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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
Q

What is the blood supply to the optic tracts?

A

Pial arteries

Branches of anterior choroidal, posterior communicating and middle cerebral

26
Q

Describe the retinotopic organisation of the optic tracts

A 
Fibres rearranged to correspond with LGN
Macular dorsolateral
Lower retinal lateral
Upper retinal medial
Peripheral retina more anterior
27
Q

What does the posterior pituitary secrete?

A

Oxytocin

ADH

28
Q

What does the anterior pituitary secrete?

A 
TSH
ACTH
FSH LH
GH
PRL
endorphins
29
Q

Where does the pituitary/hypophyseal gland sit?

A

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
Q

What are the visual field defects associated with optic chiasm damage

A

Anterior: sectoranopia
Body: Bitemporal hemianopia
Posterior: quandrantanopia

31
Q

How is the cavernous sinus different to other sinuses in the brain?

A

Traversed by septa which subdivide the blood causing sluggish blood flow

32
Q

Why is the superior orbital fissure different in a dry skull as opposed to in life?

A

In life the outer part is filled with fibrous tissue and nothing can pass through

33
Q

What forms the lateral wall of the cavernous sinus?

A

Dura

34
Q

Which foramen lie within the cavernous sinus?

A

Foramen rotundum and lateral edge of trigeminal ganglion depression
NOT foramen ovale and spinosum

35
Q

What makes up the roof of the cavernous sinus?

A

Sheet of dura between the wall of the piuitary fossa and tentorial edge

36
Q

What lies inferiorly to the cavernous sinus?

A

Middle fossa floor

37
Q

What is the posterior boundary of the cavernous sinus?

A

Anterior slope of petrosal temporal bone

38
Q

What is the contents of the cavernous sinus?

A 
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
Q

Where does the internal carotid artery leave the cavernous sinus?

A

Medially to the anterior clinoid process

In close proximity to the optic canal -this is where internal carotid gives of ophthalmic artery

40
Q

How do the trochlear and occulmotor nerves pierce the dura and cavernous sinus?

A

Occulomotor nerve sits on top of trochlear

But CN IV eventually crosses CN III to reach superior oblique

41
Q

Which is the only cranial nerve to arise from the dorsal brain stem?

A

Trochlear

42
Q

Which nerve runs with the internal carotid artery?

A

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
Q

Which veins enter the cavernous sinus?

A

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
Q

Where does blood from the cavernous sinus go?

A

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
Q

Where does the transverse sinus meet the cavernous sinus?

A

Just as it turns to form sigmoid sinus

46
Q

Which vein drains internal ear?

A

Superior petrosal sinus

47
Q

Where does the cavernous sinus communicate with the pterygoid venous plexus?

A

Via foramen ovale and foramen of Vesalius when present

OPTHT801 (20 decks)

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