anatomy and lesions of visual pathways
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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
http://www.city.ac.uk
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.
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