Assessing Sensory and Motor Fusion Flashcards
Prism moves images to the _________ and light to the _________
apex, base
What is the process by which the stimuli individually sensed by each eye is combined to form a synthesized single percept?
sensory fusion
occurs in the brain; the ability to “see” single; despite having 2 eyes with different views of the world
Which type of fusion consists of relative movements of the eys to achieve simultaneous retinal stimulation of corresponding retinal areas?
motor fusion
the movements of the eye that allow sensory fusion to occur
What is 1st degree sensory fusion?
superimposition of two distinct images
What is 2nd degree sensory fusion?
Fusion of 2D images; “flat fusion”
What is 3rd degree sensory fusion?
stereovision
What is the inability to perceive normally visibly objects in all or part of visual field?
suppression
often around fovea/macula with periphery intact
What is the cause of suppression?
active cortical inhibition
Why does suppression occur?
in order to preserve semblance of binocularity
What are the two theories of the development of suppression?
- classical model
- Pratt-Johnson
Under the classical model of suppression, how many areas must be suppressed?
two areas must be suppressed
fovea: elimination of confusion; peripheral retinal point: elimination of diplopia
Where is the zone of suppression under the classical model of suppression?
From F to Z
Under the Pratt-Johnson theory of Suppression, where does suppression occur in patients with strabismus?
strabismic patients without fusion suppress area of overlap in deviated eye
assumes a binocular field of vision
Hemi-retinal trigger in ET
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
when is suppression bilateral?
alternating strabismus
when is suppression intermittent?
intermittent strabismus
what does the depth of suppression indicate?
the ease with which suppression can be broken
correlated with the frequency of deviation, NOT the magnitude
What type of viewing conditions does shallow suppression occur?
only present under most natural viewing conditions
What type of viewing conditions does deep suppression occur under?
most viewing conditions, natural or otherwise
What are sensory and motor fusion tests done during a comprehensive exam?
sensory: stereo
Motor: NPC, vergence ranges
(RDS is highest level of sensory fusion)
What instrument is used for in-instrument evaluation of sensory and motor fusion?
major amblyoscope
What are the 4 possibilities for sensory fusion?
- sensory fusion
- unstable fusion w/o suppression
- unstable fusion w/ suppression
- suppression
How to we assess correspondence when a patient has stable fusion?
UCT
If NC, then assess motor fusion via vergences with prism bar or phoropter
What are 2 reasons for unstable fusion?
- deficient motor ability to align images
- Deficient sensory ability to combine stimuli into single percept
How do we differentiate between unstable fusion due to poor motor ability and unstable fusion due to poor sensory ability?
Decrease the motor demand by introducing prism
what should always be evaluation regardness of strabismus or sensory/motor fusion status?
stereopsis evaluation
novel stimulus of 3D images can prompt alignment of the eyes even when there is poor alignment with 2D images
What do you do if fusion is still absent or unstable after reducing motor demand?
try in instrument evaluation
what movement do we record when performing in-instrument evaluation?
net movement
What is the problem with lateral disparity tests?
monocular cues
contaminates results
constant strabs in the cotter study were unable to see which targets?
random dot e
if a patient can see random dot targets, they can not be a constant strab
can a patient with anomalous correspondence see random dot stereograms?
no
implication: if a patient has RDS acuity, then we know they have normal correspondence
how is anomalous motor fusion assessed?
prism adaptation test
in the prism adaptation test, what power is the prism used for the 2nd PACT?
the original neutralizing prism
performed after patient wears the prism for 30-45 minutes
how do we measure the strength of anomalous motor fusion?
progressive prism adaptation test
keep adding prism until the patient stops adapting
