Binocular Correspondence Flashcards
what is hering’s 2nd law of visual direction
there is a retinal point to point relationship between the 2 eyes
-for every retinal point in one eye there is a corresponding retinal point in the fellow eye w/ an identical sense of visual direction
what is hering’s 3rd law
objects on the visual axis of either eye in symmetrical convergence appear to be on the median plane of the head (straight ahead)
what is a cyclopean direction
a single visual direction in the binocular visual field
binocular egocentric direction = ___+_____
cyclopean direction+gaze registration
cyclopean directions are analagous to…
oculocentric direction
all points on the retina have a binocular corresponding point except…
at the optic nerve head
normal correspondence only dpends on the retinal points being stimulated and is nnot affected by…
image luminance contrast color size orientation
normal correspondence is very stable, altered by …
only a few minutes of arc in the foveas, and then only by extreme fusional stress
what is spatial correspondnce a property of
the brain
also evident in the somatosensory system
what is binocular disparity
stimulation of noncorresponding points
each pair of corresponding oculocenric directions form a single….
cyclopean direction
what is a single visual direction in the binocular visual field
cylclopean direction
what are some synonyms of binocular disparity
retinal disparity
physiological disparity
what can crossed disparities stimulate
- steroscropic “nearness” if not a large amount of disparity
- crossed diplopia from disparity too large
- ocular convergence can be stimulated to look at the near object
what can uncrossed disparity stimulate
- stereoscopic “farness” if disparity small enough
- uncrossed diplopia disparity too large
- ocular divergnce to look at far object
what is the horopter
the set of points in physical space that can stimulate corresponding retinal points when eyes are converged to aim at a fixation point
how is the horopter shaped
bowl-shaped surface in near vision and flattens out as you look farther away
what is the best at the horopter
stereopsis and binocular summation
-single vision also occurs here
what is the veith-muller circle (VMO)
what question does it answer
theoretical horopter
“in principle, where should you put lights in physical space to stimulate corresponding points”
what does the VMO assume
eyes are identical and optically undisorted
what do objects in the VMo stimulate
zero binocular disparity
waht can objects in the peripheral vision stimulate
cross disparity
zero disparity
uncrossed disparity
where are the images for crossed disparity
where is it in relation to the VMO
images are more temporalward on the retinas, relative to corresponding opints
-inside the VMO
where are the images for uncrossed disparity
where is it in relation to the VMO
images are more nasalward on the retinas, relavtive to correspoinding points
-outside the VMO
what is the empirical horopter
answering the question “where do i have to put lights in physical space to stimulate corresponding points in this person”
what direction do we measure the horopter
horiztonal (longtidinal) direction
what are the additional rod adjustment criteria that measure an approximate horopter
apparent fronto-parallel plane equal distance haplopia max stereo actuity zero vergence
which methods of measuring the horopter don’t reflect the effects of fixation disparity
apparent fronto-parallel plane
equal distance
which method of measuring the horopter measures the extent of panum’s area
haplopia “single vision”
what will non zero vergence make you use to see an object
vergence eye movement
how does maximum stereoscopic acuity work
finer the stereoscropic threshold, the closer a point is in space to the horopter
what results does the spatial plot of the horopter show
ELH results
what are the 3 variables to quantify the ELH
relative curvature (hering-hillebrand deviation)
skew (horopter closer to right or left)
offset (how far off the fixation plane is the horopter displaced)
does the normal horopter have more or less curvature than the VMO
normal has less than VMO bc of the asymmetry of the eye
how do wedge prisms bend stereoscropic space
creates disparity where there shouldnt be any
what does a large BO prism make a flat surface appear as?
what does a large BI prism do?
BO=concave (convex horopter)
BI=convex (concave horopter)
is the ELH or the VMO more curved in a divergence excess intermittent exotropia
- why is divergence stimulated
- uncrossed or crossed disparity?
ELH more curved than VMO in near vision (only known conidition w/ this type of ELH)
- most objects don’t fall on this horopter so stimulates divergecne (most of them are beyond this ELH)
- uncrossed disparities in near fixation may result in their tendency to diverge
what is skew a product of
horizontal aniseikonia
what are small offsets caused by
fixation disparity (FD)
waht does FD cause eyes to do
misconverge during bifxiation
does FD disrupt fusion?
what does it reduce?
too small to disrupt fusion
steropsis may be reduced
what is it called when the eyes converge too much
when the eyes converge not enough
too much = eso
too little = exo
what are large offsets caused by
what is lost in a large offset
strabismus
central steropsis is lost
what condition can cuase the horopter to have a small notch in it
-what is the notch called
esotropic strabismus
-flom notch
what is the definition of anomalous retinal correspondence (ARC)
- the centers of the foveas have diff visual directions
- the fovea of one eye has the same visual direction as a peripheral retinal point in the fellow eye
when does ARC only occur in
early-onset strabismus
- congenital OR
- acquired (very early age)
how can arc be a good predictor in the treatment of esotropia
arc present = less than 50% chance of cure
arc absent=better than 50% chance of cure
-arc prevents reflexive movements
in testing correspondence, the purpose is…
to show whether correspondence is bifoveal
when will there be correspondence
when both eyes are being used
what is testing ARC based on
visual direction judgements
when does ARC sometimes disappear
in total darkness
why does it not work if we test correspondence based on fusion? stereopsis?
patient still may be able to fuse if non correscpoinding points are stimulated
-same with stereopsis, patients with arc may present w/ normal stereo
how must the test targets be in testing correspondence
the test targets for both eyes must be unfusible but simultaneously visible (so we can assure that we are testing the visual directions of each eye)
-ned patient to see 2 images at the same time
what can void a correspondence test
image suppression or fusion
how can you make the od and os test images unfusible
spatial separation
time separation
form separation
what is spatial separation
- use polaroid glasses and pol target so each eye sees one image, keep background fusible
- large vertical disparity maintains dissociation (od image above where they are looking, os image below)
- horizontal directions are compared
- not often used in clinic
what is time separation
when can this be used
- flicker the image to the right eye then to the lef teye
- pt can’t fuse the images but can still compare the direction
- used in “major amblyoscope”
what is form separation
when can this be used
- 2 image shapes are so diff they can’t be fused
- used in afterimage test (horiz in one eye and vert in other, can compare direction of each image) and bagolini lens test (diff orientation in each eye, can’t fuse but cna compare their visual direction)
what are the 2 questions you must ask to diagnose ARC
- where did the patient see the 2 targets?
- subjective
- comparison of the visual directions btwn the 2 eyes - where were the images on the retina?
- are they both on fovea?
- stimulate foveas monocullary to ensure this
what is the afterimage test
- monocularly place afterimage on each fovea
- open both eyes
- assess visual directions: cross=foveas have same visual direction and are corres points, no ARC
if a vertical line was on the left eye and a horiz line on the right eye, what would a pt with a left esotrope w/ ARC see
horiz line to the left and vertical line to the right (crossed diplopia)
- bc the fovea of the left eye is temporal to the retinal point that is corresponding w/ the fovea of the straight eye
- afterimage is temporal to the point being used to see “straight ahead” so it will appear in the nasal field
if a ptient is strabismic with arc, what would they see with the bagolini lens
2 lines form a symmetric cross
what would a ptient with strabismus but no arc see with a bagolini lens
2 lines that are not overlapping
if the patient has a left esotropia what will they see with the bagolini lens
bulb and streak stimulate a nasal point on the left eye
- fovea stim in the right eye
- left eye will see the image in the temporal field = uncrossed dipolpia
- botton streaks, no top
what is the zero measure point
the peripheral retinal point that the fixation target image falls on on the turned eye
what is the pseudofovea (pf)
the PVD moves from the fovea to a point closer to the zero-measure point in the turned eye
in a normal left esotropic eye w/o arc, where would the patient see the image of the target
to their left w/ their left eye
-uncrossed dipolopia
what will the patient see if the pseudofovea lies on the zero measure point
single
how are ef and pf related
they both use a point other than the fovea as the PVD
- they are measured separtately bc the brain rewires these btwn binocular and monocular vision
- may be diff than the
when the pseudofovea is shifted from the physiological fovea, all other local signs…
shift with it. in the same direction and by the same amount
a patient with arc will have a psuedofovea that is closer to the zero measure point, what does this result in
smaller amount of disparity, smaler amount of diplopia
-img on the zero ref point seems to be closer to the straight ahead position
a patient w/o arc but with the same amount of eye turn of patient w/ arc will use what as their pvd
waht does this mean
fovea => thus the fixation image will be stimulated a point far from the fovea => larger diplopia
the displacement of the psuedofovea correlates with the size of…
the strabismus
why can permanent diplopia occur after strab correction surgery
patinet is still using arc
-when the ey was turned this accounted for it but now it has a straight eye and the visual directions btwn the eyes are confused
what are the 3 types of arc
harmonious: single; pf at zero measure point.
unharmonious: uncrossed diplopia=eso, crossed=exo; pf btwn the fovea and zero meausre point
paradoxical: crossed=eso, uncrossed=exo; pf more than the amount of eye turn
how many prism dioptoers is arc considered
20 prism diopters
what is burian’s sensory theory of arc (most widely accepted)
arc is a sensory adaptation to constant strabismus
- deviated local signs are remapped in visual cortex (develops slowly throughout early childhood)
- do not lose normal corres completely
- arc can be turned on and off once established
what is morgan’s motor theory of arc
arc is the result of the registration of the abnormal motor innervation that causes strab
what can morgan’s motor theory predict
what can it not easily explain
harmonious arc-no fusion or stereo bc the points on the retina do not agree
nonuniform arm
how does the motor theory best explain covariation
as the amount of the eye turn decreases, the amount of arc should decrease as well.
the amount of arc depends directly on the motor innervations of the eye muscles and the amount of eye turn
