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OD2-BVOM > 2. Visual Direction > Flashcards

2. Visual Direction Flashcards

1
Q

what is visual direction

A

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

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2
Q

what is oculocentric direction

A

visual direction relative to where an eye is looking

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3
Q

what are visual lines

A

a geometrical way to represent visual directions

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4
Q

oculocentric direction is equivalent to…

A

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

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5
Q

what is the principal visual direction

what is secondary visual direction

A

to the fixation point

to the other object in space

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6
Q

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

A

oculocentric directions

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7
Q

what is a local sign

A

an oculocentric direction associated w/ a retinal point

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8
Q

what demonstrate that local signs are fundamentally neural

A

mechanical visual phosphenes

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9
Q

what is uniqueness of local sign organization

A

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

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10
Q

what is order in local sign organization

A

visual direction is related directly to retinal position

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11
Q

what is the basis of directional discriminiation

A

local sign size

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12
Q

what is local sign size mostly determined by

A

the brain, NOT the retina

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13
Q

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

A

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

peripheral local signs are much larger than peripheral cones

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14
Q

what kind of mapping is local sign order related to

A

retinotopic mapping

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15
Q

why does kundt partition asymmetry happen

A

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
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16
Q

what can the kundt partition asymmetry test for

A

to quantify oculocentric vision problems in amblyopic patients

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17
Q

what do abnormally large local signs cause

A

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

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18
Q

local sign disorder causes…

A

distorted vision

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19
Q

what are the 4 types of visual acuity

A
  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)
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20
Q

when local sign gets smaller, how does it afftect VA

A

the smaller the local sign, the better the acuity

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21
Q

are detection and resolution functions determined by local sign?

A

no

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22
Q

how can resolution be tested

A

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)
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23
Q

how can localization be tested

A

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
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24
Q

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

what is the exception

A

refractive blur
media opacities
retinal disease

strabismic amblyopia: good resolution, bad localization

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25
Q

what are the 2 main types of amblyopia

A

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

-pt can have both

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26
Q

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

A

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)

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27
Q

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

A

patching, exercies

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

28
Q

what is metamorphopsia and what is disorderly here

A

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

29
Q

what is metamophopsia cause by

A
  1. optical problems
    - keratoconic corneal distortion
  2. neuroanatomical
    - retinal deformation in disease
    - retino-cortical connection problems in amby
30
Q

what does amsler’s grid test

-nonquantitative clinical method

A

metamorphopsia

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

31
Q

why is distortion not eveident in peripheral vision

A

bc normal peripheral spatial uncertainty masks distortion

32
Q

what is distorted in strabismic amblyopia

A

foveal local sign order

-disotortios not so evidnet bc of spatial uncertainty

33
Q

how can amblyopic distortion be measured by

A

the partitioning task

-called the bisection hyperacuity task

34
Q

can distortion be changed through vision training?

A

no

35
Q

distorted macular vision is a serious impediment to ____, even if resolution and directional discrimination are good

A

yes, it is a serious impediment to binocularity

36
Q

what is the principal visual direction (PVD)

A

the sense of looking at something (in the middle of your visual field)

  • oculocentric sense (straight ahead)
  • PVD=oculucentric zero
37
Q

the PVD tells you if you are using the _____

what happens when the PVD is stimulated and when it is not stimulated

A

PVD tells you if you are using the fovea

  • PVD stimulated is the image on fovea
  • PVD not stimulated is off foveal-image; stimulus for eye movement
38
Q

is VA testing a good test to see if the patient is using the fovea

A

no, bc could be using a diff retinal point to read the chart

39
Q

we need PVD in order to scan the world with ____

A

high resolution spatial scanning

40
Q

what is the solution for using too many brain neurons for high acuity across the entire retina

A

move a small high-resolution retinal area to scan diff parts of the retinal image sequentially
-need PVD to guide these movements

41
Q

what is eccentric fixation

A

an extrafoveal point (peripheral retina) used to fixate objects and can be used as the zero reference (PVD) for visual direction (instead of the fovea)

42
Q

who uses eccentric fixation

A
  • strabismic amblyopes

- patients with years of bilateral macular disease

43
Q

what is eccentric viewing

A

fovea is stil the zero reference but it is damanged so they use a peripheral retinal point to view an object but it appears to be off to the side

44
Q

who uses eccentric viewing (EV)

A
  • normal scotopic vision
  • short duration macular disease

patients consciously use peripheral vision to see

45
Q

what is the difference between EF and EV

A

EF=functional problem (strab amby) and EV =disease (AMD, foveal damage)
-EV pt aware of peripheral looking, EF is not

46
Q

how are EF and EV similar

A

peripheral vision is used to see images

47
Q

how do you use visuoscopy to test for EF

A

have pt look at center of grid target

  • if grid target right on the fovea then pt using fovea
  • if displaced from the fovea, then patient is using EF
  • if grid is temporal to foveal reflex pt is a temporal EF
48
Q

will you see a foveal reflex if a pt has a macular disease

A

no

49
Q

what is ocular dominance

A

the favoring of one eye for visual input

50
Q

what does ocular donimance testing assume

A

refractive error is corrected

51
Q

what are the 2 types of dominance

A
  1. acuity dominance: one eye is favored for seeing fine detail, ipmortant for prescribing monovision cl for presby, dominant eye for dist
  2. sighting dominance: one eye is favored for controlling fixation (favored PVD)
52
Q

how can you assess acuity dominance

A

by noting

  1. sight difference of VA
  2. sensitivity of each eye to small spherical lens changes
53
Q

sighting and acuity dominance usually agree, what are the exceptions

A
  1. pt w/ mild left anisometric amblyopia
  2. macular degeneration in the right eye
  3. patient selects the right eye via hole in hands, despite poor acuity
54
Q

what is egocentric direction

A

the direction of an image with respect to one’s self

where are things located relative to myself

55
Q

what are the 2 processes that interpret oculocentric directions and convert them to egocentric directions

A
  1. gaze registration aka corollary dischage: brain registers eye movements and can re-evalulate the egocentric direction
  2. visual capture
    - charactistics and details in a retinal image may reveal the egocentric direction of the object
56
Q

egocentric direction = ____ + ______

A

oculocentric direction + gaze registration

57
Q

egocentric direction is always relative to the….

A

orientation of the head

58
Q

what is the neural pathway of gaze registration

A
  1. visual cortex sends info to space perception area
  2. space perc area tells the motor area where things are located w/ respect to the body
  3. motor command tells the oculomotor neuron to tell muscles to take eyes to target
  4. copy of this action sent back to the space perception
    =>corollary discharge (anytime a nucleus sends primary info one way, secondary another) aka gaze registration
59
Q

what is visual capture

A

can deduce egocentric direction w/o gaze direction info

-looks at spatial order of lines and can deduce wehre something is relative to self

60
Q

what is visual capture based on

A

perspective textures (cues) in the retinal image

61
Q

what is visual capture best for? what is gaze registration best for?

A

visual capture is best for large objects in static (slow) photopic vision

gaze registration is best for small objects, viewing in dark, and movement
-quicker than visual capture

62
Q

when can egocentric direction be mistaken

A

if oculocentric direction, gaze registration, or visual capture are wrong

63
Q

is visual capture known to have unique disorders

A

no

64
Q

when gaze registration is wrong, it causes…

A

past pointing

65
Q

what is past pointing

A
  • used as a test of erroneous gaze registration caused by muscle paresis
  • when oculocentric direction added to gaze registration, the egocentric direction will be very large and the pt will perceive the object to be very far to the right
66
Q

why do past pointing patients no verbally report an illusory target direction?

A

gaze registration and visual capture are both running parallel during the test, when the hand is unseen, the movement of it is more strongly influenced by gaze registration

67
Q

how is past pointing used clnically

A

not usually used to diagnose the type and severity of paralysis bc there are more accurate ways

  • oculomotor adaptation to paresis reduces past pointing over many days of time
  • past pointing is useful bed-side test for acute paralysis

OD2-BVOM (6 decks)

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