L28 Visual Pathways

Question 1

define hemianopia

Answer 1

visual loss in 1/2 of the visual field (visual hemifield)

Question 2

define quadrantic anopia

Answer 2

visual loss in 1/4 of the visual field

Question 3

define homonymous anopia

Answer 3

same visual field defect for both eyes

left visual field (temporal) is affected in L eye
left visual field (nasal) is affected in R eye

Question 4

define heteronymous anopia

Answer 4

different visual field defect for both eyes

example - visual loss affecting the temporal visual field in either eye (bitemporal hemianopia) –
left visual field (temporal) in L eye
right visual field (temporal) in R eye

Question 5

what is the visual field

Answer 5

the total space seen when the eye is fixed looking straight ahead towards the center of the visual field (point of fixation)

Question 6

what is another name for left and right hemifields? what is their span?

Answer 6

nasal and temporal fields

60-90 degrees (nasal to temporal)

Question 7

the superior half of the visual field is reflected onto the _____ half of the retinal field

Answer 7

inferior + vice versa (upside down)

Question 8

the nasal half of the visual field is reflected onto the _____ half of the retinal field

Answer 8

temporal + vice versa (opposite)

Question 9

in summary, how do the visual fields reflect on the retinal field?

Answer 9

upside down

and opposite

Question 10

what is the projection pathway of retinal ganglion cells?

Answer 10

retinal ganglion cells –> optic disk –> optic nerve –> optic chiasm –> LGN (thalamus) –> primary visual cortex V1

Question 11

where is the macula located in the visual field diagram?

Answer 11

in the center

Question 12

images from the superior visual field will travel via the _______ to the ____ portion of V1

Answer 12

temporal radiation

inferior

Question 13

images from the inferior visual field will travel via ____ to the ____ portion of V1

Answer 13

parietal radiation

superior

Question 14

images from the LEFT visual field will relay to the ___ LGN and then to the ____ portion of V1

Answer 14

right

right

Question 15

images from the RIGHT visual field will relay to the ____ LGN and then to the ____ portion of V1

Answer 15

left

left

Question 16

what are the 4 places that retinal ganglion cells can terminate?

Answer 16

LGN (thalamus)
suprachiasmatic nucleus (hypothalamus)
pretectal nucleus (midbrain)
superior colliculus (midbrain)

Question 17

what is the role of the LGN

Answer 17

relay station between the retina and the primary visual cortex

Question 18

what is the role of suprachiasmatic nucleus?

Answer 18

trigger circadian clock

Question 19

what is the role of the pretectal nucleus

Answer 19

forming part of the afferent limb of the pupillary light reflex

Question 20

what is the role of the superior colliculus

Answer 20

contribute to eye movements

Question 21

What Brodmann’s area corresponds to the primary visual cortex?

Answer 21

Area 17 (superior and inferior gyrus split by calcarine sulcus)

Question 22

where is a major portion of the primary visual cortex represented

Answer 22

on the medial aspect of the brain

Question 23

where does the primary visual cortex receive most of its blood supply?

Answer 23

calcarine branches of the PCA

*note - small portion around occipital pole may also get blood from MCA (especially after an occlusion of the PCA)

Question 24

retinoptic organization of V1: the left visual fields reflects to the ____ V1

Answer 24

right V1 (vice versa)

Question 25

retinoptic organization of V1: the superior visual fields reflects to the ____ V1

Answer 25

inferior (vice versa)

Question 26

retinoptic organization of V1: the macular/central vision reflects to the _____ V1

Answer 26

superficial

Question 27

retinoptic organization of V1: the peripheral vision reflects to the ____ V1

Answer 27

deeper

Question 28

what types of columns make up the columnar organization of V1

Answer 28

occular dominance columns | orientation columns

Question 29

describe occular dominance columns

Answer 29

there are separate/infividual areas (column) dedicated to the input from each eye there are contralateral columns (C) and ipsilateral columns (I) in both the left and right V1 *visual fields from both the L and R eye can relay to a single side of V1, however that info does not actually reach identical locations

Question 30

describe orientation columns

Answer 30

there are columns of V1 that have a preference to the orientation of the image in the visual field there are various orientation columns which have varying preferences such as vertical and horizontal light as well are the intermediate variations!

Question 31

what layers of the cortex are involved in the organization of columns?

Answer 31

all of them layer 1 near pial surface layer 6 near white matter

Question 32

what are depth, motion, form and color handled

Answer 32

parallel pathways

Question 33

what is the pathway for depth and motion

Answer 33

magnocellular neurons (M-ganglion cells) of the retina --> synapse in 2/6 layers in the LGN --> follow dorsal (parietal pathway) note - similar to inferior visual field

Question 34

what is the pathway for form and color

Answer 34

start in parvocellular neurons (P-ganglion cells) of the retina --> synapse in 4/6 layers in the LGN --> follow ventral (temporal) pathway note - similar to superior visual field

Question 35

what is the confrontational visual field test

Answer 35

each quadrant of the visual field can be tested individually

Question 36

site of lesion: optic n. what is the visual field defect? what is the possible origin?

Answer 36

visual field defect: monocular blindness | what is the possible origin: optic neuritis

Question 37

site of lesion: optic chiasm what is the visual field defect? what is the possible origin?

Answer 37

visual field defect: bitemporal hemianopia | what is the possible origin: pituitary tumor

Question 38

site of lesion: optic tract what is the visual field defect? what is the possible origin?

Answer 38

visual field defect: homonymous hemianopia | what is the possible origin: temporal lobe tumor

Question 39

site of lesion: temporal radiation (Meyer's loop) what is the visual field defect? what is the possible origin?

Answer 39

visual field defect: homonymous superior quadrantic anopia | what is the possible origin: temporal or occipital lobe tumor

Question 40

site of lesion: parietal radiation what is the visual field defect? what is the possible origin?

Answer 40

visual field defect: homonymous inferior quadrantic anopia | what is the possible origin: parietal or occipital lobe tumor

Question 41

site of lesion: visual cortex what is the visual field defect? what is the possible origin?

Answer 41

visual field defect: homonymous hemianopia | what is the possible origin: PCA dysfunction

Question 42

what is color agnosia (achromotopsia)?

Answer 42

inability to distinguish colors due to cortical lesions in areas 18 and 37 = cortical color blindness

Question 43

what are the sensory cortex generalizations

Answer 43

topographical organization - retinotopic map organization in columns - occular dominance and orientiation columns input layer IV - thalamocortical fibers from LGN end here