1. 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

2. 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

3. 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.

4. 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

5. 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

6. Beginning of the Pathway
Pg. 2

7. 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)

8. 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)

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. Note: Reference point = Visual Fields
Visual Pathway
Pgs
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

17. Note: Reference point = Visual Fields
Visual Pathway
Pgs
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

18. Note: Reference point = Visual Fields
Visual Pathway
Pgs
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

19. Note: Reference point = Visual Fields
Visual Pathway
Pgs
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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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.

26. See Visual Pathway Practice Quiz