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Ocular Physiology #2 > Optic Nerve > Flashcards

Optic Nerve Flashcards

1
Q

what are the 4 parts that the optic nerve head is divided into

A

surface nerve fiber layer, prelaminar region, lamina cribrosa region, and retrolaminar

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2
Q

what is the surface nerve fiber layer

A

the inner most portion, mostly nerve fibers

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3
Q

what is the prelaminar region

A

also called the anterior portion of lamina cribrosa, mostly nerve axons and astrocytes with significant increase in astroglial tissue

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4
Q

what is the lamina cribrosa region made out of

A

fenestrated sheets of scleral connective tissue

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5
Q

what cells line the sheets and holes of the lamina cribrosa

A

astrocytes

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6
Q

what passes through the holes of the lamina cribrosa

A

bundles of axons

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7
Q

what happens in the retrolaminar region

A

decrease in astrocytes and myelin is acquired around the axons

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8
Q

what is the posterior limit of the retrolaminar region

A

not clear, but about 3-4mm

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9
Q

what is the main arterial supply to the optic nerve

A

posterior ciliary artery

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10
Q

what is the arterial supply to the nerve fiber layer

A

retinal circulation

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11
Q

what blood vessels supply the surface of the nerve fiber layer

A

arteriolar branches of central retinal artery

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12
Q

what do the arteriorlar branches of the central retinal artery of the surface nerve fiber layer anasthamose with

A

the vessels of the prelaminar region

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13
Q

what is the blood vessel supply to prelaminar and laminar regions

A

short posterior ciliary arteries

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14
Q

what do the short posterior ciliary arteries of the prelaminar and laminar regions form

A

the circle of Zinn-Haller

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15
Q

besides suppling the prelaminar and laminar regions, what else does the circle of Zinn-Haller supply

A

the peripapillary choroid

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16
Q

what is the blood supply to the retrolaminar region

A

medial and lateral perioptic nerve short posterior ciliary arteries

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17
Q

what do the medial and lateral perioptic nerve short posterior ciliary arteries form around the optic nerve

A

an elliptical arterial circle- also called Zinn-Haller

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18
Q

do the capillaries increase or decrease in number posterior to the lamina

A

decrease

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19
Q

name the 6 blood vessel supplies to the optic nerve

A
  1. central retinal artery 2. radial peripapillary capillaries 3. pial vessels 4. short posterior ciliary arteries 5. peripapillary choroidal vessels 6. Circle of Zinn-Haller
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20
Q

where are the capillaries of the optic nerve derived from

A

both retinal and ciliary circulation

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21
Q

what is the venous drainage for the optic nerve

A

all through the central retinal vein

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22
Q

what does the astroglial support do

A

provides continuous layer between nerve fiber and blood vessels of optic nerve head

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23
Q

what do the thin astrocytes do

A

accompany the axons in the nerve fiber layer

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24
Q

what do the thick astrocytes do

A

direct axons from prelaminar to laminar region

25
Q

what happens at the lamina cribrosa during glaucoma

A

glaucoma pathogenesis takes place here

26
Q

what is the lamina cribrosa an extension of

A

the sclera- porous region

27
Q

what is the lamina cribrosa made of

A

specialized extracellular matrix- fenestrated sheets of connective tissue and occasional elastic fibers

28
Q

What is found surrounding the myelin sheaths in the lamina cribrosa

A

hyaluronate

29
Q

when does hyaluronate decreases in the lamina cribrosa

A

with age and an increase in IOP

30
Q

what would cause the lamina cribrosa pores to compress

A

Glaucoma and high myopia

31
Q

which region are the pores of the lamina cribrosa larger

A

superiorly and inferiorly

32
Q

why are the superior and inferior pores larger

A

due to the arclike fibers in those places

33
Q

how far do papillomacular fibers spread

A

about 1/3 of the distal optic nerve (inferior and temporal)

34
Q

what do the papillomacular fibers intermingle with

A

extramacular fibers

35
Q

how many axons exit the optic nerve

A

1 million

36
Q

what is the axon fiber diameter

A

0.65 to 1.10 microns

37
Q

when is the optic nerve 95% of its size

A

before age 1

38
Q

what are the good and bad reasons of having the connective tissue in the lamina cribrosa incompletely developed in young children

A

potential for reversible cupping, but a greater susceptibility to damage

39
Q

why is there a progressive loss of axons (4,000-12,000 per year)

A

natural/normal aging process

40
Q

what fibers die off first with aging according to Quigley and group

A

larger cells tend to die first (larger axons)

41
Q

what is the current theory of which fibers die off first

A

the cells die at an equal rate

42
Q

what do retinal ganglion cells survival depend on

A

certain neuronal growth factors, neurotrophins (brain-derived neurotrophic factor)

43
Q

if there is axonal compression at the lamina cribrosa, what does it block

A

retrograde axopalsmic flow

44
Q

what may result from blockage of retrograde axopalsmic flow

A

retinal ganglion cell death

45
Q

when is nitric acid beneficial

A

at low concentrations as a vasodilator (more blood flow= better nutrition)

46
Q

if nitric acid is in higher concentrations what happens to the optic nerve

A

inhibits mitochondrial function and disrupts DNA

47
Q

what is the mechanical theory on the influence of IOP on axoplasmic flow

A

physical alterations, misalignment of fenestrae, backbowing of lamina cribrosa may lead to obstruction

48
Q

what is the support for the mechanical theory

A

elevated IOPs occur despite intact blood vessels- blood flow doesn’t stop

49
Q

what is the vascular theory

A

that ischemia plays a role in the obstruction of axoplasmic flow in response to elevated IOP

50
Q

what is perfusion pressure

A

the difference between arterial and venous pressure

51
Q

what is the mean ocular perfusion pressure

A

the mean blood pressure minus the IOP

52
Q

what mechanism is present in retinal vessels to maintain blood flow regardless of perfusion pressure

A

autoregulatory mechanism

53
Q

when does the auto-regulatory mechanism in the retinal vessels fail

A

in glaucoma

54
Q

what are the two types of autoregulatory mechanisms

A

metabolic and myogeneic

55
Q

what secretes the metabolic autoregulatory mechanisms

A

endothelial cells

56
Q

what are two types of metabolic autoregulatory mechanisms

A

vasodilators (nitric acid) and vasoconstrictors (endothelin 1)

57
Q

when does a myogenic autoregulatory mechanism operate

A

when blood flow is above normal

58
Q

what are some examples of evidence in favor of the vascular theory

A

delayed filling of superficial vessels of optic nerve glaucoma, association of NTG with migraines, excessive peripheral constriction of vessels to cold (Raynaud’s syndrome), nocturnal blood flow is different in glaucoma patients, and greater plasma concentration of enothelin-1

Ocular Physiology #2 (7 decks)

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