everything about anatomy of visual pathway from optic nerve to visual cortex

1. Vidushi Shukla (138)
&
Vikas N R Nama (139)
ANATOMY OF
VISUAL PATHWAY

2. Visual Pathway
Each eyeball act as camera ;
it perceives the images & relay the
sensations to the brain (occipital cortex)
via the VISUALPATHWAY.
It starts from retina consisting of
OPTIC NERVES
OPTIC CHIASMA
OPTIC TRACTS
LATERAL GENICULATE BODIES
OPTIC RADIATIONS
VISUAL CORTEX

4.  2nd cranialnerve.
 47-50 mm in length.
 Starts from optic disc & extends upto optic chiasma where the two nerves
meet.
 Backward continuation of nerve fibre layer of retina which consist of axons
originating from ganglion cells.
 Contains the afferent fibres of light reflex
1. intraocular (1mm)
2. intraorbital (30mm)
3. intra canalicular (6-9mm)
4. intracranial(10mm)
Parts:
OPTIC NERVE

5. • Starts from optic disc
• Pierces sclera and choroid
• Converting it into a sieve like structure
the lamina cribriosa
• Its continues as intraorbital part behind
the eyeball
• Extension: back of eyeball to optic foramina
• Slightly sinous to give play for the eye
movements
• Posteriorly near optic foramina it is
surrounded close to annulus of zinn.
• Fibres of SR muscle are adherent to its
sheath thus leading to painful ocular
moments in retrobulbar neuritis.
• Nerve is seperated fron muscles by orbital
fat
Intraocular part
Intraorbital part

6.  This part is closely related to
ophthalmic artery.
 it crosses the nerve from medial
to lateral side in dural sheath.
 Sphenoid & posterior
ethmoidal sinuses lie medial to
it & seperated by thin bony
lamina,
 this relation accounts for
retrobulbar neuritis following
infection of sinuses.
 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.
INTRACANALICULAR
PART
INTRACRANIAL PART

7.  Flattened structure,12 mm horizontally &
8mm anteroposteriorly.
 Ensheathed by pia & surrounded
by CSF.
 Lies over diaphragma sellae so visual field
defects seen in patient with pituitary tumor
having suprasellar extension.
 Posteriorly chiasma continous with the optic
tracts & form the anterior wall of 3rd ventricle.
 Nerve fibres arising from nasal half of two
retina decussate at the chiasma.
OPTIC CHIASMA

8. Anatomical variation in position
of normal optic chiasma
a)central : lies directly over sella, expanding
pituitary tumor involves chiasma first.
b)pre-fixed : lies more anteriorly over
tuberculum sellae,pituitary tumor involves
optic tract first.
c) post-fixed : lies more posterior over
dorsum sellae,pituitary tumor damage optic
nerve

9.  Cylindrical bundle of nerve
fibres.
 Run outwards & backwards from
posterolateral aspect of optic
chiasma ,between tuber cinereum
& anterior perforated substance to
unite with cerebral peduncle.
 Fibres from temporal half of retina of
same eye & nasal half of opposite
eye.
 Posteriorly, each optic tracts end in
LGB
OPTIC TRACTS

11. LATERAL GENICULATE
BODY
• Oval structure
• Situated at posterior
termination of optictract
• Eachgeniculate body
consists of 6 layers of
neurons (Grey Matter)
alternating with white
matter
• Fibres from 2nd order
neurons relay into these
3rd order neurons

12.  From LGB to the occipital cortex.
 Pass forwards then laterally through the
area of wernicke as optic peduncles.
 Anterior to lateral ventricle ,traversing the
retrolenticular part of internal
capsule,medial to auditory tract.
 Its fibres then spread out fanwise to
form medullary optic lamina.
 Inferior fibres subserve upper visual fields
& sweep anteroinferiorly in meyer’s loop
& temporal lobe to visual cortex.
 Superior fibres subserve inferior visual
field proceed posteriorly through parietal
lobe to visual cortex.
OPTIC RADIATIONS

13. VISUAL CORTEX
Located on the medial aspect of occipital lobe, in &
near calcarine fissure.
Visual cortex
Visuopsychic
area
Visuosensory
area
Prestriate
Area 18
Parastriate
Area 19
Striate area
17

14. Blood supply of Visual
Pathway
Arterial
Circle of
Willis
Carotid
arterial
system
Vertebral
arterial
system

15. • Surface Layer :capillaries from
retinal arterioles
• Prelaminar region : Vessels of
peripapillary choroid & lamina
cribrosa
• Lamina Cribrosa : posterior
ciliary arteries, areterial circle of
zinn
• Retrolaminar part
– Centrifugal branches of
central retinal artery
– Centrifugal branches from
Pial plexus
BLOOD SUPPLY OF
OPTIC NERVE HEAD

16. Circle of Willis

17. BLOOD SUPPLY OF
OPTIC CHIASMA
Arterial
superior aspect: ant. Cerebral & Ant Communicating Artery
Inferior aspect: Int Carotid artery, Post Communicating artery, Ant sup hypophysea
Venous:
Superior aspect:Sup Chiasmal veins into ant cerebral vein
Inferior aspect: into basilar vein