Ocular Anatomy: Optic Nerve

Axons from the peripheral retina run ______ in the nerve fiber layer and enter the _______ of the optic disc

deeper

ege

Axons from the center retina run ______ in the nerve fiber layer and enter the _______ of the optic disc

superficial

inner ednge

optic nerve head (disc)

perlaminar portion of the optic nerve

optic nerve head shape and size

slightly vertically oval

horizontal diamter 1.5 mm

(diamter of disc vries based on the diamter of the posterior scleral foramen)

the center of the optic disc is ____ mm medial and slightt ________ to the fovea

4 mm medial

slightly superior

Neuroretinal rim (NRR)

edge of optic disc to outer edge of cup

contains all the axons of the RGCs, blood vessels, astrocytes

cup

excavation in center of optic disc

size of the disc depends on

size of optic disc and teh amount of blood cessls, glial cells, and conenctive tissue

cup is not present in small scleral pts

Disc size is determined primarily by the size of the

posterior scleral foramen

(genetic factors)

the disc size influences the size of

the cup and the width of the NRR

in normal people, expect a

large cup in a large disc

Scleral crescent

scleral visible around part of the optic nerve due to the absence of the retina, RPE, and choroid

often inferior - temporal

Choroidal crescent

choroid visible around the edge of the disc due to the absence of the RPE

RPE crescent

heaping up of RPE pigment at the edge of the disc

peripapillary atrophy

thinning or the retinal and RPE around the edge of the disc

peripapillary atrophy can be caused by

caused by aging, high myopia, and glaucoma

The optic nerve extends from the

posterior pole of the eye to the optic chiasm

parts of the optic nerve

intraocular (intrascleral)

intraorbital (intraconal)

intracanalicular

intracranial

intraocular part

1.5 mm in diameter

in the eye

when the nerve leaves the eye

it becomes myelinated and covered by the meninges

expanding the diameter to 3.0mm

intraorbital portion

s shaped - creates slack for EOM movements without traction

intraorbital portion contains

optic nerve

meningeal sheaths

blood vessels

pial septa

axons are now myelinated!

______ enter/exit the intraobral optic nerve ______mm behind the globe

CRA and CRV

10-12 mm

intracranial portion

runs from the optic foramen through the middle cranial fossa to the optic chiasm

three main histological components of the optic nerve

Axons of retinal ganglion cells

glial cells

blood vessels

Glial cells

astrocytes (protective and supportive

olgiodendroglia (myeliantes axons)

microglial (phagocytoc, APCs)

as the axons of ganglion cells form the optic nerve, they are

ALWAYS insulated from connective tissue by glial cells

______ separate the blood vessels and connective tissue from axons

astrocytes

astrocytes are present at the level of

sensory retina

RPE

Bruch's membrane

choroid

sclera

Border tissue of Elschnig

collar of scleral (fibrous) tissue that runs from the peripapillary sclera forward (anterioir) to bruch;'s memrbanse opening

helps define the edge of the optic nerve

prelaminar portion surface is covered by

astrocytes NOT muller cells

internal limiting membrane of Elschnig

transition at edge of disc to the internal limiting membranee of the retina (which contains muller cells)

at the prelaminr portion the ganglion cells axons

converge, turn 90 degrees and exit through the posterior scleral foramen -Neuroretinal rim

RCG axons are segregated into

bundles or fascicles surrounded by astrocytes - circular astrocytic tubes

separating them from blood vessles and connective tissue

The center of the optic nerve contains

NO ganglion cells axos

contains glial tissue - white in color

no small blood vessels CRA and CRV only

lamina cribosa

part of the choroid and the inner 2/3 of sclera form a scaffolding over the posterior scleral foramen - reinforces PSF

lamina cribosa consists of

20-30 sheets of collagen, elastin, and fibrocytes covered with astrocytes (glia) and separated by blood vessels

the sheets contain

pores for passage of axons of ganglion cells

bundles of axons run perpendicular to laminar sheets

pores are larger

superior and inferior than the ones that are medial and temporal

less supported

more susceptible to damage if IOP is elevated

larger at 12 o clock and 6 o clock

smaller at 3 and 9 o clock

Retrolaminar portion is the transition

transition zone from lamina cribosa to intraorbital part of the optic nerve

at the retrolamina portion the thickness of the optic nerve

doubles due to myleination of axons by olgiodendroglia

nerve is now covered with meninges from CNS

Pia matter extends into the optic nerve forming

setpa

septa

enclose nerve bundle

carry blood supply

------ insulate bundles of axons from pial septa

astrocytes

intraorbital portion

axons are myelinated

optic nerve covered by meninges

in the intraorbital portion, the dura

fuses anteriorly with scleral and Tenon;s capsule

in the intraorbital portion, the arachnoid

subarachnoid space - continuous with that of the brain

extends forward to the posterior scleral foramne

CSF

in the intraorbital portion, the pia

pial septa

blood supply of the optic nerve

anterior: opthalmic artery --> central retinal artery --> posterior ciliary arteries --> short posterior ciliary arteries --> anastomisis --> circle of Zinn-Haller

posterior: ophthalmic artery --> plial plexus

Circumlinear blood vessels

small arterioles passing temporally optic nerve

value in determining size of the cup

Blood supply to nerve fiber layer

branches of CRA

Blood supply: prelaminar portion

short posterior ciliary arteries --> peripapillary chordoial vessels

blood supply to the laminar portion

SPCA

circle of Zinn-Haller

blood supply to the retro laminar portion

CRA - axial

pial plexus - peripheral

blood supply to the intraorbital portion

anterior: CRA -axial and Pial plexus peripherallyt

posterior: Pial plexus

Venous Drainage of the optic nerve

central retinal vein

translaminar pressure difference

pressure across the lamina cribosa

determined by IOP and from CFS