1 Visual Pathways Flashcards
What is the portion of space we can see while fixating?
visual field
When does visual sensitivity decrease?
with visual field eccentricity
What is a function primarily of the density of the array of retinal ganglion cell’s receptive fields?
visual sensitivity
With homonymous hemianopia–the closer in proximity the defect is to the optic chasm, the more…..?
dissimilar or incongruous the left and right visual field maps will be.
The more toward the occipital lobe the lesion is…..?
the more congruous the visual field defect will be.
T-F—the fibers for the inferior retina and superior field stay superior the entire way?
False–they stay inferior all the way
What are the degrees of views we can see horizontal and nasally? horizontal and temporally? superiorly? and inferiorly?
60%
100%
60%
75%
What is the area of the visual field seen only by one eye about 30% of the periphery in the temporal field?
temporal crescent
What do the photoreceptors connect to?
bipolar cells
What do the bipolar cells connect to?
retinal ganglion cells
What do the retinal ganglion cells do when they join together?
form the optic nerve at the optic disc
About how many (percentage) fibers cross in the optic chasm?
50%
T-F—a synapse takes place in the LGN?
True
From the LGN, what are the 2 routes of fibers?
- inferiorly to the temporal lobe
- superiorly through the parietal lobe
[to synapse in the V1 of the occipital lobe]
Does the visual field system travel horizontally or rostral caudally? What does this help us with?
horizontally
So visual field defects are helpful for determining rostral-caudal location of the lesion
What happens with increasing visual field eccentricity?
density of retinal ganglion cell field and thus reduced visual acuity
What is quantitation of the visual field?
perimetry
How does perimetry work?
patient fixates and signals when a stimulus moving from the periphery in is detected. They do this 360 degrees and make a map of visual thresholds
Small dim objects in perimetry are used to map what?
central visual field [a common location of patient visual defects]
large bright objects are used to test what in perimetry?
peripheral visual field
What are the 2 types of pre neural visual defects?
obstruction of visual image (cataracts)
Photoreceptor damage
What are the two types of hemianopic visual defects?
bitemporal
homonymous
Visual field defects within the retina respect what?
horizontal meridian
Monocular defects correspond to what?
retinal lesion
What are the 4 types of optic disc defects?
- arcuate [arc around fixation]
- altitudinal
- constriction of the visual field
- enlarged blind spot
What are the 3 main causes of defects from the optic nerve?
optic neuritis
compressive
toxic neuropathies
What are the main defects seen in optic nerve damage?
- cecocentral scotoma
- lost acuity
- loss of color vision
- relative afferent pupillar defect
- optic disc pallor
What does damage to the optic chasm cause?
bitemporal hemianopia
What is the hallmark defect of retrochiasmatic lesions?
homonymous hemianopia
The more posterior the lesion the more ______the visual field defect?
congruous
T-F—all retrochiasmatic field defects are binocular?
True
Damage to the optic tract results in?
incongruous homonymous hemianopia
What type of defects are seen in optic radiation damage?
semicongruous defects
A temporal lobe optic radiation damage would lead to what type of defect?
homonymous superior quadrantanopia
A parietal lobe optic radiation damage would lead to what type of defect?
homonymous inferior quadrantanopia
What are 3 occipital lobe damage characteristics?
- exquisitely congruous lesions
- macular sparing
- temporal crescent
Visual field defects due to lesions of the chasm or retrochiasmal area begin at and respect what?
the vertical midline
With homonymous hemianopia, the closer the defect is to the chasm, the more what?
incongruous or dissimilar the left and right visual field maps will be
T-F—fibers from the inferior retina stay inferior and contain the inferior visual field?
False, superior visual field
What is the complete homonymous hemianopia rule?
when it is complete, you can only localize the lesion to the retrochiasmatic visual system, although great congruity, destruction of all fibers anywhere along that course create same visual field defect
If there is complete homonymous hemianopia…where can you localize the lesion?
only to the retrochiasmatic visual system
What is cecocentral scotoma?
a scotoma extending from the blind spot to fixation
What is a central scotoma?
a scotoma that encompasses fixation
THERE IS A LIST OF DEFINITIONS AND A CHART OF ALL THE LESIONS ETC> ON THE LAST 2 pages. I would look at all of that.
:)
