Term
| What is the process by which two images, one from each eye, give rise to a unified percept of one single object? |
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Definition
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Term
| Which degree of fusion according to Worth is the simultaneous percept of each eyes image? |
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Definition
|
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Term
| Which degree of fusion according to Worth represents the combination or flat fusion of the two images into a single percept? |
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Definition
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Term
| Which degree of fusion includes deriving a three dimensional depth perception, or steropsis? |
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Definition
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Term
| Why is Worth's classification system not truly hierarchial? |
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Definition
| It is now known that it is not always necessary to possess flat fusion or 2nd degree stereopsis in order to appreciate stereoscopic depth perception. |
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Term
| What is the vergence eye movement reflex that brings similar contours into alignment? |
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Definition
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Term
What is the neurophysiological and psychological process by which the visual cortex combines the
superimposed views obtained independently by the two eyes into one unified percept of visual space? |
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Definition
Sensory fusion. It is a perceptual phenomena.
see p. 46 text |
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Term
| What are two potential results of the visual system being unable to fuse images? |
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Definition
1. Anomalous correspondence
2. Suppression |
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Term
| If a strabismic patient suppresses what type of fusion is inadequate? |
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Definition
| Both motor fusion and sensory fusion are inadequate |
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Term
| If a strabismic patient exhibits anomalous correspondence, what type of fusion is inadequate? |
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Definition
| Motor fusion is inadequate but sensory fusion is present |
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Term
| What are two potential mechanisms by which sensory fusion could be accomplished? |
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Definition
| Alteration and suppression |
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Term
| What are three reasons the alternate or suppression theory does not hold true? |
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Definition
1. Insufficient time to switch between eyes and maintain stereopsis
2. We can experience steropsis in less time than it takes to switch attention.
3. Regardless of which eye is stimulated reaction time is the same.
4. No apparent motion |
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Term
| Name two instances when the fusion theory does not hold true? |
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Definition
1. A very different image is presented to one eye than is presented to the other.
2. some images are fused even though they are not on corresponding points in each eye |
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Term
| What is it called when a patient is presented with images on corresponding retinal points, but makes eye movements so that the images are no longer on retinal points and thus discourages sensory fusion? |
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Definition
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Term
| Why don't we normally experience diplopia for stimuli in the rest of the visual field? |
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Definition
| We learn to ignore diplopia by attending to objects that lie on the horopter. |
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Term
| Based on the nonius lines, how do we know that Panum's fusional area exists? |
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Definition
| The nonius lines (presented monocularly) can be seen nonaligned one on top the other, while the binocularly presented target that encompasses the nonius lines is still seen as single. |
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Term
| What is fixation disparity? |
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Definition
| A small binocular misaglignment between the two eyes in which fusion and single vision are achievable. |
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Term
| What are the twelve factors that influence Panum's fusional area? |
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Definition
CLIT SAT (EST)2
1. contrast-no effect
2. luminance-change in luminance 3 log units above threshold has little effect
3. interocular inequality-Panum's fusional area decreases with increasing interocular inequality
4. target orientation-hard to quantify
5. eccentricty
6. spatial frequency
7. the influence of other objects in close proximity-like the crowding effect, closer objects reduce Panum's fusion area size
8. Exposure duration-Panum's fusional area increases with exposure time
9. Spatiotemporal frequency-larger Panum's fusional area with low spatiotemporal frequency
10. Temporal frequency
11. Small angle strabismus
12. Anomalous retinal correspondence |
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Term
| How big is Panum's fusional area at the fovea? |
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Definition
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Term
| What is the size of Panum's fusional area past five degrees from the fovea? |
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Definition
| 6.5% of the angle of eccentricity |
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Term
| Why do you start using a target that stimulates the peripheral retina when you are training a patient to fixate? |
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Definition
| Panum's fusional area is bigger in the periphery and peripherally viewed objects are easier to fuse. |
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Term
| What does increased temporal frequency do to the fusion limits of a low spatial frequency object? |
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Definition
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Term
| What does increased temporal frequency do to the fusion limits of a high spatial frequency target? |
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Definition
| nothing, small ones are reduced like big ones are |
|
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Term
| What kind of target would you start a patient off with in vision therapy? |
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Definition
1. low spatial frequency (big)
2. Low temporal frequency (slow)
3. In the periphery |
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Term
| How big does a fixation disparity need to be to indicate a binocular vision problem? |
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Definition
| larger than a few minutes of arc |
|
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Term
| Which type of disparity is difficult for someone with an esofixation disparity to handle? |
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Definition
| Uncrossed fixation disparity |
|
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Term
| What are the six tests to measure fixation disparity? |
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Definition
BAM BWD
1. Mallet box-oldest
2. Bernell Test Lantern-Distance and Near
3. AO Vectographic Slide-distance only
4. Borish Card-Near only
5. Wesson Card-Near only
6. Disparometer-Near only |
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Term
| Which is the more reliable indicator of the amount of successful prescription, associated phoria or dissociated phoria? |
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Definition
| associated phoria even though it's usually smaller |
|
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Term
| What is the x intercept in a fixation disparity curve? |
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Definition
|
|
Term
| What is the y intercept of the fixation disparity curve? |
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Definition
| The fixation disparity without added prism. |
|
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Term
| What would be a good starting point for prescribing prism to patients? |
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Definition
| 1/2 the associated phoria (x intercept) |
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Term
| Which fusional phase does a vertical phoria lack? |
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Definition
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Term
| What about a patients lifestyle would increase the slope of the forced vergence fixational disparity curve, the associated phoria, and fixational disparity? |
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Definition
| Sustained nearpoint tasks |
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Term
| What type of strabismus is usally present in children? |
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Definition
| Esophoria, while adult onset is more often exophoria |
|
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Term
| What is anomalous retinal correspondence? |
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Definition
| Stimuli presented to each fovea are perceived in a distinctly different location. |
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Term
| What do you call a precise shifting in corresponding points that matches the angle of strabismus? |
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Definition
| Harmonious anomalous correspondence |
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Term
| When is harmonious retinal correspondence most likely to be observed? |
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Definition
| Under conditions that are not grossly unusual, e.g. without red/green filters or other optical instruments |
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Term
| Name two tests to subjectively measure strabismus and HARC. |
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Definition
1. Maddox rod
2. Hess Lancaster Test |
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Term
| If the patient has a red light and tries to line it up with the examiners green light while seeing red out of his right eye and green out of his left eye, where will the light be if he has right esotropia? |
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Definition
| From the patient's perspective, to the left of the red light. |
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Term
| What is the Hering Bielschowsky test used to detect and how? |
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Definition
| Hering Bielschowsky detects anomalous retinal correspondence by bleaching a line on each fovea, one horizontal, one vertical. If the patient ARC, the lines will not be superimposed into a cross. |
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