This content outlines a systematic five-rule approach ("5 Rs") for interpreting visual field test results, crucial for diagnosing and monitoring conditions like glaucoma. It emphasizes verifying the test's validity, analyzing reliability indices, probability plots, nerve fiber layer patterns, and reaffirming the diagnosis through clinical correlation and potential retesting.
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Coming now to presenting the five Rs,
the five rules in the visual field interpretation
interpretation
and I would like thank the popular
lecture on this topic the forge lecture
focusing theology and reframing locom evaluation
evaluation
which has been done uh and sponsored by
allergen in 2013.
So starting with these five rules, five
Rs, the first R is the right test,
then reliability,
then the review of probability plots,
then the arena of layer patterns of
loss, and then reaffirming the diagnosis.
And we'll explain each rule in details
in the following slides. First rule
be sure that the rightest was used.
So the right test we should coming we
should came across all these points.
Check the strategy. Check the similar
size the field size the eye the age the
by confirming the date of birth the
pupil size and the refractive error.
We'll see here the OD which means the
right eye. We'll see here
the stimulus size. says three and wide
packaging 31.5 a post strategy saf
diameter here it's missing should be
mentioned should be more than 3 mm mm
and visual accurities also should be
mentioned and here the refractive error
plus two and here's the date of the test
the time of the test and the age of the
patient all these should be confirmed
before starting ing reading the visual
field print out. Okay.
So we'll confirm the right strategy by
confirming the SA standard as we say SA
first. It's not recommended for
patients with the gluccom because
because it can underestimate
the scotoomas. So ideally should be SA
standard the Swedish interactive fish algorithm
algorithm
here you will find it's the strategy SA
standard then you will check the right
stimulus size was used and we said that
the HR visual field analyzer use the
goldman size three
as a standard. Sometimes you can use the
size five as we said for advanced visual
field loss or decreased visual acuity.
This is the five wide stimulus in these
cases in the advanced gluccom.
Then you should
check the the right field size as we
said the 24-2 is the standard size
central 24-2 threshold test. However, 10-2
10-2
it's very important in advanced gluccom
to check the progression and it's very
important for visual field loss within
the central 10 degree of fixation as we
said like gluccom or gluccom suspect 10%
of them will be having uh defects and on
then you will check that the right age
the date of birth of patient
has been reported. Why? Why this is
important? Because there is correction
to the normative database. There's a
Goldman table that adapted from the
Humphrey field analyzer instruction
booklet. Depending on the age, they will
correct for the refractive error. For
example, if the patient is between 45 49
years, they will add plus two their
sphere. And that's why they correct
normative database. So very important
please check the age check the date of
birth for the patient and also you will
check the refractive error you will see
the refractive error for example for
this patient having minus 1.25 to five
diotric sphere and also the correct
pupil size more than 3 mm because small
pupils meio pupils or people taking
pyocarbon drops or any myotics agent
will have small pupils so they can block
the peripheral stimulus sometimes
causing uh force peripheral decreased
uh retinal sensitivity and therefore
force peripheral field effects. So it's
very important to check the correct
pupil size. Here it's mentioned 3 mm.
The second rule coming to the second
rule we should check the real
reliability of the field. Is is this
print out reliable or no? By
main three indices.
These indices are the false positives
and false negatives and the fixation
losses. I will explain these three in
details in the following sides and you
will see them in the print out
in the upside in the up left side
corner. Here you will see the details
related to the
rightness and here here you will see the
data related to the reliability indices.
The first indices is the force positive
rate which is very important indices to
check that this visual field print out reliable
reliable
and it's the percentage of the time that
patient respondent in the absence of
stimulus and the id rate is should be
should be less than 10%.
If you see false positive rate more than
3 33% this is unreliable test and you
should be cautious when you see that the
false positive rate more than 25%. Why?
Because elevated false positives
can artifactually improve the appearance
of the field. And there's some patients
they just click
keep clicking they calling calling them
trigger happy because they keep
responding in the absence of any
stimulus. So this is very important
reliability indices you should always
check it before reading the print out
and you here you see false positive
errors 2%. Ideally should be less than 10%.
10%.
Coming to the second one which is the
false negative rate. the secondary
reliability indices
uh which is the percentage of time that
patient failed to respond to a stimulus
that should have been seen based on past
responses. So it's the force negative
basically is a negative response with
brighter than the threshold stimulus in
previous tested point. So the patient
will see a point then the test
testing machine will show at the same
same location higher pressure simulas.
The patient should see it. However, the
patient will not click,
will not respond. And this seen
especially in patient falling asleep can
reflect fatigue.
And if you see it more than 33%, it's
unreliable and you should use it with
caution in more than 25% false negative
rate. However, however, some
testing algorithms
have no longer using the force negative
rate uh index. Why? Because in advanced
visual field damage, when you have
visual field damage, the false negative
rate will be higher will be high because
of the variability
in receiving the stimulus in these
advanced visual field damage location.
So they said that force negative rate
sometimes can be not related to fatigue
or falling asleep but related to
advanced visual field. So some tests
some doctors they don't depend depend on
it fully but they depend mainly on the
force positive index and the uh fixation
loss that we will say uh that we will
discuss in the following slide.
Coming to the fixation losses
reliability index. This is the
percentage of the times that the patient
responded to a stimulus that presented
as the plotted plank blind spot and this
is we call it uh
hail carac method where they present a
point to the blind spot. Okay. And the
patient will respond. So there's no way
how will he respond to a stimulus
presented at the blind spot. However,
so consider as fixation loss.
However, it has main drawback. We'll
talk about it in the following slide. So
fixation loss is usually increase if the
patient doesn't maintain fixation, keep
moving his eye,
the patient head moves or the blind spot
was incorrectly located at the beginning
of the test.
And this is the main drawback of the uh
hail kaku method where they present a
similar to the uh uh plotted blind spot
because if you locate the blind spot
incorrectly in the beginning of the test
this uh fixation loss measurements will
be unreliable and you should use with
caution when you see the rate more than
20% fixation loss and if you see that
the fixation loss rate more than 33% %
this is unreliable test. Okay.
Okay.
And here you see the fixation losses is
four out of 15.
So as we said the original method was
hail KCO method where they presented
they present similars at the plotted
blind spot mapped in the beginning of
the test. However, the main drawback
that if you incorrectly locate the blind
spot at the beginning of the test, this
will increase the fixation losses
uh flessly
and it will appear that the test is
unreliable. So what Humphrey visual
field did they
use what we call it gaze tracker where
they use infrared in order uh uh
infrared light in order to check the
gauge stability
uh during throughout the test and you
will see at the bottom of the print out
gaze stability line. You will see it
like a line like that here in these
points. it means that the gaze was was
stable. However, when you see it up, it
means that the eye move. So, upstrokes
means that there was increased eye
movement and if you see downstrokes, it
means that there was uh lead uh
movement. So, this new uh a new uh
technique by Hford visual field
analyzer, it's much better than the
original method ho method which depend
on the blind spot. However, the gaze
tracker depend on infrared light that
follow and uh control the gaze during
throughout all the test.
We have other indices
just other clues that this test is not
uh reliable is unreliable.
But this test these uh uh points are
just clues that help you to understand
the full print out. So shortterm fluctuation
fluctuation
short-term fluctuation means that they
retest 10 pre-selected points and then
they calculate the difference between
the original test and the retest
threshold. So first we they will select
10 points that the patient answered uh
to them. Then they will retest these 10
uh pre-selected points and then they
will calculate the difference between
the original test and the retest
threshold and if they uh see that the
difference more than four decibel so
this mean that the short-term
fluctuation increase and this measure
the consistency an indicator of
reliability and also can be one of the
early signs of gluccom. Sometimes the
patients see see it and some sometime
doesn't doesn't uh see it. So
uh as we said this short-term
fluctuation one of the indicator of
consistency and reliability if it's
increased there is suspicious. However
the uh SA algorithm doesn't calculate
we have what we call corrected pattern
standard deviation to the short-term uh fluctuation.
fluctuation.
Uh and this corrected uh pattern
standard deviation. We'll talk about the
pattern stand deviation the following
side the pattern send deviation will be
corrected to the short short-term fluctuation
fluctuation
and it measures the localized
variability the localized irregular
irregulatory. So if you see high
corrected but standard deviation means
high uh uh localizer regulatory and
highly suspicious for gluccomatus damage
and in octopus not in hump visual field
care always must be taken when you see
the reliability factor values more than
10%. Which is mainly depending on the
this shortterm fluctuation during the
test. So it's like intrais variability.
Not only that we have another uh or
others uh reliability indices. The
reliability is low when there is more
than 5
50 550 simulas are projected or when the
test takes more than 8 18 minutes.
Usually to to determine the threshold
point dislocation uh five stimulas are
needed. In patients with field defects
more stimulus is needed. So if you if
you see that the stimulus more than uh
550 are projected or the test takes more
than eight 18 minutes
it means that the reliability of the
test is low. Always we have very popular
uh field effect uh on the a grayscale
map individual field print out representing
representing
uh reliability index the clever leaf
pattern. If you see this clever leaf
pattern it mean that the patient
becoming fatiguable in in attentiveness
with time
and I will talk about it just in the
following slide. And also if you see
increased I upstrokes or lead
downstrokes movement on I track a line
or the gear tracker line it means that
there is some unreliability because of
the fixation. So this is the unre
unreliable field because of the clever
leaf appearance which means that the
patient becoming fatiguable becoming
inattentive becoming doesn't concentrate
losing concentration.
So they will test
in the beginning of the test very well.
However, when they coming with time they
will lose concentration, lose energy and
motivation to respond well. So this
appearance of the field like clever leaf
uh uh it will show. So uh the four
primary points around the fixation are
checked and confirmed. If you see then
here you will see this is uh all field
doses. This clever leaf patterns means
So rule number three review the
probability plots.
Coming now to the global indices the
most important one and we'll talk about
the most two important global indices.
The first one is the mean deviation the MD
MD
which is from the just the name you
understand that it's talking about the
mean average and deviation so it's the
average loss of the entire field in decibels
decibels
or in other ways the depression
the loss from compared to the age normal
hill vision as we said previously the
hill vision is like conceptual model to
understand the visual field normal and
abnormal pyramid representing the hill.
This the maximum point in the hill is
the phobia where there is the maximal
visual threshold uh sensitivity and when
you go to the periphery there is
reduction in this retinal sensitivity to
the threshold to visual threshold and if
you see in a gluccom patient they will
start losing in periphery. However
patient for example with uh ordic
nuritis will start loss of the central
uh uh hill of the pigeon. So if you see
this average loss of the entire field
decibels compared to the age normal
corrected data give you the mean deviation.
deviation.
And for example, if you have a patient
with minus4 decibel, it means that it has
has
on average four decel loss less than the
normal age adjusted population.
It means that he has four disable four
decibels depression at all points in the
field or depression of eight decibels
over half of the field. Both of them
would give uh MD or mean deviation 47.
The most important point this one the
more negative MD the more worse feel. So
if you see here minus 10 it's not like
minus one
and this probability the p values the
probabilities given for that MD would
occur normal individual. So this MD for
example it can happen in less than 5% of
normal individuals and if you say it 1%
it means that this MD mean deviation can
happen in less than 1% of normal
population. So 99% of this MD uh having
abnormal result you understand what is
the meaning of p value it's like p value
Coming now to the second most important
uh global index which is the pattern
standard deviation
which is a measurement of focal visual
loss. So it's a measurements not of a
global or focal field loss
which means that it's the standard
deviation of each point from the age
corrected normal and it measures the
variability or local irreg
irregularities of the field. The more
positive the more bad not like the MD
the more negative the more bad here the
more positive higher pattern standard
deviation means higher variability
higher irregularity in the fields which
means there is localized field field
damage and in the ocular hypertension
treatment study the PSD the pattern
standard deviation identified as one of
the out of five important contributions
contributors to the risk of developing
gluccom. coma.
However, this pattern standard deviation
in normal patients or severely affected
visual field, they will have low pattern
standard deviation because in advanced gluccom
as we say that this PSD the pattern
standard deviation can decrease because
the damage is no longer focal. It will
be all the field reduction.
there is like a generalized reduction in
the uh visual visual field uh like
tunnel vision. So because there is no
localized irregularities because of the
advanced loss the patent cell deviation
will be low. However, in general the
higher pattern cell deviations means the
As we said coming to the numeric results
and grayscales these are the numeric
results and corresponding with a map
grayscale map we have threshold
sensitivity map. This sensitivity map uh
it has numerical facial sensitivity of
each location by decibels. And this one
the this map you should depend on. And
this corresponding grayscale map should
be used for education for patients
and the higher the threshold value or
the brighter the gray scale means the
higher sensitivity. So if you see blackish
blackish
uh the gray scale means that the patient
has low sensitivity. Okay. The higher
the threshold value it means the
brighter the gray scale and the higher sensitivity.
