A presentation on the visual pathway, its lesions and tumors of the optic nerve.

1. THE VISUAL PATHWAY AND
TUMOURS OF THE OPTIC NERVE
P.SAMIR
ROLL NO.130

2. TOPICS DISCUSSED :
• Anatomy of visual pathway
• Lesions of visual pathway
• Tumours of optic nerve

3. ANATOMY OF VISUAL PATHWAY

4. Components of the visual pathway
A. Optic nerve
B. Optic chiasma
C. Optic tracts
D. Lateral geniculate bodies
E. Optic radiations
F. Visual cortex

5. A. THE OPTIC NERVE
• The optic nerve is the second cranial nerve.
• It starts from the optic disc and ends at the
optic chiasma where the two nerves meet.

6. Parts of the optic nerve:
• The optic nerve is 47-50mm in length and is divided into 4
parts:
1. Intraocular part - Starts from optic disc, pierces choroid
and sclera.Becomes continuous with intraorbital part at
back of eyeball
2. Intraorbital part – Extends from back of eyeball to optic
foramina. Closely surrounded by the annulus of Zinn and
origin of the four rectii muscles posteriorly. Anteriorly it is
separated from ocular muscles by orbital fat.

7. 3. Intracanalicular part – Closely related to the
ophthalmic artery which crosses obliquely over it
to its medial side. Medial to this are the sphenoid
and posterior ethmoidal sinuses separated by a
thin bony lamina.
4. Intracranial part – Optic nerve lies above
cavernous sinus and converges with the one from
the other side to form optic chiasma, over the
diaphragma sellae.

8. B. OPTIC CHIASMA
• Flattened structure
• Measures 12mm horizontally and 8mm
anteroposteriorly
• Lies over tuberculum and diaphragma sellae
• Fibres originating from nasal half of the retina
cross over (decussate) here.

9. C. OPTIC TRACTS
• Cylindrical bundles of nerve fibres running
outwards and backwards from the posterolateral
aspect of the optic chiasma
• Each tract consists of temporal fibres from retina
of the same side and nasal fibres of the opposite
side
• Posteriorly, each optic tract ends in the lateral
geniculate body.

10. D. LATERAL GENICULATE BODIES
• Oval structures
• Consist of 6 layers of neurons (grey matter)
alternating with white matter (formed by
optic fibres)

11. E. OPTIC RADIATIONS
• These extend from lateral geniculate bodies to
the visual cortex and consist of axons of the
third order neurons of the visual pathway.

12. F. VISUAL CORTEX
• Located medially on the occipital lobe above
and below the calcarine fissure.
• Subdivided into :
I. Visuosensory area – Striate area 17, that
receives fibres of the optic radiations
II. Visuopsychic area – Peristriate area 18 and
parastriate area 19

13. BLOOD SUPPLY OF VISUAL PATHWAY
• Mainly supplied by the pial network of vessels.
• Orbital part of optic nerve is also supplied by
an axial system derived from the central artery
of the retina.
• The pial plexus itself gets contribution from
different arteries.

15. • Blood supply of the optic nerve head :
 Surface layer- supplied by capillaries derived
from retinal arterioles
 Prelaminar region – mainly supplied by
centripetal branches of prepapillary choroid with
some contribution from vessels of lamina
cribrosa
 Lamina cribrosa – supplied by branches from
posterior ciliary arteries and arterial circle of
Zinn
 Retrolaminar part – supplied by centrifugal
branches ofrom pial plexus formed by branches
from the choroidal arteries, circle of Zinn, central
retinal artery and ophthalmic artery

17. LESIONS OF THE VISUAL PATHWAY

18. Optic nerve lesions (A,B)
Causes : Optic atrophy, traumatic avulsion, acute
optic neuritis etc.
1.Distal optic nerve lesion (A)
• Complete blindness of affected side
• Abolition of direct light reflex on affected side
• Accommodation reflex intact

19. 2. Proximal optic nerve lesion (B)
• Blindness on affected side
• Contralateral hemianopia
• Abolition of direct light reflex on affected side
• Accommodation reflex intact

20. Chiasmal lesions (C,D)
1.Central chiasmal lesion (C)
• Bitemporal hemianopia
• Bitemporal hemianopic paralysis of pupillary
reflexes
2.Lateral chiasmal lesion (D)
• Binasal hemianopia
• Binasal hemianopic paralysis of pupillary reflexes

21. Causes :
I. Intrinsic causes – Lesions which produce
thickening of chiasma. Eg. Gliomas, multiple
sclerosis
II. Extrinsic causes – Compressive lesions. Eg.
Pitutary adenoma, meningioma
III. Other causes – Include metabolic, toxic and
inflammatory syndromes. Eg. Lymphoid
hypophysitis, sarcoidosis

22. Optic tract lesions (E)
Causes :
I. Intrinsic causes – Demyelinating diseases and
infarction.
II. Extrinsic causes – Compressive lesions. Eg.
Pitutary adenomas, tumours of optic thalamus
III. Other causes – syphilitic meningitis, tubercular
meningitis

23. Optic tract lesions
• Incongruous homonymous hemianopia
• Contralateral hemianopic pupillary responses
(Wernicke’s reaction)
• Optic disc changes – Descending type of partial
optic atrophy is produced characterized by
temporal pallor on the side of the lesion and bow
tie atrophy on the contralateral side.
• Visual acuity is intact

24. Lateral geniculate nucleus lesions(E)
• Incongruous homonymous hemianopia
• Pupillary reflexes are normal as the fibres go
to pretectal nucleus and not the LGN
• Optic disc pallor may occur due to partial
descending atrophy

25. Lesions of optic radiations (F,G)
Common lesions include :
• Vascular occlusions
• Tumours
• Trauma
• Temporal lobectomy for seizures

26. Lesions of optic radiations
• Superior quadrantic hemianopia(F) – Pie in the sky
lesions. It is explained by the fact that inferior
fibres of optic radiations contain fibres from
ipsilateral lower temporal retina and contralateral
lower nasal retina.(part of optic radiations in
temporal lobe)
• Inferior quadrantic hemianopia(G) – Pie on the
floor lesions. This is the same as above. Difference
being the superior fibres are affected. (part of
optic radiations in parietal lobe)

27. • Complete homonymous hemianopia(H) –
produced when all fibres of optic radiations are
involved sometimes sparing the macular fibres as
they lie centrally.
• Pupillary reflexes are spared
• Optic disc atrophy does not occur

28. Visual cortex lesions (I,J,K)
• Congruous homonymous hemianopia –
macular field of vision is spared. It is a feature
of occlusion of posterior cerebral artery.
• Congruous homonymous macular defects –
occurs in lesions at the tip of occipital cortex
following head injuries or gun shot injuries

29. • Bilateral homonymous macular defects –
presenting like bilateral central scotoma occur in
bilateral lesions of occipital cortex
• Pupillary light reflexes are normal
• Optic atrophy doesn’t occur.
Other manifestations of occipital lobe lesions
include :
• Cortical blindness
• Dyschromatopsia

30. • Visual hallucinations
• Palinopsia – Persistent perception of visual image
• Visual anesthesia – transposition of visual stimulus
from one hemifield to another
• Polyopsia – multiple images of single object which
do not disappear on closing the eye.

31. TUMOURS OF THE OPTIC NERVE
I. Optic nerve glioma
II. Optic nerve sheath meningioma
III. Optic nerve melanocytoma

32. I. Optic nerve glioma
It is a slow growing tumour arising from the
astrocytes. Ususally occurs in the first decade
of life.
Clinical features :
• Gradual visual loss associated with gradual,
painless, unilateral axial proptosis occuring in a
child usually between 4-8 years of age
• Fundus examination may show optic atrophy or
pappiloedema and venous engorgement.

33. Diagnosis :
• X-ray showing uniform, regular, rounded
enlargement of optic foramen in 90% of the cases.
• CT scan and Ultrasonography depicting a fusiform
growth in relation to the optic nerve.
Treatment :
• Observation without treatment is
recommended for patients having stationary
tumour with good vision and non disfiguring
proptosis.

34. • Surgical excision of tumour mass by lateral
orbitotomy in case of disfiguring proptosis.
• Radiotherapy in unoperable cases
• Nowadays a technique called as gamma knife
surgery is being used for treatment. It is non
invasive and apparently doesn’t cause harm to
surrounding tissues.

35. OPTIC NERVE GLIOMA

36. II. Optic nerve sheath meningiomas
It is a rare benign tumour of meningothelial cells
of the meninges that usually occurs in mid
age. It has slight female preponderance.
Clinical features :
• Early visual loss
• Limitation of ocular movements
• Optic disc edema or atrophy

37. • Slow progressive unilateral proptosis
Treatment :
• Observation is recommended if visual acuity is
good
• Surgical excision is recommended for severe
proptosis with blind eye or threat to chiasma
• Prognosis for life is good

38. OPTIC NERVE SHEATH MENINGIOMA

39. Thank you