Basics Neurology of Vision

8/6/2019 Basics Neurology of Vision

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NEUROLOGY OF VISIONNEUROLOGY OF VISION


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VISUAL PATHWAYSVISUAL PATHWAYS

Visual stimuli originating in the retina pass toVisual stimuli originating in the retina pass tobrain in optic nerve .Fibres orginating from thebrain in optic nerve .Fibres orginating from the

retina nasal to vertical line through the foveolaretina nasal to vertical line through the foveoladecussate in the optic chiasm and joins axonsdecussate in the optic chiasm and joins axonsfrom the contralateral temporal retina in thefrom the contralateral temporal retina in theoptic tract.This synapse in the lateral geniculateoptic tract.This synapse in the lateral geniculate

body and axons from lateral geniculate bodybody and axons from lateral geniculate bodypass in the optic radiation to visual cortex in thepass in the optic radiation to visual cortex in theoccipital lobeoccipital lobe


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VISUAL PATHWAYSVISUAL PATHWAYS

Visual pathway consist ofVisual pathway consist of

1.Optic nerve1.Optic nerve2.Optic chiasm2.Optic chiasm

3.Optic tract3.Optic tract

4.Lateral geniculate body4.Lateral geniculate body5.Optic radiation5.Optic radiation

6.Visual cortex6.Visual cortex


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OPTIC NERVEOPTIC NERVE

Optic nerve is composed of axons of retinalOptic nerve is composed of axons of retinalganglion cellsganglion cells

It extends from optic disc to the optic chiasmIt extends from optic disc to the optic chiasm

It is divided into four portionsIt is divided into four portions

1.Intra ocular (1mm)1.Intra ocular (1mm)

2.Orbital (30mm)2.Orbital (30mm)3.Intra canalicular (4 to 10mm)3.Intra canalicular (4 to 10mm)\\

4.Intra cranial (10 mm )4.Intra cranial (10 mm )


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OPTIC NERVE (contd)OPTIC NERVE (contd)

1.INTRAOCULAR PORTION1.INTRAOCULAR PORTION It includes the optic disk and the portion of the opticIt includes the optic disk and the portion of the optic

nerve within the posterior scleral foramennerve within the posterior scleral foramen The optic disk is located about 3mm nasal to and 0.8mmThe optic disk is located about 3mm nasal to and 0.8mm

above the foveola and is composed of axons of ganglionabove the foveola and is composed of axons of ganglioncellscells

Choroid and all layer of retina terminate at optic diskChoroid and all layer of retina terminate at optic diskmargin except the nerve fibre layermargin except the nerve fibre layer

As the photo sensitive rods and cones are absent thisAs the photo sensitive rods and cones are absent thisarea is blindarea is blind

Posterior to the optic disk the optic nerve fibres arePosterior to the optic disk the optic nerve fibres aremyelinated whereas anterior to optic disk they are nonmyelinated whereas anterior to optic disk they are nonmyelinatedmyelinated

Optic disk has a diameter of 1.5 mmOptic disk has a diameter of 1.5 mm


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2.ORBITAL PORTION OF OPTIC NERVE2.ORBITAL PORTION OF OPTIC NERVE

It has an S shaped curve to permit movement of theIt has an S shaped curve to permit movement of theeyeeye

It is covered with dura matter, arachnoid matter and piaIt is covered with dura matter, arachnoid matter and piamattermatter

The central retina artery and vein penetrate the opticThe central retina artery and vein penetrate the opticnerve 12 mm behind the globenerve 12 mm behind the globe

At the apex of the orbit the optic nerve is surrounded byAt the apex of the orbit the optic nerve is surrounded byfibrous annulus from which the recti muscle orginatefibrous annulus from which the recti muscle orginate

Near the globe long and short ciliary arteries and nervesNear the globe long and short ciliary arteries and nervessurround the optic nervesurround the optic nerve


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3.INTRA CANALICULAR PORTION3.INTRA CANALICULAR PORTION

The optic nerve pass through the optic foramenThe optic nerve pass through the optic foramen

together with ophthalmic artery and sympathetictogether with ophthalmic artery and sympatheticnervesnerves

Within the optic canal the dura matter isWithin the optic canal the dura matter isadherent to bone , arachnoid and pia matter soadherent to bone , arachnoid and pia matter so

the nerve is firmly fixedthe nerve is firmly fixed4.INTRACRANIAL PORTION4.INTRACRANIAL PORTION

It is 10 mm long and passes medially to formIt is 10 mm long and passes medially to formthe chiasm.the chiasm.


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BLOOD SUPPLYBLOOD SUPPLY Intraocular portion is supplied by short posteriorIntraocular portion is supplied by short posterior

ciliary arteriesciliary arteries Intra orbital portionIntra orbital portion

Peripheral supply originate from the vessel of piaPeripheral supply originate from the vessel of piamattermatterCentral supply originate from central retinalCentral supply originate from central retinalarteryartery

Intracanalicular and intracranial portion of opticIntracanalicular and intracranial portion of opticnerve are supplied by branches of internalnerve are supplied by branches of internalcarotid arterycarotid artery


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OPTIC CHIASMOPTIC CHIASM

Optic chiasm is about 13mm wide and 8mm thickOptic chiasm is about 13mm wide and 8mm thick

It is situated at the junction of anterior wall and floor ofIt is situated at the junction of anterior wall and floor of33rdrd ventricleventricle

RELATIONSRELATIONS

Anteriorly anterior cerebral arteryAnteriorly anterior cerebral artery

anterior communicating arteryanterior communicating artery

optic groove of sphenoid boneoptic groove of sphenoid bone

Posteriorly floor of third ventriclePosteriorly floor of third ventricle

tuber cinereumtuber cinereum

Laterally internal carotid arteryLaterally internal carotid artery

Inferiorly diaphragma sellaeInferiorly diaphragma sellae


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OPTIC CHIASM (contd)OPTIC CHIASM (contd)

BLOOD SUPPLYBLOOD SUPPLY

By pial plexus derived fromBy pial plexus derived from

1.Internal carotid artery1.Internal carotid artery

2.Posterior communicating artery2.Posterior communicating artery

3.Anterior cerebral artery3.Anterior cerebral artery4.Anterior communicating artery4.Anterior communicating artery


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OPTIC TRACT (contd)OPTIC TRACT (contd)

The distribution of axons in the anteriorThe distribution of axons in the anteriorportion of the optic tract is similar to thatportion of the optic tract is similar to that

in the optic nerve except that the nasalin the optic nerve except that the nasalaxons are those that have crossed fromaxons are those that have crossed fromthe opposite sidethe opposite side

The axons are rapidly redistributed so thatThe axons are rapidly redistributed so thatthose from the corresponding parts ofthose from the corresponding parts ofeach retina became associated.each retina became associated.


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LATERAL GENICULATE BODYLATERAL GENICULATE BODY

It is small ovoid swelling on the under surface ofIt is small ovoid swelling on the under surface ofthe pulvinar of thalamusthe pulvinar of thalamus

Axons of retinal ganglion cells that carry retinalAxons of retinal ganglion cells that carry retinalimpulses synapse in the lateral geniculate bodyimpulses synapse in the lateral geniculate body

LGB consist of dorsal and ventral nucleusLGB consist of dorsal and ventral nucleus

Dorsal nucleus is composed of 6 cellular layersDorsal nucleus is composed of 6 cellular layers

Cells in ventral layers 1 and 2 are larger andCells in ventral layers 1 and 2 are larger andmore uniform in size and shape than cells in themore uniform in size and shape than cells in theremaining four layersremaining four layers


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LATERAL GENICULATE BODYLATERAL GENICULATE BODY

(contd)(contd) Axons from temporal retina on the same side synapse inAxons from temporal retina on the same side synapse in

layer 2 ,3, 5layer 2 ,3, 5 Axons from nasal one half of the retina of opposite eyeAxons from nasal one half of the retina of opposite eye

decussate in chiasm and terminate in layer 1,4 and 6decussate in chiasm and terminate in layer 1,4 and 6 Axons from the upper one half of the retina synapse inAxons from the upper one half of the retina synapse in

the medial portion of lateral geniculate body and axonsthe medial portion of lateral geniculate body and axonsfrom the lower half in the lateral portionfrom the lower half in the lateral portion

The large cell ( magnocellular laminae that is layer 1 to 2The large cell ( magnocellular laminae that is layer 1 to 2

) signals detection of movement and flicker.) signals detection of movement and flicker. The small cell ( parvocellular laminae that is layers 3 to 6The small cell ( parvocellular laminae that is layers 3 to 6

) appear to carry perception of colour, texture, shape) appear to carry perception of colour, texture, shapeand fine stereopsis.and fine stereopsis.


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OPTIC RADIATIONOPTIC RADIATION

Optic radiation extends from lateral geniculateOptic radiation extends from lateral geniculatebody to the superior and inferior lips of calcarinebody to the superior and inferior lips of calcarine

fissurefissure Axons from the cells located in the lateralAxons from the cells located in the lateral

aspects of the lateral geniculate body representsaspects of the lateral geniculate body representsthe inferior retinal quadrant.They pass anteriorlythe inferior retinal quadrant.They pass anteriorlyaround the tip of temporal horn of lateralaround the tip of temporal horn of lateralventrical to form the loop of Meyer.Damage toventrical to form the loop of Meyer.Damage toaxons in this loop produces superioraxons in this loop produces superiorhomonymous quadrantic field defectshomonymous quadrantic field defects


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VISUAL CORTEXVISUAL CORTEX

The axons of cells located in the lateralThe axons of cells located in the lateralgeniculate body terminate along the superiorgeniculate body terminate along the superior

and inferior lips of calcarine fissureand inferior lips of calcarine fissure This area is called striate cortex ( area 17 ofThis area is called striate cortex ( area 17 of

Brodmann ) because of prominent band ofBrodmann ) because of prominent band ofgeniculo calcarine fibresgeniculo calcarine fibres

The upper half of each retina is represented onThe upper half of each retina is represented onthe superior part of each occipital cortex and thethe superior part of each occipital cortex and thelower half covers the inferior partlower half covers the inferior part


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VISUAL CORTEXVISUAL CORTEX

Fibres representing the central retinaFibres representing the central retinaterminate at the tip of the posterior poleterminate at the tip of the posterior pole

and more peripheral portion of the retinaand more peripheral portion of the retinaare represented more anteriorlyare represented more anteriorly

Visual cortex is composed of 6 cell layersVisual cortex is composed of 6 cell layers

and most axons from the lateraland most axons from the lateralgeniculate body terminate in the layer 4geniculate body terminate in the layer 4


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Basics Neurology of Vision