CN II: Optic Nerve

OPTIC NERVE SHEATH

PAPILLEDEMA

MoA: CSF pressure in optic sheath --> compress CN II --> axonal swelling & leaking
Sx: enlarged blind spot, constricted visual field with NO change in acuity, but will change w/ distance
DDx: if psychogenic, tunnel vision will not change with distance

Papilledema

OPTIC NEURITIS

Sx: rapid loss of vision, pain w/ EOMs, local tender
Epi: young adults
A/w: retrobulbar neuritis or papillitis (edema of optic nerve head), MS (75% develop MS, 15% first sx), virus (children, BL)
Pr: in 2/3 of pts, vision returns in few wks (color blindness lingers). 1/8 recurs
Tx: steroids

ISCHEMIC OPTIC NEUROPATHY

Loc: posterior optic nerve, occlude central retinal artery
MoA: prone position with pressure --> increased intraocular pressure --> occlude central retinal artery --> ischemia
Sx: visual loss, altitudinal defect, flame hemorrhage, edema w/ disc atrophy
A/w: prone position after spine surgery, diabetes, HTN
Epi: *painless monocular blindness in pts >50 yo
DDx: no cherry red spot (vs. central retinal occlusion)
Tx: reverse Trendelenberg

OPTIC RADIATIONS

Before LGN:
-Rectotectal tract --> CL superior colliculus
-SCN

Von Willebrand's Knee

Loc: proximal optic nerve (in this pic, L)
A/w: any compressive lesion
Wilbrans knee --| L anterior medial optic chiasm --> ipsilateral optic nerve fibers, CL infero-nasal fibers loop slightly forward into ipsilateral proximal optic nerve before proceeding to optic tract--> central/junctional scotoma, CL superotemporal field cut
Max radiosurgery: 8-10Gy

Bilateral central scotoma --| both occipital poles
Homonymous altitudinal heminopsia: --| both occipital poles

VISUAL FIELD TESTING

On center / off surround
Cells: Ganglion, bipolar cells, LGN
On-center cells: stimulated by light in the center, inhibited by light in the surround
Off-center cells: opposite

V2 --> V4 and middle temporal areas (object movement & color analysis)