Anatomy and Anatomy and Manifestations of Manifestations of Visual Pathway Visual Pathway

LesionsLesionsRaed Behbehani , MD, Raed Behbehani , MD, FRCSCFRCSC

Visual PathwayVisual Pathway

Visual PathwayVisual Pathway

Visual pathwaysVisual pathways

Prechiasmal: optic nerve-chism.Prechiasmal: optic nerve-chism. Retrochiasmal: optic tract, the optic Retrochiasmal: optic tract, the optic

radiations, and the occipital cortex.radiations, and the occipital cortex.

Optic NeuropathyOptic Neuropathy

Unilateral.Unilateral. RAPD, dyschromatopsia.RAPD, dyschromatopsia. Central, cecocentral.Central, cecocentral. Arcuate (superior, inferior).Arcuate (superior, inferior). Altitudinal.Altitudinal. Generalized decrease in sensitivity.Generalized decrease in sensitivity.

Optic NerveOptic Nerve

Axoplasmic transport : clearance of Axoplasmic transport : clearance of expired organelles, structural expired organelles, structural maintainance, and energy requirements.maintainance, and energy requirements.

Interruption of axoplasmic transport : Interruption of axoplasmic transport : ischemia, compression, inflammation.ischemia, compression, inflammation.

Orthograde axonal transport : Orthograde axonal transport : away away from the cell bodyfrom the cell body LGN. LGN.

Retrograde axonal transportRetrograde axonal transport : toward : toward cell body.cell body.

ONH Blood SupplyONH Blood Supply

RGC axonsRGC axons

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Intra-orbital Optic NerveIntra-orbital Optic Nerve

Myelination (oligodendrocytes).Myelination (oligodendrocytes). 20-30 mm Long.20-30 mm Long. Axons: mylein and glial cell Axons: mylein and glial cell

(metabolic support at the nodes of (metabolic support at the nodes of Ranvier).Ranvier).

Intracranalicular Optic Intracranalicular Optic NerveNerve

Within the two bases of the LWS.Within the two bases of the LWS. Medial wall of canal forms lateral Medial wall of canal forms lateral

wall of sphenoid sinus (can be wall of sphenoid sinus (can be absent !).absent !).

Within canal : meninges, ophthalmic Within canal : meninges, ophthalmic artery and sympathetic plexus.artery and sympathetic plexus.

10 mm length.10 mm length. Tight space !Tight space ! Internal carotid artery.Internal carotid artery.

Intracranial Optic NerveIntracranial Optic Nerve

Leaves the cranial end of the optic Leaves the cranial end of the optic canal (medially, backwards, canal (medially, backwards, upwards).upwards).

4-15 m (depending on the position of 4-15 m (depending on the position of chiasm).chiasm).

Upward 45 degree-angle.Upward 45 degree-angle. Anterior cerebral and anterior Anterior cerebral and anterior

comunicating artery lie superior.comunicating artery lie superior.

ArcuateArcuate

Early Late

AltitudinalAltitudinal

CentralCentral

ChiasmChiasm

ChiasmChiasm Floor of the third ventricle.Floor of the third ventricle. 5-10 mm above the diphragma sella and the 5-10 mm above the diphragma sella and the

hypophysis cerebri.hypophysis cerebri. 12mm wide, 8mm A-P , 4 mm thick.12mm wide, 8mm A-P , 4 mm thick. Important relations: 3Important relations: 3rdrd ventricle, hypothalmus, ventricle, hypothalmus,

pituitary stalk, sella, dorsum sellam anterior pituitary stalk, sella, dorsum sellam anterior and posterior clinoid processes, cavernous and posterior clinoid processes, cavernous sinus.sinus.

Nasal fibers cross ; temporal fibers do not Nasal fibers cross ; temporal fibers do not (53:47).(53:47).

Wilband’s knee.Wilband’s knee.

ChiasmChiasm

Chiasmal syndromeChiasmal syndrome

Unilateral or Bilateral.Unilateral or Bilateral. Junctional scotoma.Junctional scotoma. Bitemporal defect.Bitemporal defect. Homonymous defects.Homonymous defects. Diplopia (III, IV, VI cranial nerves or Diplopia (III, IV, VI cranial nerves or

hemi-field slide phenomenon).hemi-field slide phenomenon).

Causes of Chiasmal Causes of Chiasmal syndromesyndrome

Pituitary adenoma Pituitary adenoma Suprasellar meningiomas Suprasellar meningiomas Supraclinoid internal carotid artery Supraclinoid internal carotid artery

aneurysms aneurysms Craniopharyngiomas Craniopharyngiomas Optic nerve gliomasOptic nerve gliomas Uncommon : Optic nerve or chiasmal Uncommon : Optic nerve or chiasmal

neuritis ,Pachymeningitis , neuritis ,Pachymeningitis , Trauma,Inflammatory (e.g., sarcoidosis) Trauma,Inflammatory (e.g., sarcoidosis)

Bitemporal defectBitemporal defect

Junctional Scotoma Junctional Scotoma (Anterior chiasmal (Anterior chiasmal

syndrome)syndrome)

Traquair scotomaTraquair scotoma

A monocular hemianopic visual field A monocular hemianopic visual field loss is referred to as junctional loss is referred to as junctional scotoma of Traquair.scotoma of Traquair.

Posterior Chiasmal Posterior Chiasmal SyndromeSyndrome

90% of chiasmal fibers have macular 90% of chiasmal fibers have macular origin (superior and posterior origin (superior and posterior portions of chiasm).portions of chiasm).

ChiasmChiasm

Band atrophyBand atrophyFrom (Practical viewing of the optic disk)

Retrochiasmal Visual Retrochiasmal Visual Pathway LesionsPathway Lesions

Bilateral.Bilateral. Homonymous.Homonymous. Complete or incomplete.Complete or incomplete. Congrous or incongrous.Congrous or incongrous.

Optic Tract LesionsOptic Tract Lesions

Contralateral RAPD Contralateral RAPD ((may be an may be an ipsilateral afferent pupillary defect if a ipsilateral afferent pupillary defect if a concomitant optic neuropathy existsconcomitant optic neuropathy exists) )

A specific form of optic atrophy (band A specific form of optic atrophy (band atrophy) due to the involvement of atrophy) due to the involvement of nasal fibers (temporal field) in the nasal fibers (temporal field) in the contralateral eye contralateral eye

An incongruous homonymous An incongruous homonymous hemianopsia. hemianopsia.

Optic TractOptic Tract

Travel around the cerebral Travel around the cerebral peduncles at dorsal midbrain.peduncles at dorsal midbrain.

Divides into lateral rootDivides into lateral root LGN , and LGN , and a smaller medial roota smaller medial root pretectal pretectal area (pupillary light reflex)area (pupillary light reflex)

Optic TractOptic Tract

Optic tract lesionsOptic tract lesions

Band Atrophy due to compressionof the left tract.Hoyt Wf,

Kommerell G. Der fundus oculi bei homonyermeinaopia.

Klin Monatsblat Augenheilkd 1973; 162: 456-464)

Lateral Geniculate Bodies Lateral Geniculate Bodies LesionsLesions

Part of the thalamus.Part of the thalamus. Hilum, medial and lateral horn.Hilum, medial and lateral horn. Six laminae (layers 1-6), crossed Six laminae (layers 1-6), crossed

fibersfibers1,4,6 , uncrossed fibers 1,4,6 , uncrossed fibers 2,3,5.2,3,5.

medial

lateral

LGBLGB

Upper quadrantUpper quadrant medial aspect of medial aspect of LGN, Lower quadrantLGN, Lower quadrant lateral lateral aspect of LGN.aspect of LGN.

Macular fibersMacular fibers central wedge of central wedge of LGN.LGN.

LGBLGB 1- Optic nerve 2- Optic chiasma 3- Optic tract 4- Lateral geniculate body 5- Optic radiation 6- Visual cortex 7-Superior colliculus of the midbrain 8- Putamen 9- Long association bundle - inferior occipitofrontal fasciculus 10- Pulvinar of the thalamus 11-Calcarine fissure 12- Posteroinferior horn of the lateral ventricle

Lateral Geniculate Lateral Geniculate NucleusNucleus

Posterior thalamus.Posterior thalamus. Mushroom-shaped structure (6 Mushroom-shaped structure (6

layers).layers). Hilum, medial and lateral horn.Hilum, medial and lateral horn. Six laminae (layers 1-6), crossed Six laminae (layers 1-6), crossed

fibersfibers1,4,6 , uncrossed fibers 1,4,6 , uncrossed fibers 2,3,5.2,3,5.

Lateral Geniculate Lateral Geniculate NucleusNucleus

Lateral Geniculate Lateral Geniculate NucleusNucleus

Upper quadrantUpper quadrant medial aspect of medial aspect of LGN, Lower quadrantLGN, Lower quadrant lateral lateral aspect of LGN.aspect of LGN.

Macular fibersMacular fibers central wedge of central wedge of LGN.LGN.

Layers 1,2: magnocellular. (motion)Layers 1,2: magnocellular. (motion) Layers 3-6: Parvocellular. (color)Layers 3-6: Parvocellular. (color)

LGB lesionsLGB lesions

An incongruous wedge defect An incongruous wedge defect tending to point toward fixation tending to point toward fixation ((spears to fixationspears to fixation) )

Usually complete or nearly Usually complete or nearly complete field homonymous defect.complete field homonymous defect.

LGB lesionsLGB lesions

Optic radiationsOptic radiations

Nerve fibers bundles with cell bodies Nerve fibers bundles with cell bodies in the LGN.in the LGN.

Loop of Meyers (around temporal Loop of Meyers (around temporal and inferior horn of LV).and inferior horn of LV).

Inferior fascicle.Inferior fascicle. Superior fascicle.Superior fascicle.

Optic radiationsOptic radiations

Inferior fascicleInferior fascicle anterior pole of anterior pole of temporal lobetemporal lobe lower calcarine lower calcarine cortex.cortex.

Superior fascicleSuperior fascicle parietal lobe parietal lobe upper calacrine cortex.upper calacrine cortex.

Parietal lesionsParietal lesions

““Pie on the floor” homonynous Pie on the floor” homonynous defect.defect.

Associated neurologic signs and Associated neurologic signs and symptoms (e.g., hemiplegia, symptoms (e.g., hemiplegia, hemisensory loss, visual, or hemisensory loss, visual, or neglect) may be present .neglect) may be present .

Anterior temporal lobeAnterior temporal lobe

““Pie on the sky” homonymous.Pie on the sky” homonymous. Often incongrous.Often incongrous. Seizures, hemiparesis, Seizures, hemiparesis,

hemianesthesia.hemianesthesia. Contralateral neglect (Non-Contralateral neglect (Non-

dominant).dominant). Aphasia (Dominant).Aphasia (Dominant).

Optic radiation lesionsOptic radiation lesions

Occipital lobe lesionsOccipital lobe lesions

Primary Visual Cortex Primary Visual Cortex

Optic radiations terminate in layer 4 Optic radiations terminate in layer 4 (lamina granularis) .(lamina granularis) .

Layer 4 is divided into 3 layers (Line Layer 4 is divided into 3 layers (Line of Gennari).of Gennari).

P-cells P-cells 4C bets. 4C bets. M-cells M-cells 4C alpha. 4C alpha. Macular fibers – terminate posterioly.Macular fibers – terminate posterioly. Lateral fibes – termriate anteriorly.Lateral fibes – termriate anteriorly.

Primary Visual Cortex Primary Visual Cortex ( V1)( V1)

Upper bank and lower bank Upper bank and lower bank (Calcarine fissure).(Calcarine fissure).

Inferior visual filed (upper bank) , Inferior visual filed (upper bank) , Superior visual field (lower bank).Superior visual field (lower bank).

Macular projections represented by Macular projections represented by 50%-60% of the area of the calcarine 50%-60% of the area of the calcarine cortex.cortex.

Occipital tip is for foveal vision.Occipital tip is for foveal vision.

Occipital cortex lesionsOccipital cortex lesions

Isolated Isolated ((ii ..ee.., without other , without other neurologic deficitneurologic deficit))زز

Congruous.Congruous. Paracentral or peripheral. Paracentral or peripheral. Complete or incomplete Complete or incomplete Macular involvement or macular Macular involvement or macular

sparing of the central 5 degrees may sparing of the central 5 degrees may occur (occipital pole involvement). occur (occipital pole involvement).

Occipital cortex lesionsOccipital cortex lesions

Visual cortexVisual cortex

--Anterior striate Anterior striate cortex (8%-10%) is cortex (8%-10%) is monocularly monocularly innervated innervated (temporal crecsent (temporal crecsent of contralateral of contralateral eye).eye).

Visual association areasVisual association areas

Visual Association AreasVisual Association Areas

V2: input from V1.V2: input from V1. V3: sends info to basal ganglia and V3: sends info to basal ganglia and

midbrain.midbrain. V3a: perceive motion and direction.V3a: perceive motion and direction. V4 : (lingual and fusiform gyrus) color.V4 : (lingual and fusiform gyrus) color. V5 : (medial temporal visual region) speed V5 : (medial temporal visual region) speed

and direction, origin of pursuit movemen.and direction, origin of pursuit movemen. V6 : (parietal) represent “extra personal V6 : (parietal) represent “extra personal

space”. space”.

““What” PathwayWhat” Pathway

Ventral stream (occipitotemporal) : Ventral stream (occipitotemporal) : object recognition , color, shape, and object recognition , color, shape, and pattern.pattern.

Continuation of the parvocellular Continuation of the parvocellular pathway.pathway.

V1V1 V2 V2V4V4 inferotemporal inferotemporal cortexcortex angular gyrus angular gyrus limbic limbic structures.structures.

Alexeia, anomia, agnosia, amenesia.Alexeia, anomia, agnosia, amenesia.

““Where” PathwayWhere” Pathway

Dorsal stream (occipitoparietal): Spatial Dorsal stream (occipitoparietal): Spatial orientation ,visual guidance of orientation ,visual guidance of movement.movement.

V1V1 V3 V3 V5 V5Parietal and Parietal and superotemporal cortex.superotemporal cortex.

Continuation of magnocellular pathway.Continuation of magnocellular pathway. Simultagnosia, optic ataxia, acquired Simultagnosia, optic ataxia, acquired

oculomotor apraxia, and hemispatial oculomotor apraxia, and hemispatial neglect.neglect.

Cortical blindnessCortical blindness

Due to bilateral occipital lobe Due to bilateral occipital lobe lesions.lesions.

Often misdiagnosed as functional Often misdiagnosed as functional vision loss.vision loss.

Stroke, severe blood loss, Eclampsia, Stroke, severe blood loss, Eclampsia, hypertension, angiography, CO hypertension, angiography, CO poisoning, cyclosporine.poisoning, cyclosporine.

DyschromatopsiaDyschromatopsia

Bilateral occipital lobe lesions in the Bilateral occipital lobe lesions in the lingual or fusiform gyri of the medial lingual or fusiform gyri of the medial occipital lobe (medial occipito-occipital lobe (medial occipito-temporal lobe).temporal lobe).

Rarely no field defect.Rarely no field defect. Unilateral involvement may cause Unilateral involvement may cause

hemidyschromatopsia.hemidyschromatopsia.

Alexia without AgraphiaAlexia without Agraphia

Loss of ability to read but can write.Loss of ability to read but can write. Left occipital lobe and splenium of Left occipital lobe and splenium of

corpus callosum. corpus callosum.

PalinopsiaPalinopsia

Persistant or recurrence of visual Persistant or recurrence of visual stimulus after it has been removed.stimulus after it has been removed.