Lecture 5 Flashcards
Does fixation disparity affect the horopter property?
yes
Which horopter criterion belongs to fixation disparity?
identical visual direction horopter
The vergence angle of the eye, the angle between the visual axis, is slightly inaccurate
The fixation point does not coincide with the actual target in space.
“Fixation disparity should not be confused with binocular disparity: fixation disparity is a misalignment of the visual axes; binocular disparity is non-correspondence of the retinal regions stimulated by a target located
off the horopter.”
fixation disparity
When a subject has exo fixation disparity, what type of binocular disparity does the intended fixation target have?
crossed binocular disparity
what type of vergence does crossed binocular disparity stimulate?
CONVERGENCE
What type of binocular disparity does an eso FD cause?
uncrossed binocular disparity
What type of vergence does uncrossed binocular disparity cause?
divergence
________ is a small purposeful error in vergence
fixation disparity
FD and heterophoria is USUALLY correlated or uncorrelated?
correlated
exophoria pt usually has what type of FD?
exo FD
esophoria pt usually has what type of FD?
eso FD
FD and heterophoria always agrees. T/F
False
FD: test under binocular condition - what type of phoria?
associated phoria
heterophoria: test under monocular condition – what type of phoria?
dissociated
ex: cover test
The amount of prism needed to eliminate fixation disparity.
associated phoria
horizontal associated phoria is usually smaller than what?
horizontal dissociated phoria
associated phoria is a more reliable indicator for what?
successful prism prescription
seen by both eyes, has an angular
width of 1.5
binocular fusion lock
seen monocularly OD sees top line, OS sees bottom line
Two Nonius lines
Clinical measurement of FD
Binocular fusion lock
Two Nonius lines
most accurate way of measuring FD
sheedy disparometer
what uses the same method of sheedy disparomter?
saladin card
Wesson Card testing principle
The polarized lines on the Wesson card are actually centered.
The lines mark the intended fixation point but each eye’s visual
axis misses it.
They appear deviated due to the fixation disparity.
if pt has exo FD, what happens with wesson card test?
top eye image compared to bottom, is more towards left side
wesson card: if arrow points to the right what type of FD?
exo FD
wesson card: if arrow points to the left what type of FD?
eso FD
sheedy: if bottom is to the left what type of FD?
exo FD
sheedy: if bottom is to the right, what type of FD?
eso FD
The sheedy disparometer marks the location of what?
visual axes of each eye; what doctor sees
the wesson card shows what?
perceived location of the fixation point relative to each visual axis; what patient sees
– The amount of prism needed to eliminate
fixation disparity
associated phoria
how is prism use with associated phoria?
used to shift the images to match the visual axis
Binocular rivalry can occur when very different images of exactly equal salience fall on corresponding points. T/F
False
Wesson Card: bottom arrow points to the right side. Half way towards the first point. How do you record FD?
4.3 min of arc exo FD
Saladin card: bottom vertical line is to the right.
How do you record FD?
Eso FD
If BI prism is placed on two eyes, what type of disparity is created?
Uncrossed binocular disparity
stimulates negative fusional vergence
Eyes diverge to maintain bifoveal fixation
uncrossed binocular disparity pt on sheedy test will see what?
top to the right
BO prism stimulates what type of vergence?
positive fusional vergence (convergence)
If we increase BI prism, what will happen to FD?
FD decreases
What if we put too much BI prism?
visual axis no longer moves, but images move farther temporally outside of visual axis –> FD increases towards eso (oppositely)
What axis for FVFD curve: amount of prism used to stimulate the vergence system
X axis
What axis for FVFD curve: fixation disparity, how closely the visual axis keeps up with the stimulus
Y axis
Y intercept on FVFD curve represents what?
FD (no prism)
X intercept on FVFD curve represents what?
associated phoria (FD=0)
Once we go beyond Panum’s fusional area, what will the patient experience?
diplopia
A greater slope across the middle section would show
that fixation disparity is slowly changing with the addition of prism.
When prisms stimulate vergence eye movements, the eyes tend to lag behind the prism, causing
a gradual change in the amount of fixation disparity. This is reflected in the slope.
The flatter the slope, the better the eyes are able to maintain what?
their starting level of fixation disparity (better vergence adaptation).
flatter and wider slope represents
a better system
What type is most common and considered a normal response?
Type I
eso FD when no prism, add BI increase the eso FD; add BO decrease eso FD till it becomes 0, then become exo FD.
Type I eso
exo FD when no prism, add BI decrease exo FD till it becomes 0, then become eso FD; add BO increase the exo FD.
Type I exo
What type curve is usually found in pt with large eso phoria?
Type II
What type of patient will respond to prism correction well?
eso heterophoria pt
What type of curve is usually found in pt with large exo phoria?
Type III
What type of curve for patient that has a small exo FD.
type 4
