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Ocular Anatomy > Lecture 11: Optic Nerve > Flashcards

Lecture 11: Optic Nerve Flashcards

1
Q

what cranial nerve is the optic nerve

A

CN II

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2
Q

CN II is axons of what?

A

retinal ganglion cells

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3
Q

is the optic nerve myelinated or unmyelinated?

A

myelinated

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4
Q

how many myelinated axons make up the optic nerve

A

~1.2 million

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5
Q

what is the length of the optic nerve?

A

~ 4 cm in length

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6
Q

where does the optic nerve pass?

A

optic canal of the lesser wing of the sphenoid bone

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7
Q

CN II is the nerve fiber tract of what nervous system?

A

CNS

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8
Q

what are nerve fibers enveloped by?

A

myelin sheath derived from oligodendrocytes (CNS)

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9
Q

T/F: the optic nerve is not prone to many diseases

A

F: the optic nerve is prone to many diseases of the CNS because it is a tract of the CNS

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10
Q

how many regions can the optic nerve be divided into and what are they?

A
  1. Intraocular (prelaminar and laminar)
  2. Intraorbital
  3. intracanalicular
  4. intracranial
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11
Q

what region is seen as the optic nerve head clinically?

A

the prelaminar portion of the intraocular region

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12
Q

the laminar portion of the intraocular region is the portion that passes where?

A

portion passes through the lamina cribrosa (LC)

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13
Q

in the intraocular region of the optic nerve, are the fibers myelinated or unmyelinated?

A

unmyelinated

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14
Q

if in the intraocular regions of the optic nerve, the fibers are myelinated what is the clinical relevance?

A

there is no visual consequence - it just makes it more difficult to evaluate the ONH.

also, a bigger blindspot will be present

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15
Q

in the intraocular region of the optic nerve, what is the height and width of the disc?

A

the disc is 1.9 mm in height, and 1.5 mm wide

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16
Q

in the intraocular region of the optic nerve, where is the cup slightly displaced?

A

temporally

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17
Q

in the intraocular region of the optic nerve, what color should the rim be and what does that mean?

A

pink - vascularized

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18
Q

what is the C/D ratio?

A

between the cup and outermost edge of the optic disc

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19
Q

what 2 things determine the size of the cup?

A
  1. amount of regression of glial tissue surrounding hyaloid vasculature
  2. size od posterior scleral foramen
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20
Q

Meniscus of Kuhnt

A

glial plaque - astrocytes

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21
Q

Inner Limiting Membrane of Elschig

A

astrocytes

22
Q

Inner Limiting Membrane of Retina

A

Müller cell fot plates

23
Q

where the ILM of the retina meets the ILM of Elschig is the site of what and outlines what?

A
  1. firm adhesion of the posterior vitreous

2. outlines the are of Martegiani

24
Q

where the ILM of the retina meets the ILM of Elschig is the site of what and outlines what?

A
  1. firm adhesion of the posterior vitreous

2. outlines the are of Martegiani

25
Q

what gives rise to Bergmeister’s Papilla?

A

excessive intermediary tissue of Kuhnt (glial plaque - astrocytes)

26
Q

where do nerve fibers become myelinated?

A

posterior to the globe

27
Q

what forms myelin sheaths?

A

oligodendrocytes

28
Q

myelination, which is completed after birth, causes the optic nerve to what?

A

approximately triple in size

29
Q

what do myelinated fibers allow for?

A

faster neuronal response

30
Q

multiple sclerosis affects vision due to what?

A

demyelination of the optic nerve which slows visual transmission

31
Q

the intraorbital post-laminar region is how long?

A
  • 25 mm in length from posterior eye to optic canal

- 6 mm longer than the distance between the posterior surface of eye and optic canal (slack for movement)

32
Q

what is enveloped by 3 meningeal sheaths?

A

intraorbital post-Laminar

33
Q

what causes lamina cribrosa to bulge inward)

A

increased CSF pressure in the subarachnoid space (papilledema)

34
Q

where do the CRV and CRA cross the SAS?

A

12 mm posterior to the eyeball

35
Q

what happens if CSF is too high?

A

may compress central vein and appear as venous engorgement

36
Q

pial sheath sends in septa to support what?

A

the nerve fascicles, CRV, and CRA

37
Q

what part of the orbit does the optic nerve lie?

A

apex

38
Q

where does the optic nerve lie within?

A

the muscle cone formed by the 4 recti muscles and their tendinous origins

39
Q

how long is the intracanalicular portion of the optic nerve?

A

5 mm

40
Q

where does the intracanalicular portion travel?

A

through the optic canal (optic foramen) formed by the optic struts of the lesser wing of the sphenoid bone with the ophthalmic artery

41
Q

how long is the intracranial portion of the optic nerve?

A

10 mm

42
Q

after leaving the optic canal, the optic nerve passes within what?

A

the SAS of the brain where it merges with optic chaism

43
Q

the optic nerve is nourished by how many arterial systems? what are they?

A
  1. pial
  2. Central Retinal Artery (CRA - arteriole)
  3. Short posterior ciliary arteries (arterioles)
44
Q

the optic nerve is nourished by how many arterial systems? what are they?

A
  1. pial
  2. Central Retinal Artery (CRA - arteriole)
  3. Short posterior ciliary arteries (arterioles)
45
Q

blood supply to ON: pre-laminar region

A

both the central and peripheral portions are supplied by vessels from the surrounding choroid

46
Q

blood supply to ON: laminar region

A
  • centrally by branches from CRA

- peripherally by branches from the pial arterial network and circle of Zinn

47
Q

blood supply to ON: retro-laminar region

A
  • centrally by branches of CRA

- peripherally by branches from the pial arterial network

48
Q

blood supply to ON: the four sources of vessels

A
  1. branches from CRA or its branches
  2. branches from the circle of Zinn (representing a system of anastomoses between branches from SPCA and pial arterial network
  3. choroidal branches
  4. pial branches
49
Q

how does the optic nerve drain?

A
  • primarily CRV

- some collateral flow through the vortex veins

50
Q

Blind spot: No what on ON

A

No PR

51
Q

what type of C/D ratio do glaucoma patients have?

A

high

52
Q

ON Atrophy

A
  • a tumor on the pituitary gland puts pressure on the nasal fibers crossing at chiasm
  • this will cause compression atrophy of the nerve fibers – which will cause a whitening of the optic nerve in these areas

Ocular Anatomy (15 decks)

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