Optic Nerve

Question 1

how many myelinated axons make up the optic nerve

Answer 1

1.2 million

Question 2

how long is the optic nerve

Answer 2

4cm

Question 3

where does the intracanalicular portion travel through

Answer 3

the lesser wing of the sphenoid bone (with the ophthalmic artery)

Question 4

what is the optic nerve called after it passes through the optic canal

Answer 4

intracranial portion

Question 5

where is the myelin derived from that surrounds the ganglion cells within the optic nerve

Answer 5

oligodendrocytes

Question 6

is the optic nerve prone to diseases that affect the central nervous system

Answer 6

yes

Question 7

what are the 3 meningeal sheaths that surround the optic nerve

Answer 7

dura mater, arachnoid, and pia

Question 8

what does the pia send into the optic nerve when it becomes the intraorbital portion

Answer 8

septa to support the nerve fiber bundles, artery, and vein

Question 9

what happens to the optic nerve if IOP is elevated too high

Answer 9

cerebralspinal fluid in the subarachnoid space will exert pressure onto the nerve and cause the lamina cribrosa to bulge forward (convex)

Question 10

where do the central artery and vein cross the subarachnoid space

Answer 10

12mm posterior to the globe

Question 11

what may be a cause of papilledema during a funduscope exam

Answer 11

if intercranial pressure increased and compressed the central retinal vein

Question 12

what are the 4 regions the optic nerve can be divided into

Answer 12

intraocular, orbital, intracanalicular, and intracranial

Question 13

how long is the intraocular portion

Answer 13

1 mm

Question 14

what is included in the intracocular portion

Answer 14

the optic disc and the portion of nerve that lies within the sclera

Question 15

what is another term for the optic disc

Answer 15

the prelaminar zone

Question 16

where is the cup situated within the disc

Answer 16

slightly off center, displaced temporally

Question 17

what lines the optic cup

Answer 17

glial plaque or the central supporting tissue of Kuhnt or meniscus of Kuhnt

Question 18

what is Bergmeister’s papilla

Answer 18

if the meniscus of Kuhnt is over-exaggerated during development

Question 19

what is the meniscus of Kuhnt continuous with

Answer 19

a thinner membrane lining the surface of the nerve head, inner limiting membrane of Elschnig

Question 20

what are the meniscus of Kuhnt and the inner limiting membrane of Elschnig composed of

Answer 20

astocytes

Question 21

what is the inner limiting membrane of Elschnig continuous with peripherally

Answer 21

the basal footplates of the Muller cells

Question 22

what do the central artery and vein share exiting the lamina cribrosa

Answer 22

a collagenous adventitial sheath that separates them from the nasal fibers of the optic nerve

Question 23

how long is the intraorbital portion

Answer 23

25mm

Question 24

how much does the optic nerve increase in size from the intraocular diameter to the intraorbital diameter

Answer 24

from 1.5mm to 3-4mm (due to myelin added)

Question 25

why is the intraorbital portion 6mm longer than the distance between the posterior surface of the eye and the optic canal

Answer 25

allows for greater movement of the eye (sinusoidal course)

Question 26

what is the intraorbital portion surrounded by

Answer 26

orbital fat

Question 27

where does the ciliary ganglion lie

Answer 27

between the lateral border of the optic nerve and lateral rectus muscle

Question 28

where do the central artery and vein pierce the dural sheath

Answer 28

about 12-16mm behind the posterior sclera, traveling obliquely in the subarachnoidal space

Question 29

how long is the intracanalicular portion

Answer 29

5mm

Question 30

how long is the intracranial portion

Answer 30

10 mm

Question 31

where does the intracranial portion travel

Answer 31

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

Question 32

what blood supplies the lamina cribrosa and the pia vasculature

Answer 32

short posterior ciliary arteries (circle of Zinn Holler)

Question 33

are the capillaries of the optic nerve fenestrated

Answer 33

no they have zonula occludens

Question 34

where does the intraorbital portion of the nerve get its blood supply

Answer 34

from the branches of the pial plexus that extend into the nerve via the pia septa

Question 35

how are the intracanalicular and intracranial portions supplied with blood

Answer 35

by the pial plexus