Fat-Suppressed, Posterior to Globe The absence of fat signals within the orbit allows differentiation of the dural sheath of ON. The cerebrospinal fluid is seen as a bright ring surrounding the darker ON. The flow void of SOY is seen below the left SR.IR = Inferior Rectus Muscle, LP = Levator Palpebrae Superiorism LR = Lateral Rectus Muscle, MR = Medial Rectus Muscle, ON = Optic Nerve, SO = Superior Oblique Musclem SOY = Superior Ophthalmic Vein, SR = Superior Rectus Muscle.