Fixation Disparity, Binocular Rivalry, and Panum's Area (F) Flashcards
What is the equation for the rate of rivalry?
1/(t(L) + t(R))
t(L) = time of seeing/cycle left eye
t(R) = time of seeing/cycle right eye
What is suppression on the orthoscope considered? 1. How does this develop? 2
- pathological suppression
2. often non-strabismic binocular vision disorders exhibit central suppresion
What do both the associated and dissociated phorias indicate?
convergence position of eyes where no fusional vergence is needed to fuse
How can diplopia be eliminated with anomalous retinal correspondence?
corresponding points shift so that common images in each eye now correspond (enable suppression and might facilitate fusion)
During rivalry, what is the suppression area size in order to eliminate confusion equal to?
Panum’s area (minimum gap size)
Why is it that if you flash targets for a brief time of flicker then the suppression zone may not be evident?
- development of rivalry takes time (>200ms)
2. Panum’s areas are small for brief exposures
When looking at the Forced vergence fixation disparity curve, what is the point where the line crosses the vertical line called? 1. The horizontal line? 2
- habitual fixation disparity
2. associated phoria
Is rivalry synchronous or asynchronous for large fields? 1. Small fields? 2
- asynchronous
2. synchronous
What causes people to experience SOLI instead of the desired SILO?
accommodative convergence micropsia because not using vergence as cue but using size change as the cue
What does the elliptical shape of Panum’s area lead to clinically?
inducing diplopia takes much less prism vertically than horizontally
How do you measure Panum’s area?
Panum’s area apparatus that measures the range of single vision laterally
What is the term for using convergence to free fuse a dioptic target?
chiastopic fusion
Does higher contrast provide more or less signal strength?
more
How do patients with strabismus avoid diplopia?
- change in retinal correspondence (ARC) to shift Panum’s area
- enlargement of Panum’s area
If the top arrow of a Borish card (OD) is at the letter A (on the right) and the bottom arrow (OS) is on the number 1 (on the left), what is the direction and magnitude of the fixation disparity?
20’ eso
How does luminance viewing with both eyes compare to that of viewing with one eye?
sum of the luminances of the two eyes
What is the maximum fixation disparity size?
when point of regard is at the edge of Panum’s area
How does increasing the contrast in the left eye impact the rivalry?
t(L) is same. t(R) decreases. Rate increases. Relative predominance increases for the left eye
What is the term for using divergence to free fuse a dioptic target?
orthopic fusion
What are the different devices or objects to measure the fixation disparity in a patient?
- Nonius line method
- disparometer
- Borish card
What is the subjective method to measure fixation disparity that uses monocular vertical lines to allow the subject to visualize the oculocentric direction of the eye?
Nonius Line Method
Is a cover test a associated phoria or a dissociated phoria value?
dissociated
Under what conditions is Panum’s the largest? 1. What is the shape of Panum’s area here? 2
- low temporal and spatial frequency
2. elliptical
What is the disparity at the far and near limits of single binocular vision equal to?
1/2 size of Panum’s area
What is the “chrome” like appearance that occurs if right and left luminances differ greatly called? 1. What amount must the difference be? 2
- luster
2. > 10:1
What is the power of contralateral suppression called?
stimulus strength
How do patients with strabismus avoid confusion?
- normal (rivalry) suppression eliminates confusion near corresponding points (within Panum’s area)
- suppression gets “embedded” in strabismus (fixing eye becomes dominant and rate of rivalry becomes slow)
What are the factors influencing stimulus strength during rivalry?
- target contrast
2. contrast sensitivity of the eye
When there is a purposeful error, what does fixation disparity provide?
stimulus to fusional vergence
What does SILO mean?
small in (closer to me), large out (further away)
Is the fusional vergence response always more or less than the stimulus?
less
What is the contrast sensitivity of the eye influenced by?
- light adaptation
2. retinal eccentricity
What is an area in the retina of one eye, which when stimulated simultaneously with a point in the retina of the other eye provides single binocular vision called?
Panum’s area
What is a constant of proportionality relating fusional vergence to fixation disparity called? 1. What is the equation for this? 2
- gain
2. gain = fusional vergence/FD
What is the idea that binocular luminance is the weighted sum of the monocular luminances?
Levelt’s Law of Complementary Shares
What is an ocular deviation less than the size of the diplopia threshold called?
fixation disparity
What is the angular size of Panum’s area equal to?
angle between inner and outer limits
How does brightness viewing with both eyes compare to that of viewing with one eye?
the same
How does increasing the contrast in both eyes impact the rivalry?
t(L) decreases. t(R) decreases. Rate increases. Relative predominance unchanged
What does the difference between each number or letter on the Borish card represent in magnitude?
10 minutes or arc
Does fixation disparity increase or decrease the measure Panum’s area?
increasesby the size of PA for the fovea
Does Panum’s area increase or decrease with an increase in spatial frequency?
decrease
What is the relationship between fixation disparity and fusional vergence (Ogle curve)?
Forced vergence fixation disparity curve
What is the idea that duration of the impression of one eye (t(L) or t(R)) decreases as the stimulus strength in the other eye increases?
Levelt’s Law
How does decreasing the contrast in the left eye impact the rivalry?
t(L) is same. t(R) increases. Rate decreases. Relative predominance increases for the right eye
What is the phoria type that removes the stimulus to fusional vergence so eyes assume posture where fusional vergence equals zero?
dissociated phoria
How can diplopia be eliminated with normal correspondence?
enlargement of Panum’s area (with only image from dominant eye being seen)
What is the phoria type that finds the position of eyes where input to maintain fusional vergence is zero so fusional vergence must be zero?
associated phoria
Does Panum’s area increase or decrease with an increase in temporal frequency (shorter duration)?
decrease
During rivalry, how is confusion eliminated?
alternate suppression of one eye
