Exam 2 Flashcards
1
Q
What is the purpose of fixation disparity?
A
Fixation disparity provides the error signal needed to stimulate continued compensation of the phoria
2
Q
Because fixation disparity can be influenced by many things, what 2 things must you include when FD is measured clinically?
A
Test distance and type of test used.
3
Q
What is associated phoria?
A
Prism to compensate the fixation disparity
4
Q
Prism that neutralizes fixation disparity is usually in the ____ direction as their dissociated phoria
A
Same direction (exo/eso)
5
Q
What is the fast response to prism?
A
Eyes use horizontal (not vertical) vergence to attempt to eliminate fixation disparity
6
Q
The disparity vergence system is the response
A
Fast response
7
Q
The vergence adaptation system is the response
A
Slow response
8
Q
What is the slow response to prism?
A
Prism reduces the demand on the disparity vergence mechanism and reduces effectiveness of prescribed prism that compensates a heterophira.
9
Q
What minimizes asthenopia during a sustained vergence demand?
A
The slow response (vergence adaptation system)
10
Q
What is the Y intercept on the Forced Vergence fixation disparity curves?
A
The Fixation Disparity in arcmin with zero prism
11
Q
What is the X intercept on the Forced Vergence fixation disparity curves?
A
It is the “associated phoria”, the amount of prism that neutralizes the fixation disparity
12
Q
The slope of the Forced Vergence fixation disparity curve as it crosses the ___ axis is important. What does flat slope indicate?
A
Y axis. Flat slope indicates healthy vergence adaptation.
13
Q
What is the prominent characteristic of type I fixation disparity pts?
A
Flatter central region, S-shaped
14
Q
Esophores that poorly adapt to base in prism are typically Type ___ Fixation disparity?
A
Type II
15
Q
Type ___ FD is found most often in highly exophoric patients who adapt poorly to BO prism
A
Type III
16
Q
Type ___ FD don’t really react to any prism
A
Type IV
17
Q
Fixation disparity is measured in ____ of arc
A
Minutes of arc
18
Q
Prism adaptation happens in the ____ part of the Fixation disparity curve.
A
Flat
19
Q
If a patient doesn’t have a flat portion on their fixation disparity curve….they will do (well/poor) with prism prescribed
A
Well with prism because steep slopes indicate poor adaptation, meaning they won’t “eat” the prism and adapt nor induce more fixation disparity
20
Q
If you do prescribe prism to relieve symptoms, get them to the ___ part of their FD curve
A
Flat part
21
Q
What is anomalous retinal correspondence?
A
It’s an adaptation to strabismus of EARLY childhood onset. It suppresses the fovea by neurologically remapping visual directions in the deviated eye. This is NOT eccentric fixation because ARC is binocular
22
Q
How do you diagnose anomalous retinal correspondence?
A
You need to make sure there is no eccentric fixation in either eye, then they can be tested with the Hering-Bielschowsky afterimage test.
23
Q
What is the Hering-Bielschowsky afterimage test? What does it test? What are the steps?
A
It’s a test that measures anomalous retinal correspondence. The strab eye looks at vertical flash, then good eye looks at horizontal flash. The after images will make a cross (or not) when pt looks binocularly at a flat surface
24
Q
What is the objective angle (H)?
A
Ocular deviation is measured wo/ pt input (cover test or Krimsky test)
25
What is the subjective angle (S)?
Ocular deviation is measured with pt input
26
What is the angle of anomaly (A)?
The difference between objective and subjective angles (A= H-S)
27
What is the angle H?
Objective angle, no pt input (use cover test or Krimsky test)
28
What is "point zero"?
The point on the retina of the deviated eye that is considered "looking straight ahead". For normal people, this is the macula but for tropes it's nasal or temporal retina.
29
What is "point a"?
The point on the retina of the deviated eye that is is the anomalous "fovea" and corresponds with looking straight ahead under binocular conditions.
30
How does point zero and point "a" match in Harmonious ARC (anomalous retinal correspondence)?
They are the same point! Both points are deviated from the fovea.
31
How does point zero and point "a" match in unharmonious ARC (anomalous retinal correspondence)?
The subjective angle (S) is is smaller than the objective angle (H). It's like subjectively the person is trying to get the image closer to their fovea. "a" is in between point 0 and Fovea
32
How does point zero and point "a" match in paradoxical ARC type 1 (anomalous retinal correspondence)?
The subjective measurement (s) is on the OPPOSITE side of "point 0" compared to what they were measured objectively. The anomalous angle is bigger and the in the same direction of objective angle (H)
33
How does point zero and point "a" match in paradoxical ARC type 2 (anomalous retinal correspondence)?
The subjective angle is even more severe than the objective angle. The angle of anomaly is smaller than subjective (s) but and is in the opposite direction.
34
What kind of strab pt can "pass" the maddox rod test?
If they have harmonious anomalous retinal correspondence, they'll pass the test because of their remapped "fovea". This because point 0 and point "a" are the same point.
35
What kind of patient will see uncrossed on the maddox rod test?
An eso with normal retinal correspondence or
| an eso with unharmonious anomalous retinal correspondence
36
What kind of patient will see crossed on the maddox rod test even though they are an esotrope?
PAC type 1 (Paradoxical anomalous retinal correspondence)
37
What kind of patient will see a HUGE uncrossed maddox rod test even though they are a small esotrope?
PAC type 2 (Paradoxical anomalous retinal correspondence)
38
What is the Hess-Lancaster test?
It subjectively measures the misalignment of the images seen by the two eyes AS SEEN BY THE PATIENT. in different positions of gaze.
Doctor uses red/green light to fixate an eye and the patient has to superimpose their light onto the doctor's.
39
What will an esotrope with NRC see on the Hess-lancaster test when the lights are physically superimposed?
They will see the lights separate and uncrossed.
40
What is Covariation?
When eyes have both NRC and ARC (anomalous retinal correspondence) as in the case of intermitant tropes, varying strabismus angles, and different tests.
41
What does the X mean in the Hess-lancaster test? The circle? What does it mean if they are crossed in the test results?
It represents the eye being tested. The circle is the fixating eye. Crossed test results means uncrossed diplopia for the maddox rod test.
42
How do we know if an object is on someone's horopter? For an observer with NORMAL binocular vision, objects that stimulate corresponding points will….3
1 Be perceived as having the same visual direction in each eye;
2. Be perceived as being equidistant from the observer as the fixation point;
3. Have ZERO binocular disparity;
4 Be perceived as single (i.e., result in “haplopia”, not “diplopia”)
5. NOT stimulate a reflexive motor vergence response when introduced
into the field of view.
43
What are the 5 ways to locate the horopter?
1 Identical visual directions (aka “nonius horopter”)
2. Equidistance (AFPP)
3. Singleness (haplopia)
4. Minimum stereoacuity threshold
5. Zero vergence
44
What is Identical visual directions?
Helps locate the horopter. Have an object appear differently to each eye and move them a proper distance so they line up
45
What is Equidistance?
It helps locate the horopter. Even though objects arc along panum's fusional area, they appear to be straight (paralell to the person's face)
46
Which horopter tool is more precise in untrained subjects?
Equidistance (things appear straight even though it's arced along horopter)
47
What is singleness (haplopia)
It helps locate the horopter. The singleness horopter is the center of Panum's fusional area where the horopter is. Moving in and out until diplopia is experienced measures the extend of PFA.
48
What is Minimum stereoacuity threshold?
A more complicated way of measuring and locating the horopter. You move the test rod until depth appears differnet (not dipolipa)
49
What is "zero vergence"
It helps locate the horopter. Sudden appearance of test rods ON Panum's fusional area should NOT cause a vergence movement
50
How do you calculate relative uniform magnification?
```
R = Tan(alpha 2) / Tan(alpha1)
or Tan(alphaR) / Tan(alpha L)
```
51
How does the observer's measured horopter compare with the V-M circle?
The observer's horopter is flatter than the theoretical one
52
When is relative magnification always 1?
On the V-M horopter because both alpha angles are exactly the same for both eyes. R=1
53
What happens to R when the point is away from the horopter on the right side?
R is higher because alpha 2 (the right eye) has a bigger angle than alpha 1 (the left eye). Objects left of the fixation point are minified (when comparing right eye to the left eye)
54
What happens to R as you move across the empirical horopter?
It goes from small to large. Perceptually, points across the horopter look to be in a straight line
55
What is Hering-Hillebrand horopter deviation?
(H), it is the difference in curvature between the empirical horopter and the VM circle. It shows a non-uniform relative mag across the visual field
56
H bigger than zero means what?
Hering-Hillebrand horopter deviation shows that the empirical horopter is flatter than V-M circle
57
H below zero means what?
Hering-Hillebrand horopter deviation shows that the empirical horopter is steeper than V-M circle
58
_____ retina has greater neural magnification than ____ retina
Temporal retina has greater neural mag than nasal retina
59
A plus lens would magnify the image, tilting the perceived horopter ____ mag eye. To get the objects to appear straight again, the points need to be adjusted ____ mag eye. (the empirical horopter is ____)
A plus lens would magnify the image, tilting the perceived horopter AWAY FROM the mag eye. To get the objects to appear straight again, the points need to be adjusted CLOSER TO the mag eye. (the empirical horopter is CLOSER)
60
What are the axis of the "analytical plot". What does the Y intercept mean? What is the slope?
X is the tan of alpha 2 (right eye). Y is the R (relative magnification, or tanAlpha2 / tanAlpha1).
The y intercept is R0 (not)
The slope is Hering-Hillebrand deviation (H)
61
What is the significance of R0?
The Y intercept of the analytical plot. It hows the perceived rotation of the original horopter.
R0 = 1 indicates no rotation.
R0 > 1 indicates rotation of the PERCEPTION of the horopter away from the RIGHT eye (i.e., image on OD is magnified relative to image OS)
R0
62
R0 = 1 indicates…
No rotation
63
R0 > 1 indicates …
R0 > 1 indicates rotation of the PERCEPTION of the horopter away from the RIGHT eye (i.e., image on OD is magnified relative to image OS). The measured horopter rotates toward mag eye
64
R0
R0
65
What is "Nasal packing"?
Images falling on nasal retina are perceived to be a smaller angle from the fovea than an object appearing on temporal retina, even when the angles are the same! This is why empirical horopters are flatter than the V-M circle. The receptor fields are more spread out nasally
66
Because of "nasal packing" how does something appear when placed on the V-M circle?
It appears closer, which is why people will push it out so that it appears to be in a straight line along their empirical horopter. This EH is tends to be flatter than the V-M circle.
67
What is "monocular asymmetry"?
The receptive fields are more spread out in nasal retina than the temporal side. This will cause people to think nasal retinal images (temporal visual field) are shorter (in the case of trying to divide a line into equal halves)
68
What is the "abathic distance"? What's the equation?
The distance a patient needs to fixate to have their flat (but still curved) horopter actually BE flat because you're so far away.
The abathic distance is proportional to their interpupillary distance and inversely proportional to their Hering-Hillebrand deviation
69
How is the empirical vertical horopter tilted? Why?
The top is tilted away instead of being vertical (as predicted theoretically).
Because ocular extorsion
70
The horopter of an exotrope is excessively _____
Concave, meaning it may lie within the VM circle
71
What is a Flom notch?
The distortion of horopter within the objective angle of deviation
72
What is the "horror fusionis"? Why do people display this?
In strabismus, their eyes might change vergence once proper fusion is obtained, causing the image to go diplopic in the opposite direction. (the image may "jump past" the point of correspondence)
This might be associated with the Flom notch.
73
How do meridional magnifiers work?
They magnify in the direction perpendicular to the cylindrical axes
74
How do prisms show non-uniform magnification?
There is greater magnification at the apex of the prism than the base.
75
What is neural aniseikonia? Why does this happen?
Images are perceived to differ even though the retinal images are the same shape and size.
This happens because the image size in spectacle correction is the same between eyes that differ in axial length, BUT the image covers FEWER receptive fields in the larger eye.
76
What is optical aniseikonia?
Images differ in size or shape between the two retinas. It can be refractive or axial.
77
Between refractive, axial, and lateral aniseikonia, which has non-uniform magnification?
what can cause this aniseikonia? What makes the aniseikonia worse?
Lateral aniseikonia. This is from prism (including induced prism from decentering lenses)
Eccentricity makes the aniseikonia worse
78
How do CLs affect myopes with eyes that differ in their axial lengths?
It works well to prevent aniseikonia because even though the image size differs between the eyes, the image covers the same number of receptive fields
79
What is the Brechner-Maddow rod method?
Can diagnose aniseikonia. Use two lights and one maddox rod. The spacing between the two dots should be equal to the spacing between the two vertical lines (made by the maddox rod). The eye that has the greater spacing is the eye that experiences more magnification.
80
What is the Space Eikonometer?
It's an old machine that uses different lines. Aniseikonic patients will see the lines closer/farther or the X will be tilted. Neutralize with afocal magnifiers
81
What is the geometric effect (on the horopter). What happens when you put the afocal magnifier at axis 90?
It causes magnification along the horizontal meridian. Space is perceived to be rotated away from the eye that has more horizontal mag, meaning the horopter tilts towards the eye that has more horizontal mag of its retinal image. Why? Because the image spans more receptive fields .
The recorded horopter will be tilted toward the greater horizontal mag eye
82
What is the "induced effect" of aniseikonia?
Placing an afocal magnifier axis 180 over one eye has the SAME result as putting an afocal magnifier axis 90 on the opposite eye!
83
If an afocal magnifier is placed axis 180 over the right eye, what happens to perspective and the horopter?
This magnifies the vertical meridian, causing the image to appear farther away in the left eye. The horopter tilts towards the left eye, away from the right eye.
84
The horopter rotates (toward/away) from the eye having greater vertical magnification
The horopter rotates AWAY from the eye having greater vertical magnification. Visual space shifts closer
85
Why does this induced effect of vertical magnification cause a perception of horizontal magnification?
The brain can better tolerate horizontal disparity than vertical (think of how vertical prism is hardly tollerated) So the brain adjusts this.
86
What does oblique magnification do?
Causes a tilting perception
87
Upward divergent aniseikonia causes upper part of plane to ….
Enlarge and tilt away. This is positive declination error
88
Downward divergent aniseikonia causes upper part of plane to ….
shrink and tilt toward observer. This is negative declination error
89
What is positive declination error?
When the top of a plane appears to enlarge and tilt away. This is from Upward divergent aniseikonia
90
What is negative declination error?
When the top of a plane appears to shrink and tilt toward observer. This is from Downward divergent aniseikonia
91
Why does uniform magnification cause less problems than meridional magnification?
Because horizontal and vertical magnification "cancel each other out" when the mag is 6%.
Higher than 6%, Geometric effect (not induced) becomes dominant over the induced effect (meaning horopter is rotated toward magnified eye, perception is rotated away from mag eye)
92
Prism has more magnification in its (base/apex}
Prism has more magnification in its apex.
93
Looking through base out prism OU creates a (concave/convex) perception and a (concave/convex) horopter curve.
Looking through base out prism OU creates a (concave) perception and a (convex) horopter curve.
This is because the apex (nasal) prism has more magnification, bringing perception farther nasally. Horopter shift is opposite to this
94
Looking through base in prism OU creates a (concave/convex) perception and a (concave/convex) horopter curve.
Looking through base in prism OU creates a (convex) perception and a (concave) horopter curve.
This is because the base (nasal) prism has hardly any magnification, bringing perception closer nasally (at midline). Horopter shift is opposite to this
95
There is ___% aniseikonia per diopter anisometropia
There is 1.4% aniseikonia per diopter anisometropia
96
What are some optical sources of aniseikonia?
Anisometropia
Unilateral aphakia
IOL implants
Monocular refractive surgery
97
Aniseikonia of __% can cause asthenopic symptoms
Aniseikonia of 1-2% can cause asthenopic symptoms
98
Aniseikonia of ___% or greater elevates stereoscopic thresholds
Aniseikonia of 5% or greater elevates stereoscopic thresholds
99
Aniseikonia of ___% or greater prevents fusion
Aniseikonia of 20% or greater prevents fusion
100
What does Knapp's Law suggest about correcting refractive vs. axial anisometropes?
Refractive anisemetropes correct well with CLs
| axial anisometropes correct well with specs but CLs work well, in clinical practice
101
Maximum adaptation to aniseikonia takes ___ days
7 days
102
What are aniseikonia symptoms?
HA, asthenopia, photophobia, reading difficulty, nausea, diplopia, etc
103
Why might lasik be bad for some anisometropes?
Axial anisometropes used to spectacles might have aniseikonia symptoms because of different image sizes because the refraction correction is now closer to the eye (instead of 12 mm)
104
Suppression has an _____ threshold for light detection
Elevated
105
Physiological vs pathological suppression?
Physiological: NOT from strab or other ocular abnormality
| Pathological: secondary to strab or from ocular abnormality
106
What kinds of stimuli are suppressed?
Dimmer, blurred, stationary, peripheral from center, and temporal retinal stimuli
as opposed to
Brighter, crisp, moving, central, and nasal retina stimuli
107
Which tend to have deeper suppression, esotropes or exotropes?
Esotropes because images tend to fall on the more sensitive nasal retina. The brain has to "work harder" to ignore this stimuli than if such an esotrope were instead an exotrope.
108
How can you use neutral density filters in practice?
You put the filters on the dominant eye and increase the filter strength until the suppressing eye "comes back in"
109
Nasal or temporal retina is more sensitive?
Nasal is more sensitive
110
How do you prevent mosaic dominance but instead have exclusive dominance input? Why?
Have a small target that is eccentric from the fovea
| This is related to the V1 hypercolumns.
111
How does the wavelength influence rivalry and suppression?
Binocular rivalry have wavelength-specific inhibition strength but suppression (pathological) does not depend on wavelength. There is equal suppression strength for all wavelengths
112
What is Da vinci stereopsis?
Depth is perceived because of a rivalry between the eyes.
113
How does the brain decide to fuse, suppress, or rival?
The most important variable is the similarity of images in each eye.
114
The size of the zone of suppression ____ with increasing spatial frequency (i.e. “skinny bars”, or more fine detail) of the targets.
The size of the zone of suppression decreases with increasing spatial frequency (i.e. “skinny bars”, or more fine detail) of the targets.
115
The size of the zone of suppression decreases with ______ spatial frequency (i.e. “skinny bars”, or more fine detail) of the targets.
The size of the zone of suppression ____ with increasing spatial frequency (i.e. “skinny bars”, or more fine detail) of the targets.
116
What is the neural origin of rivalry and suppression?
After V1, it may involve feedback from V1 to LGN and/or intracortical inhibition within V1.
117
Why was wolfe and Blake wrong about their theory of 2 monocular channels and one binocular channel?
Monocular channels don't simply alternate, as demonstrated by mosaic rivalry
118
What is the sequence of developing rivalry/suppression in strabismus?
1st diplopia and confusion, then alternating suppression (rivalry), then preferential use of one eye, deviating eye deepens suppression, then increasing chance of amblyopia
119
What is the binocular suppression scotoma for an eso? The size is proportional to the ______
It includes the fovea and nasal retina. The size is proportional to the objective angle of the deviation
120
How is the suppression field of an esotrope vs an exotrope?
For eso, it's the nasal side of the fovea and sticks out towards the nasal retina.
For exo, it's the entire temporal retina (including temporal fovea) Wider area
121
___tropia tends to be more intermittent than ___tropia
exotropia tends to be more intermittent than esotropia
122
What can detect and measure suppression?
Worth 4-dot test Phoria/vergence testing Vectograph acuity charts (polarize lights) 4 BO test (for small angle strabismus, strab readjusts when lens is introduced) Bangolini lenses ("natural" maddox rod)
