Optic nerve sheath
Vagina externa nervi optici
Sensory (eye & ear)NervesHeadLeft and right
View left in 3D View right in 3D
- What it is
- The three meningeal layers (dura, arachnoid, pia) that wrap the optic nerve from the brain to the eyeball, where the dura blends with the sclera. The subarachnoid space inside it contains cerebrospinal fluid.
- Function
- Protects the nerve and carries CSF pressure forward to the back of the eye.
- Size
- Outer diameter ~4.5-5 mm.
- Clinical note
- An optic nerve sheath diameter above ~5-6 mm on ultrasound suggests raised intracranial pressure.