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Flashcards in 2. Visual Direction Deck (67)
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what is visual direction

how the brain organizes images on each eye (from the retina)


what is oculocentric direction

visual direction relative to where an eye is looking


what are visual lines

a geometrical way to represent visual directions


oculocentric direction is equivalent to...

the angle between the principal visual direction (PVD) and a secondary visual direction


what is the principal visual direction
what is secondary visual direction

to the fixation point
to the other object in space


images fixed on the retina have constant _____, even if the eye moves

oculocentric directions


what is a local sign

an oculocentric direction associated w/ a retinal point


what demonstrate that local signs are fundamentally neural

mechanical visual phosphenes


what is uniqueness of local sign organization

no retinal point has the same visual direction as any other retinal point


what is order in local sign organization

visual direction is related directly to retinal position


what is the basis of directional discriminiation

local sign size


what is local sign size mostly determined by

the brain, NOT the retina


how are foveal local signs and foveal cones related in size?
how are peripheral local signs and periph cones related?

foveal local signs are 1/7th the size of foveal cones

peripheral local signs are much larger than peripheral cones


what kind of mapping is local sign order related to

retinotopic mapping


why does kundt partition asymmetry happen

there is a difference in optical mag on either side of the fovea
-less nasal retina stimulated than temporal so the img on the nasal retina is shorter so pt will see a shorter temporal portion of the line and will draw closer to nasal portion of the line
-visual axis is 5 degrees off of the optical axis


what can the kundt partition asymmetry test for

to quantify oculocentric vision problems in amblyopic patients


what do abnormally large local signs cause

spatial uncertainty (inability to discriminate differences of visual direction) and reduce VA


local sign disorder causes...

distorted vision


what are the 4 types of visual acuity

1. detection (can you see the object)
2. resolution (can you see 2 obj as separate)
3. localization (do you see 2 obj in diff directions)
4. recognition (is an obj recognizable)


when local sign gets smaller, how does it afftect VA

the smaller the local sign, the better the acuity


are detection and resolution functions determined by local sign?



how can resolution be tested

w/ grating acuity
-are the black and white vertial lines seen
-doesnt have to tell you about localization of lines
-grating patterns are related closely to foveal cone size (resolve 15 sec of arc)


how can localization be tested

vernier acuity
-2 lines vertically separated and horiz displaced
-compare the horiz positions of the 2 lines to see if they can accurately locatlize them


what are some examples of visual defects where poor resolution causes low VA (resoltuion and localization deficits are proportional)

what is the exception

refractive blur
media opacities
retinal disease

strabismic amblyopia: good resolution, bad localization


what are the 2 main types of amblyopia

anisometropic amblyopia: amblyopia caused by uncorrected aniso
strabismic amb: amb caused by early onset and consant unilateral strab

-pt can have both


how is the localization threshold elevation and the resolution threshold elevation related in anisomtrpic amblyopes and strabismic amblyopes

anisometropic: localization threshold elevation is about the same as the resolution threashold elevation
-due to neurological blur, low contrast sensitivity

strabismic: localization threshold elevation much higher than the resolution threshold elevation
-bc of spatial uncertainty (snellen letter directions are confused and overlapping)


how can acuity be improved w/ vision training for strab amblyopes

patching, exercies
improvement occurs due to a reduction in the spatial uncertainty and improved resolution


what is metamorphopsia and what is disorderly here

a perception of object shape that differs from the objects true shape
-local sign as being disorderly


what is metamophopsia cause by

1. optical problems
-keratoconic corneal distortion
2. neuroanatomical
-retinal deformation in disease
-retino-cortical connection problems in amby


what does amsler's grid test
-nonquantitative clinical method

-retina stretched or something => signal to local signs are scrabmbled=> localization of obj/img is incorrect