Visual Pathway - Ophthalmology - Eye

This presentation discusses in short about the visual pathway along with clinical scenarios.

1. Visual Pathway Venkatesh Karthikeyan II MBBS Velammal Medical College

2. Interpret! 30 year old patient Mr.Siddarth , a known case of Syphilis, presented to Department of Ophthalmology, VMCH with complaints of partial loss of vision. What type of visual field defect you suspect ? Why?

3. Interpret! 40 year old patient Mr.Aathreya , a known diabetic and hypertensive, presented to Department of Ophthalmology, VMCH with complaints of partial loss of vision in his left eye. He is a cigarette smoker for past 20 years.

4. What is Visual Pathway? Visual pathway or optic pathway is the nervous pathway that transmits impulses from retina to visual centre in cerebral cortex.

5. VISUAL RECEPTORS Rods and cones They synapse with dendrites of bipolar cells of inner nuclear layer of the retina.

6. FIRST ORDER NEURONS First order neurons (primary neurons) are bipolar cells in the retina. Axons from the bipolar cells synapse with dendrites of ganglionic cells.

7. SECOND ORDER NEURONS They are the ganglionic cells in ganglionic cell layer of retina. Axons of the ganglionic cells form optic nerve. Optic nerve leaves the eye and terminates in lateral geniculate body.

8. THIRD ORDER NEURONS They are in the lateral geniculate body. Fibres arising from LGB, reaches the visual cortex.

9. OPTIC NERVE Formed by the axons of ganglionic cells It leaves the eye through optic disc. The fibers from temporal part of retina are in lateral part of the nerve and carry the impulses from nasal half of visual field of same eye and vice versa.

10. „ OPTIC CHIASMA Medial fibers of each optic nerve cross the midline and join the uncrossed lateral fibers of opposite side, to form the optic tract.

11. Optic Tract Formed by uncrossed fibers of optic nerve on the same side and crossed fibers of optic nerve from the opposite side. The fibers turn around the peduncle to reach the lateral geniculate body in thalamus.

12. Here, many fibers synapse while few fibers just pass through this and run towards superior colliculus in midbrain. Fibers from fovea do not enter superior colliculus .

13. LATERAL GENICULATE BODY Majority of the fibers of optic tract terminate in lateral geniculate body, which forms the subcortical center for visual sensation. From here, the geniculocalcarine tract or optic radiation arises.

14. Other relay centres Superior colliculus : Concerned with reflex movements of eyeballs and head, in response to optic stimulus Pretectal nucleus : Concerned with light reflexes Supraoptic nucleus of hypothalamus : It is concerned with the retinal control of pituitary in animals. But in human, it does not play any important role.

15. Optic Radiation Fibers from lateral geniculate body pass through internal capsule and form optic radiation. The fibers between lateral geniculate body and visual cortex are also called geniculocalcarine fibers . Optic radiation ends in visual cortex

16. Visual Cortex Primary visual area (17) - Perception of visual impulses Secondary visual area (18) - Interpretation of visual impulses Occipital eye field (19) - Movement of eyes.

17. Visual Pathway lesions Hemianopia : Blindness over half the field of vision. Homonymous : Visual field loss on the same side of both eyes.

18. Causes of Optic Nerve Lesion Optic atrophy Traumatic avulsion of the optic nerve Indirect optic neuropathy Acute optic neuritis

19. Lesions of Chiasma Suprasellar aneurysms Tumours of pituitary gland Third ventricular dilatation due to obstructive hydrocephalus Atheroma of the carotids or posterior communicating arteries

20. Optic tract lesions Syphilitic meningitis Tuberculosis and tumours of optic thalamus Aneurysms of superior cerebellar or posterior cerebral arteries.

21. Lesion in Optic Radiation Vascular occlusions Primary and secondary tumours Trauma

22. Homonymous Hemianopia

23. Upper Homonymous Quadrantanopia

24. Lower Homonymous Quadrantanopia

25. Interpret! 30 year old patient Mr.Siddarth , a known case of Syphilis, presented to Department of Ophthalmology, VMCH with complaints of partial loss of vision. What type of visual field defect you suspect ? Why? Homonymous hemianopia due to Optic tract lesion

26. Interpret! 40 year old patient Mr.Aathreya , a known diabetic and hypertensive, presented to Department of Ophthalmology, VMCH with complaints of partial loss of vision in his left eye. He is a cigarette smoker for past 20 years. Homonymous hemianopia with macular sparing!

27. Thank you 