Week 7 Flashcards
What are the 2 stimuli to cause vergence?
- Disparity
2. Retinal Blur
Fusional vergence reduces retinal disparity to a minimum using what type of feedback system?
Negative Visual Feedback
Accommodative vergence has no direct effect on retinal blur stimulus using what type of feedback system?
Open-loop
After accommodative vergence, what vergence will correctly align the eyes?
Fusional vergence
How many msec for the accommodative vergence signal to blur?
200msec
How many msec for a disparity stimulus?
180msec
Vergence and accommodation are sped up when it occurs in association with ____?
Saccades
What eye movement is apart of a strategy to facilitary disparity-driven vergence?
Blinks - slow down convergence, divergence and saccades
What neurons must be inhibited to allow for vergence to occur?
Omnipause neurons
If someone cannot converge or diverge, what part of the brainstem are we concerned about?
Midbrain
An important component of the neural substrate for rapid vergence-saccade movements is the ____?
PPRF
The PPRF house pre-motor burst neurons that are important for ?
horizontal saccades (receives signal for vergence)
What is essential for optimal visuo-motor function?
Adaptive capability
If a prism is placed in front of an eye, then the phoria is changed by______. How long will this need to be sustained?
- will change by amount of prism (called phoria adaptation)
- must hold vergence for 30 secs
A robust phoria adaptation mechanism might limit the efficacy of prism tx. This is called ?
Eating prism - phoria adaptation mechanism overcomes effect of prism
Prism is not a good mechanism for tx of ___ ____?
Convergence insufficiency
Prism and Vergence adaptation cause what 2 things?
- Reduction in FD
2. Change in phoria toward direction of stimulus (if exo, now eso)
In response to binocular disparity, what type of fusional vergence is stimulated?
Fast fusional vergence (stressful on vergence system)
To overcome the stress, a ___ fusional vergence is evoked. This is called what?
Slow fusional vergence
- called prism adaptation
Prism adaptation converts what ?
Converts FFV to SFV
What is used as a feedback mechanism to change from fast reflex accom. to slow reflex accomm.?
Blur
What is used as a feedback mechanism to change from FFV to SFV?
Fixation disparity
CA/C sends info from the vergence system to the ____ system.
accommodative
AC/A sends info from accommodative system to ____ system?
vergence
What converts the fast reflex accom. to the slow reflex accom.?
Accom. Amplitude
Accommodation and vergence change in unision via the cross-link interaction between?
CA/C and AC/A
BD: High AC/A with?
Low accommodative Response
BD: Low AC/A with?
High accommodative response
BD: High CA/C with?
Low PA
BD: Low CA/C with?
High PA
What are the 2 ways to manage binocular disorders?
Passive and Active
What ways can we passively manage BDs?
Prisms and Lenses
- to relieve stress of system
What ways can we actively manage BDs?
Vision therapy
What are the 3 neural components needed to cause vergence eye movements?
- Cerebral Cortex
- Brainstem vergence generator
- Ocular motor neurons
Where is the brainstem vergence generator located?
Mesencephalic reticular formation
What type of cells are in the brainstem vergence generator? Which cell is found more abundantly?
Premotor convergence and divergence cells
- more convergence neurons
What 4 cortical areas are in the cerebral cortex?
- Frontal Cortex
- Parietal Cortex
- MT
- MST
What cells are involved in the cerebral cortex vergence decision?
- Near cells
- Far cells
- Size coding cells
Vergence tonic cells carry what signal?
step/position signal
Vergence burst cells carry what signal?
pulse/velocity signal
Vergence burst-tonic cells carry what signal?
both step & pulse signals
An acute lesion in a human’s cerebellum causes ?
convergence weakness
Acute ablation in a monkey’s cerebellum causes what?
transient paralysis of vergence
Jump/Saccadic Vergence refers to ? What test can we use to determine this?
- refers to quick changes and maintenance of vergence angle
- Vergence Facility testing (12BD, 3BI)
Smooth/Pursuit Vergence refers to what?
slow changes in vergence angle due to smooth tracking of target
Anisometropic correction is best using spectacles or CLs?
CLs
