Anatomy of visual pathway, field defects and its lesions.


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Anatomy of visual pathway, field defects and its lesions.

  2. 2. Visual field  Each eye sees a part of the visual space that defines its visual field.  The visual fields of both eyes overlap extensively to create a binocular visual field. The total visual field is the sum of the right and left hemifields and consists of a binocular zone and two monocular zones.
  3. 3. Visual Pathway  Each eyeball act as camera ;it perceives the images & relay the sensations to the brain(occipital cortex) via the VISUAL PATHWAY.
  4. 4. VISUAL PATHWAY  Vision is produced by photoreceptors in the retina, a layer of cells behind the eye. The information leaves the eye by manner of the optic nerve, and there is partly crossing of axons at the optic chiasm.  Afterward the chiasm, the axons are termed as the optic tract. The optic tract wraps about the midbrain to acquire to the lateral geniculate nucleus (LGN), where all axons should synapse.  From there, the LGN axons fan out via the deep white matter of the brain as the optic radiations, that will ultimately travel to primary visual cortex, at behind the brain.
  5. 5.  VISUAL PATHWAY comprises of: Optic Nerve Optic Chiasma Optic Tract Lateral Geniculate Body Optic Radiations Visual cortex
  6. 6. OPTIC NERVE  2nd cranial nerve.  47-50 mm in length.  Starts from optic disc & extends upto optic chiasma where the two nerves meet.  Backward continuation of nerve fibre layer of retina which consist of axons originating from ganglion cells.  Contains the afferent fibres of light reflex  Has 4 parts : 1)intraocular (1mm) 2)intraorbital (30mm) 3)intra canalicular (6-9mm) 4)intracranial (10mm)
  7. 7. Morphologicaly & Embryologicaly optic nerve is compared to sensory tract of Brain(white matter) :  Optic nerve is an outgrowth of brain.  Not covered by neurilemma so does not regenerate when cut.  Fibres of optic nerve are very thin(2-10 um in diameter)& are million in number.  surrounded by meninges unlike other peripheral nerves.  Both primary & secondary neurons
  8. 8. 1)Intra ocular Part :  About 1mm in size, passes through sclera , choroid & finally appears in eye as optic disc.  Divided in 4 portions from anterior to posterior :a)surface nerve fibre layer. b) prelaminar region. c) lamina cribrosa. d) retrolaminar region.
  9. 9. 2) Intraorbital part :  Extends from back of eyeball to optic foramina.  This part slightly sinuous to give play for the eye movements.  Here optic nerve is surrounded by all 3 layers of meninges & subarachnoid space.  The central retinal artery along with enters the subarachnoid space to enter the nerve on its inferomedial aspect.  Near optic foramina,optic nerve is closely surronded by annulus of zinn & the origin of four recti muscles.  Some fibres of superior & medial rectus are adherent to
  10. 10. 3) Intracanalicular Part  This part is closely related to ophthalmic artery.  it crosses the nerve from medial to lateral side in dural sheath.  Sphenoid & posterior ethmoidal sinuses lie medial to it & seperated by thin bony lamina, this relation accounts for retrobulbar neuritis following infection of sinuses.
  11. 11. 4) Intracranial part  About 10mm  Lies above cavernous sinus & converges with its fellow to form chiasma.  Ensheathed in pia mater.  Internal carotid artery runs below then lateral to it.
  12. 12. OPTIC CHIASMA  Flattened structure,12 mm horizontally & 8mm anteroposteriorly.  Ensheathed by pia & surrounded by CSF.  Lies over diaphragma sellae so visual field defects seen in patient with pituitary tumor having suprasellar extension.  Posteriorly chiasma continous with the optic tracts & form the anterior wall of 3rd ventricle.  Nerve fibres arising from nasal half of two retina decussate at the chiasma.
  13. 13. Anatomical variation in position of normal optic chiasma:  a)central : lies directly over sella, expanding pituitary tumor involves chiasma first. b)pre-fixed : lies more anteriorly over tuberculum sellae,pituitary tumor involves optic tract first. c) post-fixed : lies more posterior over dorsum sellae,pituitary tumor
  14. 14. Relations of chiasma :  Anterior - anterior cerebral arteries & its communicating arteries.  Posterior- tuber cinereum, infundibulum ,pitutary body ,posterior perforated substance.  Superior- third ventricle.  Inferior- hypophysis  Lateral- extra cavernous part of internal carotid artery& anterior perforated substance.
  15. 15. OPTIC TRACTS  Cylindrical bundle of nerve fibres.  Run outwards & backwards from posterolateral aspect of optic chiasma ,between tuber cinereum & anterior perforated substance to unite with cerebral peduncle.  Fibres from temporal half of retina of same eye & nasal half of opposite eye.  Posteriorly each ends in
  16. 16. LATERAL GENICULATE BODY  Oval structures situated at termination of the optic tracts.  Each consist of 6 layers of neurons(grey matter) alternating with white matter (optic fibres)  Fibres of 2nd order neuron coming via optic tract relay here.
  17. 17. OPTIC RADIATIONS (Geniculo- Calcarine Pathway)  From LGB to the occipital cortex.  Pass forwards then laterally through the area of wernicke as optic peduncles.  Anterior to lateral ventricle ,traversing the retrolenticular part of internal capsule,medial to auditory tract.  Its fibres then spread out fanwise to form medullary optic lamina.  Inferior fibres subserve upper visual fields & sweep anteroinferiorly in meyer’s loop & temporal lobe to visual cortex.  Superior fibres subserve inferior visual field proceed posteriorly through parietal lobe to visual cortex.
  18. 18. VISUAL CORTEX  Located on the medial aspect of occipital lobe, in & near calcarine fissure. Visual cortex Visuopsychic area Peristriate area 18 Parastriate area 19 Visuosensory area Striate area 17
  19. 19. Modified nomenclature recognizing five visual areas :
  20. 20. Blood supply of Visual Pathway Arterial Circle of Willis Carotid arterial system Vertebral arterial system
  21. 21. Circle of Willis :
  22. 22. Blood supply of Optic Nerve:  A. Intraocular part • Peripapillary choroidal vessels Prelaminar • Posterior choroidal vessels Lamina cribrosa region • Centrifugal branches from central retinal artery • Centripetal branches from pial vessels Retrolaminar
  23. 23. B . Intraorbital part : • Derived from 6 branches of internal carotid artery: ophthalmic, long & short posterior ciliary artery. • Lacrimal artery. • Central artery of retina. Periaxial system of vessels • Intraneural b/o central retinal artery. • Central collateral b/o central retinal artery. • Central artery of optic nerve. Axial system of vessels
  24. 24. C .Intracanalicular part : periaxial system of vessels. D . Intracranial part : Pial system of vessels B/o internal carotid artery B/o anterior cerebral artery B/o ophthalmic artery Twigs from anterior communicating artery
  25. 25. Venous drainage : Optic nerve head • Central retinal vein Orbital part • Peripheral pial plexus • Central retinal vein Intracranial part • Pial plexus which ends in anterior cerebral & basal vein
  26. 26. Blood supply of Optic Chiasma Arterial : Venous: • B/o anterior cerebral & anterior communicating arterySuperior aspect • B/o internal carotid artery ,posterior communicating artery ,anterior superior hypophyseal artery Inferior aspect • Superior chiasmal vein drains into anterior cerebral veinSuperior aspect • Pre-infundibular vein draining into basilar vein.Inferior aspect
  27. 27. Blood supply of optic tract:  Arterial: Pial plexus receiving contribution from posterior communicating artery, anterior choroidal artery & middle cerebral artery.  Venous drainage: anterior cerebral vein & basal vein.
  28. 28. Blood supply of lateral geniculate body: Posterior cerebral artery • Supply fibres coming from superior homonymous quadrant of retina. Anterior choroidal artery • Supply fibres coming from inferior homonymous quadrant of retina. Macular fibres over region of hilum • Supplied by anastomosis from posterior cerebral & anterior choroidal artery.
  29. 29. Blood supply of Optic radiations • Anterior choroidal arteryAnterior part • Deep optic artery b/o middle cerebral artery. Middle part • Calcarine branches from posterior cerebral artery. Posterior part
  30. 30. Blood supply of visual cortex Visual cortex Calcarine artery b/o Posterior cerebral artery Terminal b/o middle cerebral artery & anastomosis between middle& posterior cerebral artery.
  31. 31.  Venous drainage of visual cortex • Internal cerebral vein drains in great cerebral vein of galen & straight sinus Medial aspect • Inferior cerebral vein drains in cavernous sinus.Superolateral aspect
  33. 33. 1) LESIONS OF OPTIC NERVE : Causes: optic atrophy  indirect optic neuropathy acute optic neuritis traumatic avulsion of optic nerve. Characterised by: complete blindness in affected eye with loss of both direct on ipsilateral & concensual light reflex on contralateral side. Near reflex is preserved. Eg. Right optic nerve involvement
  34. 34. 2)Lesions through proximal part of optic nerve :  ipsilateral blindness.  contralateral hemianopia  abolition of direct light reflex on affected side & concensual light reflex on contralateral side.  near reflex intact.  Eg. Rt optic nerve Involvement in Proximal part
  35. 35. 3)Central lesions of chiasma (sagittal) causes:  suprasellar aneurysm  tumors of pituitary gland  craniopharyngioma  suprasellar meningioma & glioma of 3rd ventricle.  third ventricular dilatation due to obstructive hydrocephalus.  chronic chiasmal arachnoiditis.  Characterised by:  Bitemporal hemianopia  Bitemporal hemianopic paralysis of pupillary reflex. (usually lead to partial descending optic atrophy)
  36. 36. 4)Lateral chiasmal lesions : causes: • Distension of 3rd ventricle causing pressure on each side of optic chiasma • Atheroma of carotids & posterior communicating artery. Characterised by • Binasal hemianopia • Binasal hemianopic parallysis of pupillary reflex (usually lead to partial descending optic atrophy)
  37. 37. 5)Lesions of optic tract : Causes:  Syphilitic meningitis/ gumma.  Tuberculosis  Tumors of optic thalamus  Aneurysm of superior cerebellar or posterior cerebral arteries. Characterised by : • Incongruous homonymous hemianopia with C/L hemianopic pupillary reaction( wernicke’s reaction) • These lesions usually lead to partial descending optic atrophy & may be associated with C/L 3rd nerve paralysis & ipsilateral hemiplegia.
  38. 38. 6)Lesions of lateral geniculate body :  leads to homonymous hemianopia with sparing of pupillary reflexes & may end in partial optic atrophy.
  39. 39. 7)Lesions of optic radiations : Causes:  Vascular occlusion  Primary & secondary tumors  Trauma  Characterised by : TOTAL OPTIC RADIATION INVOLVEMENT COMPLETE HOMONYMOUS HEMIANOPIA( sometimes sparing macula)
  40. 40. LESIONS OF PARIETAL LOBE (involving superior fibres of optic radiations) INFERIOR QUADRANTIC HEMIANOPIA( PIE ON THE FLOOR) LESIONS OF TEMPORAL LOBE (involving inferior fibres of optic radiations) SUPERIOR QUADRANTIC HEMIANOPIA( PIE ON THE ROOF)
  41. 41.  Pupillary reactions are normal as fibres of light reflex leave the optic tracts to synapse in the superior colliculi.  Lesions of optic radiations do not produce optic atrophy as the 1st order neurons (optic nerve fibres) synapse in LGB.
  42. 42. 8)Lesions of visual cortex : pupillary light reflex is normal & optic atrophy does not occur following visual cortex lesions. Congruous homonymous hemianopia(sparing macula) Occlusion of posterior cerebral artery supplyin anterior part of occipiatl cortex Congruous homonymous macular defect Head injury/gun shot injury leading to lesions of tip of occipital cortex+
  43. 43. Thank you…