Visual

Question 1

What is the range of the visual field of each eye? Both eyes?

Answer 1

The visual field of each eye extends from 90o laterally to 60o medially, totaling 150o.

All together the visual field covered by two eyes is 180o.

Question 2

Portion of the field of view that can be seen by both eyes together?

Answer 2

The portion of the visual field that can be seen by both eyes together is the binocular segment and covers 120o.

Question 3

Lateral most FOV of eye can be seen by?

Answer 3

The lateral most 30o that can be seen by only the ipsilateral eye is the monocular segment.

Question 4

How is the visual field segmented?

Answer 4

Portions of the visual field are named with reference to the vertical or horizontal meridians (the line dividing right and left or upper and lower halves of the visual field).

We also refer to nasal and temporal segments of the visual field.

Thus, the visual field of each eye is divided into quadrants:
Upper nasal
Upper temporal
Lower nasal
Lower temporal

Question 5

Images on the retina are?

Answer 5

Inverted and reversed

Question 6

Describe how the half of FOV is transmitted to the visual cortex

Answer 6

From each eye the representation of one half of the visual field (bisected by the vertical
meridian) is projected to the contralateral (opposite) hemisphere

Therefore, the representation of the right visual field from both the left and right eyes is
passed on to the left LGN and left cortical hemisphere

Question 7

The fovea of the eye represents? Packed with what type of cells?

Answer 7

The fovea of the eye represents central vision.

When you think foveal or central vision,
think of the center of your eyes’ focus when you read.

Central vision subtends less than
1° of the visual field and is densely packed with cone photoreceptors while containing
no rods

Question 8

What gives us high acuity vision (cell type)? Visual cortex?

Answer 8

Compared to rods, cones provide much greater visual acuity.

A great emphasis is placed on the processing of foveal vision throughout the visual system; this is exemplified by the proportionally greater expanse of cortex devoted to central vision.

This so called cortical magnification is quite prominent in primary visual cortex

Question 9

Describe the cell structure of the retina

Answer 9

Rods and cones are at the back of the retina and respond to the light

They synapse on bipolar
cells which in turn synapse onto retinal ganglion cells.

Amacrine and horizontal cells
are interneurons that provide excitatory and inhibitory synapses across several bipolar
and ganglion cells.

These lateral connections form concentric, center-surround receptive fields

Question 10

Two major retinal ganglion cell types project to?

Answer 10

Lateral geniculate nucleus

Question 11

What causes the blind spot? Where is it?

Answer 11

The optic disc

On the nasal side of each eyeball retina

Question 12

Where is the fovea? Where does it focus?

Answer 12

Temporal side of each eyeball retina

Central fixation point

Question 13

Where is the blind spot for each eye?

Answer 13

Left eye = left FOV

Right eye = right FOV

Question 14

Two types of retinal ganglion cells? Functions?

Answer 14

Large parasol retinal ganglion cells = motion and spatial analysis, project to the magnocellular layers of the LGN

Small midget retinal ganglion cells = important for form and color, project to the parvocellular layers of the LGN

Question 15

Describe the laminar layers of the LGN

Answer 15

Six main layers of LGN

4 parvocellular layers, dorsal, Layers 3-6
2 magnocellular layers, ventral, Layers 1-2

Question 16

Function of magnocellular and parvocellular layers of the LGN?

Answer 16

magnocellular layers of the LGN = motion and spatial analysis

parvocellular layers of the LGN = important for form and color

Question 17

Where do parvo and magno layers of the LGN project to?

Answer 17

The 4C layer of Primary visual cortex (V1) through optic radiations

Question 18

Describe the sublayers of 4C layer of V1

Answer 18

Parvo = 4C-beta
Magno = 4C-alpha

Question 19

Describe path of magno and parvo fibers past V1

Answer 19

Tend to remain segregated in V1

Give rise to dorsal and ventral streams in subsequent visual areas such as V4, MT

Dorsal = parvo
Ventral = Magno

Question 20

Describe the optic radiations

Answer 20

Projections from LGN travel through optic radiations to get to V1

Axons fibers fan out over (lateral to) the temporal horn of the lateral ventricle then back toward primary visual cortex on the occipital pole of neocortex

Question 21

Describe lesion of optic radiation

Answer 21

Ipsilateral and contralateral eye fibers from the different LGN layers are mixed, therefore lesions
usually cause homonymous (both eyes) defects affecting the contralateral visual field

E.g. lesion in right optic tract leads to left FOV loss from both eyes

Question 22

What is Meyer’s loop? Where does it begin? End?

Answer 22

Fibers of the inferior optic radiations arc through the temporal lobe forming Meyer’s loop and terminate in the lower bank of the calcarine sulcus

Question 23

What portion of vision does Meyer’s loop provide?

Answer 23

Meyer’s loop fibers represent the superior (upper) visual field quadrant

Question 24

Describe lesion to Meyer’s loop. What causes and what happens?

Answer 24

Temporal lobe lesions, such as MCA inferior division infarcts, can cause
‘contralateral superior quadrantanopia’

Means that superior quadrant of vision is lost on FOV contralateral to lesion

Question 25

Describe sided-ness of lesions to path of information from retina to V1

Answer 25

Happens before chiasm = monocular and ipsilateral Happens at or after chiasm = homonymous and contralateral

Question 26

Describe the path of the upper optic radiations (beginning and end). What do these fibers represent?

Answer 26

Fibers of the upper (superior) optic radiations beneath the parietal lobe and terminate in the upper bank of the calcarine sulcus These upper optic radiations represent the inferior (lower) visual field quadrant

Question 27

Lesions to the entire optic radiation close to the visual cortex will result in?

Answer 27

Homonymous hemianopia Meaning loss of contralateral FOV from both eyes

Question 28

Damages to the upper and lower banks of the calcarine sulcus in V1 lead to?

Answer 28

Same as upper and lower optic radiation fibers ``` Upper = loss of lower contralateral quadrant Lower = loss of upper contralateral quadrant ```

Question 29

Lesion to superior optic radiation can cause? Caused by?

Answer 29

Lesions involving the parietal lobe, such as MCA superior division infarcts, can cause ‘contralateral inferior quadrantanopia’ Means inferior quadrant of vision is lost on FOV contralateral to lesion

Question 30

Describe the fibers from each eye once in the optic radiations

Answer 30

While fibers from the two eyes are intermingled in the optic radiations, the inputs from the two eyes remain segregated into adjacent columns in the geniculate input layer 4C.

Question 31

Describe the term ocular dominance column

Answer 31

A single neuron in an ocular dominance | column for the right eye responds to visual stimulation of the right eye only.

Question 32

Describe what happens to fibers from each eye once moving past 4C in V1

Answer 32

Beyond layer 4C, in layer 2/3 for example, the inputs from the two eyes mix. That is, a single neuron in layer 2/3 will respond to visual stimulation of either eye.

Question 33

Describe the connection between ocular dominance columns and lazy eye

Answer 33

Failure of one eye to establish cortical territory in the form ocular dominance columns is linked to amblyopia, lazy eye.

Question 34

Describe how monocular visual field loss occurs

Answer 34

(partial or complete) can only result from damage to the visual pathway prior to the optic chiasm At the level of the chiasm and beyond information from the two eyes is mixed (though not in the same neuron until beyond layer 4C of V1).

Question 35

What is amaurosis fugax?

Answer 35

phrase used to describe sudden, transient (~10min) monocular visual loss

Question 36

What causes amaurosis fugax?

Answer 36

It results from transient occlusion of the retinal artery(ophthalmic artery) in one eye caused by emboli. Occlusion of either the superior or inferior branch of the ophthalmic artery results in loss of the inferior or superior visual field, respectively, of the affected eye

Question 37

What is bitemporal hemianopia? Results from?

Answer 37

is loss of the temporal visual field of each eye, resembling ’tunnel vision’. It can only result from damage at the level of the optic chiasm, and is common with pituitary tumors.

Question 38

Retrochiasmal lesions are? What do they cause?

Answer 38

Include lesions of the optic tracts, LGN, optic radiations, or visual cortex ``` Generally cause ‘homonymous’ visual field defects (the same regions of the visual fields for both eyes are affected) ```

Question 39

What is macular sparing?

Answer 39

Macular sparing occurs because of the relatively large representation of the foveal representation throughout the visual pathway. Partial lesions therefore may spare this larger region. Exactly which parts of the visual field are affected and whether one or both eyes are involved tell us where in the visual pathway the lesions have occurred.

Question 40

Describe modes to prevent binocular blindness to a particular vision field.

Answer 40

the segregation of eye inputs can help prevent binocular blindness to a particular visual field. In addition, alternative pathways, for example through the superior colliculus and pulvinar can provide crude visual capabilities, especially related to motion and spatial vision (dorsal stream).

Question 41

Describe the layers of the LGN. Which eye goes to which layer?

Answer 41

Layer 1 is ventral; 6 is dorsal ``` Ipsilateral = 2,3,5 Contralateral = 1,4,6 ```

Question 42

What lobe of brain is important for specific shape recognition?

Answer 42

The ventral temporal cortex

Question 43

Describe the heirarchy from simple to complex shape processing

Answer 43

From LGN (small dots) to V1 (orientation, disparity, and some color) to V4 (color, basic 2D, 3D, curvature) to VTC (complex features and objects)

Question 44

Primary visual cortex is also known as what Broca's area? What about visual association cortex?

Answer 44

Primary = 17 Association = 18

Question 45

V5 is also known as?

Answer 45

MT Higher order visual association cortex

Question 46

Describe magnocellular cells

Answer 46

``` Large cell body •Fat axons •Get input from many photoreceptors •Rapid conduction velocity •Transient Firing ``` Motion information

Question 47

Describe parvocellular cells

Answer 47

* Small cell body * Thin axons * Pool input from fewer neurons * Sustained firing Detail and color

Question 48

Describe visual damage to higher visual areas

Answer 48

Lesions to V2 and higher visual areas result in more functionally specific lesions: the higher the visual area the more general vision is retained and the more specialized the deficit becomes. For example lesions in IT cortex can result in an inability to recognize faces, but one can still see that there is a face.

Question 49

What is visual agnosia?

Answer 49

the inability to recognize particular objects due to lesions of higher order ventral stream areas Example is prosopagnosia