-weighted MRI of representative normal subject in contiguous, 2-mm-thick axial planes centered (middle column) on the optic nerve (ON) and including inferior and superior planes to illustrate the full diameter of the ON sheath. MRI was repeated in right (top row), center (middle row), and left (lower row) gazes. Note ON redundancy in central gaze and abduction, with the ON either sinuous within the same plane or between adjacent axial planes. However, in adduction of each eye, the ON is straightened and becomes apposed to the straight ON sheath surrounding it. ON length was measured from the posterior globe to the orbital apex as illustrated in the lower image. Anteroposterior (AP) orbit length was measured from the apex, the location of the common tendonous origin of the rectus muscles, to the anterior border of the orbital fat in the axial image plane closest to the center of the ON in central gaze.