It starts from retina, optic nerves, optic

chiasma, optic tracts, lat.geniculate

bodies, optic radiations & visual cortex.

2nd cranial nerve.

Starts from optic disc & travels upto

chiasma where the 2 nerves meet.

Backward continuation of retinal nerve

fibre layer

Contains axons originating from ganglion

cells of retina,& also afferent fibres of

pupillary light reflex.

optic nerve is comparable to sensory

tract.

It is not covered by neurilemma.

Fibres of optic N.about million are very

fine of 2 um

Total length of optic nerve—47-50 mm

1) Intraocular part:-1mm

2) Intraorbital:- 30 mm

3) Intracanalicular:-6-9 mm

4) Intracranial:- 10 mm

Intraocular:- from optic disc pierces

sclera and choroid converting into

“lamina cribrosa”.

at the back of eye ball it becomes

continuous with intraorbital part.

Intraorbital part: from back of the eyeball to optc foramina.

It is sinious to give scope for eye movements.

Posteriorly it is closely associated with annulus of zinn & origin of 4 rectimuscles.

Sup.rectus muscle fibres are adherent to the nerve fibre sheath so very painful movement will be manifested in retro bulbar neuritis.

Intra canalicular:- closely related to

ophthalmic artery lies inferolateral to it &

crosses obliquely over it,enters the orbit

lies on its medial side.

Sphenoid&post.ethmoidal sinuses lies

medial to it seperated by thin lamina,so

if infection of these sinuses will lead to

retrobulbar neuritis.

Intra cranial part:-lies above the cavernous sinus &meets ts fellow part over diaphragma sellae to form optic chiasma.

Meningeal sheaths: piamater, dura&arachnoid covering the brain continuous over optic N.

Subarachnoid and subdural spaces also continuous along with brain

Flat structure

Anterio posteriorly 8mm

Horizontally 12 mm

Lies over tuberculum&diaphragma sellae

Fibres of nasal halves of retina cross here.

Cylindrcal bundles of nerve fibres running

outwards and backwardsfrom postero

lateral aspect of the optic chiasma.

Each optic tract has fibres from temporal

half of retina of same eye & nasal half of

opposite eye .

Each optic tract ends in lateral

geniculate body.

2 oval structures situated at posterior

terminaton of optic tracts.

Each has 6 layers of neurons alternating

with white matter.

Fibres of 2nd order neurons relay In these

neurons

Extend from lateral geniculate bodies to

visual cortex & consists of 3rd order

neurons of visual pathway.

Located on medial aspect of occipital

lobe,above and below the calcarine

fissure.

Subdivided into 2 parts

Visuosensory (striate area 17)

Visuopsychic area (peri striate area 18;

para striate area 19)

Receives the radiations

Mainly supplied by pial network of

vessels except orbital part of optic nerve

Optic nerve supplied by axial system

derived from central retinal artery.

Pial network composed by internal

carotid A., middle cerebral A.,

Ant.choroidal A.,Post.cerebral A.,deep

optic artery.

Surface layer of optic disc by capillaries of retinal arterioles.

Prelaminar region by centripetal branches of peri papillary choroid with some contribution from vessels of lamina cribrosa.

Lamina cribrosa by post.ciliaryarteries&arterial circle of zinn.

Retro laminar part by centrifugal branches from central retinal artery & centripetal from choroidal arteries, central retinalA, &ophthalmic.A

Lesions of optic N.:-loss of vision/blindness

common causes:opticatrophy,traumatic

avulsion of opticN., indirect optic

neuropathy&acute optic neuritis.

Near reflex intact.

Lesions through proximal part of opticN:

ipsilateral blindness,contralateral hemi

anopia,absence of light reflex on the

affected side and consensual on the

contralateral side.

---near reflex intact.

Sagittal(central) lesions of the chiasma:

characterised by bitemporal

hemianopia.

Common causes:supra sellar

aneurysms,tumors of pituitary

gland,supra sellar meningioma and

glioma of 3rd ventricle,obstructive hydro

cephalus,chr. Chiasmal arachnoiditis.

Lateral chiasma lesions: binasal hemi

anopia

Common causes :distension of 3rd

ventricle,atheroma of

carotids/post.communicating arteries

Lesions of optic tract: incongruous homonymous hemianopia associated with contralateral hemianopic pupillaryreactions.

May lead to decending optic atrophy with ipsilateral hemiplegia& contralateral3rd nerve paralysis.

Common causes:syphiliticmeningitis/gumma,TB/tumors of optic thalamus,post.cerebral/sup.cerebellar A.

Lesions of lat.geniculate body:

homonymous hemi anopia with sparing

of pupllary reflexes & may end in partial

optic atrophy.

Lesions of optic radiations:

Total involvement lead to complete

homonymous hemi anopia(some times

sparing macula)

Sup.fibres of optic radiation(lesions of

parietal lobe) causes inf.quadrantic

hemianopia (pie on floor)

Inf.fibres of optic radiation(lesions of

temporal lobe) causes sup.quadrantic

hemi anopia(pie in the sky)

Lesions not produce optic atrophy

Common lesions:vascular

occlusions,primary & secondary

tumors,trauma

Lesions of the visual cortex:

Occlusion of post.cerebral A which

supplying ant.part of cerebral cortex

causes congruous homonymous hemi

anopia sparing macula.

Congruous homonymous macular

defect occur in tip ofoccipital cortex

following head injury/gun shot injuries.

Pupillary reflexes normal& optic atrophy

doesn’t occur in these lesions