visual pathway.pptx

THE PATHOLOGIES OF THE PATHWAY

1. THE VISUAL PATHWAY PRESENTER: DR SADIA ABDIKARIM MODULATOR: DR LUSOBYA Dept. OF ophthalmology MAKERERE University 18 th NOVEMBER 2019

2. OUTLINE Visual Pathway Retina Optic Nerve Chasism Optic Tract Lateral Geniculate Nucleus Optic Radiations Cortex Clinical Applications

3. Optic Nerve 2nd Cranial Nerve, Length: 47 -50 mm. Starts from the optic disc and extends to the optic chiasm where the two nerves meet. Consists of about 1 – 1.2 million axons originating from ganglion cells of the retina and extends posteriorly towards the occipital cortex.

4. Topography of Optic Nerve 4 Portions : Intraocular (1mm) Intraorbital (30mm) Intracanalicular (6-9mm) Intracranial (10-16mm)

5. Intraorbita l Part About 30 mm mm in length Extends up to the Optic Canal. The extra length allows for unimpeded globe rotation as well as axial shifts within the orbit.

6. Intracranial Part About 10 mm in length Lies above cavernous sinus Converges with its fellow to form chiasmag Ensheathed in pia matter Internal Carotid runs below and lateral

7. Arrangement of the Nerve Fibres in the Optic Nerve Arrangement of fibres in on head and distal region Arrangement of fibres in proximal region of on

8. THE OPTIC CHIASMA The optic chiasm makes up part of the anterior inferior floor of the third ventricle. It is surrounded by pia and arachnoid and is richly vascularized. Its essentially aflattened bundle of nerve fibers located anterior to hypothalamus and 3 rd ventricle, The chiasm is approximately 12 mm wide, 8 mm long in the anteroposterior direction, and 4 mm thick. The extramacular fibers from the inferonasal retina cross anteriorly in the chiasm at the "Wilbrand knee" before passing into the optic tract. Extramacular superonasal fibers cross directly to the opposite tract. Extramacular temporal fibers remain uncrossed in the chiasm and optic tract .

9. Continue….. The macular projections are located centrally in the optic nerve and constitute 80%-90% of the total volume of the optic nerve and the chiasma fibers . The temporal macular fibers pursue a direct course through the chiasm as a bandle of uncrossed fibers. Nasal macular fibers cross in the posterior part of the chiasma Approximately 53% of the optic nerve fibers are crossed, and 47% are uncrossed .

10. FIBRES IN THE OPTIC CHIASMA Nasal fibres from optic nerve cross in chiasma and temporal fibres remain uncrossed Inferonasal fibres cross and loop anteriorly in contralateral optic nerve before they head to the optic trach forming Von Willebrands Knee

11. Anatomical Variations in position of Normal Optic Chiasma Central:(79%) lies directly over sella, expanding pituitary tumours involves chaisma first Pre-fixed: (17%) lies more anteriorly over tuberculum sellae , pituitary tumour involves optic tract first. Post-fixed:(4%) lies more posterior over dorsum sellae , pituitary tumour damages ON first

12. Anatomical Relations of the Optic Chiasma ANTERIOR RELATIONS LATERAL AND POSTERIOR

13. SUPERIOR AND INFERIOR RELATIONS Superior: 3 rd ventricle, lamina terminalis and medial roof of olfactory tract. Imp: Chiasma is vulnerable to compression or stretching by tumours in 3 rd ventricle or raised pressure. Inferior: Pituitary gland, cavernous sinus, oculomotor nerve

14. SUPERIOR AND INFERIOR RELATIONS

15. BLOOD SUPPLY OPTIC CHIASMA Superior: Proximal segment of Anterior cerebral arteries Internal carotid and communicating arteries Central branches of distal segment of cerebral arteries Inferior: Internal carotid Anterior communicating arteries

16. Optic Tract Optic tract emerges from the posterolateral angles of optic chiasma a cylindrical bands, passes posterolaterally b/n the mamilary bodies and anterior perforated substances laterally. The tracts become flattened winds up and around the lateral margin o the upper part of cerebral peduncle. Each optic tract contains ipsilateral temporal and contralateral nasal fibers from the optic nerves . Fibers (both crossed and uncrossed) from the upper retinal projections travel medially in the optic tract; lower projections move laterally . The macular fibers adopt a dorsolateral orientation as they course toward the lateral geniculate body.

17. Optic tract- Arrangement of fibres Macular- dorsolateral Upper peripheral- medially Lower peripheral- Laterally

18. Anatomic Relations Inferior - PCA,AChA Superiorly - Basal Ganglia- Globus pallidus Media l- Internal capsule to form cerebral peduncel Ant- Ant perforating substance Post - Lateral perforating substance, tuber cinereum

19. Termination of the Optic Tract Lateral geniculate body Superior colliculus Pretectal area Suprachiasmatic nucleus of the hypothalamus

20. Optic tract Arterial supply Pial plexus-ant choroidal and posterior cerebral and posteri- Or communicating A. And some branches from middle cerebral arteries. Venous drainage Anterior cerebral and basal vein

21. Lateral Geniculate Body The lateral geniculate body, or nucleus, is the synaptic zone for the higher visual projections. It is an oval, caplike structure that lie undersurface of pulvinar of the thalamus, receives approximately 70% of the optic tract fibers within its 6 alternating layers of gray and white matter . Layers 1, 4, and 6 of the lateral geniculate body contain axons from the contralateral optic nerve. Layers 2, 3,and 5 arise from the ipsilateral optic nerve . The 6 layers, numbered consecutively from below upward, give rise to the optic radiations.

22. Lateral Geniculate Body- Inputs 4 sup layers: .P-cell axons, smaller receptive field for maximal resolution and colour perception 2 inferior layers:M-cell fibers, larger receptive field sensitive to motion

23. LGB- Topographic arrangement Macular : occupy posterior 2/3 Upper retinal: fibres : medial ½ of anterior 1/3 Lower retinal fibres : lateral ½ of anterior 1/3 The topographic arrangement of the ganglion-receptive fields is maintained in the LGN, so that each layer contains a complete map of the retina. As the fibers approach the lateral geniculate, the superior fibers move superomedially and the inferior fibers swing inferolaterally. Overall, the retinal representation rotates almost 90°, with the superior fibers moving medially and the inferior fibers laterally. The macular fibers tendto move superolaterally.

24. LATERAL GENICULATE BODY Arterial Supply Posterior cerebral artery Anterior Choroidal Artery Anastomosis of PCA and ( AChA ) Region of hilum i.e. macular fibres Venous Drainage Basal vein & Middle cerebral vein

25. Optic Radiations The optic radiations connect the lateral geniculate body with the cortex of the occipital lobe. The fibers of the optic radiations leave the lateral geniculate body and wind around the temporal horn of the lateral ventricle, approaching the anterior tip of the temporal lobe, or loop of Meyer . They then sweep backward toward the visual area of the occipital lobe. Damage to the optic radiation in the anterior temporal lobe gives rise to a wedge-shaped, upper homonymous "pie in the sky" visual field defect.

26. Optic radiation -splits into two: Upper tracts(inferior retina)- Tract anteriorly then loop over the lateral ventricle – Meyers/ archambault’s loop Lower tracts(superior retina)- Tract straight through the parietal lobe- Baums Loop

27. OPTIC RADIATION ANTERIOR Anterior Choroidal Artery MIDDLE Middle cerebral artery POSTERIOR Middle cerebral and posterior cerebral arteries VENOUS DRAINAGE Basal vein Middle cerebral vein 29

28. Visual Cortex The visual cortex, the thinnest area of the human cerebral cortex, has 6 cellular layers and occupies the superior and inferior lips of the calcarine fissure on the posterior and medial surfaces of the occipital lobes . Macular function is extremely well represented in the visual cortex and occupies the most posterior position at the tip of the occipital lobe. The most anterior portion of the calcarine fissure is occupied by contralateral nasal retinal fibers only. The posterior cerebral artery, a branch of the basilar artery, supplies the visual cortex almost exclusively. However, the blood supply to the occipital lobe does show anatomical variation; in some individuals, the middle cerebral artery contributes.

29. Visual Cortex Found in the occipital lobe Primary :V1 Along horizontal calcarine fissure Also the striate cortex, broadmann area 17 Secondary : V2-V5 also association areas

30. Primary visual cortex structure 6 cortical layers Optic radiation fibres terminate in 4 th layer 4 th layer has 3 sublayers: 4A , 4B , 4C 4C sublayer subdivided 4C α and 4C β Magnocellular input → 4C α Parvocellular input → 4C β 32

31. Topography Macular Fibres- Terminate posteriorly -80% cortex devoted to macular activity within 30degrees Superior retina : superior portion Most lateral visual field(temporal crescent CL): most anterior portion

32. Secondary Visual Cortex Relates visual information received by primary visual area to past visual experiences hence ability to recognize objects. Integrate two halves of visual fields by means of commissural fibres (corpus calosum splenium )

33. Visual processing pathway Consists of Occipitotemporal :ventral -what Occipitoparietal : dorsal- where

34. Secondary Visual cortex V2 :(AREA 18) receives V1 connections and forwards to V3 V4 V5 V3: AREA 19 receives v2 v1and forwards to pulvinar and mid brain. involved in visual integration

35. V5 Location- Anterior and lateral to area V4) Receives ipsilateral V1 and direct input from m-cells (LGB) Is the origin of pursuit movements Sensitive to movement and direction 37