ANATOMY OF OPTIC NERVE.pdf ophthalmology topic

Anatomy of optic nerve- simplified

1. ANATOMY
OF
OPTIC NERVE
BY -DEEPAK THAKUR
ROLL NO. -32

2. COMPONENTS OF VISUAL PATHWAY
1. Retina
2. Optic nerve
3. Optic chiasma
4. Optic tract
5. Lateral geniculate body
6. Optic radiation

3. OPTIC NERVE
■Second cranial nerve
■Starts from optic disc and extends up to optic chiasma,
where two nerves meet.
■Backward continuation of nerve fibre layer
Of retina.
■It also contains afferent fibres of pupillary light reflex.

4. MORPHOLOGICALLY AND
EMBRYOLOGICALLY
Optic nerve as comparable to a sensory tract:
■It is not covered by neurilemmaunlike peripheral
nerves. So it does not regenerate when cut.
■Fibres of optic nerve are very fine
( 2 –10 micrometer in diameter)
■Covered by meninges like other parts of CNS.

5. PARTS OF OPTIC NERVE :
■About 47-50 mm in length
Divided into 4 parts :
■Intraocular(1 mm)
■Intraorbital( 30 mm)
■Intracanalicular( 6 –9 mm)
■Intracranial part(10 mm)

6. INTRAOCULAR PART
■Starts from Optic disc pierces the sclera
( converting it into a seive–like structure
lamina cribrosa).
■At the back of eyeball, it becomes continuous
with the intraobital part.

7. INTRAOCULAR PART
■Is further divided into
1.SNFL (Superficial Nerve Fibre Layer)
2.Prelaminar region
3.Lamina cribrosa region
4.Retrolaminar region

8. INTRAORBITAL PART
■Extends from back of the eyeball to optic foramina.
■Slightly sinuous to give play for the eye movements.
■Posteriorly, near optic foramina, it is closely surrounded
by annulus of Zinn.
■Some fibres of superior rectus are adherent to its
sheath here, and accounts for painful ocular
movements seen in retrobulbar neuritis.

9. INTRACANALICULAR PART
■Closely related to ophthalmic artery which lies
inferolateral to it and crosses obliquely over it
■As it enters the orbit, to lie on its medial side.
■Sphenoid and posterior ethmoidal sinuses lie
medial to it and are seperated by a thin bony lamina.
■This reaction accounts for retrobulbar neuritis
following infection of the sinuses.

10. INTRACRANIAL PART
■Lies above the cavernous sinus and converges with
its fellow ( over the diaphragma sellae ) to form optic
chiasma.

11. MENINGEAL SHEATHS
■Pia mater, arachnoid and dura covering the brain are
continuous over the optic nerves.
■In the optic canal, the dura is firmly adherent with
the surrounding bone.
■Subarachnoid and subdural spaces around the optic
nerve are also continous with those of brain.

12. BLOOD SUPPLY OF OPTIC NERVE

13. BLOOD SUPPLY OF OPTIC NERVE HEAD
■Surface layer of optic disc is supplied by capillaries
derived from retinal arterioles.
■Prelaminar region is mainly supplied by centripetal
branches of peripapillary choroid with some
Contribution from the vessels of lamina cribrosa.
■Lamina cribrosa is supplied by branches from
the posterior ciliary arteries and circle of zinn.

14. BLOOD SUPPLY OF OPTIC NERVE HEAD
■Retrolaminar part of optic nerve is supplied by
centrifugal branches from central retinal artery
■And centripetal branches from pial plexus formed by
branches from choroidal arteries, circle of zinn,
central retinal artery and ophthalmic artery.

15. VENOUS DRAINAGE
■Chiefly by Central retinal vein.
■Lesser extent via pial venous system.
■Both system drain into ophthalmic venous system
in the orbit and less commonly directly into
cavernous sinus.

16. OPTIC NERVE LESIONS
■ Lesion of Distal part of optic nerve
C/f:
1.Complete ipsilateral blindness
2.Abolition of Direct light reflex
on I/L side and consensual on
contralateral side.
3. Accommodation reflex is present.

17. OPTIC NERVE LESIONS
■Lesion of proximal part of optic nerve
C/f:
1.Contralateral supero- temporal quadrantanopia it occurs due to
inferonasal fibres loop in the proximal part of opposite optic nerve.
2.Abolition of DLR on affected side and
consensual light reflex on opposite
Side.
3. Near reflex is intact.

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