Transverse T2w HR-MRI image of the retrobulbar region Dotted lines: the rectus muscles 1) dorsal, 2) medial, 3) ventral and 4) lateral; surrounded by continuous lines are the retractor muscles (5, 6, 7 and 8), 9) optic nerve surrounded by 10) a rim of T2 hyperintense CSF within the optic nerve sheath, 11) optic nerve sheath, 12) portions of the periorbita, 13) dorsal external ophthalmic vein, 14) ventral ophthalmic vein, 15) Zygomatic gland, 16) periorbita