Scheme to demonstrate the optic nerve/sheath complex. (A) Oblique coronal T2-weighted fast-recovery fast spin-echo sequence (T2WI-FRFSE) image with fat suppression for demonstrating the optic nerve/sheath complex taken at 3 mm behind the globe perpendicular to the optic nerve axis (digital field of view = 4, window width = 2,000, window level = 1,000). The nerve parenchyma is the hypodense area inside of the hypertense ring of cerebrospinal fluid. (B) Schematic drawing of the optic nerve/sheath complex including the optic nerve (the black area represents optic nerve), surrounding cerebrospinal fluid space (white rim area), and the optic nerve sheath (at the conjunction of the cerebrospinal fluid space rim and the orbital fat). OND, optic nerve diameter; ONSD, optic nerve sheath diameter.