Visual pathway

1. DISEASES OF VISUAL PATHWAY
• It consists of the optic nerve, optic chiasma, optic
tract, optic radiation and occipital cortex
• Optic nerve passes backwards from posterior part
eye ball to the orbit apex and through optic
foramen/canal into the cranium.
• The two ophthalmic nerves meet at the optic
chiasma just above the pituitary fossa. Nasal fibres
decussate in the optic chiasma
• Two optic tracts emerge from the optic chiasma and
pass around the brainstem to lateral geniculate
body

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4. Visual pathways
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5. - Fibres from the lateral geniculate body pass in the
optic radiation pass to occipital cortex at posterior
part of cerebral hemisphere.
-Few fibres from optic tract regulate pupil size, pass
to midbrain where they synapse in pretectal nucleus
and also with oculomotor nucleus of both sides.
-At optic chiasma all the nasal fibres of the retina
cross over to the opposite side and in this way the
left of the field of vision in each eye is seen on the
by right side of the brain.

6. • Definitions
• Optic neuropathy refers to optic nerve damage
from any cause.
• Optic neuritis refer to inflammation of the optic
nerve
• Forms of optic neuritis
• Papillitis its inflammation of intraocular portion of
the optic nerve
• Fundus appearance shows slight of blurring of the
disc margins

7. • Retrobulbar neuritis is inflammation of intraocular
portion of the optic nerve behind the eye ball
• Fundus = normal, marked visual loss and pain on
moving eye ball superiorly
• NB. retrobulbar neuritis patient cannot see and
doctor does not any sign on funduscopy.
• Papilloedema/disc oedema refers to swelling of
optic disc/swollen with fluid , but with little or no
visual loss.
Common causes- raised intracranial pressure and
sever hypertension

8. • Papilloedema vs Papillitis
• Papilloedema there obvious swelling of optic disc
with little visual loss
• The reverse occurs for papillitis
• Papilloedema usually bilateral and papillitis is
unilateral.
• Optic atrophy is a sign of andvanced retinal disease
or optic neuritis when significant number of nerve
fibres have degenerated
• loss of vision, papilllary reflexes are diminished or
absent, loss if brightness and colour discrimination.

9. • Primary optic atrophy occurs without initial
swelling of optic discs.
• Lesions affecting visual pathway from posterior part
of eye ball to lateral geniculate body.
• Lesions anterior to optic chiasma cause unilateral
atrophy and the posterior, cause bilateral atrophy
• Signs- well defined disc margins and pale disc
• Secondary optic atrophy is preceded by swelling
optic disc as in optic neuritis & papilloedema.
• The optic disc is white or grey, with ill-defined
margins.

10. Causes of optic neuritis/Neuropathy /atrophy
- Malnutrition – vitamin B12 deficiency
- Toxins Tobacco & cassava contain cyanide leads
vitB12 deficiency/Cassava tropical disease
- Methylalcohol is metabolized into formaldehyde or
formic acid, patients present with headache ,
nausea & delirium & blindness after recovery
- Drugs Ethambutol quinine at times used in abortion,
arsenicals

11. • Infections severe infections like measles, typhoid
and any type of meningititis
• Chronic infections like syphilis causes
chorioretinitis,optic atrophy ,iritis and corneal
scarring
• Onchocerciasis.
• Vascular –hypertension, cranial arteritis or giant cell
arteritis
• Diabetic retinopathy
• Head injuries especially on the temporal side causes
small vessels to rupture in optic foramen
• Degenerative disease like multiple sclerosis leads to
loss sheath and degeneration

12. •
• Tumours- orbital tumour/chiasmal and pituitary, cranial
pharyngioma and meningioma
• Intracranial tumours cause elevation ICP and
papilloedema
• Retinal diseases like CMV retinitis, Herpes simplex,
retinitis pigmentosa and vascular occlusion leads to
destruction of gangilion cells followed by optic atrophy.
• Glaucoma is a common cause of optic neuropathy
xtised by a cupped disc and constricted visual field.
• Degenerative disease like multiple sclerosis leads to
loss sheath and degeneration
•

13. Management
- Diagnosis is from the history, examination and
investigations
- Pupillary reaction ie diminished or absent, afferent
or efferent pupillary defect
- Funduscopy
- Measure of intraocular pressure

14. Visual fields
- Confrontation test and visual field machine
- Defects with the horizontal edge suggest ischaemic
optic neuropathy
- Vertical edge suggest chiasma lesions
- Central defects suggest toxic or optic neuritis
- Bitemporal hemianopia
- Homonymous hemianopia

15. • Investigations
• VDRL/TPHA
• CBC AND ESR,
• C – Reactive proteins
• CT scan
• X- Ray
• Treatment
• According to the cause
• Advanced optic atrophy nothing may be done
• Vit B Complex
• Hydroxycobalamin
• Systemic steroids
• Pituitary tumours requires surgery

16. Diseases of posterior visual pathway
-Optic tracts lateral geniculate body, optic radiation and
visual cortex are less susceptible to diseases.
-Affects the same part of the visual field in each eye.
-Disorders of the left side of the brain produce defects in
the right visual field of each eye
• And vice versa homonymous hemianopia.
• Causes include cerebrovascular accident, tumours of the
cortex, encephalitis in children.

17. Congentital abnormalities of the optic disc
• Optic nerve hypoplasia the nerve and disc are small
and poorly developed & generalised loss of vision.
• Coloboma –Defect in segment of optic disc often
choroid and retina are involved hence a white sclera is
seen and visual field defects superior half.
• Embryonic blood vessels from optic disc may be seen
usually disappear after birth
• Optic pit is small deep hole in the centre of the disc
there may be oedema of macula and blurring