Visual System

Question 1

Pathway of visual system

Answer 1

Retina - lateral geniculate nuclei - primary visual cortex (PVC)

Question 2

Images on the retina are

Answer 2

1. Inverted

2. Reversed

Question 3

Normal visual fields

Answer 3

Extends from ~80-90 temporally
~50-60 nasally and superiorly
~60-75 inferiorly

Question 4

Fovea

Answer 4

Central fixation point.
Highest visual acuity
Represented by half of the fibers in the optic nerve and half of the fibers in the visual cortex
Surrounded by the macula
What is represented on the fovea is projected on the occipital pole

Question 5

Optic disk

Answer 5

Axons leaving the retina as they enter the optic nerve
No photoreceptors here. Small blind spot
No functional deficit when both eyes are used - when one one used visual system “fills in” the blind spot

Question 6

Photoreceptors

Answer 6

Outermost layer of retina- respond to light

1. Rods - low level lighting, low resolution, outnumber cones
2. High resolution, highly represented in fovea, detect color

Question 7

Bipolar cells

Answer 7

Middle layer of retina

Receive synapses from photoreceptors

Question 8

Ganglion cell layer

Answer 8

Innermost layer of retina
Receives synapses from bipolar cells
Sends axons into the optic nerve
1. Parasol cells - gross stimulus features and movement
2. Midget cells - fine visual detail and colors

Question 9

Optic chiasm

Answer 9

Partial crossings of the optic nerve fibers where they meet.
Nasal fibers crossover in chiasm and are responsible for temporal hemifields of vision
Visual info from both eyes in contain in optic chiasm

Question 10

Optic tracts

Answer 10

Ends at LGN

Contains visual info from ipsilateral hemiretinas of each eye.

Question 11

Right hemiretinas of both eyes

Answer 11

End up in the right optic tract

Question 12

Left hemiretinas of both eyes

Answer 12

End up in L optic tract

Question 13

Ipsilateral hemiretinas represent

Answer 13

Contralateral visual fields

Question 14

Lateral geniculate nucleus

Answer 14

Axons in optic tracts wrap about the midbrain (laterally) to synapse at the LGN - axons leaving LGN project back to primary visual cortex
Layers 1-2 motion and spatial analysis
3-6 detailed form and color
-info from L and R eyes remain segregated while passing through the LGN - synapse on different layers

Question 15

Extrageniculate pathways

Answer 15

Small number of fibers in the optic tract bypass the LGN to enter the superior colliculus and pretectal areas

Question 16

Pretectal area

Answer 16

Front portion of rectus

Involved in the pupillary light reflex

Question 17

Pretectal area and superior colliculus

Answer 17

Involved in directing visual attention and eye movements toward visual stim

Question 18

Optic radiations

Answer 18

Axons projecting from LGN to PVC - sweep over and around the lateral ventricle
Pass through temporal and parietal lobes
Ipsilateral optic radiations carry info from contralateral visuals fields

Question 19

Inferior optic radiations

Answer 19

Arc slightly forward and into temporal lobe forming Meyers loop.
Carry visual info from inferior retina (superior visual field)
Project to lower bank of calcarine fissue

Question 20

Superior optic radiations

Answer 20

Pass through lower parietal lobe
Carry visual info from superior retina (inf. Visual field)
Project to upper bank of calcarine fissue

Question 21

Primary visual cortex

Answer 21

Upper bank/gurus and lower bank/gyrus of the calcarine tissue in the medial portion of the occipital lobe
Reinotopically organized
Fovea occupies about half of it - very disproportion cortical representation despite the small retinal areas

Question 22

Calcarine fissure

Answer 22

Cuneus - upper
Lingual - lower

PVC peripheral regions of visual fields are represented more atneriorly along the calcarine fissure

Question 23

Analysis of motions and spatial relations

Answer 23

Dorsal/upper pathways project to parietal-occipital association cortex
“Where” analyzing motion and spatial rln b/n objects as well as between the body and visual stim

Question 24

Analysis of form and color

Answer 24

Ventral/lower pathways project to occipitotemporal associated cortex
“What?” Form w/ specific regions IDying colors, faces, letters, and other visual stim

Question 25

Assessment of visual disturbances

Answer 25

1. Nature - time course, positive phenomena, negative phenomena
2. Visual field

Question 26

Positive phenomena

Answer 26

Simple - lights, colors, geometric shapes (arising from disturbances located anywhere from eye to cortex)

Formed - people, animals, or complex scenes (arising from
inferior temporal-occipital visual association cortex)

Question 27

Assessment of visual disturbances 2

Answer 27

• Distinction between a monocular or binocular visual disturbance is essential for localization
• Visual disturbances are often described as being “in one eye”, when in reality the left or right visual field is affected for both eyes
• Blurred vision is hard to interpret without further description and examination
• Could be attributed to a variety of things from a cornea problem to a lesion in the visual cortex

Question 28

Localization of visual field deficits

Answer 28

• Visual Field Testing- Tests for crude deficits in the visual fields
• Test each quadrant while making sure patient’s eyes stay centrally fixated (neuroexam.com-video 27)
• Test each eye using wiggling fingers and/or have pt count the number of fingers being held up
• Fields recorded as if viewing own visual field
• Blink to threat can be used on lethargic/uncooperative patients (neuroexam.com-video 28)

Question 29

The most important information for localization of problems in the visual pathways

Answer 29

What is the position and shape of the visual loss?

Does it affect one or both eyes?

Question 30

Blood supply of the visual pathway

Answer 30

Optic tracts, chiasm and nerves receive blood supply from numerous small branches of ACA and MCA, clinically signficant infants of these are rarely seen

Optic radiations passing through parietal lobe (superior) MCA superior division

Optic radiations passing through temporal lobe (inferior) MCA inferior

PVC by PCA