Assessing Sensory and Motor Fusion Flashcards

1
Q

Prism moves images to the _________ and light to the _________

A

apex, base

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2
Q

What is the process by which the stimuli individually sensed by each eye is combined to form a synthesized single percept?

A

sensory fusion

occurs in the brain; the ability to “see” single; despite having 2 eyes with different views of the world

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3
Q

Which type of fusion consists of relative movements of the eys to achieve simultaneous retinal stimulation of corresponding retinal areas?

A

motor fusion

the movements of the eye that allow sensory fusion to occur

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4
Q

What is 1st degree sensory fusion?

A

superimposition of two distinct images

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5
Q

What is 2nd degree sensory fusion?

A

Fusion of 2D images; “flat fusion”

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6
Q

What is 3rd degree sensory fusion?

A

stereovision

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7
Q

What is the inability to perceive normally visibly objects in all or part of visual field?

A

suppression

often around fovea/macula with periphery intact

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8
Q

What is the cause of suppression?

A

active cortical inhibition

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9
Q

Why does suppression occur?

A

in order to preserve semblance of binocularity

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10
Q

What are the two theories of the development of suppression?

A
  1. classical model
  2. Pratt-Johnson
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11
Q

Under the classical model of suppression, how many areas must be suppressed?

A

two areas must be suppressed

fovea: elimination of confusion; peripheral retinal point: elimination of diplopia

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12
Q

Where is the zone of suppression under the classical model of suppression?

A

From F to Z

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13
Q

Under the Pratt-Johnson theory of Suppression, where does suppression occur in patients with strabismus?

A

strabismic patients without fusion suppress area of overlap in deviated eye

assumes a binocular field of vision

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14
Q

Hemi-retinal trigger in ET

A

trigger of a temporal point (by prism, or surgery), leads to diplopia while trigger of a nasal point will lead to suppression

XT is opposite

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15
Q

when is suppression bilateral?

A

alternating strabismus

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16
Q

when is suppression intermittent?

A

intermittent strabismus

17
Q

what does the depth of suppression indicate?

A

the ease with which suppression can be broken

correlated with the frequency of deviation, NOT the magnitude

18
Q

What type of viewing conditions does shallow suppression occur?

A

only present under most natural viewing conditions

19
Q

What type of viewing conditions does deep suppression occur under?

A

most viewing conditions, natural or otherwise

20
Q

What are sensory and motor fusion tests done during a comprehensive exam?

A

sensory: stereo
Motor: NPC, vergence ranges

(RDS is highest level of sensory fusion)

21
Q

What instrument is used for in-instrument evaluation of sensory and motor fusion?

A

major amblyoscope

22
Q

What are the 4 possibilities for sensory fusion?

A
  • sensory fusion
  • unstable fusion w/o suppression
  • unstable fusion w/ suppression
  • suppression
23
Q

How to we assess correspondence when a patient has stable fusion?

A

UCT

If NC, then assess motor fusion via vergences with prism bar or phoropter

24
Q

What are 2 reasons for unstable fusion?

A
  1. deficient motor ability to align images
  2. Deficient sensory ability to combine stimuli into single percept
24
Q

How do we differentiate between unstable fusion due to poor motor ability and unstable fusion due to poor sensory ability?

A

Decrease the motor demand by introducing prism

25
Q

what should always be evaluation regardness of strabismus or sensory/motor fusion status?

A

stereopsis evaluation

novel stimulus of 3D images can prompt alignment of the eyes even when there is poor alignment with 2D images

25
Q

What do you do if fusion is still absent or unstable after reducing motor demand?

A

try in instrument evaluation

26
Q

what movement do we record when performing in-instrument evaluation?

A

net movement

27
Q

What is the problem with lateral disparity tests?

A

monocular cues

contaminates results

28
Q

constant strabs in the cotter study were unable to see which targets?

A

random dot e

if a patient can see random dot targets, they can not be a constant strab

29
Q

can a patient with anomalous correspondence see random dot stereograms?

A

no

implication: if a patient has RDS acuity, then we know they have normal correspondence

30
Q

how is anomalous motor fusion assessed?

A

prism adaptation test

31
Q

in the prism adaptation test, what power is the prism used for the 2nd PACT?

A

the original neutralizing prism

performed after patient wears the prism for 30-45 minutes

32
Q

how do we measure the strength of anomalous motor fusion?

A

progressive prism adaptation test

keep adding prism until the patient stops adapting