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Cranial Nerve II and Visual Pathways.pptx
- 1. CRANIAL NERVES II Mr Mickey Banda Assistant Professor, Anatomy School of Medicine Texila American University - Zambia
- 2. 1. Definition of visual field 2. Normal vision 3. What are the causes of visual field defect? 4. Anatomy of Visual pathways Optic nerve Optic chiasm Retrochiasm 5. Visual Reflex and Visual field deficits. Objectives:
- 3. Vision and Visual Field VISION (Visual Perception): Visual perception is the ability to interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. VISUAL FIELD: The visual field refers to the total area in which objects can be seen in the side (peripheral) vision as you focus your eyes on a central point. A normal visual field is an island of vision measuring 90 degrees temporally to central Fixation, 50 degrees superiorly and nasally, and 60 degrees inferiorly.
- 4. Vision and Visual Field VISUAL ACUITY: Visual acuity (VA) commonly refers to the clarity of vision. Visual acuity is dependent on optical and neural factors, i.e., (i) the sharpness of the retinal focus within the eye, (ii) the health and functioning of the retina, and (iii) the sensitivity of the interpretative faculty of the brain. Visual acuity is expressed as a fraction, such as 20/20. Having 20/20 vision means that your visual acuity at 20 feet away from an object is normal.
- 5. CLASSIFICATION • Sensory cranial nerves: contain only afferent (sensory) fibers • Ⅰ Olfactory nerve • Ⅱ Optic nerve • Ⅷ Vestibulocochlear nerve • Motor cranial nerves: contain only efferent (motor) fibers • Ⅲ Oculomotor nerve • Ⅳ Trochlear nerve • Ⅵ Abducent nerve • Ⅺ Spinal Accessory nerve • Ⅻ Hypoglossal nerve • Mixed nerves: contain both sensory and motor fibers • Ⅴ Trigeminal nerve, • Ⅶ Facial nerve, • Ⅸ Glossopharyngeal nerve • Ⅹ Vagus nerve
- 6. OPTIC NERVE Name : Optic nerve Foramen : Optic canal Fiber Type : Special sensory Function : Retina, Vision Branches : None Embryo : Diencephalon Others : Optic chiasm is in front of pituitary sensory= opticchiasm optictract opticnerve
- 7. • Function: Special sensory (special somatic afferent) that is, the special sense of vision. • Optic nerves (CN II) develop in a completely different manner from the other cranial nerves. The structures involved in receiving and transmitting optical stimuli (the optical fibers and neural retina, together with the pigmented epithelium of the eyeball) develop as evaginations of the diencephalon). • The optic nerves are anterior extensions of the forebrain (diencephalon) OPTIC NERVE
- 9. The nerve passes posteromedially in the orbit, exiting through the optic canal to enter the middle cranial fossa, where it forms the optic chiasm Here, fibers from the nasal (medial) half of each retina decussate in the chiasm and join uncrossed fibers from the temporal (lateral) half of the retina to form the optic tract. The partial crossing of optic nerve fibers in the chiasm is a requirement for binocular vision, allowing depth-of-field perception (three-dimensional vision). OPTIC NERVE
- 10. • The visual field is what is seen by a person who has both eyes wide open and who is looking straight ahead • Most fibers in the optic tracts terminate in the lateral geniculate bodies of the thalamus. From these nuclei, axons are relayed to the visual cortices of the occipital lobes of the brain. OPTIC NERVE
- 11. IN THE OPTIC NERVE JUST BEHIND THE EYEBALL Optic nerve (head) arrangement of fiber exactly same as retina
- 12. IN THE OPTIC NERVE JUST NEAR THE CHIASM Proximal region of optic nerve -macular fibers present centraly -Temporal fibers present temporaly and nasal fibers present nasally
- 13. OPTIC CHIASM Temporal fibers: from retina remains uncrossed and runs backward in lateral part of optic chaisma. Nasal peripheral fibers: ¾ of fibers Cross over to enter medial part of opposite optic tract in following manner lower nasal fibers in optic tract traverse chiasma low and anteriorly Upper nasal fibers in optic tract trasverse chiasma high and posteriorly
- 14. OPTIC CHIASM Macular fibers- Some fibers crossed and runs backward in opposite optic tract. Some fibers uncrossed and runs on same side in optic tract.
- 15. OPTIC TRACT & LGB OPTIC TRACT: Macular fibers – occupy dorso-lateral aspect of the optic tract Upper peripheral fibers – situated medially in the optic tract
- 16. OPTIC RADIATION Upper retinal fibers – upper part of optic radiations Lower retinal fibers – lower part of optic radiations Macular fibers – central part of optic radiations
- 17. Visual Pathways
- 19. Anatomy of Visual Pathways Meyer’s Loop Baum’s Loop
- 20. PUPILLARY REFLEX
- 29. Testing for vision Snellen Chart - Visual acuity Moving finger Test - Visual fields
- 30. Colour vision
- 31. Fundoscopy *Papilloedema *Optic atrophy *Pigmentary retinal degeneration *Vascular disease
- 32. LEARNING OUTCOMES 1. Students must be able to explain the Visual Sensory Pathways. 2. Students must be able to brief the Auditory and Vestibular Special-Sensory Pathways. 3. Students must be able to explain the structural and functional organization of Visual, Auditory and Vestibular pathways and its clinical significance.