VISUAL PATHWAY (part 1)_watermark[1].pdf

Visual pathway of human

1. VISUAL PATHWAY:-
ANATOMY OF OPTIC NERVE
P R E S E N T E D B Y :-
S A Y O K I G H O S H
B . O P T O M , M . O P T O M

2. CONTENTS
•Introduction
•Parts of visual pathway
•Parts of optic nerve
•Optic chiasma
•Optic tract
Sayoki Ghosh

3. INTRODUCTION
The visual pathway from the retina may be divided into seven levels :
1.optic nerve
2. optic chiasma;
3. optic tract;
4. lateral geniculate body;
5. optic radiation;
6. striate cortex;
7. Prestriate cortex.
Sayoki Ghosh

4. INTRODUCTION
Sayoki Ghosh

5. https://youtu.be/BYw8ApmQ3fc?si=YFbyEvwAzcHwvxI7
Sayoki Ghosh

6. OPTIC NERVE
•Each optic nerve (2
nd
cranial nerve) starts from the optic disc and
extends up to optic chiasma.
•Backward continuation of the nerve fiber layer which consists of 1-2
million of the axons originating from the ganglion cells.
•Contains afferent fibers of the light reflex and some centrifugal fibers.
•Morphologically and embryologically , the optic nerve is comparable to
a sensory tract (white matter ) of the brain, because of the following
points:-
•Outgrowth of the brain.
•Unlike peripheral nerves , covered by neurilemma ( unable to
generate)
•47-50mm in length
•Fibers of optic nerve:- 2-10µm in diameter as compared to 20µm in
sensory nerve.

Sayoki Ghosh

7. COURSE OF OPTIC NERVE
Sayoki Ghosh

8. PARTS OF OPTIC NERVE
The optic nerve begins anatomically
at the optic nerve head (ONH) but
physiologically and functionally
within the ganglion cell layer that
covers the entire retina and
continues to optic chiasma:-
•Intraocular part
•Intraorbital part
•Intracanalicular part
•Intracranial part
Sayoki Ghosh

9. INTRAOCULAR PART
•Also known as optic nerve head.
•1mm in length
•Starts at the optic disc where the axons forming nerve fiber layer of retina make an
orthogonal turn and pass through the lamina cribrosa to appear at the back of eye as
intraorbital part of the optic disc.
•Dimension:- Average diameter:- 1.5mm
Expands approax 3 mm just behind the sclera ( where neurons acquire
the myelin sheath)
•The size of Optic nerve head varies greatly:- 1.76mm horizontally and 1.92mm
vertically.
•The central region or cup, is slightly temporal to the geometric center of the nerve head
and represents an axon-free region.
•The main branches of central retinal artery and the central retinal vein pass through the
center of the cup.

Sayoki Ghosh

10. STRUCTURE OF OPTIC NERVE HEAD
Sayoki Ghosh

11. SURFACE NERVE FIBER LAYER
•Essentially composed of axonal bundles i.e. nerve fibers of retina (94%) which
converge at the optic disc and astrocytes (5%).
•The optic disc is covered by thin layer of astrocytes , the internal limiting
membrane of Elsching,( separates vitreous and is continuous with the ILM of
retina).
•The central portion of the membrane is thickened→Central meniscus of kunht.

•All the layers of the retina , except the nerve fiber layer , are separated from each
other by a pertial rim of glial tissue called intermediary tissue of Kunht .
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12. Sayoki Ghosh

13. PRELAMINAR REGION
•The predominant structures are neurons and a significantly increased quantity of
astroglial cells.
•Wicket basket of the astrocytic glial cells – The astrocytes form a shallow, cap like
basket which supports the axon bundles and performs protective and nutritive
function.
•Segregated in bundles, or fascicles, that pass through the lamina cribrosa
•The border tissue of Jcoby ( a cuff of astrocytes) separates the nerve from the
choroid.
•When the hyaloid artery (which arises from the arteria centralis) degenerates, the
neuroglial cells surrounding its origin persist anteriorly as an astrocytic lamella, the
Central tissue meniscus of Kunht.
•The loose glial cells do not bind the axon bundles as do the Muller cells in the
retina and the fibers are easily separable. Therefore , we can explain why the disc
swells so easily in papilledema while the adjacent retinal fibers does not.
•The axons are separated from the connective tissue of the scleral canal and/or
choroid by a cuff of astrocytes of varying thickness, termed the Border tissue of
Jcoby.

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14. LAMINA CRIBROSA
•Fibrillar sieve-like structure made up of fenestrated sheets of scleral
connective tissue lined by glial cells.
•Bridges posterior scleral foramina or the scleral canal.
•The bundles of the optic nerve fibers leave the eye through these fenestrations
.
•When the hyaloid artery (which arises from the arteria centralis) degenerates,
the neuroglial cells surrounding its origin persist anteriorly as an astrocytic
lamella, the Central tissue meniscus of Kunht.
•A rim of collagenous connective with some admixture of glial cells which
intervenes between the choroid and sclera and optic nerve fibers is called
Border tissue of Elsching.
•The lamina cribrosa gets its rich supply form the Circle of Zinn.
•The lamina contains type I and type III collagens, abundant elastin, laminin,
and fibronectin. Astrocytes surround the axon bundles, and small blood
vessels are present.
•The lamina cribrosa serves the following 3 functions: •
• scaffold for the optic nerve axons •
• point of fixation for the CRA and CRV •
•reinforcement of the posterior segment of the glob
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15. Sayoki Ghosh

16. RETROLAMINAR REGION
Characterized by decreased astrocytes and the acquisition of myelin that is supplied
by oligodendrocytes.
•Diameter increases from 1.5 mm to 3.0mm as it passes through the sclera
•The posterior extent is not clearly defined.
•The retrolaminar nerve is part of the intraorbital optic nerve, and as such is
invested in a thick sheath of Dura, arachnoid and pia mater.
•The nerve bundles lie in polygonal spaces formed by connective tissue septa .
•The axons are separated from the vessels and other connective tissue by an
astroglial layer at all times.
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17. Sayoki Ghosh

18. INTRAORBITAL PART
•25mm in length.
•Extends from back of the eyeball to the optic foramina and exceeds the anterior
posterior distance from the globe to the optic foramina by 8mm.
•This part is slightly sinuous to give play for the eye movement.
Sayoki Ghosh

19. •Optic nerve in the orbit is covered by Dura , arachnoid and pia. The pial sheath
contains capillaries and sends septa to divide the nerve fasciculi. The
subarachnoid space containing cerebrospinal fluid ends blindly at the sclera and
continues intracranially.
•Central retinal artery along with other accompanying veins crosses the
subarachnoid space to enter the nerve on its inferomedial aspect about 10mm
from the eyeball.
•Anteriorly the nerve is separated from the extra ocular muscles by orbital fat.
•Posteriorly , the optic nerve is surrounded by Annulus of Zinn (the origin of the
four rectus muscle). Some fibers of the superior and medial rectus muscle are
adherent to its sheath here and account for the painful movement during retro
bulbar neuritis.
•Long and short ciliary nerves and arteries surround the optic nerve before they
enter the eyeball.

Sayoki Ghosh

20. Meningeal sheath:-
•It is a vascular connective tissue coat, covered with meningothelial cells, that sends
numerous septa into the optic nerve, dividing its axons into bundles. (The
meningothelial cells can give rise to optic nerve sheath meningioma.)
•Continues throughout the Intraorbital and intracranial part and ends before optic
chiasma.
•The septa provide mechanical support for the nerve bundles and nutrition to the
axons and glial cells.
•A mantle of astroglial cells prevent direct contact of pia matter and septa with the
nerve axons.
•The internal sheath, the innermost meningeal sheath of the optic nerve, is
continuous with the pia mater and arachnoid mater, which cover the brain and
spinal cord
•Arachnoid sheath:- Composed of collagenous tissue and small amounts of
elastic tissue.
•Lined to Dural sheath.
•Connected to internal sheath(of optic nerve) across subarachnoid space.
•The external, or dural, sheath of the optic nerve is the thick outermost
meningeal sheath and is continuous with the dura mater in the brain.
•0.3–0.5 mm thick
•consists of dense bundles of collagen and elastic tissue that fuse
anteriorly with the outer layers of the sclera
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21. Sayoki Ghosh

22. ANNULUS OF ZINN
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23. INTRACANALICULAR PART
•The optic nerve and surrounding
arachnoid sheath are tethered to the
periosteum of the bony canal in the
intracanalicular region.
•n. In blunt trauma, particularly over the
eyebrow, the force of injury can be
transmitted to the intracanalicular region,
causing shearing and interruption of the
blood supply to the nerve in this area.
•This part is closely related to the
ophthalmic artery which crosses the nerve
inferiorly from medial to lateral side in the
dural sheath and then leaves the sheath
at orbital end of the canal.
•Sphenoid and posterior ethmoidal sinuses
lie medial to it and are separated by a thin
bony lamina. This relation accounts for
retro bulbar neuritis following infection of
sinus.
Sayoki Ghosh

24. INTRACRANIAL PART
•This part of the optic nerve about
1cm in length , lies above the
cavernous and converges with its
fellow (over the diaphragma sellae)
to form the chiasma.
•Intracranial part is about 4.5mm in
diameter.
•It is ensheathed in pia mater only,
but receives arachnoid and dural
sheaths at the point of its entry into
optic canal.
•The internal carotid artery runs, at
first below and then lateral to it. The
ophthalmic artery arises from the
internal carotid artery below the optic
nerve at about its middle.
Sayoki Ghosh

25. OPTIC CHIASMA
•Flattened structure measuring about 12mm horizontally and 8mm
anteroposteriorly.
•Ensheathed by pia matter and surrounded by cerebrospinal fluid.
•Lies over the diaphragma sellae, and therefore , presence of a visual field defect in
patients with pituitary tumor indicated suprasellar extension.
•Nerve fibers arising from the nasal halves of the two retinae (about 53% fibers)
decussate at the chiasma.
•Variations in the location of the chiasma may have important clinical significance:-
•Central chiasma is present in about 80% of normal cases. It lies directly above
the sella, so the expanding pituitary tumors involve the chiasma first.
•Prefixed chiasma is present in about 10% of normal cases. It is located more
anteriorly over the trabeculae sellae. In such a situation, the pituitary tumor
may involve the optic tract first.
•Post fixed chiasma is present in the remaining 10% of the normal case. It is
located more posteriorly over the dorsum sellae so that pituitary tomors are
apt to damage the optic nerve first.
Sayoki Ghosh

26. https://www.allaboutvision.com/eye-care/eye-anatomy/optic-chiasm/
Sayoki Ghosh

27. Sayoki Ghosh

28. RELATION OF THE CHIASMA
•Anterior:- Ant. Cerebral arteries and their communicating arteries.
•Posterior:- Tuber cinereum, infaundibulum (hypopheseal stalk), pituitary body,
mamillary body and posterior perforated substance.
•Superior( above):- Third ventricle
•Inferior (below):- Hypophysis
•Lateral:- Extracavernous part of the internal carotid artery and the anterior
perforated subsatnce.
Sayoki Ghosh

29. https://www.aao.org/education/bcscsnippetdetail.aspx?id=92f4a382-9edb-4497-b8b1-5f3180d6b635
https://clinicalgate.com/visual-pathway/
Sayoki Ghosh

30. OPTIC TRACT
•Cylindrical bundles of nerve fibers
running outwards and backwards
from the poster lateral aspect of the
optic chiasma , between the tuber
cinereum and anterior perforated
substance to unite with the cerebral
peduncle.
•Each optic tract consists of fibers
from the temporal half of the retina of
the same eye and the nasal half of
the opposite eye.
•Posteriorly each optic tract ends in
the lateral geniculate body . The
pupillary reflex fibers pass on to the
superior colliculi through the superior
brachium.
Sayoki Ghosh

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