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Afferent Visual Pathway Amr Hassan, M.D.,FEBN Associate Professor of Neurology Cairo University 2017

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Afferent Visual Pathway Amr Hassan, M.D.,FEBN Associate Professor of Neurology Cairo University 2017 NOTE: To change the image on this slide, select the picture and delete it. Then click the Pictures icon in the placeholde r to insert your own image. Afferent visual pathway Amr Hassan, M.D.,FEBN Associate professor of Neurology Cairo University 2017 Agenda • Anatomy of visual pathway • Visual pathway disorders • Quiz 2 Agenda • Anatomy of visual pathway • Visual pathway disorders • Quiz 3 The Visual Pathway VISUAL FIELD Pathway extends from the „front‟ to the „back‟ of the RETINA brain. ON OC OT LGN OPTIC RADIATIONS ON = Optic Nerve OC = Optic Chiasm OT = Optic Tract LGN = Lateral Geniculate Nucleus of Thalamus VISUAL CORTEX 4 The Visual Pathway Eyes & Retina Light >> lens >> retina (inverted and reversed image). Eyes & Retina Eyes & Retina • Macula: oval region approximately 3-5 mm that surrounds the fovea, also has high visual acuity. • Fovea: central fixation point of each eye// region of the retina with highest visual acuity. Eyes & Retina • Optic disc: region where axons leaving the retina gather to form the Optic nerve. Eyes & Retina • Blind spot located 15° lateral and inferior to central fixation point of each eye. Object to be seen Peripheral Retina Central Retina (fovea in the macula lutea) 11 Photoreceptors © Stephen E. Palmer, 2002 Photoreceptors Cones • Cone-shaped • Less sensitive • Operate in high light • Color vision • Less numerous • Highly represented in the fovea >> have high spatial & temporal resolution >> they detect colors. © Stephen E. Palmer, 2002 Photoreceptors Rods • Rod-shaped • Highly sensitive • Operate at night • Gray-scale vision • More numerous than cons- 20:1, have poor spatial & temporal resolution of visual stimuli, do not detect colors >> vision in low level lighting conditions © Stephen E. Palmer, 2002 Retina up-close Light Ganglion cells axons form the optic nerve Bipolar cells Rods and Cones (Receptors) 16 Photoreceptors Photoreceptors The Visual Pathway VISUAL FIELD Pathway extends from the „front‟ to the „back‟ of the RETINA brain. ON OC OT LGN OPTIC RADIATIONS ON = Optic Nerve OC = Optic Chiasm OT = Optic Tract LGN = Lateral Geniculate Nucleus of Thalamus VISUAL CORTEX 19 Retinal Quadrants Right retina Left retina Vertical Meridian UTQ UNQ UNQ UTQ nose LTQ LNQ LNQ LTQ Horizontal Meridian Macula with Papilla (optic fovea centralis nerve head) Retina as you would see it through the ophthalmoscope & the patient‟s pupil Temporal Hemiretina Nasal Hemiretina UTQ = upper temporal quadrant UNQ = upper nasal quadrant LTQ = lower temporal quadrant LNQ = lower nasal quadrant The blind spot in the Visual Field corresponds to the location of the optic nerve head on the NASAL side of the retina. 20 Monocular Visual Fields Definition: The entire area that can be “seen” by the patient Temporal Field of Nasal Field of without movement of the head Left Eye Left Eye and with the eyes fixed on a single spot. Vertical Horizontal Meridian Meridian UTQ UNQ Mapping of Visual Fields: Eye Left • Confrontational method of Field Upper LTQ LNQ F F Left Eye Left Lower of Field Lower Normal Monocular Visual Normal Monocular Visual • Perimetry (Manual or Field of Left Eye Field of Right Eye Automated) Monocular Visual Fields: • Each eye is tested separately. • The monocular visual field is plotted with the Fovea (F) at the center. • The monocular visual field (colored area -- blue for left; green for right in this example) is not round. • Horizontal and Vertical Meridians correspond to those of the retina and divide the visual21 field into upper temporal, upper nasal, lower temporal and lower nasal quadrants. Monocular Visual Fields Temporal Field of Nasal Field of Blind Spot Left Eye Left Eye • 15° to the temporal side of the visual field of each eye Eye • On the horizontal meridian Leftof Field Upper F F • Corresponds to the location of the optic Eye nerve head 15° to the Lower Leftof Field Lower nasal side of the retina of Normal Monocular Visual Normal Monocular Visual each eye. Field of Left Eye Field of Right Eye Demonstration of the Blind Spot: • Draw the star and box on a piece of paper. • Close your left eye; Look at the star with your right eye; Move paper back and forth until the green box disappears. • Open your left eye and the box can be seen because even though it was falling on the blind spot of the right eye, it is not falling on the blind spot of your left eye. • With both eyes open & binocular vision intact, you don‟t realize that there is a blind spot since the corresponding spot on the contralateral retina will see the object. 22 Temporal Field of Nasal Field of Binocular Visual Left Eye Left Eye Fields F F • Understand the difference between the “monocular visual field of the left eye” vs. the “Left Visual Field” Normal Monocular Visual Normal Monocular Visual Field of Right Eye • and vice versa for the right Field of Left Eye counterparts. Left Visual Field Right Visual Field Upper Fields F Lower Fields Normal Binocular Visual Field 23 Temporal Field of Nasal Field of Binocular Visual Left Eye Left Eye Fields F F • Binocular vision is dependent upon the extraocular muscles aligning the eyes so that an image falls on Normal Monocular Visual Normal Monocular Visual “corresponding points” on the Field of Left Eye Field of Right Eye retina of each eye. Left Visual Field Right Visual Field • This is essential for the brain Upper Fields to perceive a single image. F Lower Fields • Diplopia occurs when the images are not aligned to fall on corresponding points of each retina. Normal Binocular Visual Field 24 The Visual Pathway Monocular Crescent of Monocular Crescent of Binocular Left Eye Right Eye Visual Field Retina of Left Eye Retina of Right Eye 25 Visual Pathway Left visual field Right visual field VISUAL FIELDS: Upper field • Optic Nerve (ON) Hatched = binocular Lower field Stippled = monocular • = Axons of ganglion cells in the retina Central area = macula of the corresponding eye • Outgrowth of diencephalon, so is a CNS tract & not a „true‟ cranial nerve. • Myelinated by oligodendrocytes. Left retina Right retina • Optic Chiasm (OC) Nasal ON • Located just anterior to pituitary Left retina Right Temporal Nasal temporal temporal Nasal Temporal retina retina • Partial crossing of optic nerve axons III OC Ciliary in the OC is essential to binocular ganglion vision Left LGN Right LGN OT LVF LVF UVF • Axons from temporal fields cross UVF lateral medial III medial lateral midbrain • Axons from nasal fields do not E.W. cross pretectal • “Wilbrand‟s knee” may be artifact nuclei Retinotopic representation cuneus • Central (macular) vision • Peripheral vision lingual Calcarin gyrus e sulcus Left visual cortex Right visual 26 cortex Visual Pathway Left visual field Right visual field VISUAL FIELDS: Upper field Post-Chiasmatic portion of the pathway: Hatched = binocular From optic tract to visual cortex, each side of the brain Lower field Stippled = monocular deals with the contralateral visual field. Central area = macula • Optic Tract (OT) • Optic nerve fibers from the optic chiasm continue as the optic tract & terminate in Left retina Right retina the lateral geniculate nucleus of thalamus. • Each tract contains axons that carry input from the contralateral visual field. Nasal ON Left retina Right • Left OT receives from R. visual field TemporaNasal temporal temporal Nasal Tempora l retina retina l III • Right OT receives from the L. visual OC Ciliary field ganglion Left LGN Right LGN OT • Lateral Geniculate Nucleus (LGN) UVF LVF LVF UVF lateral medial III medial lateral • Primary termination of OT fibers midbrain E.W. • Each LGN receives input from the contralateral visual field. pretectal • OT Projections to pretectum for reflexes nuclei Retinotopic representation cuneus • Central (macular) vision • Peripheral vision lingual gyrus Left visual cortex Right visual 27 cortex Visual Pathway Left visual field Right visual field VISUAL FIELDS: Post-Chiasmatic portion of the pathway: Upper field Hatched = binocular From optic tract to visual cortex, each side of the brain Lower field Stippled = monocular deals with the contralateral visual field. Central area = macula • Geniculocalcarine Tract (= optic radiations) • Axons of LGN neurons travel to primary Left retina Right retina visual cortex (Area 17) via the geniculocalcarine tract located in the retrolenticular and sublenticular portions Nasal ON of the internal capsule. Left retina Right TemporaNasal temporal temporal Nasal Tempora l retina retina l III OC Ciliary ganglion Left LGN Right LGN OT UVF LVF LVF UVF lateral medial III medial lateral midbrain E.W. Meyer‟s loop pretectal • Axons from upper visual fields take a nuclei Optic radiation or geniculocalcarine looping course into the temporal lobe on tract the way to visual cortex. (=Meyer‟s loop) cuneus • Axons from lower visual fields take a more direct route to visual cortex. • Macular fibers are in an intermediate lingual Calcarin gyrus e sulcus location in the optic radiation. Left visual cortex Right visual 28 cortex Visual Pathway Left visual field Right visual field VISUAL FIELDS: Upper field • Primary Visual Cortex (Area 17) Hatched = binocular • Located on either side of & within the Lower field Stippled = monocular Central area = macula calcarine fissure. • Upper fields project to the lingual gyrus. • Lower fields project to the cuneus. • Macular representation is most caudal in Left retina Right retina Area 17. • Peripheral field representation is in the Nasal rds ON rostral 2/3 of Area 17. Left retina Right TemporaNasal temporal temporal Nasal Tempora l retina retina l • Lesions
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