visual pathway
DESCRIPTION
visual pathwayTRANSCRIPT
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VISUAL PATHWAY
Presenter: Dr Pooja Adappa G
Department of Ophthalmology
YMC
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Objectives:
ANATOMY OF DIFFERENT COMPONENTS OF
VISUAL PATHWAY
ARRANGEMENT OF THE VISUAL FIBRES
LESIONS OF THE VISUAL PATHWAY
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OPTIC NERVE
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Development of the Optic Nerve:
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Embryonic optic stalk
Progressively gets
occupied by axons
ganglion cells of retina
Myelin sheath
oligodendrocytes
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Parts of Optic Nerve:
47-50 mm in length
Intraocular (1 mm)
Intraorbital (25-30 mm)
Intracanalicular (5-9 mm)
Intracranial (10-16 mm)
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Intra Ocular Part
(optic papillae or optic disc):
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1a-Internal limiting membrane of retina
1b-Inner limiting membrane of Elschnig
2-Central meniscus of Kuhnt
3- Spur of collagenoustissue separating the anterior lamina cribrosa (6) from the choroid
4-Border tissue of Jacoby
5- Intermediary tissue of Kuhnt
7-Posterior lamina cribrosa
Internal limiting membrane of
Elschnig
Central meniscus of Kuhnt
Border
tissue of
Elschnig
Border
Tissue
Of
Jacoby
Intermediat
e
Tissue
Of
Kuhnt
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INTRA ORBITAL PART:
Anteriorly: Separated from extraocular muscle by orbital fat
Posteriorly: Annulus of Zinn
Laterally: Ciliary ganglion,Division of 3rd nerve, Nasociliary nerve,
Sympathetic plexus, Abducent nerve
Ophthalmic artery
Superior ophthalmic vein cross optic nerve from lateral to medial
Nasociliary nerve
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INTRA CANALICULAR PART:
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•Enters the optic canal through the optic foramen
•Closely related to ophthalmic artery which crosses nerve
inferiorly from medial to lateral side in the dural sheath
than leaves the sheath at the orbital end of the canal
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INTRA CRANIAL PART:
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Lies above the
cavernous sinus
Optic chiasma
is formed just
above the sellae
Covered by Pia
only
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Meningeal sheath of optic nerve
Intracranial part pia
Intracanalicular & intraorbital
all 3 layers of meninges
Dural Sheaths, subarachnoid
& subdural spaces are
continuous with that of brain
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OPTIC CHIASMA
Flattened band,
embedded in anterior
wall of 3rd ventricle
between the thalami
Transversely 13mm
Sagittally 8mm
3-5mm thick
10mm above the
pituitary gland
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Nasal fiberscross
Temporal
fibersuncrossed
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ANTERIORLY :
Anterior cerebral
artery and their
communicating
artery
POSTERIORLY:
Tuber cinerium,
Hypophyseal stalk,
Pituitary body,
mamillary body,
posterior perforated
substance
SUPERIORLY:3rd
ventricle
INFERIORLY:
Pituitary gland
LATERALLY:
Extracavernous part
of ICA & Anterior
perforated
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OPTIC TRACT:
* Flattened cylindrical band that
travel posteriolaterally from
angle of chiasma
* Between tuber cinereum and
anterior perforated substance
upto lateral geniculate body.
* Each tract contains
uncrossed temporal
fibres and crossed nasal fibres .
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LATERAL GENICULATE BODY:
Elevation produced by
lateral geniculate
nucleus in which most
optic tract fibers end
Axons of ganglion cells
of retina synapse with
dendrites of LGB cells
3rd order neurons
begins
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LATERAL GENICULATE BODY
Dorsal nucleus
Ventral nucleus (rudimentary)
6 laminae( alternating grey & white matter)
Axons from the ipsilateral eye –
2, 3, 5
Axons from the contralateral eye - 1, 4,6
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Lateral Geniculate Body:
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Large magnocellularneurons (M cells) - 1 and 2 layer-Y ganglion cells
perception of movement, gross depth, and small differences in brightness
Small parvocellularneurons (P cells)- 3,4,5,6 layer- X ganglion cells
Colour perception, texture shape & fine depth
Koniocellular cells(K cells or interlaminar cells)
Short-wavelength "blue" cones
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OPTIC RADIATIONS:Geniculocalcarine pathway
extend from lateral geniculatebody visual cortex
MEYERS LOOP(inferior retinal fibers)-pass through temporal lobe looping around inferior horn of lateral ventricle
BARUMS LOOP(superior retinal fibers)- directed posteriorlythrough parietal lobe, occipital lobe,internal capsule and relay on visual cortex
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Visual Cortex:
Striate cortex Extrastriate cortex
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ARRANGEMENT OF FIBERS IN
DIFFERENT PART OF VISUAL PATHWAY
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RETINA
TEMPORAL NASAL
Srf
irf
saf
iaf
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Peripheral fibers
deep in Retina
superficially in optic
nerve
Fibers close to optic
nerve head superficial
in retina central in
optic nerve
OPTIC NERVE HEAD:
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In the Distal Region of optic nerve (just behind
eye):
macula
Upper temporal
Lower temporal
Lower nasal
Upper nasal
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In the Proximal Region of optic nerve(near
chiasma):
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OPTIC CHIASMA
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Uncrossed temporal
fibers
Crossed Nasal fibers
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Anterior
Knee of
Von-wille
Brand
Posterio
r
Knee of
Von-
wille
Brand
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Macular fibers separate
at the center of chiasma
Posterior part of
chiasma decussate(
near supraoptic recess)
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OPTIC TRACT:
Macular fibers (crossed & uncrossed) occupy dorsolateral aspect of optic tract
Upper peripheral fibers(crossed & uncrossed)medially situated
Lower peripheral fibers laterally situated
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Fibers from optic tract:
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Superior
ColliculusPretectal
nucleus
Dorsal
Lateral
geniculate
nucleus
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LATERAL GENICULATE BODY:
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Macular fibres - posterior
2/3 of LGB
Upper retinal fibres -
medial half of anterior 1/3
of LGB
Lower retinal fibres -
lateral half of anterior 1/3
of LGB
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LATERAL GENICULATE BODY:
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CROSSED FIBERS- 1,4,6
UNCROSSED FIBERS- 2,3,5
CORRESPONDING PART OF 2
RETINA END IN NEIGHBOURING
PART OF ADJACENT LAMINAE
smallest lesion of retina results in
degeneration of 3 laminae of LGB in
which the retinal fiber end
Optic radiation begins from all 6
laminae lesion of visual cortex will
cause degeneration of all 6 laminae
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OPTIC RADIATION:
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Inferior
retinalower
part of optic
radiation
superior retina
upper part of
optic radiation
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VISUAL CORTEX(CORTICAL RETINA):
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•Impulse from
corresponding 2 points
of retina meet
•Right visual
cortexreceive
impulse left half of
visual field
•Left visual
cortexreceive
impulse from right half
visual field
MACULA posteriorly
PERIPHERAL RETINA anteriorly
UPPER RETINA above calcarine sulcus
LOWER RETINA below the calcarine sulcus
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TWO STREAM HYPOTHESIS:
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Ventral
Ventral
Pathway(parvocellular)
temporal lobe
Dorsal
Pathway(magnocellular
) parietal lobe
Recognistion
&
indentification
Spatial
location
Visual
agnosia
Visual
neglec
t
Parvocellula
r “what”
pathway
Magnocellula
r
“where”
pathway
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LESIONS OF VISUAL PATHWAY
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1) LESIONS OF OPTIC NERVE :
Causes:
1. Optic atrophy
2. Indirect optic neuropathy
3. Acute optic neuritis
4. Traumatic avulsion of optic nerve.
Characterised by:
Complete blindness in affected eye with loss of both
direct on ipsilateral & consensual light reflex on
contralateral side.
Near reflex is preserved.
Eg. Right optic nerve
involvement
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2)CHIASMAL LESIONS:
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Anterior
Chiasmal
lesions
Middle
Chiasm
al
lesions
Posterior
Chiasmal
lesions
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ANTERIOR CHIASMAL LESIONS:
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Affects the ipsilateral optic nerve fibers and
the contralateral inferonasal fibers
Ipsilateral optic neuropathy manifested as a
central scotoma and a defect involving the
contralateral superotemporal fieldalso known as a
junctional scotoma
Abolition of direct light reflex on affected side &
consensual light reflex on contralateral side.
Near reflex intact.
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MIDDLE CHIASMAL LESIONS:
CENTRAL LESIONS OF CHIASMA
(SAGITTAL)
Causes:Suprasellar aneurysm
Tumors of pituitary gland
Craniopharyngioma
Suprasellar meningioma &
glioma of 3rd ventricle.
Third ventricular dilatation
due to obstructive hydrocephalus.
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Characterised by:
Bitemporal hemianopia
Paralysis of pupillary reflex(usually
lead to partial descending optic
atrophy)
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LATERAL CHIASMAL LESIONS :
Causes:
Distension of 3rd ventricle causing pressure on each
side of optic chiasma
Atheroma of carotids & posterior communicating
artery.
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Characterised by :
Binasal hemianopia
Parallysis of pupillary reflex
(usually lead to partial descending optic atrophy)
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POSTERIOR CHIASMAL SYNDROME
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macular fibers cross more posteriorly in the chiasm
paracentral bitemporal field loss
Posterior lesions may also involve the optic tract
and cause a contralateral homonymous hemianopia.
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3)LESIONS OF OPTIC TRACT :
Causes:
1. Syphilitic meningitis/ Gumm
2. Tuberculous meningitis
3. Tumors of optic thalamus
4. Aneurysm of posterior
cerebral arteries.
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Characterised by :
Incongruous homonymous hemianopia with C/L hemianopic
pupillary reaction( wernicke’s reaction)
These lesions usually lead to partial descending optic
atrophy & may be associated with C/L 3rd nerve
paralysis(RAPD) & ipsilateral hemiplegia
Wernickes pupil
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4)LESIONS OF LATERAL GENICULATE BODY :
Leads to homonymous hemianopia with sparing of
pupillary reflexes & may end in partial optic atrophy.
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5)LESIONS OF OPTIC RADIATIONS :
Causes:
Vascular occlusion(Anterior choroidal artery,middle cerebral or
posterior cerebral artery)
Primary & secondary tumors
Trauma
Characterised by : No Optic Atrophy
Normal pupillary reactions
TOTAL OPTIC RADIATION INVOLVEMENT
COMPLETE HOMONYMOUS
HEMIANOPIA
( sometimes sparing macula)
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INFERIOR QUADRANTIC
HEMIANOPIA
Lesion of temporal lobe
(pie on sky)
SUPERIOR QUADRANTIC
HEMIANOPIA
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Lesion of parietal lobe
(pie on floor)
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6)LESIONS OF VISUAL CORTEX :
Congruous homonymous
hemianopia(sparing macula)
Occlusion of posterior cerebral artery supplying anterior part of occipital cortex
Congruous homonymous
macular defect
Head injury/gun shot injury leading to lesions of tip of
occipital cortex
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Normal pupillary reactions and no optic
atrophy
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Summary:
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REFERENCES:
Wolff E. The visual pathway. In Anatomy Of The Eye & Orbit. 8th ed. London:HK Lewis;1997: 489-596
Sihota & Tandon. The neurology Of vision.In Parsons’ Diseases Of The Eye. 21st ed. London,Elsevier2011: 13-6
A K Khurana& Indu Khurana. In retina,visual pathway and physiology of vision. Anatomy And Physiology Of Eye. 2nd ed. 2006: 140-270
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