Intraorbital Optic Nerve
The intraorbital portion of the optic nerve is approximately 30 mm long, which allows for eye movement without traction on the insertion of the nerve onto the globe. The optic nerve is 4 mm in diameter and is surrounded by the internal sheath, the arachnoid sheath, and the dural sheath, which are continuous with the pia mater, arachnoid mater, and dural mater covering the brain. The dura mater covering the posterior portion of the intraorbital optic nerve fuses with the annulus of Zinn at the orbital apex and is continuous with the periosteum of the optic canal.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.