Visual pathways

Visual pathways

1. VISUAL PATHWAY vidya

2. Beginning in the retina, the visual pathway continues through the optic nerves, optic chiasm, and optic tracts to synapse in the lateral geniculate nucleus (LGN). From the LGN, it extends through the temporal and parietal lobes to terminate in the occipital lobes

3. The retina is a thin, multilayered tissue sheet containing three developmentally distinct, interconnected cell groups that form signal processing networks: • Class 1 :: sensory neuroepithelium (SNE) :: photoreceptors and BCs • Class 2 :: multipolar neurons :: GCs, ACs, and axonal cells ( AxCs ) • Class 3 :: gliaform neurons :: horizontal cells (HCs)

4. Enlargement of blind spot

5. Altitudinal field defect Ischaemic optic neuropathy Branch retinal artery occlusion Inferior retinal coloboma

6. OPTIC NERVE 10

7. Development of the Optic Nerve:  Embryonic optic stalk Progressively gets occupied by axons ganglion cells of retina Myelin sheath  oligodendrocytes 11

8. Parts of Optic Nerve:  47-50 mm in length Intraocular (1 mm) Intraorbital (25-30 mm) Intracanalicular (5-9 mm) Intracranial (10-16 mm) 12

9. Intra Ocular Part   13

10. 1a-Internal limiting membrane of retina 1b-Inner limiting membrane of Elschnig 2-Central meniscus of Kuhnt 3- Spur of collagenous tissue separating the anterior lamina cribrosa (6) from the choroid 4-Border tissue of Jacoby 5- Intermediary tissue of Kuhnt 7-Posterior lamina cribrosa 14 Internal limiting membrane of Elschnig Central meniscus of Kuhnt Border tissue of Elschnig Border Tissue Of Jacoby Intermediate Tissue Of Kuhnt

11. INTRA ORBITAL PART:  Anteriorly : Separated from extraocular muscle by orbital fat Posteriorly : Annulus of Zinn Laterally: Ciliary ganglion,Division of 3 rd nerve, Nasociliary nerve, Sympathetic plexus, Abducent nerve Ophthalmic artery Superior ophthalmic vein cross optic nerve from lateral to medial Nasociliary nerve 15

12. INTRA CRANIAL PART:  16 Lies above the cavernous sinus Optic chiasma is formed just above the sellae Covered by Pia only

13. 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 & consensual light reflex on contralateral side. Near reflex is preserved. Eg . Right optic nerve involvement 17

14. 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: 3 rd 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.

15. Chiasm

16. Location of chiasma Central fixation -80%- above the sella Pre fixed chiasm-10%-located anteriorly- so pitutary tumour involves the optic tract first [lower temporal fields first] Post fixed chiasm-10%-located posteriorly- so optic nerve gets involved first [upper temporal fields first]

17. Pitutary adenoma Visual fields ; bitemporal hemianopia,junctional scotoma, bitemporal hemianopic scotoma Colour vision; early red deficit Visual acuity tends to reduce Optic disc- bow tie atrophy rarely papilloedema Extraocular movements: cranial nerve palsies,see saw nystagmus,spasm nutans.

18. Wilbrand’s knee

19. OPTIC TRACT:  * Flattened cylindrical band that travel posteriolaterally from angle of chiasma * Between tuber cinereum and anterior perforated substance upto lateral geniculate body. * Each tract contains uncrossed temporal fibres and crossed nasal fibres . 25

20. OPTIC TRACT: Macular fibers (crossed & uncrossed)  occupy dorsolateral aspect of optic tract Upper peripheral fibers (crossed & uncrossed) medially situated Lower peripheral fibers laterally situated 26

21. OPTIC TRACT LESIONS & ITS FIELD DEFECTS

22. OPTIC TRACT Carries ipsilateral temporal fibres and controlateral nasal fibres and pupillary fibres. So right optic tract lesion will cause left homonymous hemianopia

23. ASSOCIATIONS Controlateral pyramidal signs. Incongruous homonymous hemianopia. Wernicke's hemianopic pupil Optic atrophy

24. Fibers from optic tract: 30 Superior Colliculus Pretectal nucleus Dorsal Lateral geniculate nucleus

25. LATERAL GENICULATE BODY: Elevation produced by lateral geniculate nucleus in which most optic tract fibers end   Axons of ganglion cells of retina synapse with dendrites of LGB cells 3rd order neurons begins 31

26. LATERAL GENICULATE BODY Dorsal nucleus Ventral nucleus (rudimentary) 6 laminae ( alternating grey & white matter) Axons from the ipsilateral eye – 2, 3, 5 Axons from the contralateral eye - 1, 4,6 32

27. Lateral Geniculate Body:  Large magnocellular neurons (M cells) - 1 and 2 layer-Y ganglion cells   perception of movement, gross depth, and small differences in brightness Small parvocellular neurons (P cells)- 3,4,5,6 layer- X ganglion cells Colour perception, texture shape & fine depth Koniocellular cells(K cells or interlaminar cells) Short-wavelength "blue" cones 33

28. LATERAL GENICULATE BODY: 34 Macular fibres - posterior 2/3 of LGB Upper retinal fibres - medial half of anterior 1/3 of LGB Lower retinal fibres - lateral half of anterior 1/3 of LGB

29. OPTIC RADIATION: 36 Inferior retina lower part of optic radiation superior retina upper part of optic radiation

30. OPTIC RADIATIONS: Geniculocalcarine pathway extend from lateral geniculate body  visual cortex MEYERS LOOP(inferior retinal fibers)- pass through temporal lobe looping around inferior horn of lateral ventricle 37

31. OPTIC RADIATION AND ITS FIELD DEFECTS

32. OPTIC RADIATIONS The corresponding retinal elements lie progressively closer, so congruous hemianopia. Passes through the temporal lobe and pareital lobe and ends in the visual cortex.

33. TEMPORAL LOBE Controlateral congruous homonymous superior quadrantanopia[pie in the sky] Controlateral hemisensory disturbance Mild hemiparesis Paraxysomal olfactory and uncinate fits. Formed visual hallucinations Seizures and receptive dysphasia.

34. VISUAL CORTEX(CORTICAL RETINA):   41 Impulse from corresponding 2 points of retina meet Right visual cortex receive impulse left half of visual field Left visual cortex receive impulse from right half visual field MACULA  posteriorly PERIPHERAL RETINA anteriorly UPPER RETINA  above calcarine sulcus LOWER RETINA below the calcarine sulcus

35. Pie in the sky

36. PAREITAL LOBE Controlateral congruous homonymous inferior quadrantanopia[pie on the floor] Visual perception difficulties Right-left confusion Acalculia Assymmetric OKN.[OKN response diminished towards the side of the lesion.]

37. Pie on the floor

38. Visual Cortex:  Striate cortex Extrastriate cortex 45

39. 46 Anterior Knee of Von- wille Brand Posterior Knee of Von- wille Brand

40. LATERAL GENICULATE BODY:   47 CROSSED FIBERS- 1,4,6 UNCROSSED FIBERS- 2,3,5 CORRESPONDING PART OF 2 RETINA END IN NEIGHBOURING PART OF ADJACENT LAMINAE  smallest lesion of retina results in degeneration of 3 laminae of LGB in which the retinal fiber end Optic radiation begins from all 6 laminae  lesion of visual cortex will cause degeneration of all 6 laminae

41. TWO STREAM HYPOTHESIS: Ventral 48 Ventral Pathway( parvocellular )  temporal lobe Dorsal Pathway( magnocellular ) parietal lobe Recognistion & indentification Spatial location Visual agnosia Visual neglect Parvocellular “what” pathway Magnocellular “where” pathway

42. Striate calcarine cortex Congruous homonymous hemianopias with macular sparing, macular involvement alone. Formed visual hallucinations. Anton's syndrome[ denial of blindness] Riddoch phenomenon

43. 52