VISUAL_PATHWAY

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VISUAL PATHWAY:

VISUAL PATHWAY Dr. Anuja Desai 1 st Year Resident Dhiraj Hospital

PowerPoint Presentation:

ANATOMY OF DIFFERENT COMPONENTS ARRANGEMENT OF VISUAL FIBRES BLOOD SUPPLY LESIONS OF VISUAL PATHWAY

ANATOMY OF DIFFERENT COMPONENTS:

ANATOMY OF DIFFERENT COMPONENTS

PowerPoint Presentation:

OPTIC NERVE OPTIC CHIASMA OPTIC TRACT LATERAL GENICULATE BODY OPTIC RADIATIONS VISUAL CORTEX

Optic Nerve (2nd ):

Optic Nerve (2 nd ) Outgrowth of the brain. Not covered by Neurilemma so does not regenerate when cut. Fibres are 2-10 um in diameter. Surrounded by meninges . Both the neurons are in the retina.

Parts of Optic Nerve:

Parts of Optic Nerve 47-50 mm in length Intraocular (1 mm) Intraorbital (25 mm) Intracanalicular (9 mm) Intracranial (16 mm)

Intra Ocular Part:

Intra Ocular Part Sclera, Choroid and finally appears in the eye as optic disc Divided into 4 parts- Surface Nerve Fibre Layer Prelaminar Region Lamina Cribrosa Retrolaminar Region

PowerPoint Presentation:

Surface Nerve Fibre Layer Contiguous with RNFL All layers of retina except RNFL are separeted by rim of glial tissue called intermediate tissue of Kuhnt . Prelaminar Region Consistes of nerve fibre bundles and astroglia Border tissue of Jcoby (cuff of astrocytes ) separates the nerve from choriod .

PowerPoint Presentation:

Lamina Cribrosa Connective and elastic tissue and contains fenestrations for passage of nerve fibres and blood vessels. Maintains IOP bet intra and extra ocular spaces. Blood Supply from Circle of Zinn Retrolaminar Region Myelinated nerve fibres This doubles the diameter from 1.5mm to 3 mm

Intra Orbital Part:

Intra Orbital Part Back of the eyeball upto optic foramina Covered by all 3 meninges Protects the nerve during eye movements or in event of up to 9mm of proptosis . Post there is origin of 4 rectus muscle-> painful ocular movements seen in retrobulbar neuritis.

Intra Canalicular Part:

Intra Canalicular Part It enters the optic canal through the optic foramen Medial canal wall is the thinnest and most likely to fracture. Fixed tightly within the optic canal Spheniod and post ethmoidal sinuses lie medial to it  retrobulbar neuritis following sinus infection

Intra Cranial Part:

Intra Cranial Part Covered by pia only Above lie the gyri recti of the frontal lobes of the brain. Lateral side lie the internal carotid artery, or alternatively the anterior cerebral and middle cerebral arteries. Ophthalmic artery lies to the lateral side and below the nerve. Proximity of cavernous sinus makes it possible for tumors to produce cranial nerve palsies in combination with an optic neuropathy.

Optic Chiasma:

Optic Chiasma 10mm above the pituitary gland  presence of pituitary tumour will cause visual field defects. Crossing over of nasal fibers to the opposite optic tracts and the direct passage of temporal fibers to the ipsilateral optic tracts. Posteriorly it forms the anterior wall of third ventricle.

PowerPoint Presentation:

Prefixed Chiasma - (10%) over the tuberculum sellae  tumour involves optic tracts 2 . Central Chiasma - (80%) above the sellae  tumour involves the chiasma 3 . Postfixed Chiasma - (10%) over the dorsum sellae  tumour damages optic nerve

Optic Tract:

Optic Tract Connect the optic chiasma to the lateral geniculate body. Each tract contains uncrossed temporal fibres and crossed nasal fibres .

Lateral Geniculate Body:

Lateral Geniculate Body

Lateral Geniculate Body:

Lateral Geniculate Body 3rd order neurons Axons of ganglion cells synapse with dendrites of LGB cells 6 laminae Axons from the contralateral eye - 1, 4,6 Axons from the ipsilateral eye - 2, 3, 5.

Lateral Geniculate Body:

Lateral Geniculate Body Neuronal size: Large magnicellular neurons (M cells) - 1 and 2 Motion detection Low spatial frequency Contrast sensitivity Small parvicellular neurons (P cells) - 3,4,5,6. Colour perception High spatial frequency Contrast sensitivity

Optic Radiations:

Optic Radiations Geniculocalcarine pathway extend from lateral geniculate body to visual cortex The fibres of optic radiation spread out fanwise to form medullary optic lamina The inferior fibres of optic radiation subserve upper visual field & the superior fibres subserve lower visual field .

Visual Cortex:

Visual Cortex Medial aspect of the occipital lobe Brodmann area 17 or V1 Neurons receive information via the mylinated strip of Gennari . Central vision posterior half Peripheral visionanterior half

Visual Cortex:

Visual Cortex Secondary Visual Cortex (V2)- Brodmann’s area 18 and 19 Ventral Pathway-impulse to the temporal lobe for recognizing objects. Dorsal Pathway- impulse to the parietal lobe for locating objects.

ARRANGEMENT OF NERVE FIBRES:

ARRANGEMENT OF NERVE FIBRES

Retina:

Retina Nasal half  Superior and inferior radiating fibres Macula  Temporal part as pappillomacular bundle Temporal arch  Superior and inferior arcuate fibres

PowerPoint Presentation:

Optic Nerve (a) In the optic disc Periphery of retina lie deep but occupy superficial part. Closer to ONH lie superficial in retina but occupy deep portion of disc.

Optic Nerve (b) In the Proximal Region:

Optic Nerve (b) In the Proximal Region Upper and Lower temporal situated on the temporal side separated by macular fibres . Upper and Lower nasal situated on the nasal side.

Optic Nerve (c) In the Distal Region:

Optic Nerve (c) In the Distal Region Macular fibres are centrally placed.

Chiasma:

Chiasma

PowerPoint Presentation:

Upper Nasal fibres involved first by lesions coming from above eg . craniopharyngiomas Lower nasal fibres first affected in tumours of pituitary gland  upper temporal field defects. Ipsilateral blindness is associated with contralateral field defects.

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Temporal fibres

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Macular Fibres

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Macular fibers crossing through the chiasm do so in its central and posterior portion. Lesions  bitemporal hemianopia

Optic Tract:

Optic Tract Macular fibres  dorsolateral part Upper peripheral fibres  medially Lower peripheral fibres  laterally

Lateral Geniculate Body:

Lateral Geniculate Body Macular fibres  posterior 2/3 Upper retinal fibres  medial half of anterior 1/3 Lower retinal fibres  lateral half of anterior 1/3

PowerPoint Presentation:

Fibres from corresponding part of 2 retina end adjacent to each other So lesion in the retina will cause degeneration of 3 laminae in which the fibres end Since the optic radiation begin from all 6 laminae , lesion in cortex will cause degeneration of all 6 laminae .

Optic Radiation:

Optic Radiation

PowerPoint Presentation:

Fibres from inferior retina (Meyer’s loops) Pass through temporal lobe looping around the inferior horn of lateral ventricle. Information from the superior part of visual field. Loss of vision in superior quadrant ( quadrantanopia or ‘pie in sky defect’)

PowerPoint Presentation:

Fibres from superior retina (Baum’s loop) Parietal lobe occipital lobe internal capsule visual cortex Information from the inferior part of visual field. Vascular lesion of internal capsulehemiplegia & homonymous hemianopia

Visual Cortex(cortical retina):

Visual Cortex(cortical retina) Impulses originating from corresponding points of 2 retina meet Right cortex  temporal half of right retina and nasal half of left retina Left cortex temporal half of left retina and nasal half of right retina

PowerPoint Presentation:

Upper dorsal lip- lower quadrant of binocular field on opp side. Inferior ventral lip- superior quadrant of opp side Periphery of retina- represented most anteriorly Macula- represented posteriorly . This is imp in cases of bullet wounds

BLOOD SUPPLY OF VISUAL PATHWAY:

BLOOD SUPPLY OF VISUAL PATHWAY

PowerPoint Presentation:

Carotid Arterial system- Ophthalmic Artery Small branches of Internal Carotid Artery Posterior Communicating Artery Anterior Cerebral Artery Middle Cerebral Artery Vertebral Arterial System- Posterior Cerebral Artery Cortical Central Choroidal

Retina:

Retina

PowerPoint Presentation:

Outer 4 layers  Choriocapillaries Inner 6 layers  Central Retinal Artery Outer Plexiform Layer  Choriocappilaries and Central Retinal Artery Macula Superior and Inferior temporal branches of Central Retinal Artery Celioretinal Artery is seen in some cases at temporal margin of the disc Supplies the macula and retains central vision in cases of CRAO

Optic Nerve:

Optic Nerve Intraocular Part: Surface Nerve Fibre Layer-Capillaries from retinal arterioles. Prelaminar Region- Ciliary vessels Lamina Cribrosa - Ciliary vessels from short posterior ciliary arteries and arterial circle of Zinn -Haller Retrolaminar Region- Ciliary and Retinal circulation

PowerPoint Presentation:

2) Intraorbital Part- The Periaxial System- Ophthalmic Artery Long & Short Posterior Ciliary Arteries Lacrimal Artery Central Retinal Artery Axial System- Intraneural branch of CRA Central Collateral Arteries from CRA 3) Intracanalicular Part- mainly from branches of Ophthalmic Artery

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4)Intracranial Part -Branches from Internal Carotid Artery Branches from Anterior Cerebral Artery Recurrent Branches from Ophthalmic Artery Branches from Anterior Communicating Artery Venous Drainage Optic nerve head- Central Retinal Vein Orbital Part- Peripheral Plial Plexus Central Retinal Vein Intracranial Part- Plial Plexus which ends in Anterior Cerebral and Basal Vein

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Optic Chiasma

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Superior Part- Branches from Anterior Cerebral and Anterior Communicating Arteries Superior Chiasmal Vein Anterior Cerebral Vein Inferior Part- Branches from Internal Carotid Artery,Anterior Superior Hypophyseal Artery and Posterior Communicating Artery. Pre infundibular Vein Basal Vein

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Optic Tract Posterior Communicating artery Anterior Choroidal Artery Middle Cerebral Artery Venous Drainage Superior- Anterior cerebral Vein Inferior- Basal Vein

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Lateral Geniculate Body Posteromedial Aspect- Posterior Cerebral Artery Anterolateral aspect- Anterior Choroidal Artery Macular fibres - anastomosis from both arteries VENOUS DRAINAGE Basal Vein

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Optic Radiations Anterior- Anterior Choroidal Artery Middle- Deep Optic Artery from Middle Cerebral Artery Posterior- Calcarine branches of Posterior Cerebral Artery Perforating branch of Middle Cerebral Artery VENOUS DRAINAGE Basal Vein Partly by Middle Cerebral Vein

PowerPoint Presentation:

Visual Cortex Posterior Cerebral Artery Middle Cerebral Artery Venous Drainage Medial- Internal Occipital Vein Superolateral - Inferior Cerebral Vein

LESIONS OF VISUAL PATHWAY:

LESIONS OF VISUAL PATHWAY

PowerPoint Presentation:

Lesion of Optic Nerve- Complete blindness on the affected side. Causes -Optic Atrophy Traumatic avulsion of optic nerve Indirect optic neuropathy Acute optic neuritis 2)Lesion through proximal part of optic nerve- Ipsilateral blindness and contralateral hemianopia

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Arcuate scotoma - annular or cuneate shaped apex points towards the blind spot perimetry -vertical meridian

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b) Junctional Scotoma - lesion at junction of nerve and chiasma . perimetry - junctional scotoma of Traquair sign of prechiasmal compression

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c) Centrocecal scotoma - damage to the macular fibres scotoma in central fixation damage to peripapillary zoneenlargement of blind spot

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3) Central lesion of the Chiasma - Bitemporal hemianopia partial descending optic atrophy Causes- Suprasellar aneurysms Tumours of pituitary gland Craniopharyngioma

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4)Lateral Chiasmal lesions- Binasal Hemianopiapartial descending optic atrophy Causes- Distention of 3 rd ventricle Atheroma of carotids

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5)Lesions of Optic Tract- Incongruous Homonymous hemianopia  partial descending optic atrophy(bow tie atrophy) contralateral 3 rd N palsy ipsilateral hemiplegia Causes- Syphilitic meningitis TB and tumours of optic thalamus

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6)Lesions of LGB- Occlusion of Anterior Choroidal Artery (ICA)- upper and lower field defects.

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6)Lesions of LGB- Occlusion of Lateral Choroidal Artery (PCA)- homonymous horizontal defect.

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7)Lesions of Optic Radiations- Total optic radiations complete homonymous hemianopia Lesions of parietal lobeinferior quadrantic hemianopia (pie on the floor)

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Lesions of temporal lobe superior quandrantic hemianopia (pie in the sky)

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8)In the Visual Cortex- Occlusion of posterior cerebral artery congruous homonymous hemianopia (sparing macula) Lesions of occipital cortex (head injury or gunshot injury)congruous homonymous macular defect (altitudinal scotoma ) Inferior>Superior venous sinus or brain stem

PowerPoint Presentation:

Cortical blindness or Anton Syndrome- Denial of blindness Bilateral blindness Normal pupillary reflex Bilateral occipitocortical lesion. Tunnel Vision- Bilateral occlusion of post cerebral arteries Infarction of occipital lobe Involvement of cortex ant to post polecentral keyhole of vision. Middle cerebral artery supplies macula

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Thank You