The visual pathway refers to the neuronal networks that extend from the retina to the visual cortex. It includes the optic nerve, optic chiasma, optic tracts, lateral geniculate bodies, optic radiations, and visual cortex. Lesions along the visual pathway can cause different types of visual field defects, including hemianopias and quadrantanopias, while sparing pupillary reflexes except in the case of optic nerve lesions. Central lesions of the optic chiasma cause bitemporal hemianopia, while lateral lesions cause binasal hemianopia. Lesions of the optic tract or lateral geniculate body cause homonymous hemianopias.

1. THE VISUAL PATHWAY
ANATOMY

2. • Visual Pathway refers to Neuronal networks
that extend from the Retina to Visual cortex
• It comprises of
• Optic Nerve
• Optic Chiasma
• Optic Tract
• Lateral Geniculate Body
• Optic Radiations
• Visual cortex

3. OPTIC NERVE
• 2nd cranialnerve
• Optic disc to Optic chiasma
• It contains 1.2 million axons
• Afferent fibres for light reflex
• About 47 – 50 mm length, having four parts
1)Intra ocular (1mm)
2)Intra orbital (30mm)
3)Intra canalicular (6-9mm)
4)Intra cranial (10mm)

4. OPTIC NERVE HEAD – INTRAOCULAR PART
• About 1mm in size, passes through sclera,choroid &
finally appears in eye as optic disc.
• Divided in 4 portions (ant – post)
1)Surface nerve fibre layer
2)Prelaminar region
3)Lamina cribrosa
4)Retrolaminar region

5. 1)Surface nerve fibre layer
• Composed of axonal bundles, covered by thin layer of Astrocytes
INT. LIM. MEM. ELSCHING- thickened portion MENISCUS OF
KUHNT
• Retinal layers separated from OPT. N/V by INTERMEDIARY TISSUE
OF KUHNT
2)Prelaminar region
• > Astroglial tissue, separated from choroid by TISSUE OF JCOBY
3)Lamina cribrosa
• Sieve structure by scleral connective tissue
• Rim of connective tissue fibre btw S,C,Opt. N/V – BORDER
TISSUE OF ELSHING
4)Retrolaminar region
• < in astrocytes, Myelination by oligodents (1.5mm ->3mm)

6. INTRA ORBITAL PART
• About 25-30 mm in length , from globe to orbital apex
• Takes slightly curved paths for the eye movements.
• Here optic nerve is surrounded by all 3 layers of
meninges & subarachnoid space.
• Some fibres of medial and superior rectus are
adherent to its sheath (retrobulbar neuritis)
• The Central retinal artery along with vein enters the
subarachnoid space to enter the nerve on its
inferomedial aspect
• Optic n/v and Lateral rectus – Ciliary Ganglion
• L -> M cross over superiorly – Ophth.artery, vein and
Nasociliary n/v

7. INTRACANALICULAR PART
• 6- 9mm long
• This part is closely related to Ophthalmic
artery.(crosses the nerve from lateral to
medial side in Dural sheath)
• Sphenoid & posterior ethmoidal
sinuses lie medial to it & separated by
thin bony lamina, this relation accounts
for retrobulbar neuritis following infection
of sinuses.
• Frequently affected in Traumatic
neuropathies

8. INTRACRANIAL PART
• About 10mm
• Lies above cavernous sinus &
converges with its fellow to form
chiasma.
• Ensheathed in pia mater.
• Internal carotid artery runs below
then lateral to it. (Aneurysm of ICA
may compress)

9. AXONS IN OPTIC NERVE
IN THE OPTIC NERVE –
BEHIND THE EYEBALL
IN THE OPTIC NERVE –
NEAR THE CHIASMA

10. OPTIC CHIASMA
• Flattened structure,12 mm horizontally and
8mm anteroposteriorly
• Cross over of two Optic nerves covered by PIA
and CSF
• Nerve fibres arising from nasal half of two
retina decussate at the chiasma.
• Lies over diaphragma sellae so visual field
defects seen in patient with pituitary tumour
having suprasellar extension
• Posteriorly chiasma continuous with the optic
tracts & form the anterior wall of 3rd ventricle

11. RELATIONS OF OPTIC CHIASM
• Anterior - Anterior cerebral arteries & its
communicating arteries
• Posterior- Tuber cinereum, pituitary body,
posterior perforated substance.
• Superior- Third ventricle.
• Inferior- Hypophysis
• Lateral- Extra cavernous part of
internal carotid artery

12.  ANATOMICAL VARITAIONS IN POSITION
a)Central(80%): lies directly over Sella, expanding
pituitary tumour involves chiasma first.
b)Pre-fixed(10%) : lies more anteriorly over
tuberculum sellae, pituitary tumour involves optic tract
first.
c)Post-fixed(10%): lies more posterior over dorsum
sellae, pituitary tumour damage optic nerve
 ORGANISATION OF OPTIC CHIASMA
Fibres from the Inferior Nasal Retina cross and loop
anteriorly in the C/L Optic nerve before heading to the
optic tract – VON WILLEBRANDS KNEE

13. OPTIC TRACTS
• 5mm long, Cylindrical bundle of nerve fibres, that
run from chiasm to LGB
• Fibres from temporal half of retina of same eye & nasal
half of opposite eye.
• Run outwards & backwards from posterolateral aspect
of optic chiasma , between tuber cinereum & anterior
perforated substance to unite with LGB
• Pupillary Reflex fibres end at Superior Colliculi through
the Superior Brachium
• FIBRES IN OPTIC TRACT
Macular fibres (C&UC) grey – Dorso lateral of O.Tract
Superior fibres (C&UC) pink – Medial part of O.Tract
Inferior fibres (C&UC) orange– Lateral part of O.Tract

14. LATERAL GENICULATE BODY
• Oval structures situated at termination of
the optic tracts (lateral mid brain)
• Fibres of 2nd order neuron coming via
optic tract relay here
• Each consist of 6 layers (Laminas) of
neurons(grey matter) alternating with
white matter (optic fibres)
• Crossed fibres end in Lamina 1,4,6 &
Uncrossed end in 2,3,5.

15. • Layers 1 & 2 Magnocellular – Large cells,
Input from Y-Ganglion cells. Transmit
signals for movement
• Layers 3 - 6 Parvocellular – Small cells, X-
Ganglion cells. Transmit signals for Color
vision, Depth
ARRANGEMENT OF FIBRES
• Macular – Posterior 2/3 of LGB
• Upper retinal – Medial ½ of Anterior 1/3
• Lower retinal – Lateral ½ of Anterior 1/3

16. OPTIC RADIATIONS (GENICULO CALCARINE TRACT)
• From LGB to the occipital cortex
• Pass forwards then laterally through the area of
Wernicke as OPTIC PEDUNCLE
• Inferior fibres subserve upper visual fields ,
sweep anteroinferiorly in MEYER'S LOOP & then
to Temporal lobe to visual cortex
• Superior fibres subserve inferior visual field
directly proceed posteriorly through Parietal lobe
to visual cortex

17. ARRANGEMENT OF FIBRES
 Fibres then spread out fanwise to form
medullary optic lamina -Temporal rotation of
fibres

18. VISUAL CORTEX (cortical retina)
 Located on the medial aspect of occipital
lobe, near calcarine fissure
 ARRANGEMENT OF FIBRES
MODIFIED NOMENCLATURE
Visual cortex
Peristriate
area 18
Parastriate
area 19
Visuopsychic
area
Visuosensory
area
Striate
area 17

19. BLOOD SUPPLY OF VISUAL PATHWAY
ARTERIAL
CIRCLE OF
WILLIS
CAROTID
ARTERIAL
SYSTEM
VERTEBRAL
ARTERIAL
SYSTEM

20. BLOOD SUPPLY OF OPTIC NERVE
 INTRAOCULAR PART
• PERIPAPILLARY CHOROIDAL
VESSELS
PRELAMINAR
• POSTERIOR CHOROIDAL
VESSELS – CIRCLE OF ZINN
LAMINA
CRIBROSA
REGION
• CENTRIFUGAL BRANCHES
FROM CENTRAL RETINAL
ARTERY
• CENTRIPETAL BRANCHES FROM
PIAL VESSELS
RETROLAMINAR

21. • 6 B/O INTERNAL CAROTID
ARTERY
OPHTHALMIC, LONG & SHORT
POSTERIOR CILIARY ARTERY.
LACRIMAL ARTERY.
CENTRAL ARTERY OF RETINA
• INTRANEURAL B/O CENTRAL
RETINAL ARTERY.
• COLLATERAL B/O CENTRAL
RETINAL ARTERY.
• CENTRAL ARTERY OF OPTIC NERVE
PERIAXIAL
SYSTEM OF
VESSELS
AXIAL
SYSTEM OF
VESSELS
 INTRAORBITAL PART
 INTRACANALICULAR PART - BY PERIAXIAL
SYSTEM OF VESSELS

22. B/O INTERNAL
CAROTID ARTERY
B/O ANTERIOR
CEREBRALARTERY
B/O OPHTHALMIC
ARTERY
TWIGS FROM
ANTERIOR
COMMUNICATING
ARTERY
 INTRACRANIAL PART – BY PIAL PLEXUS
 VENOUS DRAINAGE OF OPTIC NERVE
OPTIC NERVE HEAD
• Central Retinal
vein
ORBITAL PART
• Peripheral Pial
plexus
• Central Retinal
vein
INTRACRANIAL PART
• Pial plexus which ends
in Anterior Cerebral &
Basal vein

23.  BLOOD SUPPLY OF OPTIC CHIASM
•B/O ANTERIOR CEREBRAL &
ANTERIOR COMMUNICATING
ARTERY
SUPERIOR ASPECT
• B/O INTERNAL CAROTID ARTERY
,POSTERIOR COMMUNICATING
ARTERY,ANTERIOR HYPOPHYSEAL
ARTERY
INFERIOR ASPECT
• SUPERIOR CHIASMAL VEIN
DRAINS INTO ANTERIOR
CEREBRAL VEIN
SUPERIOR ASPECT
• PRE-INFUNDIBULAR VEIN
DRAINING INTO BASILAR
VEIN
INFERIOR ASPECT
VENOUS
ARTERIAL

24.  BLOOD SUPPLY OF LGB
• ARTERIAL : Pial plexus receiving contribution
from Posterior Communicating Artery,
Anterior Choroidal Artery & Middle
Cerebral Artery.
• VENOUS DRAINAGE: Anterior cerebral vein &
Basal vein.
 BLOOD SUPPLY OF OPTIC TRACT
• SUPERIOR FIBRES OF RETINA – by Post. Cerebral Artery
• INFERIOR FIBRES OF RETINA – by Ant. Choroidal Artery
• MACULAR FIBRES - by Anast. Btw PCA & Ant. Choroidal

25. • Anterior part – ANTERIOR CHOROIDAL ARTERY
• Middle part – DEEP OPTIC ARTERY (B/o MCA)
• Posterior part – CALCARINE BRANCH (B/o PCA)
 BLOOD SUPPLY OF OPTIC RADIATIONS
 BLOOD SUPPLY OF VISUAL CORTEX
ARTERIAL
• CALCARINE ARTERY (OTHER B/o Posterior cerebral artery)
(HENCE SPARING MACULA)
• B/O MIDDLE CEREBRAL ARTERY & Anast. Btwn MCA & PCA
VENOUS
• Medial aspect – INTERNAL CEREBRAL VEIN -> GREAT
CEREBRAL VEIN OF GALEN & STRAIGHT SINUS
• Superolateral aspect – INFERIOR CEREBRAL VEIN ->
CAVERNAL SINUS

26. LESIONS IN VISUAL PATHWAY

27. LESIONS OF THE OPTIC NERVE
 Causes
• Optic atrophy
• Acute optic neuritis
• 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.
LEFT OPTIC NERVE INVLOVED

28. LESIONS AT OPTIC CHIASMA
 CENTRAL LESION
 CAUSES
• Suprasellar aneurysm
• Tumors of pituitary gland
• Craniopharyngioma
• Third ventricle dilation
• Obstructive
 Characterised by
• Bitemporal hemianopia
 LATERAL LESION
 CAUSES
• Distension of 3rd ventricle(side)
• Atheroma of carotids &
posterior communicating
artery
 Characterised by
• Binasal hemianopia

29.  CAUSES
• Syphilitic meningitis/ gumma.
• Tuberculosis
• Tumours of optic thalamus
• Aneurysm of superior cerebellar or posterior cerebral arteries
 Characterised by
• Incongruous homonymous hemianopia with C/L hemianopia
pupillary reaction( Wernicke's reaction)
LESIONS AT OPTIC TRACT
LESIONS AT LGB
• Homonymous hemianopia
• Sparing of pupillary reflexes

30.  CAUSES
• Vascular occlusion
• Primary & secondary tumors
• Trauma
 Characterised by
• Total optic radiation involvement leading HOMONYMOUS
HEMIANOPIA (may spare macula)
• Lesion involving inferior fibres (TEMPORAL LOBE) -
SUPERIOR QUADRANTIC HEMIANOPIA(PIE ON THE ROOF)
• Lesion involving superior fibres (PARIETAL LOBE) - INFERIOR
QUADRANTIC HEMIANOPIA(PIE ON THE FLOOR)
 NORMAL PUPILARRY REACTIONS
LESIONS AT OPTIC RADIATIONS

31. • 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
• Pupillary light reflex is normal
LESIONS AT VISUAL CORTEX

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