Visual pathway

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

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

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

INTRA CRANIAL PART:

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Lies above the

cavernous sinus

Optic chiasma

is formed just

above the sellae

Covered by Pia

only

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

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

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:

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

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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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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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

OPTIC RADIATION:

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Inferior

retinalower

part of optic

radiation

superior retina

upper part of

optic radiation

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

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

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

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.

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)

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)

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.

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

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)

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

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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