Optic Nerve Flashcards
what are the 4 parts that the optic nerve head is divided into
surface nerve fiber layer, prelaminar region, lamina cribrosa region, and retrolaminar
what is the surface nerve fiber layer
the inner most portion, mostly nerve fibers
what is the prelaminar region
also called the anterior portion of lamina cribrosa, mostly nerve axons and astrocytes with significant increase in astroglial tissue
what is the lamina cribrosa region made out of
fenestrated sheets of scleral connective tissue
what cells line the sheets and holes of the lamina cribrosa
astrocytes
what passes through the holes of the lamina cribrosa
bundles of axons
what happens in the retrolaminar region
decrease in astrocytes and myelin is acquired around the axons
what is the posterior limit of the retrolaminar region
not clear, but about 3-4mm
what is the main arterial supply to the optic nerve
posterior ciliary artery
what is the arterial supply to the nerve fiber layer
retinal circulation
what blood vessels supply the surface of the nerve fiber layer
arteriolar branches of central retinal artery
what do the arteriorlar branches of the central retinal artery of the surface nerve fiber layer anasthamose with
the vessels of the prelaminar region
what is the blood vessel supply to prelaminar and laminar regions
short posterior ciliary arteries
what do the short posterior ciliary arteries of the prelaminar and laminar regions form
the circle of Zinn-Haller
besides suppling the prelaminar and laminar regions, what else does the circle of Zinn-Haller supply
the peripapillary choroid
what is the blood supply to the retrolaminar region
medial and lateral perioptic nerve short posterior ciliary arteries
what do the medial and lateral perioptic nerve short posterior ciliary arteries form around the optic nerve
an elliptical arterial circle- also called Zinn-Haller
do the capillaries increase or decrease in number posterior to the lamina
decrease
name the 6 blood vessel supplies to the optic nerve
- central retinal artery 2. radial peripapillary capillaries 3. pial vessels 4. short posterior ciliary arteries 5. peripapillary choroidal vessels 6. Circle of Zinn-Haller
where are the capillaries of the optic nerve derived from
both retinal and ciliary circulation
what is the venous drainage for the optic nerve
all through the central retinal vein
what does the astroglial support do
provides continuous layer between nerve fiber and blood vessels of optic nerve head
what do the thin astrocytes do
accompany the axons in the nerve fiber layer
what do the thick astrocytes do
direct axons from prelaminar to laminar region
what happens at the lamina cribrosa during glaucoma
glaucoma pathogenesis takes place here
what is the lamina cribrosa an extension of
the sclera- porous region
what is the lamina cribrosa made of
specialized extracellular matrix- fenestrated sheets of connective tissue and occasional elastic fibers
What is found surrounding the myelin sheaths in the lamina cribrosa
hyaluronate
when does hyaluronate decreases in the lamina cribrosa
with age and an increase in IOP
what would cause the lamina cribrosa pores to compress
Glaucoma and high myopia
which region are the pores of the lamina cribrosa larger
superiorly and inferiorly
why are the superior and inferior pores larger
due to the arclike fibers in those places
how far do papillomacular fibers spread
about 1/3 of the distal optic nerve (inferior and temporal)
what do the papillomacular fibers intermingle with
extramacular fibers
how many axons exit the optic nerve
1 million
what is the axon fiber diameter
0.65 to 1.10 microns
when is the optic nerve 95% of its size
before age 1
what are the good and bad reasons of having the connective tissue in the lamina cribrosa incompletely developed in young children
potential for reversible cupping, but a greater susceptibility to damage
why is there a progressive loss of axons (4,000-12,000 per year)
natural/normal aging process
what fibers die off first with aging according to Quigley and group
larger cells tend to die first (larger axons)
what is the current theory of which fibers die off first
the cells die at an equal rate
what do retinal ganglion cells survival depend on
certain neuronal growth factors, neurotrophins (brain-derived neurotrophic factor)
if there is axonal compression at the lamina cribrosa, what does it block
retrograde axopalsmic flow
what may result from blockage of retrograde axopalsmic flow
retinal ganglion cell death
when is nitric acid beneficial
at low concentrations as a vasodilator (more blood flow= better nutrition)
if nitric acid is in higher concentrations what happens to the optic nerve
inhibits mitochondrial function and disrupts DNA
what is the mechanical theory on the influence of IOP on axoplasmic flow
physical alterations, misalignment of fenestrae, backbowing of lamina cribrosa may lead to obstruction
what is the support for the mechanical theory
elevated IOPs occur despite intact blood vessels- blood flow doesn’t stop
what is the vascular theory
that ischemia plays a role in the obstruction of axoplasmic flow in response to elevated IOP
what is perfusion pressure
the difference between arterial and venous pressure
what is the mean ocular perfusion pressure
the mean blood pressure minus the IOP
what mechanism is present in retinal vessels to maintain blood flow regardless of perfusion pressure
autoregulatory mechanism
when does the auto-regulatory mechanism in the retinal vessels fail
in glaucoma
what are the two types of autoregulatory mechanisms
metabolic and myogeneic
what secretes the metabolic autoregulatory mechanisms
endothelial cells
what are two types of metabolic autoregulatory mechanisms
vasodilators (nitric acid) and vasoconstrictors (endothelin 1)
when does a myogenic autoregulatory mechanism operate
when blood flow is above normal
what are some examples of evidence in favor of the vascular theory
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
