3. • Optic nerve is a tract of the brain, an
outgrowth of the cerebral vesicle,
whose fibres possess
no neurolemma [ so , doesn’t
regenerate when cut ] and which is
surrounded by meninges, unlike any
peripheral nerve.
• Primary and secondary sensory
neurons of the visual pathway are in
the retina.
4. • Ensheathed in pia , the optic nerve
extends posteromedially from the
globe at the optic nerve head to the
chiasma in the cranial cavity.
• As it passes to the optic foramen,
the optic nerve takes a sinuous
course which allows for ocular
movements
5. Cross section of optic nerve
• Within the orbit round
• In the canal oval
• nerve leaves the canal piriform
6. • The total length of the nerve is about
47 to 50 mm ,and divided into 4
parts
1)Intraocular 1 mm
2) Intraorbital 30 mm
3) Canalicular 6 -9 mm
4)Intracranial 10mm
7. INTRA OCULAR NERVE HEAD
K/A (OPTIC PAPILLA / OPTIC DISC)
• Extends from its anterior surface ,in
contact with the vitreous to a plane
which is level with that of the posterior
scleral surface (about 1 mm )
• The choroid ends abruptly here, as do all
elements of the retina except its axons.
• These axons bend at a right-angle into
the nerve head and pass posteriorly
through the scleral canal
8. Zones of nerve head
1) Superficial nerve fibre layer
2) Prelaminar zone
3) Lamina cribrosa
4) Retrolaminar
9. Superficial nerve fibre layer
• This is covered by the inner limiting
membrane of Elschnig
• which is composed of astrocytes and is in
continuity with the inner limiting membrane
of retina
• Glial cells and interaxonal processes are
relatively sparse here but increase
progressively towards the retrolaminar nerve.
10. • The Muller cells of nerve fiber layer are in
continuity with the ,astrocytes where the retina
terminates at the optic disc edge.
• The Muller cells form the internal limiting
membrane of Elschnig
• In some specimens, Elschnig's membrane is
thickened in the central part of the disc to form
the central meniscus of Kuhnt .
• A glial lining called the Intermediary tissue of
Kuhnt at the termination of the retina.
12. Prelaminar zone
• The prelaminar region contains bundles of axons
lying within astrocytic channels. The astrocytic
processes are largely circumferential.
• Wolter described glial processes around axonal
bundles and between individual axons in
prelaminar region
• On the nasal side choroidal stroma is directly
adjacent to the astrocytes surrounding the nerve.
This collection of astrocytes surrounding the
canal is known as the border tissue of Jacoby.
13. • This loose glial tissue does not bind the axon
bundles together as do the Muller cells of the
retina and therefore fibres here are more
easily separated…
• This may explain why the disc swells so easily
in papilloedema while the adjacent retina
does not.
14. Lamina cribrosa
• The lamina cribrosa forms a band of dense
compact connective tissue across the scleral
foramen.
• Its sieve-like arrangement (the cribriform
plate) transmits the axon bundles of the nerve
and the central retinal vessels, through a
series of round or oval apertures embraced by
strong trabeculae
15. • Each trabecula results from the ingrowth of a
branch of the short ciliary arteries or circle of
Zinn, accompanied by glia and scleral
connective tissue.
• So ,Each trabecula, therefore, has a vessel in it
surrounded by collagen bundles and elastic
fibres. External to this are glial cells.
• Lamina cribrosa gets its rich blood supply from
circlemof zinn
16. Retrolaminar portion
• The retrolaminar nerve axons are myelinated,
unlike those of the retina and nerve head
proper.
• Myelination accounts almost entirely for the
doubling of nerve diameter from 1.5 to 3.0
mm after traversing the lamina cribrosa.
• However, glial cell numbers also increase in a
centripetal direction.
17.
18. Relations of nerve head
To neighbouring retina
• The layers of the retina, except the stratum
opticum (Retinal nerve fiber layer) are
separated from the optic nerve by the
Intermediary tissue of Kuhnt
• These glial cells lack tight Junctions and
therefore no blood-brain barrier exist in
between the peripapillary choriocapillaris and
the optic nerve head at this level,,,
19. • This probably explains the late fluorescence of
the nerve head , which occurs with fundus
fluorescein angiography (FFA)
20. Relation to neighbouring choroid
• The two layers of the basal lamina of Bruch's
membrane end almost together, at the entry
of the nerve.
• i.e Choroid ends abruptly at optic nerve head.
21. Relation to neighbouring sclera
• marginal tissue of Elschnig ,is an annular
region of neuroglia between choroid, sclera
and optic nerve fibres.
22. Ophthalmoscopic features of the optic
nerve head
• That part of the nerve head visible with the
ophthalmoscope is termed the optic disc. Its
intrapapillary parts are the optic cup and the
neuroretinal rim,,,
Optic disc colour
• The pink colour of the disc is due to the rich
capillary supply to its rim, which can be
demonstrated by fluorescein angiography.
23. • This is most noticeable inferotemporally
where the rim is widest..
• The white appearance of the cup is due to
scattering of light by the lamina cribrosa and
the sparse vascularity of this region.
• Nerve fibre loss in chronic glaucoma leads to
increasing exposure of the lamina as axons are
lost so that its pores become more visible as
the cup enlarges.
24. Disc shape
• The optic disc may be round, but is usually
oval in shape, its vertical diameter being on
average 9% longer than its horizontal. The cup
is 8% wider in the horizontal, so that the rim is
wider above and below
25. Disc size
• Disc size Normal disc area ranges widely, from
0.86 mm2 to 5.54 mm2 with a mean of 2.69 ±
0.7 mm2
• Ophthalmoscopically, the disc corresponds in
size to the internal opening of the scleral
canal.
26. Optic cup
. optic disc is excavated by a funnel-shaped
depression
. Cup area correlates with disc area and, hence,
is large in large discs and small in small discs.
27. Normal disc with small shallow cup. A
hyperpigmented alpha zone is present on the
nas
since the cup is horizontally oval, the
neuroretinal rim is widest below , then above
and then nasally..
28. • Zone alpha is the more peripheral zone and is
an irregular hypo or hyperpigmented region
associated histologically with irregularities of
the retinal pigment epithelium and
parapapillary choiroid.
• Peripherally, it is adjacent to the retina and
centrally, to zone beta.
• This zone corresponds to the choroidal
crescent, in which it was envisaged that the
pigment epithelium failed to extend to the
disc margin
29. • Zone beta is related to the disc centrally and
to the retina
• It corresponds to the scleral crescent
• Always closer to the optic disc than zone alpha
In the normal nerve head.
30. Neuroretinal rim
• The tissue outside the cup is termed the
neuroretinal rim.
• Contains the retinal nerve axons as they enter
the nerve head.
• Rim area ranges from 0.8-4.66 mm2 and
correlates with disc area.
• It is broadest in the lower segment of the disc,
then above, then nasally and then temporally.
It is narrowest in the temporal horizontal disc
region in 99.2% of all discs.
31. • This typical rim configuration correlates with
the diameter of the retinal artery and vein,
which is larger below and temporal than
above and temporal..
• nerve fibre visibility more detectable in the
inferior temporal arcade than the superior.
• This implies that there is a greater retinal
axonal mass and vascularity in the
inferotemporal sector.
32. Clinical significance
• In primary open angle and other forms of
chronic glaucoma a progressive loss of retinal
ganglion cells occurs.
• This leads to a characteristic pattern of axonal
loss at the neuroretinal rim, with enlargement
of the cup, particularly at the upper and lower
poles of the disc.
• The vertically-oval cup of chronic glaucoma
contrasts with the horizontontally-oval cup of
the normal disc.
33. • Characteristic and early sign of glaucomatous
optic nerve damage is the occurrence of
flame-shaped haemorrhages on the rim
,usually at the inferior or superior temporal
margin.
34. Cup/disc ratio
• The cup/disc ratio is the ratio of cup and disc
width, measured in the same meridian ,usually
the vertical or horizontal.
• Because the disc is vertically oval and the cup
horizontally oval , the cup/disc ratio is normally
lower in the vertical meridan in the majority of
individuals .
• It increases in chronic glaucoma.
35. • The ratio has a median value of 0.3.
• an asymmetry of greater than 0.2 has been
taken to signify enlargement and to be of
diagnostic importance in glaucoma.
• Since small discs commonly have no cup, the
presence of a cup/disc ratio of 0.2-0.3 in a
small disc may in fact indicate early
glaucomatous nerve damage..
• whereas in a primary macrodisc, cup/disc ratio
of 0.8 may be entirely normal
36. RELATIONS OF THE OPTIC NERVE IN
THE ORBIT
• As the nerve traverses the annular tendon at the
optic foramen, the attachments of the superior
and medial recti are adherent to its dural
sheath…
• This may explain the pain in extreme movement
and characteristic of retrobulbar neuritis
• Between the nerve and lateral rectus are the
oculomotor, nasociliary, sympathetic and
abducent nerves and sometimes the ophthalmic
vein
37. • Anteriorly ,nerve is seperated from extra
ocular muscles by orbital fat.
• Posteriorly , near optic foramena , optic nerve
closely surrounded by annulus of zin and
origin of 4 recti muscles
• The ciliary ganglion lies between the nerve
and lateral rectus.
38. RELATIONS OF THE OPTIC NERVE IN
THE OPTIC CANAL
• The pial sheath is adherent to the nerve. The
dura, lining the canal as periosteum, splits at
its orbital end to become the periorbita and
the dural sheath of the optic nerve..
• Intra canalicualr part of optic nerve closely
related to ophthalmic artery.
• Sphenoid and post ethemoid sinuses lies
medial to it
39.
40. INTRACRANIAL RELATIONS OF THE
OPTIC NERVE
• The nerve is superior to the diaphragma
sellae, & anterior part of the cavernous sinus.
• Between the nerves and anterior to the
chiasma is a triangular space covered by the
diaphragma, overlying part of the hypophysis
cerebri.
• Above rs the anterior perforated substance,
medial root of the olfactory tract.
41. SHEATHS OF THE OPTIC NERVE
• In the cranial cavity the optic nerve is
surrounded only by pia, but in the optic canal
arachnoid and dura are present.
• At the optic foramen the cranial dura splits
into periosteum (periorbita) and the dural
covering of the optic nerve….
• Thus in the canal and in the orbit the nerve is
surrounded by sheaths of all three meninges.
42.
43. BLOOD SUPPLY OF THE OPTIC NERVE
• Intra ocular part of optic nerve
• Surface nerve fiber layer , supplied by
capillaries derived from retinal arterioles ,
which anastamose with vessels of pre laminar
region
• Pre laminar region supplied by vessels of
ciliary ganglion
44. • Lamina cribrosa region..supplied by ciliary
vessels , derived from short post ciliary
arteries , and arterial circle of zinn-haller.
• Retro laminar region…by both ciliary and
retinal circulation..
45.
46.
47. Intra orbital part blood supply
• By 2 systems…
1)Peri axial system of vessels
2)axial system of vessels
- Peri axial system of vessels , derived from 6
branches of ICA ,
- i.e 1)ophthalmic artrey
- 2) long post ciliary arteries
- 3) short post ciliary arteries
48. • 4)lacrimal artery
• 5)central artery of retina
• AXIAL SYSTEM OF VESSELS..
.Intra neural branches of central retinal artery
.central collateral arteries which come from
central retinal artery , before it pierces the nerve
. Central artery of optic nerve
49. Blood supply of Intra canalicular part
• By peri axail system of vessels…
• Pial plexus in this part supplied by branches of
ophthalmic artery.
Blood supply of intra cranial part..
.supplied exclusively by periaxial system of
vessels
50. Venous drainage
• Optic nerve head is primarily by CENTRAL
RETINAL VEIN
• ORBITAL PART…peripheral pial plexus and
central retinal vein distally
• Intra cranial part….pial plexus
51. Signs of optic nerve dysfunction
• Reduced visual acuity for distance and
near is common, but is non-specific;
acuity may be relatively preserved in
some conditions.
• Relative afferent pupillary defect
(RAPD)
• Dyschromatopsia is impairment of
colour vision, which in the context of
optic nerve disease mainly affects red
and green.
