Optic Nerve Flashcards
how many myelinated axons make up the optic nerve
1.2 million
how long is the optic nerve
4cm
where does the intracanalicular portion travel through
the lesser wing of the sphenoid bone (with the ophthalmic artery)
what is the optic nerve called after it passes through the optic canal
intracranial portion
where is the myelin derived from that surrounds the ganglion cells within the optic nerve
oligodendrocytes
is the optic nerve prone to diseases that affect the central nervous system
yes
what are the 3 meningeal sheaths that surround the optic nerve
dura mater, arachnoid, and pia
what does the pia send into the optic nerve when it becomes the intraorbital portion
septa to support the nerve fiber bundles, artery, and vein
what happens to the optic nerve if IOP is elevated too high
cerebralspinal fluid in the subarachnoid space will exert pressure onto the nerve and cause the lamina cribrosa to bulge forward (convex)
where do the central artery and vein cross the subarachnoid space
12mm posterior to the globe
what may be a cause of papilledema during a funduscope exam
if intercranial pressure increased and compressed the central retinal vein
what are the 4 regions the optic nerve can be divided into
intraocular, orbital, intracanalicular, and intracranial
how long is the intraocular portion
1 mm
what is included in the intracocular portion
the optic disc and the portion of nerve that lies within the sclera
what is another term for the optic disc
the prelaminar zone
where is the cup situated within the disc
slightly off center, displaced temporally
what lines the optic cup
glial plaque or the central supporting tissue of Kuhnt or meniscus of Kuhnt
what is Bergmeister’s papilla
if the meniscus of Kuhnt is over-exaggerated during development
what is the meniscus of Kuhnt continuous with
a thinner membrane lining the surface of the nerve head, inner limiting membrane of Elschnig
what are the meniscus of Kuhnt and the inner limiting membrane of Elschnig composed of
astocytes
what is the inner limiting membrane of Elschnig continuous with peripherally
the basal footplates of the Muller cells
what do the central artery and vein share exiting the lamina cribrosa
a collagenous adventitial sheath that separates them from the nasal fibers of the optic nerve
how long is the intraorbital portion
25mm
how much does the optic nerve increase in size from the intraocular diameter to the intraorbital diameter
from 1.5mm to 3-4mm (due to myelin added)
why is the intraorbital portion 6mm longer than the distance between the posterior surface of the eye and the optic canal
allows for greater movement of the eye (sinusoidal course)
what is the intraorbital portion surrounded by
orbital fat
where does the ciliary ganglion lie
between the lateral border of the optic nerve and lateral rectus muscle
where do the central artery and vein pierce the dural sheath
about 12-16mm behind the posterior sclera, traveling obliquely in the subarachnoidal space
how long is the intracanalicular portion
5mm
how long is the intracranial portion
10 mm
where does the intracranial portion travel
leaves the optic canal, passes within the subarachnoid space of the brain and merges with the optic chiasm in the floor of the 3rd ventricle
what blood supplies the lamina cribrosa and the pia vasculature
short posterior ciliary arteries (circle of Zinn Holler)
are the capillaries of the optic nerve fenestrated
no they have zonula occludens
where does the intraorbital portion of the nerve get its blood supply
from the branches of the pial plexus that extend into the nerve via the pia septa
how are the intracanalicular and intracranial portions supplied with blood
by the pial plexus
