Anatomy of the visual pathways and visual cortex


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Anatomy of the visual pathways and visual cortex

  1. 1. Anatomy and Physiology of the Visual pathways Raed Behbehani , MD, ABO
  2. 2. Outline
  3. 3. The optic nerve 1.2 Milllion RGC axons. Different types of RGC (parvocellular, magnocellular). Parvocellular : high spatial resolution, color vision, fine stereopsis. Magnocellular : low spatial resolution, motion, gorss stereopsis. Parvocellulae layer 4c-alpha Magnocellular layer 4c beta.
  4. 4. RGC axons
  5. 5. Optic Nerve Lamina cribrosa provides structural support. Lamia cribrosa: Type I,III,V,VI with intersposed elastic fibers. Ophthalmic artery short PCA (segmental) Watershed area (PCA anastomoses are scant). Circle of Zinn-Haller.
  6. 6. ONH Blood Supply
  7. 7. Optic Nerve Cross Section
  8. 8. Intracanalicular Optic Nerve Within the two bases of the LWS. Medial wall of canal forms lateral wall of sphenoid sinus (can be absent !). Within canal : meninges, ophthalmic artery and sympathetic plexus. 10 mm length. Tight space ! Internal carotid artery.
  9. 9. Intra-orbital Optic Nerve Myelination (oligodendrocytes). 20-30 mm Long. Axons: mylein and glial cell (metabolic support at the nodes of Ranvier).
  10. 10. Optic nerve (Intracranial) Leaves the cranial end of the optic canal (medially, backwards, upwards). 4-15 m (depending on the position of chiasm). Upward 45 degree-angle. Anterior cerebral and anterior comunicating artery lie superior.
  11. 11. Physiology of the Optic Nerve Axoplasmic transport : clearance of expired organelles, structural maintainance, and energy requirements. Interruption of axoplasmic transport : ischemia, compression, inflammation. Orthograde axonal transport : away from the cell body LGN. Retrograde axonal transport : toward cell body.
  12. 12. Physiology of the Optic Nerve Orthograde  fast and slow speeds. Proteins, transmitters transported in smooth surface vesicles at 400 mm/day (5 hours to LGB). Elements of cytoskeleton (microtubules, neurofilaments) dependant on actin, kinesin and dynein. Mitochondria moving in both orthograde and retrograde fashion.
  13. 13. Chiasm
  14. 14. Chiasm
  15. 15. Optic chisam Floor of the third ventricle. 5-10 mm above the diphragma sella and the hypophysis cerebri. 12mm wide, 8mm A-P , 4 mm thick. Important relations: 3rd ventricle, hypothalmus, pituitary stalk, sella, dorsum sellam anterior and posterior clinoid processes, cavernous sinus. Nasal fibers cross ; temporal fibers do not (53:47). Wilband’s knee.
  16. 16. Chiasm
  17. 17. Chiasm
  18. 18. Chiasm
  19. 19. Chiasm 90% of chiasmal fibers have macular origin (superior and posterior portions of chiasm). Supraclinoid portions of carotid artery lie lateral to chiasm.
  20. 20. Wilbrand’s knee
  21. 21. Optic tracts Travel around the cerebral peduncles at dorsal midbrain. Divides into lateral root LGN , and a smaller medial root pretectal area (pupillary light reflex).
  22. 22. Lateral Geniculate Bodies Part of the thalamus. Hilum, medial and lateral horn. Six laminae (layers 1-6), crossed fibers1,4,6 , uncrossed fibers 2,3,5. medial lateral
  23. 23. LGN Upper quadrant medial aspect of LGN, Lower quadrant lateral aspect of LGN. Macular fibers central wedge of LGN. Layers 1,2: magnocellular. (motion) Layers 3-6: Parvocellular. (color)
  24. 24. Optic radiations Nerve fibers bundles with cell bodies in the LGN. Loop of Meyers (around temporal and inferior horn of LV). Inferior fascicle. Superior fascicle.
  25. 25. Optic radiations Inferior fascicle anterior pole of temporal lobe lower calcarine cortex. Superior fascicle parietal lobe upper calacrine cortex.
  26. 26. Visual cortex Upper bank and lower bank (Calcarine fissure). LGN input into layer 4 (Stria of Gennari ). Inferior visual filed (upper bank) , Superior visual field (lower bank).
  27. 27. Visual cortex-Maculr projections represented by50%-60% of the area of the calcarinecortex.-Occipital tip is for foveal vision.-Anterior striate cortex (8%-10%) ismonocularly innervated (temporalcrecsent of contralateral eye).
  28. 28. Visual association areas
  29. 29. Visual association areas Ventral stream (occipitotemporal) : “what” pathway i.e. object recognition , continuation of the parvocellular pathway. V4- color perception (lingual,fusiform gyri) Dorsal stream (occipitoparietal): “where” pathway i.e. spatial orientation , continuation of magnocellular pathway. V5-motion perception.
  30. 30. Higher visual functions
  31. 31. Problem 1 72 year old with progressive vision loss over the last 2 years. Visual acuity: 20/20 , 20/40
  32. 32. Problem 1
  33. 33. Problem 2 A 55 year old patient with sudden, pain less vision loss in her left eye. Visual acuity : OD-20/200 OS-20/25 Color vision : OD- Nil OS-8/8
  34. 34. Problem 2
  35. 35. Problem 2
  36. 36. Problem 2
  37. 37. Problem 3