Optic nerve and visual pathway
Optic nerve
• The optic nerve is the second cranial nerve situated
in the posterior part of the globe
• It transmits visual impulses from the retina to the
brain
• The head of the optic nerve is called optic disc
Visual pathway
Retinal fibers leave half of the image in opposite side
Mutual crossing is known as optic chiasm
Nasal fibers mix with uncrossed temporal sector to form optic tract
Cell station in brain lateral geniculate body (relay station)
Fibers spread out to reach their final destination the visual cortex
Symptoms of optic nerve disease
• Loss of vision
• Scotomata
• Disturbances in color vision
• Pain is conspicuously absent, except (retrobulbar)
Signs of optic nerve disease
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Relative afferent pupillary defect (RAPD)
Margins, surface, color of the disc
Pulsation of the central retinal vein
Shape and size of the physiological disc
Diseases of optic nerves
• Optic neuritis
– Neuroretintis
– Retrobulbar neuritis
• Anterior Ischaemic optic neuropathies (AION)
• Papillitis
• Optic atrophy
Abnormalities
• Drusen :
Two kinds of drusen occur in the optic nerve
• Common drusen • Giant drusen
Disc margins blurred appearance, visual field
defect
Astrocytic hamartomas, that occur with
tuberous sclerosis
• Conus:
It is congenital cresent, choroid and retinal pigment
epithelium do not extend upto the optic disc.
Defective vision, hypermetropic astigmatism and visual
fields defect
• Coloboma :
Incomplete closure of the embroynic fissure causes optic
nerve defects ranging from a deep physiological cup to a pit
in the optic disc
AION
• It is a segmental infarction of the anterior part of the optic nerve, caused
by the occlusion of short posterior ciliary arteries.
• Symptoms :
Headache, scalp tenderness, jaw claudication, pain and
stiffness of the proximal muscles.
• Investigation : Fields, ESR, C-reactive protein
• Treatment : High dose of oral steroids (tapering dose)
Papillodema
• Papillodema is the bilateral non inflammatory passive swelling of the optic
disc, produced by raised intracranial tension.
• Symptoms: Headache, vomiting without nausea, focal neurological deficit
Optic atrophy
• Optic atrophy is the degeneration of optic nerve fibers with loss of their
myelin sheaths and characterised by the pallor of the optic disc.
• Symptoms :
– sudden or gradual loss of field vision
– color vision impaired
– RAPD
• Investigations :
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Central field
FFA
X-ray skull
CT scan brain