anatomy of optic nerve

1. Anatomy
- Pravda Chaturvedi

2.  Optic nerve head is formed in late embryonic
period as optic stalk encloses the hyloid artery.
(8th week)
 Physiological cupping develops at 15th week.
 Optic nerve develops from embryonic optic
stalk (4th week ) and connects optic vesicle to
fore brain.
 As the stalks lengthens, nerve becomes thinner
and is progressively occupied by axons growing
from ganglion cell layer.
 Myelination begins centrally, progresses in
centrifugal direction. Myelination is completed
shortly after birth.

3.  Second cranial nerve.
 Starts from optic disc, extends upto
chiasma.
 Backward continuation of nerve fibre
layer of retina.
 Also contains afferent fibres for light
reflex.

4.  An out growth of brain.
 Not covered by neurilemma, so doesn’t
regenerate.
 Surrounded by meninges.
 Fiber diameter 2-10 microns. Sensory
nerve fiber diameter ~20 microns.
 Both primary and secondary neurons in
retina.

5. Total length 47-50mm
Divided into four parts:-
intra ocular part- 1mm
intra orbital part- 30mm
intra canalicular part- 6-9mm
intra cranial part- 10mm

6.  Passes through sclera , choroid and
appears as optic disc.
 1.5 mm vertical diameter.
 Itself divided into:
 Surface Nerve Fiber Layer
 Prelaminar layer
 Lamina cribosa
 Retrolaminar region

8.  Extends from back of the eyeball to the
optic foramina.
 Tortuous course to give room for ocular
movements.
 Covered by dura, arachnoid and pia.
 Pial sheath contains capillaries and send
septa to divide nerve into fasciculi.
 Near optic foramen, optic nerve is
closely surrounded by annulus of zinn.

9.  The long and short cilliary nerve and
arteries surround the nerve.
 b/w optic nerve and lateral rectus
muscle are situated cilliary ganglion,
divisions of occulomotor, sympathetic
and abducent nerve.
 The ophthalmic artery, sup ophth vein
and nasocilliary nerve cross the optic
nerve superiorly from lat to med side.

11. Closely related to ophthalmic
artery.
Leaves the sheath at the orbital
end of canal.
Sphenoid and post ethmoidal
sinuses lie medial to it and are
separated by thin bony lamina.

12. About 1cm in length.
Lies above cavernous sinus and
converges with the fellow nerve to
form optic chiasma over
diaphragma sellae.
Internal carotid runs first below
and then lateral to it.
The ant perforated substance, med
root of olfactory nerve and ant
cerebral artery lie above it.

13.  In optic nerve head:
Same as in retina.
 In distal region:
Temporal fibers situated in temporal half.
Upper and lower fibers separated by
pappilomacular bundle. Nasal fibers situated on
nasal side.
 In proximal region:
macular fibers placed centrally.

15. 1. Intraocular:
.SNFL- by anastomoses b/w
CRA, choriocapillaries and (if
present) cilioretinal arteries.
.Prelaminar and laminar
region- from short post
cilliary arteries.
.Retrolaminar region-pial
blood capillaries.

17. 2. Intraorbital part :
supplied by two systems: axial and
periaxial.
Periaxial:
6 branches of ICA i.e. ophthalmic,
LPCA,SPCA, Lacrimal and central.
Axial:
intaneural branches of CRA.

19. 3. Intracanalicular:
ophthalmic artery is sole supply.
4. Intracranial part:
perichiasmal artery ( a branch of
sup hypophyseal branch of ICA)

21. Choroid smaller proportion.
Mainly by CRV and to alesser
extent by pial venous system.
Both systems drain into
ophthalmic venous system and
ultimaely into cavernous sinus.

22. Capillaries have non fenestrated
endothelial linings with tight
junction.
It is incomplete due to continuity
b/w extracellular space in choroid
and optic nerve.
There is no barrier present at the
level of choroid.