Lecture 3 Flashcards
All points along the circumference of the VMO stimulates what?
corresponding points
All objects located on VMO stimulate what?
0 binocular disparity
The horopter is approximately ________ in near vision
bow-shaped
The 3 assumption for VMO
Both retinas are spherical.
Both retinas have symmetric distribution of local signs across nasal and temporal retinas.
Right and left retina are the same size with the same local sign geometry.
When we actually do an experiment on a human, we find that the locations in space that have identical monocular visual directions are what?
imaged onto corresponding points, are not the same as the Vieth-Müller Circle.
The empirical longitudinal horopter is generally ______________ than the VMO.
less concave
Methods of Measuring ELH
Horopter criteria:
1) Identical visual direction
2) Equidistance (Stereoscopic depth matching)
3) Singleness (haplopia)
4) Minimum stereoscopic threshold
5) Zero vergence
*first 2 are more commonly used methods
When 2 targets, each presents to one eye, are perceived as lying in a single visual direction, the images of those targets must be formed on what?
corresponding points
What is the only true horopter criterion (most accurate) and why?
Identical visual direction because it’s the only one that directly measures the visual direction.
Nonius Horopter is aka
identical visual direction
Equidistance Horopter is aka
steroscopic depth matching or apparent frontoparallel plane (AFPP) method
Advantage of equidistance horopter
examiner can actually see the shape of the horopter directly
disadvantage of equidistance horopter
AFPP method does not reflect the effects of fixation disparity, unlike the Identical visual direction
fixation disparity
most people have an error so our eyes look either ahead or behind the actual target; only observed with nonius horopter
The most popular way to measure horopter
Howard—Dolman Apparatus
The Singleness (haplopia) horopter actually measures what?
the extent of Panum’s area at the fovea and at eccentric locations.
The width of the zone of singleness reflects what?
PANUMS SPACE
What is the most commonly used horopter?
equidistance
Horopter is a collection of points which have what?
the exact same visual direction on each eye
What is the most accurate horopter?
identical visual direction
Why is the empirical longitudinal horopter different from the theoretical horopter?
all of the above? go back to check
Two variables that affect the shape of the ELH
Skew (Relative magnification, R)
Curvature (Hering-Hillerbrand deviation, H)
Regarding skew, “External” referring to being outside of the eye because?
we can not directly measure these angles.
The inferred angle is influenced by
the optics of the eye.
What is R?
the relative magnification of the retinal images between the two eyes.
When target on the horopter,
α1=α2, R=1, will have what magnification?
no relative magnification
When one eye image is magnified or minified relative to the other eye, as in aniseikonia
α1≠α2, R ≠ 1, what happens to the target?
target no longer falls on the horopter
How do we make α1=α2 again?
observer has to move the target
review relative magnification slides
boo
The horopter is skewed toward which eye?
magnified eye
The perception of frontal plane is mirror image of what?
horopter
The difference in curvature between the horopter and
Hering- the VMO, as
Hillerbrand deviation
measured at the fixation point, is called
Hering-Hillerbrand deviation (H)
The value of H typically ranges from what?
+0.1 to +0.2
Does H indicate a flatter or steeper horopter than VMO?
flatter
Why H>0 usually? Why ELH is flatter than VMO?
Both retinas are spherical.
Both retinas have symmetric distribution of local signs across nasal and temporal retinas.
—“Nasal packing” phenomenon: local sign in nasal retina are spaced closer together
—Temporal visual space is overestimated
Right and left retina are the same size with the same local sign geometry.
Which visual space is overestimated?
temporal visual space
What happens to the shape of horopter when we increase fixation distance?
curvature changes so that it goes from covex to flat than concave
*however, the changes in curvature of the horopter mirror changes in curvature of the VM circle, yielding no net change in the value of H
the viewing distance at which the apparent and objective frontal plane coincide
Abathic distance
When is the horopter truly flat?
abathic distance
What is the abathic distance
6 meters
fixation disparity
misalignment of the visual axes
binocular disparity
non-correspondence of the retinal regions stimulated by a target located off the horopter
Two eyes slightly under- converge, fixation point behind the target
Exo Fixation Disparity
Two eyes slightly over- converge, fixation point in front of the target
Eso Fixation Disparity
a small purposeful error in vergence.
fixation disparity
Factors affecting offset of ELH
fixation disparity
strabismus
Strabismus affecting ELH
– Horopter shifts toward the intersection of the
visual axis
– Abnormal, seen in some strabismus – Sensory fusion is disrupted
Fixation Disparity regarding ELH
normal, does not disrupt sensory fusion
aniseikonia and horopter
Geometric effect
Induced effect
size lens
geometric effect
magnification along horizontal meridian
two eyes image size are different from each other
aniseikonia
magnification along vertical meridian
induced effect
special lens that only change the image size with no optical effect
Meridional size lens: only change the size alone one meridion.
size lens
When an axis 90 meridional magnifier is placed in front of right eye, where is the image magnified?
horizontally, producing retinal disparities that yield a percept of the world tilting AWAY from the right eye
Induced effect can be measured by what?
the AFPP horopter apparatus (Howard-Dolman)
Nonius horopter will not rotate because what?
no physical horizontal binocular disparity being created.
what causes nonuniform magnification?
Prisms
*More magnification at the apex than at the base
BI prisms in front of both eyes:
Temporal side more magnified than the nasal side
Horopter bends toward observer at the temporal side
Perceived world is a mirror image of the horopter
Perceived world bends away from observer
T/F: EHL is more curved than the VMO
true
*when H is less than 0
Clinical situations of curvature change where H < 0
- Divergence excess
* Intermittent esotropia
3 clinical situations for irregular horopter
-
Regional spatial distortion, may be a result of
anomalous retinal correspondence
Flom Notch
