1. Visual pathway lesions can occur prechiasmally in the optic nerve or retrochiasmally in the optic tract, lateral geniculate nucleus, optic radiations, and occipital cortex. 2. Optic neuropathy manifestations include visual field defects such as arcuate scotomas. Optic tract lesions cause incongruous homonymous hemianopsia. 3. Lateral geniculate nucleus lesions result in an incongruous wedge defect pointing toward fixation. Occipital cortex lesions cause homonymous field defects that can be paracentral or peripheral.

1. Anatomy andAnatomy and
Manifestations of VisualManifestations of Visual
Pathway LesionsPathway Lesions
Raed Behbehani , MD, FRCSCRaed Behbehani , MD, FRCSC

2. Visual PathwayVisual Pathway

3. Visual PathwayVisual Pathway

4. Visual pathwaysVisual pathways
 Prechiasmal: optic nerve-chism.Prechiasmal: optic nerve-chism.
 Retrochiasmal: optic tract, the optic radiations,Retrochiasmal: optic tract, the optic radiations,
and the occipital cortex.and the occipital cortex.

5. 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.

6. Optic NerveOptic Nerve
 Axoplasmic transport : clearance of expiredAxoplasmic transport : clearance of expired
organelles, structural maintainance, and energyorganelles, structural maintainance, and energy
requirements.requirements.
 Interruption of axoplasmic transport : ischemia,Interruption of axoplasmic transport : ischemia,
compression, inflammation.compression, inflammation.
 Orthograde axonal transport :Orthograde axonal transport : away from the cellaway from the cell
bodybody LGN.LGN.
 Retrograde axonal transportRetrograde axonal transport : toward cell body.: toward cell body.

7. ONH Blood SupplyONH Blood Supply

8. RGC axonsRGC axons
http://www.city.ac.uk

9. Intra-orbital Optic NerveIntra-orbital Optic Nerve
 Myelination (oligodendrocytes).Myelination (oligodendrocytes).
 20-30 mm Long.20-30 mm Long.
 Axons: mylein and glial cell (metabolic supportAxons: mylein and glial cell (metabolic support
at the nodes of Ranvier).at the nodes of Ranvier).

10. Intracranalicular Optic NerveIntracranalicular Optic Nerve
 Within the two bases of the LWS.Within the two bases of the LWS.
 Medial wall of canal forms lateral wall ofMedial wall of canal forms lateral wall of
sphenoid sinus (can be absent !).sphenoid sinus (can be absent !).
 Within canal : meninges, ophthalmic artery andWithin canal : meninges, ophthalmic artery and
sympathetic plexus.sympathetic plexus.
 10 mm length.10 mm length.
 Tight space !Tight space !
 Internal carotid artery.Internal carotid artery.

11. Intracranial Optic NerveIntracranial Optic Nerve
 Leaves the cranial end of the optic canalLeaves the cranial end of the optic canal
(medially, backwards, upwards).(medially, backwards, upwards).
 4-15 m (depending on the position of chiasm).4-15 m (depending on the position of chiasm).
 Upward 45 degree-angle.Upward 45 degree-angle.
 Anterior cerebral and anterior comunicatingAnterior cerebral and anterior comunicating
artery lie superior.artery lie superior.

12. ArcuateArcuate
Early Late

13. AltitudinalAltitudinal

14. CentralCentral

15. ChiasmChiasm

16. ChiasmChiasm
 Floor of the third ventricle.Floor of the third ventricle.
 5-10 mm above the diphragma sella and the5-10 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 andpituitary stalk, sella, dorsum sellam anterior and
posterior clinoid processes, cavernous sinus.posterior clinoid processes, cavernous sinus.
 Nasal fibers cross ; temporal fibers do notNasal fibers cross ; temporal fibers do not
(53:47).(53:47).
 Wilband’s knee.Wilband’s knee.

17. ChiasmChiasm

18. 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 hemi-fieldDiplopia (III, IV, VI cranial nerves or hemi-field
slide phenomenon).slide phenomenon).

19. Causes of Chiasmal syndromeCauses of Chiasmal syndrome
 Pituitary adenomaPituitary adenoma
 Suprasellar meningiomasSuprasellar meningiomas
 Supraclinoid internal carotid artery aneurysmsSupraclinoid internal carotid artery aneurysms
 CraniopharyngiomasCraniopharyngiomas
 Optic nerve gliomasOptic nerve gliomas
 Uncommon : Optic nerve or chiasmal neuritisUncommon : Optic nerve or chiasmal neuritis
,Pachymeningitis , Trauma,Inflammatory (e.g.,,Pachymeningitis , Trauma,Inflammatory (e.g.,
sarcoidosis)sarcoidosis)

20. Bitemporal defectBitemporal defect

21. Junctional Scotoma (AnteriorJunctional Scotoma (Anterior
chiasmal syndrome)chiasmal syndrome)

22. Traquair scotomaTraquair scotoma
 A monocular hemianopic visual field loss isA monocular hemianopic visual field loss is
referred to as junctional scotoma of Traquair.referred to as junctional scotoma of Traquair.

23. Posterior Chiasmal SyndromePosterior Chiasmal Syndrome
 90% of chiasmal fibers have macular origin90% of chiasmal fibers have macular origin
(superior and posterior portions of chiasm).(superior and posterior portions of chiasm).

24. ChiasmChiasm

25. Band atrophyBand atrophy
From (Practical viewing of the optic disk)

26. Retrochiasmal Visual PathwayRetrochiasmal Visual Pathway
LesionsLesions
 Bilateral.Bilateral.
 Homonymous.Homonymous.
 Complete or incomplete.Complete or incomplete.
 Congrous or incongrous.Congrous or incongrous.

27. Optic Tract LesionsOptic Tract Lesions
 Contralateral RAPDContralateral RAPD ((may be an ipsilateralmay be an ipsilateral
afferent pupillary defect if a concomitant opticafferent pupillary defect if a concomitant optic
neuropathy existsneuropathy exists))
 A specific form of optic atrophy (band atrophy)A specific form of optic atrophy (band atrophy)
due to the involvement of nasal fibers (temporaldue to the involvement of nasal fibers (temporal
field) in the contralateral eyefield) in the contralateral eye
 An incongruous homonymous hemianopsia.An incongruous homonymous hemianopsia.

28. Optic TractOptic Tract
 Travel around the cerebral peduncles at dorsalTravel around the cerebral peduncles at dorsal
midbrain.midbrain.
 Divides into lateral rootDivides into lateral root LGN , and a smallerLGN , and a smaller
medial rootmedial root pretectal area (pupillary lightpretectal area (pupillary light
reflex)reflex)

29. Optic TractOptic Tract

30. Optic tract lesionsOptic tract lesions
Band Atrophy due to compression
of the left tract.Hoyt Wf,
Kommerell G. Der fundus oculi bei homonyermeinaopia.
Klin Monatsblat Augenheilkd 1973; 162: 456-464)

31. Lateral Geniculate Bodies LesionsLateral Geniculate Bodies Lesions
 Part of the thalamus.Part of the thalamus.
 Hilum, medial and lateral horn.Hilum, medial and lateral horn.
 Six laminae (layers 1-6), crossed fibersSix laminae (layers 1-6), crossed fibers1,4,6 ,1,4,6 ,
uncrossed fibersuncrossed fibers 2,3,5.2,3,5.
medial
lateral

32. LGBLGB
 Upper quadrantUpper quadrant medial aspect of LGN,medial aspect of LGN,
Lower quadrantLower quadrant lateral aspect of LGN.lateral aspect of LGN.
 Macular fibersMacular fibers central wedge of LGN.central wedge of LGN.

33. 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

34. Lateral Geniculate NucleusLateral Geniculate Nucleus
 Posterior thalamus.Posterior thalamus.
 Mushroom-shaped structure (6 layers).Mushroom-shaped structure (6 layers).
 Hilum, medial and lateral horn.Hilum, medial and lateral horn.
 Six laminae (layers 1-6), crossed fibersSix laminae (layers 1-6), crossed fibers1,4,6 ,1,4,6 ,
uncrossed fibersuncrossed fibers 2,3,5.2,3,5.

35. Lateral Geniculate NucleusLateral Geniculate Nucleus

36. Lateral Geniculate NucleusLateral Geniculate Nucleus
 Upper quadrantUpper quadrant medial aspect of LGN,medial aspect of LGN,
Lower quadrantLower quadrant lateral aspect of LGN.lateral aspect of LGN.
 Macular fibersMacular fibers central wedge of LGN.central wedge of LGN.
 Layers 1,2: magnocellular. (motion)Layers 1,2: magnocellular. (motion)
 Layers 3-6: Parvocellular. (color)Layers 3-6: Parvocellular. (color)

37. LGB lesionsLGB lesions
 An incongruous wedge defect tending to pointAn incongruous wedge defect tending to point
toward fixationtoward fixation ((spears to fixationspears to fixation))
 Usually complete or nearly complete fieldUsually complete or nearly complete field
homonymous defect.homonymous defect.

38. LGB lesionsLGB lesions

39. Optic radiationsOptic radiations
 Nerve fibers bundles with cell bodies in theNerve fibers bundles with cell bodies in the
LGN.LGN.
 Loop of Meyers (around temporal and inferiorLoop of Meyers (around temporal and inferior
horn of LV).horn of LV).
 Inferior fascicle.Inferior fascicle.
 Superior fascicle.Superior fascicle.

40. Optic radiationsOptic radiations
 Inferior fascicleInferior fascicle anterior pole of temporalanterior pole of temporal
lobelobe lower calcarine cortex.lower calcarine cortex.
 Superior fascicleSuperior fascicle parietal lobeparietal lobe upperupper
calacrine cortex.calacrine cortex.

41. Parietal lesionsParietal lesions
 ““Pie on the floor” homonynous defect.Pie on the floor” homonynous defect.
 Associated neurologic signs and symptomsAssociated neurologic signs and symptoms
(e.g., hemiplegia, hemisensory loss, visual, or(e.g., hemiplegia, hemisensory loss, visual, or
neglect) may be present .neglect) may be present .

42. Anterior temporal lobeAnterior temporal lobe
 ““Pie on the sky” homonymous.Pie on the sky” homonymous.
 Often incongrous.Often incongrous.
 Seizures, hemiparesis, hemianesthesia.Seizures, hemiparesis, hemianesthesia.
 Contralateral neglect (Non-dominant).Contralateral neglect (Non-dominant).
 Aphasia (Dominant).Aphasia (Dominant).

43. Optic radiation lesionsOptic radiation lesions

44. Occipital lobe lesionsOccipital lobe lesions

45. Primary Visual CortexPrimary Visual Cortex
 Optic radiations terminate in layer 4 (laminaOptic radiations terminate in layer 4 (lamina
granularis) .granularis) .
 Layer 4 is divided into 3 layers (Line ofLayer 4 is divided into 3 layers (Line of
Gennari).Gennari).
 P-cellsP-cells  4C bets.4C bets.
 M-cellsM-cells  4C alpha.4C alpha.
 Macular fibers – terminate posterioly.Macular fibers – terminate posterioly.
 Lateral fibes – termriate anteriorly.Lateral fibes – termriate anteriorly.

46. Primary Visual Cortex ( V1)Primary Visual Cortex ( V1)
 Upper bank and lower bank (Calcarine fissure).Upper bank and lower bank (Calcarine fissure).
 Inferior visual filed (upper bank) , SuperiorInferior visual filed (upper bank) , Superior
visual field (lower bank).visual field (lower bank).
 Macular projections represented by 50%-60% ofMacular projections represented by 50%-60% of
the area of the calcarine cortex.the area of the calcarine cortex.
 Occipital tip is for foveal vision.Occipital tip is for foveal vision.

47. Occipital cortex lesionsOccipital cortex lesions
 IsolatedIsolated ((ii..ee.., without other neurologic deficit, without other neurologic deficit))‫ز‬‫ز‬
 Congruous.Congruous.
 Paracentral or peripheral.Paracentral or peripheral.
 Complete or incompleteComplete or incomplete
 Macular involvement or macular sparing of theMacular involvement or macular sparing of the
central 5 degrees may occur (occipital polecentral 5 degrees may occur (occipital pole
involvement).involvement).

48. Occipital cortex lesionsOccipital cortex lesions

49. Visual cortexVisual cortex
--Anterior striate cortexAnterior striate cortex
(8%-10%) is monocularly(8%-10%) is monocularly
innervated (temporalinnervated (temporal
crecsent of contralateralcrecsent of contralateral
eye).eye).

50. Visual association areasVisual association areas

51. Visual Association AreasVisual Association Areas
 V2: input from V1.V2: input from V1.
 V3: sends info to basal ganglia and midbrain.V3: sends info to basal ganglia and 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 andV5 : (medial temporal visual region) speed and
direction, origin of pursuit movemen.direction, origin of pursuit movemen.
 V6 : (parietal) represent “extra personal space”.V6 : (parietal) represent “extra personal space”.

52. ““What” PathwayWhat” Pathway
 Ventral stream (occipitotemporal) : objectVentral stream (occipitotemporal) : object
recognition , color, shape, and pattern.recognition , color, shape, and pattern.
 Continuation of the parvocellular pathway.Continuation of the parvocellular pathway.
 V1V1 V2V2V4V4 inferotemporal cortexinferotemporal cortex
angular gyrusangular gyrus limbic structures.limbic structures.
 Alexeia, anomia, agnosia, amenesia.Alexeia, anomia, agnosia, amenesia.

53. ““Where” PathwayWhere” Pathway
 Dorsal stream (occipitoparietal): SpatialDorsal stream (occipitoparietal): Spatial
orientation ,visual guidance of movement.orientation ,visual guidance of movement.
 V1V1 V3V3 V5V5Parietal and superotemporalParietal and superotemporal
cortex.cortex.
 Continuation of magnocellular pathway.Continuation of magnocellular pathway.
 Simultagnosia, optic ataxia, acquired oculomotorSimultagnosia, optic ataxia, acquired oculomotor
apraxia, and hemispatial neglect.apraxia, and hemispatial neglect.

54. Cortical blindnessCortical blindness
 Due to bilateral occipital lobe lesions.Due to bilateral occipital lobe lesions.
 Often misdiagnosed as functional vision loss.Often misdiagnosed as functional vision loss.
 Stroke, severe blood loss, Eclampsia,Stroke, severe blood loss, Eclampsia,
hypertension, angiography, CO poisoning,hypertension, angiography, CO poisoning,
cyclosporine.cyclosporine.

55. DyschromatopsiaDyschromatopsia
 Bilateral occipital lobe lesions in the lingual orBilateral occipital lobe lesions in the lingual or
fusiform gyri of the medial occipital lobe (medialfusiform gyri of the medial occipital lobe (medial
occipito-temporal lobe).occipito-temporal lobe).
 Rarely no field defect.Rarely no field defect.
 Unilateral involvement may causeUnilateral involvement may cause
hemidyschromatopsia.hemidyschromatopsia.

56. 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 corpusLeft occipital lobe and splenium of corpus
callosum.callosum.

57. PalinopsiaPalinopsia
 Persistant or recurrence of visual stimulus afterPersistant or recurrence of visual stimulus after
it has been removed.it has been removed.