Anatomy of Optic Nerve

1. ANATOMY OF OPTIC NERVE
PRESENTER: DR NORHIDAYAH
SUPERVISOR: DR EVELYN

2. EMBRYOLOGY OF
OPTIC NERVE

3. Optic stalk formation 3
Formation of the optic cup & lens vesicle through the interaction of the optic
vesicle and the overlying surface ectoderm 3

4. EMBRYOLOGY OF THE OPTIC NERVE 1
1. Formed from inner neuroblastic layer from inner layer of optic cup, the
ganglion cells of the retina develop axons that converge to a point where the
optic stalk leaves the posterior surface of optic cup (later become optic disc)
2. Axons pass among cells of inner layer of optic stalk
3. Inner layer encroaches on cavity of optic stalk, until inner and outer layers
fuse, and the cavity disappears
4. The stalk together with optic axons, forms the optic nerve
5. Axons of optic nerve begin to develop their myelin sheath just before birth,
and continue for some time after birth
6. The hyaloid artery and vein become the central artery and vein of the retina

7. 7. By the 7th week of embryonic development, the optic/ choroidal
fissure (a groove at the inferior aspect of optic stalk, which is
continuous with the inferior edge of optic cup) closes, forming a
tube, the optic canal, inside the optic stalk
8. Failure of the fissure to close completely results in coloboma
formation of pupil, ciliary body, and choroid or optic nerve

8. ANATOMY OF OPTIC NERVE 1
The optic nerve is composed of about 1.2 million myelinated axons, about 90%
being of small diameter (1um, originate from midget ganglion cells associated
with cones), and remainder measuring 2- 10um (related to ganglion cells
associated with rods)

9.  Divided into four main portion
A. Intraocular (1mm)
B. Orbital (25-30mm)
C. Intracanalicular (4-10mm)
D. Intracranial (10mm)

10. 1. Passes through sclera, choroid and appears in eye as
optic disc
2. Average diameter of 1.5mm, expands to 3mm just
behind the sclera (with myelin)
3. It is further divided into 4 portions:
a. Surface nerve fibre layer
b. Prelaminar region
c. Lamina cribrosa
d. Retrolaminar region
A. Intraocular portion of optic nerve (optic
nerve head)

11. a. Surface nerve fibre layer
- Nerve fibres of retina (94%) + astrocytes (5%)
- Optic disc covered by a thin layer of astrocytes (internal limiting membrane of Elschnig) which is
continuous with internal limiting membrane of retina
- Thickened central portion of this membrane is called the central meniscus of Kuhnt
- All layers of retina are separated from optic nerve by partial rim of glial tissue called the
intermediate tissue of Kuhnt
b. Prelaminar region
- Increased amount of astroglial tissue
- Border tissue of Jacoby (cuff of astrocytes) separates nerve from choroid

12. c. Lamina cribrosa
- Fibrillar sieve- like structure: fenestrated sheets of scleral connective tissue lined by glial tissue
- Bundles of optic nerve fibres leave the eye via these fenestrations
- Border tissue of Elschnig: a rim of collagenous tissue with admixture of glial cells which
intervenes between the choroid and sclera and optic nerve fibres
d. Retrolaminar region
- Decreased amount of astrocytes
- Myelination starts, supplied by oligodendrocytes
- Axonal bundles surrounded by connective tissue septa

14. 1. Extends from back of globe to optic foramina
2. Covered by dura, arachnoid and pia (pial sheath sends septa to divide
nerve into about 1000 fasciculi), with subarachnoid space which contains
cerebrospinal fluid ends blindly at sclera but continues intracranially
3. Central retinal artery along with central retinal vein pierces inferomedial
surface of dural sheath 12mm behind eyeball, and artery crosses
subarachnoid space obliquely before entering optic nerve
B. Intraorbital portion of optic nerve

16. 1. Optic nerve passes through optic canal which lies within lesser
wing of sphenoid bone, surrounded by its 3 meningeal sheaths
2. Dural sheath fuses with periorbita lining the canal, fixing the nerve
3. Ophthalmic artery on inferolateral border of optic nerve,
accompanied by postganglionic sympathetic nerves
4. Sphenoid and posterior ethmoidal sinuses lie medial to it,
separated by a thin bony lamina
C. Intracanalicular portion of optic nerve

17. 1. The optic nerve, ensheathed in pia, leaves canal and
passes backward, upward and medially within subarachnoid
space to reach the optic chiasm in the floor of 3rd ventricle
2. It is related above to the olfactory gyrus, the gyrus rectus,
and the anterior cerebral artery; related laterally to the
internal carotid artery
D. Intracranial portion of optic nerve

18. BLOOD SUPPLY OF OPTIC NERVE
A. Intraocular region (optic nerve head)
i. Surface nerve fibre layer- supplied by capillaries from retinal arterioles, which
anastomose with vessels of prelaminar region, occasional by cilioretinal artery (15-
20% of population, from ciliary vessels)
ii. Prelaminar region- supplied by ciliary vessels
iii. Lamina cribrosa region- supplied by ciliary vessels from short posterior ciliary arteries
and arterial circle of Zinn- Haller (derived from small branches of short posterior ciliary
arteries)
iv. Retrolaminar region- supplied by recurrent pial vessels

20. B. Intraorbital region
i. Periaxial system of vessels- branches of central retinal artery including
small meningeal branches supply the pial sheath, branches from long
and short posterior ciliary arteries
ii. Axial system of vessels- intraneural branches of the central retinal
artery; and central collateral branches from central retinal artery, before
pierces optic nerve, and pass together towards lamina cribrosa

21. C. Intracanalicular region
- Supplied by branches from pial plexus (which receives recurrent branches from
ophthalmic artery), and the periaxial system of vessels
D. Intracranial region
- Supplied by pial plexus (suppled by recurrent branch of the anterior superior
hypophyseal artery from internal carotid artery, branches from anterior cerebral artery,
small recurrent branches of ophthalmic artery, and branches from anterior
communicating artery)

23. VENOUS SUPPLY
1. Optic nerve head primarily by central retinal vein
2. Orbital part by peripheral pial plexus and central retinal
vein
3. Intracranial part by pial plexus which ends in anterior
cerebral and basal vein

24. REFERENCES
1. Snell Clinical Anatomy of The Eye. 2nd Edition
2. Anatomy and Physiology of Eye. 2nd Edition
3. Warning A et al. Embryology of the Eye and Ocular Adnexa. AAO.
https://eyewiki.aao.org/Embryology_of_the_Eye_and_Ocular_Adnexa
4. Fundamentals and Principles of Ophthalmology. Part I: Anatomy.
Chapter 3: Cranial Nerves: Central and Peripheral Connections. Optic Nerve
(Second Cranial Nerve). 2020-2021.
https://www.aao.org/education/bcscsnippetdetail.aspx?id=c875dc98-
86d7-4de9-8631-67b215a5fcf0

25. REFERENCES
5. Kolb H, Fernandez E, Nelson R, editors. Webvision: The
Organization of the Retina and Visual System [Internet]. Salt Lake City
(UT): University of Utah Health Sciences Center; 1995
6. Alfredo A. Sadun. Encyclopedia of neurological science. Optic
Nerve (Cranial Nerve II). 2003.
https://www.sciencedirect.com/sdfe/pdf/download/eid/3-s2.0-
B0122268709005827/first-page-pdf
7. Lorenzo Crumbie MBBS, BSc . Optic nerve. 2022.
https://www.kenhub.com/en/library/anatomy/the-optic-nerve

26. THANK YOU