Visual pathway and lesion

Visual pathway and lesion by Dr Vikas Khatri

1. VISUAL PATHWAY AND LESIONS DR. VIKAS KHATRI DNB Resident Sadguru Netra Chikitsalaya

2. First order neuron - Bipolar cell in the inner nuclear layer of retina Second Order Neuron - Retinal Ganglion Cells Axons of which pass through the Inner nuclear layer and forms the OPTIC NERVE; anterior half of each optic nerve lies within the orbit Nasal Fibres decussate and form the OPTIC CHIASMA - suspended in the basal cistern 5 to 10 mm above the hypophysis and forms part of the floor of the third ventricle Posterior half lies within the optic canal of the sphenoid bone and within the cranial cavity

3. OPTIC TRACTS - encircle the cerebral peduncles and are laterally covered by the foreparts of the temporal lobes Third order neurons – LGB gray masses of cell bodies situated at the posterior lateral margin of the peduncles. OPTIC RADIATIONS or the geniculo-calcarine pathway –lie in the external sagittal stratum close to the outer walls of the lateral ventricles Visual cortex - medial aspect of the occipital lobe near the calcaerine fissure

4. OPTIC NERVE 2nd cranial nerve. Length - 47-50mm. 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) 30mm 6-9mm 1 0mm 1mm

5. INTRAOCULAR PART : About 1mm in size, passes through sclera ,choroid & finally appears in eye as Optic Disc. Divided in 4 portions from anterior to posterior : Surface nerve fibre layer Prelaminar region Lamina cribrosa Retrolaminar region Retina Choroid Sclera

6. INTRAORBITAL PART: Extends from back of eyeball to optic foramina. Sinuous Path to give play for the eye movements . Covered 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. Some fibres of superior & medial rectus are adherent to sheath- Painful Ocular Movement ( Retrobulbar Neuritis) Near optic foramina,optic nerve is closely surronded by annulus of zinn & the origin of four recti muscles .

7. INTRACANALICULAR PART: Closely related to ophthalmic artery. Ophthalmic Artery crosses the nerve from medial to lateral side in dural sheath . Posterior ethmoidal and Sphenoid sinuses lie medial separated by thin bony lamina, Infection of sinuses → Retrobulbar neuritis

8. INTRACANALICULAR PART: Closely related to ophthalmic artery. Ophthalmic Artery crosses the nerve from medial to lateral side in dural sheath . Posterior ethmoidal and Sphenoid sinuses lie medial separated by thin bony lamina, Infection of sinuses → Retrobulbar neuritis

9. 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. Intracranial Part Optic Nerve

10. Arrangement of nerve fibres in the Optic Nerve Head and Distal Region : Upper and Lower nasal fibres – Nasal side Upper and L ower Temporal fibres – Temporal side ; separated by the Macular fibres Macular fibers - occupy temporal sector of the optic nerve at first; dip into the nerve-lie centrally throughout its posterior portion

11. Upper and Lower temporal fibres – Temporal side Upper and Lower nasal fibres – Nasal side Macular fibres – Centrally Arrangement of nerve fibres in the Optic Nerve Proximal Region (Near Chiasma) :

12. Lesions of Optic Nerve : Ipsilateral loss of vision and direct light reflex Loss of consensual light reflex on the opposite side Causes : Hereditay optic nerve disorders Acquired optic nerve Disorders Optic atrophy Optic neuritis Traumatic avulsion of optic nerve Papiloedema Ischaemic Optic neuropathies Chorioretinal disorders

13. Flattened structure , 12mm 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 continuous with the optic tracts & form the anterior wall of 3rd ventricle. Nerve fibres arising from nasal half of two retina decussate at the chiasma OPTIC CHIASMA 12mm 8mm

14. Flattened structure , 12mm 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 continuous with the optic tracts & form the anterior wall of 3rd ventricle. Nerve fibres arising from nasal half of two retina decussate at the chiasma OPTIC CHIASMA Cavernous Sinus Piamater Diaphragma Sellae Pituitary Gland

15. Anatomical variation in Position of optic chiasma: Central Chiasma(80%) : lies directly over sella , expanding pituitary tumour involves chiasma first . Prefixed Chiasma(10%) : lies more anteriorly over Tuberculum sellae , pituitary tumour involves optic tract first. Postfixed Chiasma(10%) : lies more posterior over dorsum sellae , pituitary tumor damage optic nerve first.

16. Relations of chiasma : Anterior Comunicating Artery Anterior Cerebral Artery Post. Perforated Substance Pituitary Body Infundibulum Tuber Cinereum Anteriorly Posteriorly

17. Laterally Third Ventricle Hypophysis Ant. Perforated Substance Internal Carotid Artery ( Extracavernous Part) Superiorly Inferiorly

18. Arrangement of nerve fibres in the Optic Chiasma : Nasal Fibres – Cross to enter the opposite side of optic tracts Macular fibres which occupy central part of nerve remain central in the Ant part of chiasma . Nasal macular fibres decussate and send a bundle obliquely and upwards  lesions here will cause central temporal hemianopic scotoma . Temporal fibres – Remain in the lateral part of chiasma Behind the chiasm, all the nerve fibers concerned with one half of the visual field lie within the opposite half of the visual pathway

19. Lesions of Optic Chiasma : Bitemporal hemianopia that may be peripheral, central, or a combination of both with or without splitting of the macula Causes - Suprasellar aneurysm Tumours of pituitary Craniopharyngioma Suprasellar meningioma Glioma of third ventricle Body of the Optic Chiasma :

20. Binasal Hemianopia Partial descending optic atrophy Causes – Distension of third ventricle Atheroma of the carotids or posterior communicating arteries Lateral Chiasmal Lesion:

21. Lower nasal fibres transverse the chiasma low and anteriorly First fibres to be affected in pituitary tumours – Upper Temporal Quadrantic Field Defects Upper nasal fibres transverse the chiasma high and posteriorly lesions coming from up affect them first e.g. craniopharyngiomas Some fibres make a loop in the ipsilateral optic tract before crossing Lesions of Proximal most part of optic nerve ; Above fibres form convex loops in terminal part of the opposite optic nerve - produce ips-ilateral blindness and contra-lateral field defects)

22. JUNCTIONAL FIELD DEFECTS: 1. Complete Monocular Plus Incomplete Contralateral Ocular One Optic Nerve at Junction of Optic Chiasm Involvement of lower nasal fibre of Contralateral optic nerve at Chiasma

23. 2. Homonymous Hemianopia Plus Junction of Optic Tract and Optic Chiasm Superior Temporal visual field is spared because the inferonasal fibers serving this field decussate anteriorly within the optic chiasm

24. 3. Bitemporal Hemianopia Plus Temporal field defects (Both Eyes) + Nasal field defect (one or both eyes) Causes – Post Fixed Chiasma Asymmetrical Progression of Pituitary tumour Aneurysms of the anterior communicating artery

25. 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 Lateral Geniculate Body. OPTIC TRACTS Optic Tract

26. Arrangement of nerve fibres in the Optic Tracts : Macular fibres – dorsolateral Upper peripheral fibres - medially Lower peripheral fibres - laterally Incongruous homonymous hemianopia with contralateral hemianopic pupil ( wernicke’s pupil ) Causes Syphilitic meningitis or gumma Tuberculosis Tumours of thalamus Posterior cerebral artery pathologies Lesions of Optic Tract : Upper Retinal Fibres Macular Fibres Lower Retinal Fibres

27. 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. LATERAL GENICULATE BODY Lateral Geniculate Body

28. Arrangement of nerve fibres in Lateral Geniculate Body : Upper Retinal Fibres Macular Fibres Lower Retinal Fibres Macular fiibres - posterior 2/3 Upper retinal fibres – medial half of anterior one third Lower retinal fibres – lateral half of ant one third Homonymous hemianopia Rarely the site of an isolated field defect Lesions in Lateral Geniculate Body:

29. 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. OPTIC RADIATION ( Geniculo-Calcarine Pathway) Optic Radiation

30. Arrangement of nerve fibres in Lateral Geniculate Body : Upper retinal fibres – Upper most part Lower retinal fibres – Lower part Macular fibres – Central part

31. Lesions in the Optic Radiation: Lesions in temporal lobe Superior homonymous quadrantanopia . Pie in the sky defect Temporal lobe lesions are accompanied by other neurologic deficits – A graphia A lexia H emiplegia Supranuclear type of facial weakness

32. Lesions in the parietal lobe Superior homonymous quadrantanopia . Pie on the floor defect Common causes for optic radiations injury Vacular occlusion Tumours Trauma All the lesions can extend further into a complete homonymous hemianopia

33. VISUAL CORTEX Located in the medial aspect of occipital lobe in and near calcarine fissure Newer Nomenclature First Visual Area (V1) → in area 17 Second visual area (V2) → occupying greater area of area 18 Third visual area (V3) → narrow strip over anterior part area 18 Fourth visual area(V4) → within area 19 Fifth visual area(V5) → posterior part of superior temporal gyrus

34. Visual Cortex(Cortical Retina) – True copy of retinal image Right visual cortex → impulses from the Temporal half of the Right Retina and Nasal half of the Left Retina Left visual cortex → impulses from the Temporal half of the Left retina and Nasal half of the Right retina Macular fibres → large posterior area of visual cortex Fibres from the anterior retina end in the anterior to macular fibres Arrangement of nerve fibres in Visual Cortex:

35. Lesions in the Visual Cortex: Posterior Cerebral Artery Block Macular Sparing Congruous homonymous hemianopia Supplied by 2 Artery : Anterior Part of Visual Cortex : Posterior Cerebral Artery Tip of Visual Cortex : Middle Cerebral Artery

36. Middle Cerebral Artery Block Macular Congruous homonymous hemianopia Lesions in the Visual Cortex: Supplied by 2 Artery : Anterior Part of Visual Cortex : Posterior Cerebral Artery Tip of Visual Cortex : Middle Cerebral Artery

37. Thank You