5. ANATOMY OF DIFFERENT COMPONENTS OF
VISUAL PATHWAY
OPTIC NERVE
Starts from the optic disc and extends up to the optic chiasma.
Backward continuation of the nerve fibre layer of the retina.
6. OPTIC NERVE
Morphologically and embryologically- comparable
to sensory tract (white matter) of the brain
Outgrowth of the brain
Not covered by neurilemma(does not regenerate when cut)
Fibres of the optic nerve-million in number,2-10 micrometre in
diameter.
Surrounded by meninges
Both the primary and secondary sensory neurons are in the
retina.
7. PARTS OF THE OPTIC NERVE
47-50 mm in length
Divided into 4 parts
1.INTRAOCULAR PART(1mm)
2.INTRAORBITAL PART(20-30mm)
3.INTRACANALICULAR PART(6-9mm)
4.INTRACRANIAL PART(10mm)
9. INTRAOCULAR PART OF OPTIC NERVE
(OPTIC NERVE HEAD)
Starts at the optic disc
3-4mm nasal to fovea
1mm in length
STRUCTURE OF OPTIC NERVE HEAD
1.SURFACE
NERVE FIBRE
LAYER
2.PRELAMINAR
REGION
3.LAMINA
CRIBROSA
4.RETROLAMINAR
REGION
10. OPTIC NERVE HEAD
Central meniscus of Kuhnt
Internal limiting membrane
of retina
Internal limiting membrane of Elschnig
11. STRUCTURE OF OPTIC NERVE HEAD
1.SURFACE NERVE FIBRE LAYER
Nerve fibres of retina(94%) + Astrocytes(5%)
Optic disc covered by a thin layer of astrocytes
When central portion of this membrane thickened
All the layers of retina except the nerve fibre layer are
separated from optic nerve by a partial rim of glial tissue
INTERNAL LIMITING MEMBRANE OF
ELSCHNIG
CENTRAL MENISCUS OF KUHNT
INTERMEDIARY BORDER TISSUE OF KUHNT
12. STRUCTURE OF OPTIC NERVE HEAD
2.PRELAMINAR REGION
Predominant structures:
1.Neurons
2.Increased quantity of astroglial tissue
Separating the optic nerve from choroid
BORDER TISSUE OF JCOBY
(a cuff of astrocytes)
13. STRUCTURE OF OPTIC NERVE HEAD
3.LAMINA CRIBROSA:
Main structural support of the optic nerve as it exits the globe.
Fibrillar seive like structure
Fenestrated sheets of scleral connective tissue lined by glial tissue
Bridges posterior scleral foramina or scleral canal
Rim of collagenous connective tissue with admixture of glial cells
intervening between choroid and sclera and optic nerve fibres
BORDER TISSUE OF ELSCHNIG
14. STRUCTURE OF OPTIC NERVE HEAD
4.RETROLAMINAR REGION:
Decrease in astrocytes
Acquisition of myelin supplied by oligodendrocytes
Addition of myelin sheath doubles the diameter of the optic nerve
(from 1.5-3mm) as it passes through sclera
15. INTRAORBITAL PART OF THE OPTIC NERVE
Extends from back of the eyeball to optic foramina.
25mm in length
Exceeds the antero-posterior distance from the globe to the optic foramina by 8mm
Sinuous to give play for the eye movements
16. INTRACANALICULAR PART OF THE OPTIC NERVE
Enters the optic canal, which sits within the two bases of the lesser wing of the
sphenoid bone.
6-9mm in length
Optic canal contains :1.meninges
2.optic nerve
3.ophthalmic artery
The dura and the optic nerve are fixed to the periosteum throughout the canal.
17. INTRACRANIAL PART OF THE OPTIC NERVE
Lies above cavernous sinus and converges with its fellow(over the
diaphragma sellae) to form the chiasma.
1cm in length
4.5mm in diameter
The course of the intracranial optic nerve is upward at a 45 degree angle to
reach the chiasm.
18. MENINGEAL SHEATH OF OPTIC NERVE
Intraorbital and intracanalicular
all 3 layers of meninges
Intracranial part
pia mater
Dural sheaths,subarachnoid and
subdural spaces are continuous
with that of brain
19. OPTIC CHIASMA
Flattened structure
Lies over the diaphragma sellae,10 mm above the pituatary gland.
Posteriorly continuous with the optic tracts.
12mm horizontally and 8mm antero-posteriorly.
Ensheathed by the pia and surrounded by CSF.
22. OPTIC TRACT
Cylindrical bundles of nerve fibres running outwards and backwards
from postero-lateral aspect of optic chiasma.
Tract fibres mostly synapse within lateral geniculate nucleus.
Some depart from the optic tract to complete afferent limb of pupillary
light reflex.
23. LATERAL GENICULATE BODY:
Elevations produced by lateral geniculate nucleus
Axons of ganglion cells of retina synapse with dendrites of LGB cells.
Consist of 6 layers of neurons(grey matter) alternating with white
matter(formed by optic nerve fibres)
3-6=Parvocellular
layers
1-2=Magnocellular
layers
25. LATERAL GENICULATE BODY
Large Magnocellular Neurons(M cells)
1 and 2 layers
Y ganglion cells
Perception of movement,gross depth
and small differences in brightness
Small Parvocellular Neurons(P cells)
3,4,5,6 layers
X ganglion cells
Colour perception,texture shape and fine
depth
Koniocellular cells(K cells or
interlaminar cells)
Short wavelength “blue”cones
26. OPTIC RADIATIONS OR GENICULOCALCARINE
PATHWAY
Post synaptic fibres from LGN form the optic radiations.
Lateral geniculate body to visual cortex.
MEYERS LOOP(inferior retinal fibres)-pass through temporal lobe
looping around inferior horn of lateral ventricle.
BAUMS LOOP(superior retinal fibres)-directed posteriorly through
parietal lobe,occipital lobe and internal capsule and relay on visual
cortex.
27. VISUAL CORTEX
On medial aspect of the occipital lobe in and near the calcarine fissure
VISUAL CORTEX
VISUOSENSORY (V1)
BRODMANN’S AREA 17
PERISTRIATE (V2)
AREA 18
PARASTRIATE (V3)
AREA 19
28. ARRANGEMENT OF NERVE FIBRES IN DIFFERENT
PARTS OF THE VISUAL PATHWAY
Arrangement of nerve fibres in the retina
29. IN THE OPTIC NERVE
1.In the optic nerve head
2.In the distal region(behind the eye) 3.In the proximal region(near chiasma)
33. STRIATE CORTEX
Upper bank of striate cortex –superior to calcarine fissure
Lower bank of striate cortex-below the calcarine fissure
34. STRIATE CORTEX
Fibres from medial aspect of the LGN
(carrying information from superior retina)
Fibres from lateral aspect of the LGN
(carrying information from inferior retina)
Left and right occipital lobes
Upper bank of calcarine cortex(inferior visual fields)
Lower bank of calcarine cortex(superior visual fields)
Left and right visual fields respectively
35. BLOOD SUPPLY OF VISUAL PATHWAY
CIRCLE OF WILLIS
INTERNAL CAROTID ARTERY
36. BLOOD SUPPLY OF OPTIC NERVE
OPTIC NERVE HEAD
SURFACE NERVE
FIBRE LAYER
PRELAMINAR
REGION
LAMINA
CRIBROSA
RETROLAMINAR
REGION
1.Capillaries from
retinal
arterioles,which
anastomose with
vessels of
prelaminar region
1.Vessels from
ciliary region
derived from
peripapillary
choroidal system
or short posterior
ciliary arteries
1.Ciliary vessels
from short
posterior ciliary
arteries and
arterial circle of
Zinn-Haller
1.Ciliary
circulation from
recurrent pial
vessels
2.Retinal
circulation-
centrifugal
branches from
central retinal
artery and
centipetal
branches from pial
plexus
38. BLOOD SUPPLY OF OPTIC NERVE
INTRAORBITAL PART:
Periaxial system of vessels
Derived from 6 branches of internal
carotid artery
1.Ophthalmic artery
2.Long and short posterior ciliary arteries
3.Lacrimal artery
4.Central artery of retina
5.Circle of Zinn
Axial system of vessels
1.Intraneural branches of the central
retinal artery
2.Central collateral arteries from central
retinal artery
3.Central artery of optic nerve
40. BLOOD SUPPLY OF OPTIC NERVE
INTRACANALICULAR PART:
INTRACRANIAL PART:
Periaxial system of vessels
Pial plexus in this part-mainly by ophthalmic artery
Periaxial system of vessels
Branches from internal
carotid artery either directly
or through recurrent branch
of internal carotid artery
Branches from anterior cerebral
artery
Small recurrent branches from ophthalmic artery
Supply inferior aspect of optic
nerve containing lower retinal fibres
Supply superior aspect of optic
nerve containing upper retinal
fibres
Twigs from anterior communicating artery
41. BLOOD SUPPLY OF OPTIC NERVE
VENOUS:
OPTIC NERVE HEAD Central retinal vein
INTRAORBITAL PART
Peripheral pial plexus
Central retinal vein
INTRACRANIAL PART
Pial plexus which ends in
anterior cerebral vein
43. BLOOD SUPPLY OF OPTIC CHIASMA
ARTERIAL:
VENOUS:
SUPERIOR
ASPECT
BBranches from anterior cerebral and
anterior communicating arteries
INFERIOR
ASPECT
Branches from internal carotid artery,
anterior superior hypophyseal artery,
posterior communicating artery
SUPERIOR
ASPECT
Superior chiasmal vein drains into anterior
cerebral vein
INFERIOR
ASPECT
Pre-infundibular vein drains into basal vein
45. BLOOD SUPPLY OF OPTIC TRACT
ARTERIAL:
VENOUS:
Pial plexus receiving contributions from
1.Posterior communicating artery
2.Anterior choroidal artery
3.Branches from middle cerebral artery
Superior aspect Anterior cerebral vein
Inferior aspect Basal vein
46. BLOOD SUPPLY OF LATERAL GENICULATE BODY
ARTERIAL:
VENOUS:
Post cerebral artery
Supplies postero-medial aspect of LGB
and nourishes the fibres coming from
superior homonymous quadrants of the
retinae
Anterior choroidal artery
Supplies anterolateral aspect of LGB and
nourishes the fibres coming from inferior
homonymous quadrants of the retinae
Anastomosis from
posterior cerebral and
anterior choroidal arteries
Macular fibres over region of hilum
Basal vein
47. BLOOD SUPPLY OF OPTIC RADIATIONS
ARTERIAL:
VENOUS:
Anterior part
Middle part
Posterior part
Anterior choroidal artery
Deep optic artery branch of middle
cerebral artery
Calcarine branches of posterior
cerebral artery and perforating
branches from middle cerebral artery
Basal vein(main)
Middle cerebral vein
48. BLOOD SUPPLY OF VISUAL CORTEX
ARTERIAL:
VENOUS:
Calcarine branch of
posterior cerebral artery
Terminal branches of
middle cerebral artery
Supply anterior end of calcarine
sulcus and lateral aspect of occipital
pole
Anastomosis between
posterior and middle
cerebral arteries
Supply posterior pole
Internal occipital vein
which ends into Great
cerebral vein of Galen
and straight sinus
Medial aspect of occipital cortex
Inferior cerebral vein
which ends in cavernous
sinus
Superolateral aspect of occipital
cortex
