Figure 3.

Quasi-coronal, T2 MRI of normal left orbit demonstrating measurements of the immediately retrobulbar optic nerve diameter (ON diam.), ON sheath outer diameter, sheath thickness, and cerebrospinal fluid gap (subarachnoid space). Diameters of circular structures were inferred from cross-sectional areas to achieve subpixel resolution, and circular symmetry with constant sheath and gap thickness was assumed. IR, inferior rectus muscle; LPS, levator palpebrae superioris; LR, lateral rectus muscle; MR, medial rectus muscle; SO, superior oblique muscle; SOV, superior ophthalmic vein.