Lecture 11: Optic Nerve Flashcards
what cranial nerve is the optic nerve
CN II
CN II is axons of what?
retinal ganglion cells
is the optic nerve myelinated or unmyelinated?
myelinated
how many myelinated axons make up the optic nerve
~1.2 million
what is the length of the optic nerve?
~ 4 cm in length
where does the optic nerve pass?
optic canal of the lesser wing of the sphenoid bone
CN II is the nerve fiber tract of what nervous system?
CNS
what are nerve fibers enveloped by?
myelin sheath derived from oligodendrocytes (CNS)
T/F: the optic nerve is not prone to many diseases
F: the optic nerve is prone to many diseases of the CNS because it is a tract of the CNS
how many regions can the optic nerve be divided into and what are they?
- Intraocular (prelaminar and laminar)
- Intraorbital
- intracanalicular
- intracranial
what region is seen as the optic nerve head clinically?
the prelaminar portion of the intraocular region
the laminar portion of the intraocular region is the portion that passes where?
portion passes through the lamina cribrosa (LC)
in the intraocular region of the optic nerve, are the fibers myelinated or unmyelinated?
unmyelinated
if in the intraocular regions of the optic nerve, the fibers are myelinated what is the clinical relevance?
there is no visual consequence - it just makes it more difficult to evaluate the ONH.
also, a bigger blindspot will be present
in the intraocular region of the optic nerve, what is the height and width of the disc?
the disc is 1.9 mm in height, and 1.5 mm wide
in the intraocular region of the optic nerve, where is the cup slightly displaced?
temporally
in the intraocular region of the optic nerve, what color should the rim be and what does that mean?
pink - vascularized
what is the C/D ratio?
between the cup and outermost edge of the optic disc
what 2 things determine the size of the cup?
- amount of regression of glial tissue surrounding hyaloid vasculature
- size od posterior scleral foramen
Meniscus of Kuhnt
glial plaque - astrocytes
Inner Limiting Membrane of Elschig
astrocytes
Inner Limiting Membrane of Retina
Müller cell fot plates
where the ILM of the retina meets the ILM of Elschig is the site of what and outlines what?
- firm adhesion of the posterior vitreous
2. outlines the are of Martegiani
where the ILM of the retina meets the ILM of Elschig is the site of what and outlines what?
- firm adhesion of the posterior vitreous
2. outlines the are of Martegiani
what gives rise to Bergmeister’s Papilla?
excessive intermediary tissue of Kuhnt (glial plaque - astrocytes)
where do nerve fibers become myelinated?
posterior to the globe
what forms myelin sheaths?
oligodendrocytes
myelination, which is completed after birth, causes the optic nerve to what?
approximately triple in size
what do myelinated fibers allow for?
faster neuronal response
multiple sclerosis affects vision due to what?
demyelination of the optic nerve which slows visual transmission
the intraorbital post-laminar region is how long?
- 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)
what is enveloped by 3 meningeal sheaths?
intraorbital post-Laminar
what causes lamina cribrosa to bulge inward)
increased CSF pressure in the subarachnoid space (papilledema)
where do the CRV and CRA cross the SAS?
12 mm posterior to the eyeball
what happens if CSF is too high?
may compress central vein and appear as venous engorgement
pial sheath sends in septa to support what?
the nerve fascicles, CRV, and CRA
what part of the orbit does the optic nerve lie?
apex
where does the optic nerve lie within?
the muscle cone formed by the 4 recti muscles and their tendinous origins
how long is the intracanalicular portion of the optic nerve?
5 mm
where does the intracanalicular portion travel?
through the optic canal (optic foramen) formed by the optic struts of the lesser wing of the sphenoid bone with the ophthalmic artery
how long is the intracranial portion of the optic nerve?
10 mm
after leaving the optic canal, the optic nerve passes within what?
the SAS of the brain where it merges with optic chaism
the optic nerve is nourished by how many arterial systems? what are they?
- pial
- Central Retinal Artery (CRA - arteriole)
- Short posterior ciliary arteries (arterioles)
the optic nerve is nourished by how many arterial systems? what are they?
- pial
- Central Retinal Artery (CRA - arteriole)
- Short posterior ciliary arteries (arterioles)
blood supply to ON: pre-laminar region
both the central and peripheral portions are supplied by vessels from the surrounding choroid
blood supply to ON: laminar region
- centrally by branches from CRA
- peripherally by branches from the pial arterial network and circle of Zinn
blood supply to ON: retro-laminar region
- centrally by branches of CRA
- peripherally by branches from the pial arterial network
blood supply to ON: the four sources of vessels
- branches from CRA or its branches
- branches from the circle of Zinn (representing a system of anastomoses between branches from SPCA and pial arterial network
- choroidal branches
- pial branches
how does the optic nerve drain?
- primarily CRV
- some collateral flow through the vortex veins
Blind spot: No what on ON
No PR
what type of C/D ratio do glaucoma patients have?
high
ON Atrophy
- 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
