Exam 2 shuffle Flashcards
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.
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)
What is the Hering-Bielschowsky afterimage test? What does it test? What are the steps?
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
Esophores that poorly adapt to base in prism are typically Type ___ Fixation disparity?
Type II
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.
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
What is the prominent characteristic of type I fixation disparity pts?
Flatter central region, S-shaped
What is Da vinci stereopsis?
Depth is perceived because of a rivalry between the eyes.
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)
The horopter of an exotrope is excessively _____
Concave, meaning it may lie within the VM circle
Downward divergent aniseikonia causes upper part of plane to ….
shrink and tilt toward observer. This is negative declination error
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)
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)
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.
What is the Y intercept on the Forced Vergence fixation disparity curves?
The Fixation Disparity in arcmin with zero prism
R0 = 1 indicates…
No rotation
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.
How do you calculate relative uniform magnification?
R = Tan(alpha 2) / Tan(alpha1) or Tan(alphaR) / Tan(alpha L)
When is relative magnification always 1?
On the V-M horopter because both alpha angles are exactly the same for both eyes. R=1
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.
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 closer nasally. Horopter shift is opposite to this
Prism has more magnification in its (base/apex}
Prism has more magnification in its apex.
H below zero means what?
Hering-Hillebrand horopter deviation shows that the empirical horopter is steeper than V-M circle
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
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)
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
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
What is the sequence of developing rivalry/suppression in strabismus?
1st diplopia and confusion, then alternating suppression (rivalry), then preferential use of one eye, deviation eye deepens suppression, then increasing change of amblyopia
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
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 farther nasally (at midline). Horopter shift is opposite to this
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.
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!
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
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)
How does the observer’s measured horopter compare with the V-M circle?
The observer’s horopter is flatter than the theoretical one
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.
What are aniseikonia symptoms?
HA, asthenopia, photophobia, reading difficulty, nausea, diplopia, etc
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.
What kinds of stimuli are suppressed?
Dimmer, blurred, stationary, peripheral from center, and temporal stimuli as opposed to Brighter, crisp, moving, central, and nasal stimuli
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.
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
Type ___ FD don’t really react to any prism
Type IV
What is associated phoria?
Prism to compensate the fixation disparity
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
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)
What is negative declination error?
When the top of a plane appears to shrink and tilt toward observer. This is from Downward divergent aniseikonia
The slope of the Forced Vergence fixation disparity curve as it crosses the ___ axis is important. What does flat slope indicate?
Y axis. Flat slope indicates healthy vergence adaptation.
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)
