Visual Pathway Med 6573: Nervous System University of Minnesota Medical School Duluth Donna J....

Visual PathwayVisual Pathway

Med 6573: Nervous System

University of Minnesota Medical School Duluth

Donna J. Forbes, Ph.D.

29 February 2008

2

• 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

Pg. 1

References

http://thalamus.wustl.edu/course/basvis.html

3

• 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.

Pg. 1

Eyes are the window to the brain!Eye Exam

Learning Objectives 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 reflexPupillary dilationAccommodation 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. 1

5

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.

The Visual PathwayPg. 2

OT

ON OC

VISUAL CORTEX

RETINA

VISUAL FIELD

LGNOPTIC

RADIATIONS

ON = Optic Nerve

OC = Optic Chiasm

OT = Optic Tract

LGN = Lateral Geniculate Nucleus of Thalamus

6

Beginning of the PathwayPg. 2

7

Cells of the Retina

Pg. 2

Rods and Cones (Receptors)

Ganglion cells axons form the optic nerve

Bipolar cells

8

Object to be seen

Peripheral Retina

The next slide looks at the retina as if you are looking through

the patient’s pupil via your

ophthalmoscope.

Central Retina (fovea in the macula lutea)

Pg. 2

9

Retinal Quadrants

nose

UTQ UTQ

LTQ LTQLNQLNQ

UNQ UNQ

Right retina Left retina

Papilla (optic nerve head)

Macula with fovea centralis

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

Horizontal Meridian

Vertical Meridian

Pg. 2

The blind spot in the Visual Field corresponds to the location of the optic nerve head on the NASAL side of the retina.

10

Visual Fields & the Visual PathwayPg. 2

OT

ON OC

VISUAL CORTEX

RETINA

VISUAL FIELD

LGNOPTIC

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.

11

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.

Visual Fields Pg. 3

Mapping of Visual Fields:• Confrontational method

(see Dr. Meyerson’s “Neurological Exam” notes)

• Perimetry (Manual or Automated)

Temporal Field of Left Eye

Nasal Field of Left Eye

F

Normal Monocular Visual Field of Right Eye

Normal Monocular Visual Field of Left Eye

F

Monocular Visual Fields

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.

Vertical Meridian

Horizontal Meridian

Upp

er F

ield

of

Left

Eye

Low

er F

ield

of

Left

Eye

UTQ

LTQ

UNQ

LNQ

12

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.

Visual Fields

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.

Pg. 3




F F


Upp

er F

ield

of

Left

Eye

Low

er F

ield

of

Left

Eye

13

Visual Fields: Binocular

Pg. 3

Normal Binocular Visual Field

F

Right Visual FieldLeft Visual Field

Upper Fields

Lower Fields




F F


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.

• 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.

Monocular Crescent of Right Eye

Monocular Crescent of

Left Eye

14

Visual Fields: Binocular

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.

Pg. 3

Normal Binocular Visual Field

F

Right Visual FieldLeft Visual Field

Upper Fields

Lower Fields




F F


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.

15

Visual Fields Pg. 4

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.

Retina of Left Eye

Retina of Right Eye

NOTE:

DOTTED OUTLINE = MONOCULAR FIELD OF LEFT EYE

SOLID OUTLINE = MONOCULAR FIELD OF RIGHT EYE

Binocular

Visual Field

Monocular Crescent of Right Eye

Monocular Crescent of

Left Eye

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.

16

Visual Pathway• 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

Note: Reference point = Visual Fields

Pgs. 4 - 5

Retinotopic representation• Central (macular) vision• Peripheral vision

Left visual field Right visual field

Right retinaLeft retina

Left LGN

Temporal

Nasal Temporal

Nasal

lateral lateralmedial medial

LVFLVF UVFUVF

E.W.

Right visual cortex

midbrain

Right LGN

Left visual cortex

Left temporal

retina

Right temporal

retina

Nasal retina

Ciliary ganglion

pretectal nuclei

cuneus

lingual gyrus

Calcarine sulcus

III

III

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular

Stippled = monocular

Central area = macula

ON

OC

OT

17

• 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

Pgs. 4 - 5





Left LGN

Temporal

Nasal Temporal

Nasal


LVFLVF UVFUVF

E.W.

Right visual cortex

midbrain

Right LGN

Left visual cortex

Left temporal

retina

Right temporal

retina

Nasal retina

Ciliary ganglion

pretectal nuclei

cuneus

lingual gyrus

III

III

Visual PathwayPost-Chiasmatic portion of the pathway:

From optic tract to visual cortex, each side of the brain deals with the contralateral visual field.

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular



ON

OC

OT• Lateral Geniculate Nucleus (LGN)

• Primary termination of OT fibers

• Each LGN receives input from the contralateral visual field.

• OT Projections to pretectum for reflexes

18


• 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.

Pgs. 4 - 5




Left LGN

Temporal

Nasal Temporal

Nasal


LVFLVF UVFUVF

E.W.

Right visual cortex

midbrain

Right LGN

Left visual cortex

Left temporal

retina

Right temporal

retina

Nasal retina

Ciliary ganglion

pretectal nuclei

cuneus

lingual gyrus

Calcarine sulcus

III

III

Meyer’s loop

Optic radiation or geniculocalcarine

tract

Visual PathwayPost-Chiasmatic portion of the pathway: From optic tract to visual cortex, each side of the brain

deals with the contralateral visual field.

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular



ON

OC

OT

19

Visual PathwayPgs. 4 - 5





Left LGN

Temporal

Nasal Temporal

Nasal


LVFLVF UVFUVF

E.W.

Right visual cortex

midbrain

Right LGN

Left visual cortex

Left temporal

retina

Right temporal

retina

Nasal retina

Ciliary ganglion

pretectal nuclei

cuneus

lingual gyrus

Calcarine sulcus

III

III

Meyer’s loop

Optic radiation or geniculocalcarine

tract

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular



ON

OC

OT

• 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.

20

Lesions of the Visual Pathway1. 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

RightLeft

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 - # 6Masked area = area

of visual loss

Pg. 6

Aka “field cuts”

Fields, not retinal

quadrants

21

Lesions of the Visual Pathway1. 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

RightLeft

Pg. 6

22

Right Left

Pupillary Constriction(Miosis)

Nolte 17-38

Afferent limb = Optic Nerve (SSA)

Efferent limb = Oculomotor Nerve (GVE)

Postganglionic

Preganglionic

Direct Reflex

Consensual Reflex

Pg. 7

AKA Pupillary Light Reflex

23

Right Left

B

C

Right Left

Right Left

Nolte 17-38

Reflex abolished if afferent or efferent is damaged.Pg. 7

Afferent defect

Efferent defect

24

Pupillary Dilation(Mydriasis)

Decreased light to pupil

Severe pain

Strong emotional stimulus

Reticular Formation

Reticulospinal fibers

Preganglionic Sympathetic Neurons in Thoracic Cord (T1-

T2)

(pre-ganglionic sympathetic)

Dilation of pupil

Superior Cervical Ganglion

(post-ganglionic sympathetic)

Cortex, Thalamus & Hippocampus

? Hypothalamus (CNS control center

for ANS)

?

Horner’s Syndrome• Pupillary Constriction• Ptosis• Flushed & Dry Skin

• Loss of Sympathetics• Lesion can be in CNS or PNS• Deficits ipsilateral to lesion

Pg. 7-8

25

Accommodation (or “Near”) Reflex1. Initiated by shift in gaze from far to near.

3. Efferent limb: GSE & GVE of Oculomotor

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

Argyll Robertson pupil: Pupillary constriction occurs as part of the accommodation reflex, but not in response to light.

2. Three components:Ocular convergencePupillary constrictionLens thickening

4. Afferent limb & Central Connections:

Pg. 8

26

See Visual Pathway Practice Quiz

27

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Date post:	17-Jan-2016
Category:	Documents
Upload:	janice-perry
View:	215 times
Download:	2 times

Visual Pathway Med 6573: Nervous System University of Minnesota Medical School Duluth Donna J....

Documents