Optic nerve and visual Optic nerve and visual pathwaypathway

Optic nerveOptic nerve

• The optic nerve is the second cranial nerve The optic nerve is the second cranial nerve situated in the posterior part of the globesituated in the posterior part of the globe

• It transmits visual impulses from the retina It transmits visual impulses from the retina to the brainto the brain

• The head of the optic nerve is called optic The head of the optic nerve is called optic disc disc

Visual pathwayVisual 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 Symptoms of optic nerve diseasedisease

• Loss of visionLoss of vision

• ScotomataScotomata

• Disturbances in color visionDisturbances in color vision

• Pain is conspicuously absent, except Pain is conspicuously absent, except

(retrobulbar)(retrobulbar)

Signs of optic nerve Signs of optic nerve diseasedisease

• Relative afferent pupillary defect Relative afferent pupillary defect (RAPD)(RAPD)

• Margins, surface, color of the discMargins, surface, color of the disc• Pulsation of the central retinal vein Pulsation of the central retinal vein • Shape and size of the physiological Shape and size of the physiological

discdisc

Diseases of optic nervesDiseases of optic nerves

• Optic neuritisOptic neuritis– NeuroretintisNeuroretintis– Retrobulbar neuritisRetrobulbar neuritis

• Anterior Ischaemic optic neuropathies (AION)Anterior Ischaemic optic neuropathies (AION)• PapillitisPapillitis• Optic atrophyOptic atrophy

AbnormalitiesAbnormalities• Drusen : Drusen : Two kinds of drusen occur in the optic nerveTwo kinds of drusen occur in the optic nerve

• Common drusenCommon drusen -- Disc margins blurred Disc margins blurred appearance, visual field appearance, visual field defectdefect

• Giant drusenGiant drusen -- Astrocytic hamartomas, that occur Astrocytic hamartomas, that occur with with tuberous sclerosistuberous sclerosis

• Conus: Conus: It is congenital cresent, choroid and retinal It is congenital cresent, choroid and retinal pigment pigment epithelium do not extend upto epithelium do not extend upto the optic disc.the optic disc.

Defective vision, hypermetropic astigmatism Defective vision, hypermetropic astigmatism and visual and visual fields defectfields defect

• Coloboma : Coloboma : Incomplete closure of the embroynic fissure Incomplete closure of the embroynic fissure causes optic causes optic nerve defects ranging from a deep nerve defects ranging from a deep physiological cup to a pit physiological cup to a pit in the optic discin the optic disc

AIONAION• It is a segmental infarction of the anterior part of the optic It is a segmental infarction of the anterior part of the optic

nerve, caused by the occlusion of short posterior ciliary nerve, caused by the occlusion of short posterior ciliary arteries.arteries.

• Symptoms :Symptoms : Headache, scalp tenderness, jaw claudication, Headache, scalp tenderness, jaw claudication, pain and stiffness of the proximal muscles.pain and stiffness of the proximal muscles.

• Investigation :Investigation : Fields, ESR, C-reactive protein Fields, ESR, C-reactive protein• Treatment : High dose of oral steroids (tapering dose)Treatment : High dose of oral steroids (tapering dose)

PapillodemaPapillodema• Papillodema is the bilateral non inflammatory passive

swelling of the optic disc, produced by raised intracranial tension.

• Symptoms: Headache, vomiting without nausea, focal neurological deficitt

Optic atrophyOptic 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 : – Central field– FFA– X-ray skull– CT scan brain