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

References Nolte Chapter 17 Netter: Plates 86 and 114 Pg. 1 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

Eyes are the window to the brain! Eye Exam Pg. 1 Eyes are the window to the brain! 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 localizing the lesion.

Learning Objectives 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: Direct & consensual pupillary light reflex Pupillary dilation Accommodation 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 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. VISUAL FIELD RETINA ON OC OT LGN OPTIC RADIATIONS ON = Optic Nerve OC = Optic Chiasm OT = Optic Tract LGN = Lateral Geniculate Nucleus of Thalamus VISUAL CORTEX

Beginning of the Pathway Pg. 2

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

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)

Pg. 2 Retinal Quadrants Right retina Left retina Horizontal Meridian Vertical Meridian UTQ LTQ LNQ UNQ nose Macula with fovea centralis Papilla (optic nerve head) Retina as you would see it through the ophthalmoscope & the patient’s pupil Temporal Hemiretina UTQ = upper temporal quadrant LTQ = lower temporal quadrant Nasal Hemiretina UNQ = upper nasal 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.

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

Visual Fields Monocular Visual Fields Pg. 3 F Normal Monocular Visual Field of Right Eye Normal Monocular Visual Field of Left Eye Monocular Visual Fields Definition: The entire area that 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 Nasal Field of Left Eye Vertical Meridian Horizontal Meridian Upper Field of Left Eye UTQ LTQ UNQ LNQ Mapping of Visual Fields: Confrontational method (see Dr. Meyerson’s “Neurological Exam” notes) Perimetry (Manual or Automated) Lower Field of Left Eye 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 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.

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

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

Visual Fields: Binocular Temporal Field of Left Eye Nasal Field of Left Eye Pg. 3 Normal Monocular Visual Field of Left Eye F F Normal Monocular Visual Field of Right Eye 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. Normal Binocular Visual Field F Right Visual Field Left Visual Field Upper Fields Lower Fields 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.

Monocular Crescent of Left Eye Monocular Crescent of Right Eye Visual Fields Pg. 4 Retina of Left Eye Retina of Right Eye Monocular Crescent of Left Eye Binocular Visual Field Monocular Crescent of Right Eye NOTE: DOTTED OUTLINE = MONOCULAR FIELD OF LEFT 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. The literature is not consistent in its terms of reference--so be sure that you know whether a given source is referring to visual fields or retinal quadrants. Note: To avoid confusion and abide by convention, central representation, visual deficits, etc. will be described in terms of visual fields and not retinal quadrants.

Note: Reference point = Visual Fields Visual Pathway Pgs. 4 - 5 Left visual field Right visual field VISUAL FIELDS: Hatched = binocular Stippled = monocular Central area = macula Upper field Optic Nerve (ON) = Axons of ganglion cells in the retina of the corresponding eye Outgrowth of diencephalon, so is a CNS tract & not a ‘true’ cranial nerve. Myelinated by oligodendrocytes. Optic Chiasm (OC) Located just anterior to pituitary Partial crossing of optic nerve axons in the OC is essential to binocular vision Axons from temporal fields cross Axons from nasal fields do not cross “Wilbrand’s knee” may be artifact Lower field Left retina Right retina Nasal retina Left temporal retina ON Right temporal retina Temporal Nasal Nasal Temporal Ciliary ganglion III OC Left LGN Right LGN OT UVF LVF LVF UVF lateral medial medial lateral “Wilbrand’s knee” is where nerve fibers from upper temporal fields after crossing in the optic chiasm-- were thought to loop up into the base of contralateral optic nerve -- before they continue on into the optic tract. See the lesions slide (#3 case). There is now some evidence that it does not exist. midbrain E.W. pretectal nuclei Retinotopic representation Central (macular) vision Peripheral vision cuneus Calcarine sulcus lingual gyrus Note: Reference point = Visual Fields Left visual cortex Right visual cortex

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

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

Note: Reference point = Visual Fields Visual Pathway Pgs. 4 - 5 Left visual field Right visual field Primary Visual Cortex (Area 17) Located on either side of & within the calcarine fissure. 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 2/3rds of Area 17. Lesions of Area 17 result in blindness in the contralateral visual field. Association Visual Cortex (Areas 18 & 19) Input from Area 17 & elsewhere Deals with complex aspects of vision Lesions of result in visual agnosia. VISUAL FIELDS: Hatched = binocular Stippled = monocular Central area = macula Upper field Lower field Left retina Right retina Nasal retina Left temporal retina ON Right temporal retina Temporal Nasal Nasal Temporal III OC Ciliary ganglion Left LGN Right LGN OT UVF LVF LVF UVF lateral medial III medial lateral Association visual cortex: --deals with complex aspects of vision such as recognition of subjects and their significance --sends projections to the superior colliculus via the optic radiation & brachium of he superior colliculus; involved in automatic scanning movements and the accomodation-convergence reflex. midbrain E.W. Meyer’s loop pretectal nuclei Optic radiation or geniculocalcarine tract Retinotopic representation Central (macular) vision Peripheral vision cuneus lingual gyrus Calcarine sulcus Note: Reference point = Visual Fields Left visual cortex Right visual cortex

Lesions of the Visual Pathway Pg. 6 1. Normal visual fields 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 Right Left Fields, not retinal quadrants Definitions Strabismus Diplopia Amblyopia Scotoma Quadrantanopsia - # 3, 6 Hemianopsia - # 4, 5, 7 Heteronymous Defects - # 3, 4 Homonymous Defects - # 5, 6, 7 Congruous Defects - # 5, 6, 7 Incongruous Defects - # 3 Altitudinal Defects - # 6 Aka “field cuts” STRABISMUS (squint): Failure of coordination of extraocular eye muscles, resulting in deviation of the affected eye & diplopia. DIPLOPIA: Double vision due to failure of the image to be aligned on corresponding points of the left & right retinae. AMBLYOPIA (lazy eye): Decreased visual acuity in the absence of anatomical defects in the visual pathway. Secondary to strabismus; to avoid diplopia, the vision in one eye is suppressed at the level of the cerebral cortex. Occurs in children with the critical period variously reported as ending by age 3/4 yrs and up to 8 yrs. SCOTOMA: Area or “island” of visual loss within the visual field QUADRANTANOPIA: Defective vision or blindness in approx. one-fourth of the visual field HEMIANOPSIA: Defective vision or blindness in approx,. one-half of the visual field HOMONYMOUS DEFECTS: Visual defects restricted to either the right or the left visual field (post-chiasmatic defects) HETERONYMOUS DEFECTS: Visual defects involving parts of both the left & right visual fields CONGROUS DEFECTS: Visual defects are equivalent in each monocular visual field INCONGROUS DEFECTS: Visual defects are NOT equivalent in each monocular field ALTITUDINAL DEFECTS: Visual defects are in the upper or lower aspect of the visual fields Masked area = area of visual loss

Lesions of the Visual Pathway Pg. 6 Left Right 1. Normal visual fields 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 Example # 3 involves” Wilbrand’s knee”, i.e. the fibers from the contralateral upper fields are damaged along with the optic nerve on the ipsilateral side. As mentioned earlier, this may not exist in humans & other primates. A visual deficit such as the one illustrated could possibly be due to compression of part of the optic chiasm along with the damage of the optic nerve. 7. Left homonymous hemianopsia with macular sparing

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

Reflex abolished if afferent or efferent is damaged. Pg. 7 Right Left Right Left B Afferent defect C Right Left ---In a patient with total blindness in one eye due to an afferent defect, a consensual light reflex can be elicited in the “blind” eye upon stimulation of the “good” eye. (illustrated in this slide) ---Marcus Gunn Pupil = afferent defect due to damage to the Optic Nerve. Tested with the Swinging Flashlight Test. Intact consensual light reflex in ‘good’ eye but paradoxical pupillary dilation to direct light that ‘swings’ from the good eye to the eye with the damaged optic nerve. Not illustrated in this slide. ---Blindness due to a lesion in the optic radiation or visual cortex would NOT result in loss of the pupillary light reflex since this is a SUBCORTICAL pathway. Efferent defect Nolte 17-38

Pupillary Dilation (Mydriasis) Pg. 7-8 Cortex, Thalamus & Hippocampus ? Hypothalamus (CNS control center for ANS) ? Decreased light to pupil Severe pain Strong emotional stimulus Reticular Formation Reticulospinal fibers Dilation of pupil Superior Cervical Ganglion (post-ganglionic sympathetic) Preganglionic Sympathetic Neurons in Thoracic Cord (T1-T2) (pre-ganglionic sympathetic) Horner’s Syndrome Pupillary Constriction Ptosis Flushed & Dry Skin Loss of Sympathetics Lesion can be in CNS or PNS Deficits ipsilateral to lesion

Accommodation (or “Near”) Reflex Pg. 8 1. Initiated by shift in gaze from far to near. Ocular convergence Pupillary constriction Lens thickening 2. Three components: 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  Superior Colliculus  Oculomotor Nuclei  Oculomotor Nerve Components of the response: --Ocular convergence > Medial recti contract to align the image (GSE in III) --Pupillary constriction > smooth muscle constrictors of the pupil contract to sharpen the image (GVE in III) --Lens thickening > Ciliary muscle contracts, increasing the refractive power of the lens for focusing on a near object (GVE in III) Argyll Robertson pupil may be seen in patients with tabes dorsalis/tertiary syphilis, system lupus erythematosus and diabetes mellitus. -Indicates that the pathways for pupillary constriction associated with the light reflex vs. the accommodation reflex are somewhat different. -Some evidence that the lesion associated with an Argyll Robertson pupil may be located in the pretectal area. Argyll Robertson pupil: Pupillary constriction occurs as part of the accommodation reflex, but not in response to light.

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