Optic Nerve

Question 1

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

Answer 1

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

Question 2

what is the surface nerve fiber layer

Answer 2

the inner most portion, mostly nerve fibers

Question 3

what is the prelaminar region

Answer 3

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

Question 4

what is the lamina cribrosa region made out of

Answer 4

fenestrated sheets of scleral connective tissue

Question 5

what cells line the sheets and holes of the lamina cribrosa

Answer 5

astrocytes

Question 6

what passes through the holes of the lamina cribrosa

Answer 6

bundles of axons

Question 7

what happens in the retrolaminar region

Answer 7

decrease in astrocytes and myelin is acquired around the axons

Question 8

what is the posterior limit of the retrolaminar region

Answer 8

not clear, but about 3-4mm

Question 9

what is the main arterial supply to the optic nerve

Answer 9

posterior ciliary artery

Question 10

what is the arterial supply to the nerve fiber layer

Answer 10

retinal circulation

Question 11

what blood vessels supply the surface of the nerve fiber layer

Answer 11

arteriolar branches of central retinal artery

Question 12

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

Answer 12

the vessels of the prelaminar region

Question 13

what is the blood vessel supply to prelaminar and laminar regions

Answer 13

short posterior ciliary arteries

Question 14

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

Answer 14

the circle of Zinn-Haller

Question 15

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

Answer 15

the peripapillary choroid

Question 16

what is the blood supply to the retrolaminar region

Answer 16

medial and lateral perioptic nerve short posterior ciliary arteries

Question 17

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

Answer 17

an elliptical arterial circle- also called Zinn-Haller

Question 18

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

Answer 18

decrease

Question 19

name the 6 blood vessel supplies to the optic nerve

Answer 19

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

Question 20

where are the capillaries of the optic nerve derived from

Answer 20

both retinal and ciliary circulation

Question 21

what is the venous drainage for the optic nerve

Answer 21

all through the central retinal vein

Question 22

what does the astroglial support do

Answer 22

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

Question 23

what do the thin astrocytes do

Answer 23

accompany the axons in the nerve fiber layer

Question 24

what do the thick astrocytes do

Answer 24

direct axons from prelaminar to laminar region

Question 25

what happens at the lamina cribrosa during glaucoma

Answer 25

glaucoma pathogenesis takes place here

Question 26

what is the lamina cribrosa an extension of

Answer 26

the sclera- porous region

Question 27

what is the lamina cribrosa made of

Answer 27

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

Question 28

What is found surrounding the myelin sheaths in the lamina cribrosa

Answer 28

hyaluronate

Question 29

when does hyaluronate decreases in the lamina cribrosa

Answer 29

with age and an increase in IOP

Question 30

what would cause the lamina cribrosa pores to compress

Answer 30

Glaucoma and high myopia

Question 31

which region are the pores of the lamina cribrosa larger

Answer 31

superiorly and inferiorly

Question 32

why are the superior and inferior pores larger

Answer 32

due to the arclike fibers in those places

Question 33

how far do papillomacular fibers spread

Answer 33

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

Question 34

what do the papillomacular fibers intermingle with

Answer 34

extramacular fibers

Question 35

how many axons exit the optic nerve

Answer 35

1 million

Question 36

what is the axon fiber diameter

Answer 36

0.65 to 1.10 microns

Question 37

when is the optic nerve 95% of its size

Answer 37

before age 1

Question 38

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

Answer 38

potential for reversible cupping, but a greater susceptibility to damage

Question 39

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

Answer 39

natural/normal aging process

Question 40

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

Answer 40

larger cells tend to die first (larger axons)

Question 41

what is the current theory of which fibers die off first

Answer 41

the cells die at an equal rate

Question 42

what do retinal ganglion cells survival depend on

Answer 42

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

Question 43

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

Answer 43

retrograde axopalsmic flow

Question 44

what may result from blockage of retrograde axopalsmic flow

Answer 44

retinal ganglion cell death

Question 45

when is nitric acid beneficial

Answer 45

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

Question 46

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

Answer 46

inhibits mitochondrial function and disrupts DNA

Question 47

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

Answer 47

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

Question 48

what is the support for the mechanical theory

Answer 48

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

Question 49

what is the vascular theory

Answer 49

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

Question 50

what is perfusion pressure

Answer 50

the difference between arterial and venous pressure

Question 51

what is the mean ocular perfusion pressure

Answer 51

the mean blood pressure minus the IOP

Question 52

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

Answer 52

autoregulatory mechanism

Question 53

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

Answer 53

in glaucoma

Question 54

what are the two types of autoregulatory mechanisms

Answer 54

metabolic and myogeneic

Question 55

what secretes the metabolic autoregulatory mechanisms

Answer 55

endothelial cells

Question 56

what are two types of metabolic autoregulatory mechanisms

Answer 56

vasodilators (nitric acid) and vasoconstrictors (endothelin 1)

Question 57

when does a myogenic autoregulatory mechanism operate

Answer 57

when blood flow is above normal

Question 58

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

Answer 58

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