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OPTHT801 > Visual pathway > Flashcards

Visual pathway Flashcards

1
Q

Where is the optic nerve myelinated?

A

Unmyelinated in eyeball

Myelinated posterior to disc

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2
Q

How many nerve fibres in optic nerve?

A

1.2 million

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3
Q

What are the divisions of the optic nerve?

A

Intraocular 1mm
Intraorbital 25-30mm
Intracanalicular 4-10mm
Intracranial 10mm

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4
Q

What are the coating of the optic nerve?

A

Covered by dura, arachnoid and pia -blend with sclera anteriorly
Myelin produced by oligodendryocytes
Divided into fibrous septa

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5
Q

Which part of the anatomy is responsible for optic disc swelling in raised intracranial pressure?

A

A swollen lamina cribosa

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6
Q

What are the four divisions of the intraocular optic nerve?

A

Superficial nerve fibre-> optic disc area
Prelaminar area
Laminar area
Retrolaminar area

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7
Q

What is the lamina cribosa?

A

10 connective tissue plates
Pores transmit unmyelinated axon cells from the eyeball
Provides scaffolding for optic nerve axons
Provides scaffold for central retinal artery and vein
And reinforces posterior area of the globe

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8
Q

How does diameter of optic nerve change behind lamina cribosa?

A

Increases to 3mm due to myelination

1.5mm within eyeball

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9
Q

Which vessels pass through optic nerve head?

A

Central retinal artery and vein

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10
Q

Where is the intraorbital part of the optic nerve?

A

25mm long s shaped
Runs from lamina cribosa to optic foramen
Lies within annulus of zinn at orbital apex
Anterior: long and short ciliary nerves and arteries
Lateral: ciliary ganglion (parasympathetic)
Posterior: nasociliary nerve and ophthalmic artery
Inferior: CN III +central retinal artery and vein

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11
Q

What travels with the intracanalicular portion of the optic nerve?

A

Opthalmic artery
Sympathetic nerve
Meninges
Dural sheath fuses with periosteum at this stage
Sphenoid and posterior air cells lie medially

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12
Q

What is the blood supply of the intraocular optic nerve?

A

Intraocular: anastomotic circle of Zinn from short posterior ciliary arteries

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13
Q

What is the blood supply of the intraorbital and intracanalicular optic nerve?

A

Pial plexus

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14
Q

What is the blood supply of the intracranial optic nerve?

A

Pial plexus

and branches of internal carotid

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15
Q

Describe the histology of the optic nerve

A

Supporting glial cells and blood vessels
Nerve bundles
Surrounding meninges

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16
Q

What are the function of the optic nerve?

A

transmits all visual information
Contrast visual acuity
Colour perception brightness perception
Conducts visual impulses; light reflex and accommodation reflex

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17
Q

Why do we test red saturation?

A

Difference in optic nerve colour perception

Decreased saturation = optic neuritis/pathology

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18
Q

Where does the central retinal artery enter the optic nerve?

A

1.2cm from the globe

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19
Q

Where is the optic chiasm?

A

Junction of anterior wall and floor of 3rd ventricle
Continuous anteriorly with optic nerve and posteriorly with optic tracts
12mm long, 8mm wide and 3mm thick

20
Q

What are the relations of the optic chiasm?

A

Anterior: anterior cerebellar and anterior communicating arteries
Lateral: internal carotid artery ascending from cavernous sinus
Posterior: interpeduncular space with infundibulum below and 3rd ventricle above
Superior: 3rd ventricle cavity and anterior wall
Inferiorly: diaphragma sellae, hypophysis cerebri and cavernous sinus

21
Q

What is a prefixed/postfixed optic chiasm?

A

79% overlies dorsum sellae
17% lies more anterior (prefixed)
4% lies more posterior (postfixed)

22
Q

Describe the retinotopic organisation of the optic chiasm

A

Nasal fibres from retina cross over to the opposite optic tract
Temporal fibres do not cross
Inferior nasal fibres cross in anterior chiasm
Superior nasal fibres cross in posterior chiasm
Macular fibres occupy central chiasm

23
Q

What is the blood supply to the optic chiasm

A

Pial plexus branches of internal carotid

Superior hypophyseal posterior communicating anterior cerebral and anterior communicating arteries

24
Q

Describe the optic tracts

A

Pass posteriolaterally between tuber cinereum medially and anterior perforated substance laterally
Winds around cerebral peduncle adherent to midbrain
90% of lateral root fibres go to LGN, 10% to superior colliculus (visual body reflexes) and pretectal nucleus (light reflexes)

25
What is the blood supply to the optic tracts?
Pial arteries | Branches of anterior choroidal, posterior communicating and middle cerebral
26
Describe the retinotopic organisation of the optic tracts
``` Fibres rearranged to correspond with LGN Macular dorsolateral Lower retinal lateral Upper retinal medial Peripheral retina more anterior ```
27
What does the posterior pituitary secrete?
Oxytocin | ADH
28
What does the anterior pituitary secrete?
``` TSH ACTH FSH LH GH PRL endorphins ```
29
Where does the pituitary/hypophyseal gland sit?
Small ovoid structure 8-12mm diameter Sits in sella turcica on superior sphenoid roof of fossa formed from dura called diaphgrama sellae Central perforation for infundibulum connecting hypophysis to floor of 4th ventricle Circle of willis lies superiorly
30
What are the visual field defects associated with optic chiasm damage
Anterior: sectoranopia Body: Bitemporal hemianopia Posterior: quandrantanopia
31
How is the cavernous sinus different to other sinuses in the brain?
Traversed by septa which subdivide the blood causing sluggish blood flow
32
Why is the superior orbital fissure different in a dry skull as opposed to in life?
In life the outer part is filled with fibrous tissue and nothing can pass through
33
What forms the lateral wall of the cavernous sinus?
Dura
34
Which foramen lie within the cavernous sinus?
Foramen rotundum and lateral edge of trigeminal ganglion depression NOT foramen ovale and spinosum
35
What makes up the roof of the cavernous sinus?
Sheet of dura between the wall of the piuitary fossa and tentorial edge
36
What lies inferiorly to the cavernous sinus?
Middle fossa floor
37
What is the posterior boundary of the cavernous sinus?
Anterior slope of petrosal temporal bone
38
What is the contents of the cavernous sinus?
``` Internal carotid artery Separated from sinus by vascular endothelium but in the case of ruptured aneurysm, a fissure may form CNIII CN IV CNVI V1 V2 ```
39
Where does the internal carotid artery leave the cavernous sinus?
Medially to the anterior clinoid process | In close proximity to the optic canal -this is where internal carotid gives of ophthalmic artery
40
How do the trochlear and occulmotor nerves pierce the dura and cavernous sinus?
Occulomotor nerve sits on top of trochlear | But CN IV eventually crosses CN III to reach superior oblique
41
Which is the only cranial nerve to arise from the dorsal brain stem?
Trochlear
42
Which nerve runs with the internal carotid artery?
Abducens Leaves posterior cranial fossa by crossing petrous temporal bone and enters the cavernous sinus on top of the ICA and runs with it until it heads dorsally Abducens continues on to reach the fibrous ring and the orbit
43
Which veins enter the cavernous sinus?
Just behind the apex of the orbit-superior ophthalmic vein Drains through the superior orbital fissure Inferior ophthalmic vein drains mostly to pterygoid venous plexus but some to cavernous Sphenoparietal sinus Superficial middle cerebral vein Transverse sinus Pterygoid venous plexus
44
Where does blood from the cavernous sinus go?
Posteriorly via inferior petrosal sinus Inferior petrosal sinus drains back down temporal bone, lying between petrous temporal laterally and occipital medially Opens into the jugular foramen to join internal jugular vein
45
Where does the transverse sinus meet the cavernous sinus?
Just as it turns to form sigmoid sinus
46
Which vein drains internal ear?
Superior petrosal sinus
47
Where does the cavernous sinus communicate with the pterygoid venous plexus?
Via foramen ovale and foramen of Vesalius when present

OPTHT801 (20 decks)

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