Ocular Anatomy 11 Visual Pathway Flashcards
What are the components of the visual pathway?
Neural reitna
Optic nerve
Chiasm
Optic tract
LGN lateral geniculate nucleus
Optic radiations
Visual cortex
What is the optic nerve formed from
{rimitive optic stalk
What are the parts of the optic nerve
Intraocular (1mm)
Intraorbital (25mm)Wh
Intracanalicular (5mm)
Intracranial (10mm)
What is the optic disc? Diameter?
The intraocular potion of the optic nerve where it pierces the sclera
1.5mm
What is the intraorbital potion of the optic nerve?
Central retinal artery enters and central retinal vein exits the dural sheath 12mm from teh eyeball
Nerve comprises of ganglion cell neurones which become myelinated only posterior to the lamina cribrosa
where does myelination of axons of the optic nerve begin?
Posterior to lamina cribrosa
Nerve becomes 3-4mm diameter
What are the components of the optic nerve sheath? Blood supply?
Dura
Arachnoid
Pia mater
Pial plexus from teh branches of ophthalmic artery and central retinal artery
Where does the optic canal lie? How long is it and what does it contain?
LEsser wing of sphenoid bone
5mm long
Optic nerve and meningeal sheaths
Ophthalmic arter
What direction does the optic nerve move intracranially? Where does it end?
Superiorly, posteriorly and medially to reach the optic chiasm in the floor of the third ventricle.
What os blood supply to the intracranial optic nerve
Pial plexus form the superior hypophyseal aretery, ICA, ophthalmic artery
What is the relation of the optic nerve to the ophthalmic artery?
Optic nerve runs superomedially to the ophthamic artery in optic canal in lesser wing of sphenoid and enters orbital apex within the muscular cone
Where does the central reitnal artery pass in relation to the optic nerve and where does it enter the globe?
Passes inferior to the optic nerve and pierces the inferomedial aspect of the dural sheath 12mm behind the globe
Where does the ciliary ganglion lie?
Lateral to optic nerve between ON and lateral rectus
What is the optic chiasm?
Pont at which fibres from teh respective nasal retinas decussate to contralateral optic tract
Temporal fibres reamin in the ipsilateral optic tractW
Where to inferior nasal retina fibres cross at the hciasm? Superior?
Inferior nasal retina nerve fibres cross at the anterior chiasm
Superior nasal retina fibres cross at the posteiror chiasm
Where does the chiasm lie? What is above it?
Inferior to the floor of the third ventricle
ere is the chiasm in relation to the diaphragma sellae?
Superior to diaphragma sellae (which transmits the pituitary stalk.
What lies anterior to the optic chiasm? Posterior? Laterally?
Anterior - The anterior cerebral arteries and anterior communicating arteries
Posterior Tuber cinereum
Lateral ICA and cavernous sinus
What is the blood supply to the optic tract?
Pial vessels from ICA, superiro hypophyseal branch of ICA, ACA and anterior communicating artery
What is the blood supply to the intraocular portion of the optic nerve?
Short posterior ciliary arteries forming the circle of Zinn
What are the optic tracts?
Optic tracts emerge from the posterolateral aspect of the optic chiasm
Pass posteriolaterally, lateral to the tuber cinereum (part of hypothalamus to which pituitary is attached),
Winds around the lateral margin of the upper part of the cerebral peduncle.
Go to lateral geniculate nucleus
10% pass to pretectal nucleus for light reflex
How are nerve fibres in optic tracts rotated?
90 degrees with inferior fibres located laterallys
What is the blood supply to the optic tracts?
Pial vessels from ACA, MCA and posteiror communicating artery
what is the lateral geniculate nucleus? Where is it located? Structure? Blood supply
Under the pulvinar of the thalamus
6 layers of cells separated by optic nerve fibres
Temporal half of ipsilateral retina (2,3,5)
Nasal half of contralateral retina (1,4,6)
Blood: from anterior choroidal branch of the MCA, thalamogeniculate branches of PCA, lateral choroidal arteries
What are the optic radiations?
Geniculocalcarine tracts
Fromed from nerve fibres that originate in the lamellae of the lateral geniculate body
What is the location of the primary visual cortex?
In the walls of the calcarine sulcus found int medial aspect of the cerebral hemisphere
Extends from the junction of the calcarine and parieto-occipital sulci to the occipital pole posteriorly
Brodmann’s area 17
What are the areas above and below the calcarine fissure
area above the calcarine fissure is known as the cuneus gyrus and that below the fissure known as the lingual gyrus.
Where does each primary visual cortex receive information from?
From ipsilateral LGN, hence right half of visual field is represented in left cerebral cortex
Visual cortex above the calcarine sulcus recevies fibres from superior retina (ipsilateral superior temporal fibres and contralateral superior nasal fibres) - inferior visual field
Visual cortex below the calcarine sulcus receives fibres from inferior retina (superior visual field)
Where is the macula represented in the visual cortex
Large representation posterior aspect of calcarine sulcus, estends ot the posterior lateral aspect of the occipital lobe
1/3 of the visual cortex
What are the secondary visual cortex?
Areas 18 and 19
Afferent fibres from the primary visual areas, cortical areas and thalamus
Relates visual information form the primary area to previous visual experience
Important in sensory motor coordination and control of cranial nerve eye mvoement
What is the blood supply to the visual cortex?
Mostly PCA, some MCA
MCA over the occipital pole - may explain the macular sparing aspect of occipital lobe strokes
