Visual Pathway Med 6573 Nervous System University of

Visual Pathway Med 6573: Nervous System University of Minnesota Medical School Duluth Donna J. Forbes, Ph. D. 29 February 2008

Pg. 1 References • Nolte Chapter 17 • Netter: Plates 86 and 114 • Related materials from other faculty • Dr. Downing: Histology of the Eye • Dr. Stauffer: Physiology of the Eye • Dr. Trachte: Pharmacology of the Eye • Dr. Hollenhorst: Clinical Ophthalmology • Dr. Meyerson: Neurological Exam • Washington University: The Basic Visual Pathway http: //thalamus. wustl. edu/course/basvis. html 2

Eye Exam Eyes are the window to the brain! Pg. 1 • Visual Acuity: Eye, CN II & beyond in the visual pathway • Visual Fields: Central & Peripheral Vision (retina to cortex) • Ocular Motility: (CN III, IV, VI) • Reflexes • Pupillary Light Reflex (CN II & III) • Accommodation (Near) Reflex • Corneal Reflex (CN V & VII) • Retina including Optic disc: (Increased intracranial pressure; status of blood vessels reflecting hypertension, diabetes, etc. ) • Visual Pathway: Since it is precisely organized & extends from the rostral to caudal aspect of the hemispheres, lesions along the pathway produce specific deficits that can aid in 3 localizing the lesion.

Learning Objectives ü ü ü ü ü Pg. 1 Relationship of bipolar & ganglion cells to the visual pathway Relationship of retinal quadrants to visual field quadrants Understanding of monocular vs. binocular visual fields Importance of “corresponding points” on the retinae & the “Blind spot” Components of the visual pathway; nuclei involved; location of decussations, etc. Representation of the visual field within the structures of the visual pathway. [Upper vs. lower fields; Nasal vs. Temporal fields; Macular vs. Peripheral fields representation] Visual field deficits associated with damage along the visual pathway Components & basis of the: üDirect & consensual pupillary light reflex üPupillary dilation üAccommodation or near reflex Definition or description of terms: amblyopia, Argyll Robertson pupil, diplopia, hemianopsia, heteronymous, homonymous, Horner’s syndrome, Meyer’s loop, quadrantanopsia, retinotopic, scotoma, strabismus

Pg. 2 The Visual Pathway VISUAL FIELD RETINA ON OT OC Pathway extends from the ‘front’ to the ‘back’ of the brain. • Precise retinotopic organization • Deficits due to lesions of the pathway give valuable localizing information. LGN OPTIC RADIATIONS ON = Optic Nerve OC = Optic Chiasm OT = Optic Tract LGN = Lateral Geniculate Nucleus of Thalamus VISUAL CORTEX 5

Beginning of the Pathway Pg. 2 6

Pg. 2 Ganglion cells axons form the optic nerve Bipolar cells Rods and Cones (Receptors) Cells of the Retina 7

Pg. 2 Object to be seen The next slide looks at the retina as if you are looking through the patient’s pupil via your ophthalmoscope. Peripheral Retina Central Retina (fovea in the macula lutea) 8

Pg. 2 Retinal Quadrants Left retina Right retina Vertical Meridian UTQ UNQ LNQ UTQ LNQ LTQ nose Macula with fovea centralis Horizontal Meridian Papilla (optic 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. 9

Pg. 2 Visual Fields & the Visual Pathway VISUAL FIELD RETINA ON OT OC The following slides begin with the visual fields and then follow the pathway from the retina to the visual cortex. LGN OPTIC RADIATIONS ON = Optic Nerve OC = Optic Chiasm OT = Optic Tract LGN = Lateral Geniculate Nucleus of Thalamus VISUAL CORTEX 10

Visual Fields Pg. 3 Monocular Visual Fields Definition: The entire area that • Confrontational method (see Dr. Meyerson’s “Neurological Exam” notes) • Perimetry (Manual or Automated) Monocular Visual Fields: Nasal Field of Left Eye Vertical Horizontal Meridian UTQ UNQ F F Lower Field of Left Eye Mapping of Visual Fields: Upper Field of Left Eye can be “seen” by the patient without movement of the head and with the eyes fixed on a single spot. Temporal Field of Left Eye LTQ LNQ Normal Monocular Visual Field of Left Eye Normal Monocular Visual Field of Right Eye • 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 visual field into upper temporal, upper nasal, lower temporal and lower nasal quadrants. • Imagine that this is your visual field, i. e. all that you can see with your left eye and your right eye (tested separately) when you look straight ahead and do not move your head or eyes. 11

Visual Fields Pg. 3 Blind Spot F F Normal Monocular Visual Field of Left Eye Normal Monocular Visual Field of Right Eye Lower Field of Left Eye • On the horizontal meridian Nasal Field of Left Eye Upper Field of Left Eye • 15° to the temporal side of the visual field of each eye Temporal Field of Left Eye • Corresponds to the location of the optic nerve head 15° to the nasal side of the retina of each 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. 12

Visual Fields: Binocular Temporal Field of Left Eye Pg. 3 Nasal Field of Left Eye F F • Binocular field combines the two monocular visual fields with the foveas (F) aligned with. Normal Monocular Visual one another. (i. e. the ‘pink area’ in the image Field of Left Eye Left Visual Field to the right) Normal Monocular Visual Field of Right Eye Right Visual Field • Left Visual Field seen by both the left & right eyes. • Right Visual Field seen by both the left & right eyes. Monocular Crescent of Left Eye Upper Fields F • Monocular crescent for each eye (blue for left eye & green for right eye) is only seen by the nasal retina of the same eye. Monocular Crescent of Right Eye Lower Fields Normal Binocular Visual Field Understand the difference between the “monocular visual field of the left eye” vs. the “binocular left visual field” and vice versa for the right counterparts. 13

Visual Fields: Binocular Demonstration of the Binocular Visual Field & Monocular Crescent: • Look straight ahead • Close your right eye • Move your finger to the right until it disappears • Open right eye to see the pencil -- in the right temporal monocular crescent of your visual field. Temporal Field of Left Eye Pg. 3 Nasal Field of Left Eye F F Normal Monocular Visual Field of Left Eye Normal Monocular Visual Field of Right Eye Binocular vision is dependent upon the extraocular muscles aligning the eyes so that an image falls on “corresponding points” on the retina of each eye. This is essential for the brain to perceive a single image. Diplopia occurs when the images are not aligned to fall on corresponding points of each retina. Left Visual Field Right Visual Field Upper Fields F Lower Fields Normal Binocular Visual Field 14

Visual Fields Monocular Crescent of Left Eye Binocular Pg. 4 Monocular Crescent of Right Eye Visual Field Retina of Left Eye NOTE: DOTTED OUTLINE = MONOCULAR FIELD OF LEFT EYE Retina of Right Eye SOLID OUTLINE = MONOCULAR FIELD OF RIGHT EYE The image of an object in the visual field is inverted and reversed right to left on the retina. • Temporal field of left eye (red & purple) is seen by the nasal retina of the left eye • Nasal field of the left eye (green & yellow) is seen by the temporal retina of the left eye. • Superior field of the left eye (red & green) is seen by the inferior retina of the left eye. • Inferior field of the left eye (purple & yellow) is seen by the superior retina of the left eye. • Similarly, the image is inverted & reversed for the right eye. Note: To avoid confusion and abide by convention, central representation, visual 15 deficits, etc. will be described in terms of visual fields and not retinal quadrants.

Visual Pathway Left visual field Pgs. 4 - 5 Right visual field VISUAL FIELDS: Upper field • Optic Nerve (ON) Hatched = binocular Stippled = monocular Lower field • = Axons of ganglion cells in the retina of the corresponding eye Central area = macula • Outgrowth of diencephalon, so is a CNS tract & not a ‘true’ cranial nerve. • Myelinated by oligodendrocytes. Right retina Left retina • Optic Chiasm (OC) • Located just anterior to pituitary Temporal Nasal • Partial crossing of optic nerve axons in the OC is essential to binocular vision • Axons from temporal fields cross Nasal Temporal Ciliary ganglion Right LGN Left LGN UVF lateral LVF medial • “Wilbrand’s knee” may be artifact Note: Reference point = Visual Fields Right temporal retina III OC • Axons from nasal fields do not cross Retinotopic representation • Central (macular) vision • Peripheral vision Nasal ON retina Left temporal retina OT LVF midbrain UVF medial III lateral E. W. pretectal nuclei cuneus lingual gyrus 16 Left visual cortex Right visual cortex Calcarine sulcus

Visual Pathway Left visual field Post-Chiasmatic portion of the pathway: From optic tract to visual cortex, each side of the brain deals with the contralateral visual field. Pgs. 4 - 5 Right visual field VISUAL FIELDS: Upper field Hatched = binocular Stippled = monocular Lower field Central area = macula • Optic Tract (OT) • Optic nerve fibers from the optic chiasm continue as the optic tract & terminate in the lateral geniculate nucleus of thalamus. Right retina Left retina • Each tract contains axons that carry input from the contralateral visual field. • Left OT receives from R. visual field Temporal Nasal • Right OT receives from the L. visual field Right temporal retina III OC Nasal Temporal Ciliary ganglion Right LGN Left LGN • Lateral Geniculate Nucleus (LGN) • Primary termination of OT fibers Nasal ON retina Left temporal retina UVF lateral LVF medial OT LVF midbrain UVF medial III lateral E. W. • Each LGN receives input from the contralateral visual field. pretectal nuclei • OT Projections to pretectum for reflexes Retinotopic representation • Central (macular) vision • Peripheral vision Note: Reference point = Visual Fields cuneus lingual gyrus 17 Left visual cortex Right visual cortex

Visual Pathway Left visual field Post-Chiasmatic portion of the pathway: From optic tract to visual cortex, each side of the brain deals with the contralateral visual field. Pgs. 4 - 5 Right visual field VISUAL FIELDS: Upper field Hatched = binocular Stippled = monocular Lower field Central area = macula • Geniculocalcarine Tract (= optic radiations) • Axons of LGN neurons travel to primary visual cortex (Area 17) via the geniculocalcarine tract located in the retrolenticular and sublenticular portions of the internal capsule. Right retina Left retina Temporal Nasal • Axons from upper visual fields take a looping course into the temporal lobe on the way to visual cortex. (=Meyer’s loop) Nasal Temporal Ciliary ganglion Right LGN Left LGN UVF LVF medial • Macular fibers are in an intermediate location in the optic radiation. Note: Reference point = Visual Fields Right temporal retina III OC • Axons from lower visual fields take a more lateral direct route to visual cortex. Retinotopic representation • Central (macular) vision • Peripheral vision Nasal ON retina Left temporal retina OT LVF midbrain UVF medial III E. W. pretectal nuclei lateral Meyer’s loop Optic radiation or geniculocalcarine tract cuneus lingual gyrus 18 Left visual cortex Right visual cortex Calcarine sulcus

Visual Pathway Left visual field • Primary Visual Cortex (Area 17) Pgs. 4 - 5 Right visual field VISUAL FIELDS: Upper field • Located on either side of & within the calcarine fissure. Hatched = binocular Stippled = monocular Lower field Central area = macula • Upper fields project to the lingual gyrus. • Lower fields project to the cuneus. • Macular representation is most caudal in Area 17. • Peripheral field representation is in the rostral 2/3 rds of Area 17. • Lesions of Area 17 result in blindness in the contralateral visual field. Temporal Nasal • Association Visual Cortex (Areas 18 & 19) Right retina Left retina Nasal Temporal Ciliary ganglion Right LGN Left LGN UVF lateral LVF medial • Deals with complex aspects of vision OT LVF midbrain UVF medial III E. W. pretectal nuclei • Lesions of result in visual agnosia. Note: Reference point = Visual Fields Right temporal retina III OC • Input from Area 17 & elsewhere Retinotopic representation • Central (macular) vision • Peripheral vision Nasal ON retina Left temporal retina lateral Meyer’s loop Optic radiation or geniculocalcarine tract cuneus lingual gyrus 19 Left visual cortex Right visual cortex Calcarine sulcus

Pg. 6 Lesions of the Visual Pathway Left 1. Normal visual fields Right Fields, not retinal quadrants 2. Blindness of the right eye Definitions üStrabismus üDiplopia 3. Blindness of right eye + contralateral left upper quadrantanopia üAmblyopia üScotoma üQuadrantanopsia - # 3, 6 4. Bitemporal heteronymous hemianopsia üHemianopsia - # 4, 5, 7 5. Left homonymous hemianopsia Aka “field cuts” üHeteronymous Defects - # 3, 4 üHomonymous Defects - # 5, 6, 7 6. Left upper homonymous quadrantanopsia üCongruous Defects - # 5, 6, 7 üIncongruous Defects - # 3 7. Left homonymous hemianopsia with macular sparing Masked area = area of visual loss üAltitudinal Defects - # 6 20

Pg. 6 Lesions of the Visual Pathway Left 1. Normal visual fields Right 2. Blindness of the right eye 3. Blindness of right eye + contralateral left upper quadrantanopia 4. Bitemporal heteronymous hemianopsia 5. Left homonymous hemianopsia 6. Left upper homonymous quadrantanopsia 7. Left homonymous hemianopsia with macular sparing 21

Pg. 7 Pupillary Constriction Right Direct Reflex Afferent limb = Optic Nerve (SSA) (Miosis) Left Consensual Reflex AKA Pupillary Light Reflex Efferent limb = Oculomotor Nerve (GVE) Postganglionic Preganglionic Nolte 17 -38 22

Reflex abolished if afferent or efferent is damaged. Pg. 7 Right Left B Afferent defect C Right Left Efferent defect 23 17 -38 Nolte

Pupillary Dilation Pg. 7 -8 (Mydriasis) Decreased light to pupil Severe pain Strong emotional stimulus ? Cortex, Thalamus & Hippocampus Hypothalamus (CNS control center for AN S) ? Reticular Formation Reticulospinal fibers Dilation of pupil (post-ganglionic sympathetic) Superior Cervical Ganglion (pre-ganglionic sympathetic) Preganglionic Sympathetic Neurons in Thoracic Cord (T 1 T 2) Horner’s Syndrome • Pupillary Constriction • Ptosis • Flushed & Dry Skin • Loss of Sympathetics • Lesion can be in CNS or PNS • Deficits ipsilateral to lesion 24

Pg. 8 Accommodation (or “Near”) Reflex 1. Initiated by shift in gaze from far to near. Ocular convergence 2. Three components: Pupillary constriction Lens thickening 3. Efferent limb: GSE & GVE of Oculomotor 4. Afferent limb & Central Connections: Optic nerve Optic tract Lateral Geniculate Nucleus Optic Radiation Primary Visual Cortex Association Visual Cortex Optic Radiation Br. of Superior Colliculus Oculomotor Nuclei Oculomotor Nerve Argyll Robertson pupil: Pupillary constriction occurs as part of the accommodation reflex, but not in response to light. 25

See Visual Pathway Practice Quiz 26

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