how to read Humphrey field report 2

1
To have a system while reading the Humphrey’s field printout, we can follow
the letters of the word WANDER, where:
W stands for ” What was done”
A stands for “Accuracy”
y of what was done
N stands for “Is it Normal or abnormal”
D stands for “any Defect pattern present”
E to “ Evaluate compatible disease” that produce such pattern
And finally R to “Review” the literature regarding the possible diagnosis and
the differential diagnosis.
2
“What was done?” : this point will include two items, the area tested, and the
strategy used while conducting the test.
Tested area: the test of the field of vision can involve the central 60o,
30o, 24o and 10o.
Strategy used : the commonly used strategies used are full threshold,
SITA standard and screening
3
Parts of the Humphrey’s field’s report :
1. Reliability indices
2. Strategy used
3 Gray scale
3.
4. Numerical values
5. Total deviation
6. Pattern deviation
7. Key for the probability plot graft
8. Glaucoma hemifield test
9. Global indices
4
We notice number 30 is written to the side of the plot. So it is either 24o or 30o
pattern. This is a report of the central 24 o test the outermost ring has only two
dots on the nasal area. (see next slide for the difference between 24o and 30o
test pattern)
We notice
W
i that
h The
Th blind
bli d spot is
i to the
h left
l f side
id off mid
id li
line so this
hi iis a print
i
of a left eye.
5
In 30o and 24o test, test locations are separated 6 degrees apart.
In 24o pattern, the outermost ring is omitted from the test except the two nasal
points, the will reduce tested locations from 76 locations in the 30o test to 54
locations in the 24o test, thus reducing the number of tested locations by 29%,
this
hi will
ill shorten
h
the
h time
i off the
h test, thus
h reducing
d i patient’s
i ’ fatigue
f i
andd
avoiding lack of attendance of the patient.
These two nasal dots are not omitted from the 24otest being commonly
involved in glaucomatous damage .
6
In the central 10o test pattern, the distance between test locations is only 2o
thus more locations are tested compared to the 24o or 30o test pattern. Thus
the central 10o test pattern provides better information of any damage in this
area compared to 24o . To illustrate the next two slides are of the same patient
test with 24o then with 10o test pattern.
pattern
7
In the correct plot deviation we notice that all points in the central 10o are
involved except one point only (arrow).
8
When the same patient was tested with the 10o test pattern, we notice many
points (10 points : arrow) are still within the normal range of sensitivity. Thus
if any further deterioration of the field happens with time, the 10o test pattern
can demonstrate such changes.
9
10
Five stimuli are presented to each test location in order to reach the sensitivity
of that point.
11
A “bracketing” technique is used to threshold each test point. An initial
stimulus is presented at a level the patient is expected to see. If seen, the
stimulus intensity is decreased in 4 decibel steps (0.4 log units) until the
patient no longer sees the stimulus; if not seen, it is increased in 4 dB steps
until seen. The instrument then changes direction, moving in 2 dB steps until a
change in patient response is made. The last stimulus seen by the patient is
recognized as the threshold for that point.
12
This is the standard testing strategy for the Swedish Interactive Thresholding
Algorithm (SITA).
SITA-Standard cuts testing time in half relative to the Full Threshold strategy
without compromising test reproducibility.
It is available in the 700 series of the Humphrey machine.
Starts by 4-2 type algorithm
SITA strategy relies on models of visual fields (both normal and
abnormal ), thus using an artificial intelligence type of programming &
really on guesses where the threshold is.
SITA – Standard : If 90% accuracy compared to standard threshold…
when the machine determines it is about 90% right it stops. It is
comparable to standard threshold yet done in half the time only.
SITA - Fast : if you accept 80% accuracy of that guess …. when the
machine determines that it is about 80% right it stops.
The SITA stragegy does not determine Short term Fluctuation.
13
The actual threshold is not determined, so results are given in symbols
Only detect rather large changes (greater than 4 – 5 dB below normal )
Early glaucomatous defects may not be detected.
Screening tests are much faster than threshold tests.
Positive screening test must be followed by quantitative test.
14
Two level screening test : seen points presented by opened symbol and unseen
points are presented by black square.. Disturbed points are concentrated in
temporal field whereas nasal field is essentially normal. This patient has
chiasmal compression.
15
Not seen points are retested with brighter target. So it differentiates the defect :
shallow or absolute
16
The second item is the word WANDER is accuracy …… we look at the
upper right corner of the printout at the reliability indices.
17
Reliability indices include fixation loss, false positive and false negative.
Also in some strategies the short term fluctuation is examined,(see later), and
this will also information regarding the reliability of the test. A short term
fluctuation less than 2.5 means a test of good accuracy.
For Full Threshold and FastPac tests, false positive errors, false negative
errors, and fixation losses are printed as a ratio, such as “3/10” . The first
number represents the number of errors committed, while the second number
represents the number of times the instrument checked for each of these errors.
In SITA-Standard and SITA-Fast tests, fixation losses are also printed as a
ratio, but false negative and false positive errors are printed as a percentage,
such
as “25%”.
18
Before starting the test, the patient is asked to keep fixing a central location at
the bowl of the machine. The blind spot has a known size and location. It is
located on the temporal side of point of fixation, having a size of 5o X 7o
and its centre is located 12.5o from point of fixation and slightly below the
horizontal line.
line
During the test, a stimulus is presented to the blind spot, normally the patient
should not see it, so if the patient reported that he noticed it, this means
change of fixation. Fixation loss is the number of times a patient responds to
a target placed in the blind spot.
Example : fixation loss
3/20, this means that 20 times a stimulus was presented to the blind spot area
and 3 times the patient notice that stimulus so three times there was fixation
l
loss.
When
Wh fixation
fi ti loss
l
is
i more than
th 33 % the
th test
t t is
i nott reliable.
li bl
19
False positive error : is the number of times a patient responds to the audible
click of the perimeter's shutter when no target is presented.
In Humphrey machine, an audible sound heart when the stimulus is presented,
and some patients start to respond to the sound rather than to the light
stimulation.
i l i
So
S to avoid
id that
h problem,
bl
dduring
i the
h test an audible
dibl soundd is
i
presented to patient without any light stimulus. If patient respond positively,
then is a false positive error.
Example false positive error 4/9 meaning 9 times an audible sound was
presented and 4 of them patient responded that he seen the light stimulus.
Again of false positive error is 33% or more, test is not reliable.
20
False negative error : is the number of times a patient fails to respond to a
suprathreshold target placed in a seeing area of the visual field. That is to see,
the sensitivity of one location was determined, and later a strong stimulus was
presented to that location, and the patient should be able to see it, but he does
not Example false negative error 1/5 meaning patient was tested 5 times and
not.
one of them he failed to respond to a suprathreshold stimulus.
Thresholds decline the longer the test goes on, and fatigue typically accounts
for this phenomenon.
High false negative error rate tends to make the visual field seem worse.
NB. Patients with significant visual field loss, including scotomata with steep
edges, can demonstrate high false-negative rates that do not indicate
unreliability. This effect appears to arise from presentation of stimuli at the
edges of deep scotomata, where short-term threshold fluctuation can be quite
variable.
21
Third point in WANDER is to see whether the test in normal or abnormal.
The results of the test are shown in different forms namely : the gray scale,
the numerical values, the total deviation , the pattern deviation, the global
indices and finally the glaucoma hemifield test.
22
The Gray Scale (Halftone) give a reasonable impression that can be
used to explain to the patient his condition but we do not depend on
it for evaluation of field damage. This is due to the fact that only
points are actually tested (54 -76 points ), and at the same time
2000 symbolic representations are used to draw the gray scale
scale. So
what actually happens is that the software fill the spaces between
the actual tested points.
23
And also one symbol is given for a range of sensitivities , so the actual
sensitivity of a location may change with time (for example drop from 35 to 31
) but still the same symbol is used. NOT sufficiently accurate to follow fields
over time.
24
Numerical values are the estimated sensitivity of each test location. These
values are used by the software to make different calculation and also the
treating doctor use them to estimate the severity damage and to detect any
progressive deterioration of the field of vision (see later).
Normality or abnormality
A cluster of 2 or more points depressed ≥5 dB compared with surrounding
points is suspicious.
A single point depressed >10 dB is very unusual but is of less value on a single
visual field than a cluster, because cluster points confirm one another.
Corresponding points above and below the horizontal midline should not vary
markedly;
k dl normally
ll the
th superior
i field
fi ld is
i depressed
d
d 1–2
1 2 dB comparedd with
ith the
th
inferior field.
We have to keep in mind that we cannot compare printout of different
machines e.g. Humphrey and Octopus because the test locations are not the
same and also because the decibel values used byy different manufacturers mayy
not be comparable owning to differences in background luminance and test
object intensity.
25
Total Deviation :
The test would not start unless the date of birth of the patient is entered. Saved
in the machine are the normal values of each test location of normal persons
having the same age of the patient under test.
The software start to compare the estimated sensitivity of each test location
with that value of the normal population of the same age, and the difference is
recorded. So if you look at the printout of total deviation and found a value of
-4 this means that the estimated value of our patient is less by 4 db form the
normal values of persons of the same age. A recorded value of +2 means that
our patient showed a higher value of 2 than the normal. A value of zero
means that the patient value is the same as the normal population.
So we can defined the total deviation as the difference between the
measured threshold of each individual test location & the agecorrected normal value for that location
26
Comparing the patient’s recorded values with those of normal persons of same
age is a must because the sensitivity of the retina decreases with age. It is
known that Visual field thresholds decline with age at a rate of 0.5-1.0dB
per decade.
27
The graphic probability plots of total deviation :
To understand this point we need to revise the meaning of
p
probability.
y
28
The frequency distribution curve :
Suppose we measured a value (e.g. the height) among a sample of the
population, then we start to plot a curve where on the X arm we recorded the
height and on the Y arm we recorded the number of persons having a particular
value.
l
This
Thi curve is
i known
k
as the
h frequency
f
distribution
di ib i curve. If we record
d
that curve, then we can tell the percentage of occurrence of any value among
that sample of people.
In the above example suppose person of 151 cm occurs in only 0.5% of that
population, and a person of 153 cm occurs in 1% and a person of 155 cm
occurs in 5% of the population. Now suppose we have encountered a person
coming from height of 155 cm we can say that this person is quite short as
most of the people are much taller than him and he is abnormally short, that
is can be accepted but the value of 155 occurs in 5% of the normal persons so
our assumption that this person is short might be wrong and the probability
that we are wrong is 5%
If we a person with height of 151 cm we can assume he is abnormally short
and he is not a normal person as most people are taller than that but still we my
be wrongg in our assumption
p
by
y 0.5% as this vaule of 151 cm occurs in 0.5%
of the normal population.
29
The frequency distribution curve of sensitivity of each tested location of field
is determined in the normal population. For example a sensitivity of 17 db
occurs in 0.5% of the normal population and a sensitivity of 18 db occurs in
1% and of 19 db occurs in 5%. Now suppose the sensitivity of that location in
the patient undergoing field test was found to be 17 db,
db then the program will
give a sign to that point being abnormally low and will use the sign indicating
0.5% meaning that this particular point is depressed and abnormally low yet
this assumption has a probability of error of 0.5% as this value normally
occurs in 0.5% of the normal population.
30
So these signs Indicate how frequently a value at a particular test location is
found in the normal population.
We have to keepp in mind that the P value does not signify
g y that at the field is
pathologic; it indicates how much the field deviates from age-adjusted normal
values.
When the most of the dots are labeled being abnormally low, then we say that
there is a generalized depression of the field of vision. Generalized
depression is seen in cases of cataracts and miosis. However, in patients with
uniform concentric cupping due to elevated IOP,
IOP a generalized loss of retinal
sensitivity may be the first sign of glaucomatous visual field loss.
31
In Total deviation : the difference between the measured
threshold of each individual test location & the age-corrected
normal value for that location are calculated and printed . (the
age-corrected normal value is the normal value of that location
at a particular age). Each patient results are compared with
those
h
of
f the
h normall person of
f the
h same age because
b
visual field
thresholds decline with age, usually at a rate in the range 0.5-1.0 dB per
decade.
Generalized depression is seen in cases of cataracts and miosis.
miosis However,
However in
patients with uniform concentric cupping due to elevated IOP, a generalized
loss of retinal sensitivity may be the first sign of glaucomatous visual field
loss.
32
Pattern deviation is derived from the total deviation via adjustment of the
measured thresholds upward or downward by an amount which reflects any
generalized change in the threshold of the least-damaged portion . To
understand how that is done see the next example :
33
Example : we have group of students attending ophthalmology course every 2
months. Suppose we made an examination for group of students (group A) and
their makes were good. Two months later, group B of students were examined
and some questions were difficult and non of students could not answer so the
group had low marks.
marks So we decided to raise the marks of group b to
eliminate the effect of those difficult questions. We decided to adopt a system
so that we can re use when ever needed in the future. The system is as follows
: we will arrange the results of group A (the standard group in our example)
from highest to lowest number. And do the same with the group to be adjusted
(group B in the present example). Then we go to rank 85% ( position 85%)
and see the mark of the student occupying that location and compare it with
the mark of student occupying position 85% in group A.
A The different is used
to adjust marks of the whole group A either up or down. For example in the
slide we see that position 85% in group B has 19 while in group A is 94 so the
difference is 94-19 = 75 so the numbers of each member of e group B will be
increased by 75. suppose the reverse, the mark of the 85% position of group
B was 99 then the each member of group B will be reduced by 5.
34
35
The same is done in Pattern deviation plot. The measured sensitivity of tested
locations of our patient is arranged from highest to lowest. The saved
sensitivity of a normal person of the same age is arranged also from highest to
lowest. Then the sensitivity of position 85% of our patient is compared to that
of the 85% position of the normal age matched individual
individual. The difference is
then used to adjust our patients results either up or down. The is done to
remove the effect of generalized media opacity on the recorded sensitivity of
the patient. A cataract or corneal opacity would reduce the sensitivity of the
whole points (like the difficult questions would affect the marks of the whole
students of group B). Thus in the pattern deviation plot the effect of
generalized media opacity is got rid off and any low values should be due to
localized changes in that area of the field.
field
36
After adjusting the sensitivity of each tested location of the patient up or down,
the new adjusted values are compared with the normal values of the same age
and the difference is recorded as the pattern deviation.
So pattern deviation is the difference between the adjusted threshold
of each individual test location & the age-corrected normal value
for that location
NB. The adjustment of the measured thresholds upward or downward is
by an amount which reflects any generalized change in the threshold of
the least-damaged
least damaged portion .
37
The graphic probability plots Of the total deviation or the pattern
deviation indicate how frequently a total or pattern deviation value at a
particular test location is found in the normal population
38
In the plot, the total deviation shows many locations marked abnormally low
while the pattern deviation shows few points in the central marked abnormal.
This patient has a generalized media opacity and only a localized lesion in
the central area.
39
Here we see mainly pure generalized depression of the field with scattered
dots of localized affection
40
Here we see pure localized defect of the field ( same points are seen on both
the pattern deviation and the total deviation)
41
This is a printout of an unreliable field with high false-positive results of a
young boy aged 11 yrs. He is a happy trigger patient, the numerical plot shows
quite high values of supra normal sensitivity. On the pattern deviation the
adjustment was down, so after adjustment, the values of the adjusted values
are quiet low to occur in the normal and the graphic plot shows many points of
abnormal values.
You cannot mistake this print out as localized field difficult because pure
localized defects should also appear exactly on the total deviation area.
42
Global indices : To aid the clinician in interpreting the numerical data
generated by threshold tests, field indices have been developed by perimeter
manufacturers.
You should keep in mind that the statistical interpretation of the data depends
on how
h accurately
l the
h data
d were gathered.
h d
Global indices include : Mean Deviation (MD) ,Pattern Standard
Deviation (PSD), Corrected Pattern Standard Deviation
(CPSD) and Short Term Fluctuation (SF)
43
The mean is one value that represent a group of values.
In this example the means is one value to represent the height individuals of
this group. The sum of heights divided by the numbers of the individuals.
44
Suppose we have a group of normal persons (in white) and another group of
short individuals (in green), if we want to know how much the group of short
persons are deviated from the normal we can see the difference of each person
from the corresponding individual then we can calculate the mean for these
differences then we will have one value to describe the deviation of the group
differences,
in green from the normal individuals.
So The mean deviation (MD) is a measure of the average departure of each
test location from the age-corrected normal value.
45
Light blue represents the hill of vision of a normal person , and the reddish
plot represents that of our patient. Small arrows represent the difference
(drop) in sensitivity of each of patient’s points and those of the normal.
If we calculate the mean for these values then we have one value to describe
the
h difference
diff
between
b
the
h hill off vision
i i off our patient
i andd the
h normal.
l ( the
h
mean deviation)
46
In glaucoma, the severity of damage is considered mild if the value of MD is
below 6, moderate if the value is between 6-12 and severe if the value is more
than 12
47
It is seen from the previous slide that the MD give information about the
height of the field of vision, the smaller the MD the higher the field, close to
the normal. And the bigger the MD the lower the field, away from the normal.
48
Pattern standard deviation PSD is nothing but the SD calculated for the
differences of each test location of that patient and that of the normal of the
same age.
49
It is known that the Standard deviation is zero or very low when the whole
values are quite close to the mean.
And if some value(s) are away from the mean the SD will be quite large
50
PSD is the standard deviation of the differences between the threshold value at
each test location and the expected value. In upper graph, almost all points are
equally depressed the SD is quite low as all points are quite close to the mean.
In middle graph, some points are more depressed than others, so the SD is
higher while in bottom graph some points are quite away from normal,
normal so the
SD is even higher and higher.
It is noticed that PSD gives impression about the shape of the field : whether it
is homogenously depressed or some points are quite depressed that the
remaining.
51
Remember that MD points toward the height of the field while PSD indicates
the shape of the field
52
(1) If the MD is normal and PSD is normal
: we are dealing with a normal
field
((2)) If the MD is abnormal and PSD is normal
: we are dealingg with a ppure
generalized depression
(3) If the MD is normal and PSD is abnnormal : we are dealing with a small,
purely localized defect or an artifact is present
(4) If the MD is abnormal and PSD is abnormal : we are dealing with a large
defect present with a significant localized component
53
Short term fluctuation –SF : Variability of the of the threshold of test location
when determined within the same session
10 points are thesholded twice during the test. The differences represent the
variability of the patient's responses during the test .
The differences bet. 1st & 2nd values are statistically evaluated by calculating
the SD of these values.
54
Normally in Young : SF = +/- 1 –1.5 dB and in Old
SF= +/- 2.5 dB.
High than 3 is unusual : indicates
1. inattentive pt (SF of less than 2.5 means good accuracy
:reliable test))
2. or an early sign of pathology. IThe average fluctuation
between 2 determinations should be less than 2 dB in a normal field, less than
3 dB in a field with early damage, and less than 4 dB in a field with moderate
damage.
55
56
CPSD represents deviation from normal reference hill after adjusting for
short term fluctuation
57
On 24-2 and 30-2 tests taken using the SITA-Standard, SITA-Fast or Full
Threshold strategies, the Glaucoma Hemifield Test (GHT) evaluates five zones
in the superior field and compares these zones to their mirror image zones in
the inferior field. The GHT evaluates the severity of
disturbed
di
b d points
i in
i eachh zone pair,
i relative
l i to its
i normative
i database,
d b
andd prints
i
one of these messages: GHT WITHIN NORMAL LIMITS, OUTSIDE
NORMAL LIMITS, or BORDERLINE.
58
Glaucoma hemifield test GHT can be :
1.
Outside normal limits
2.
Borderline
3
3.
Generalized reduction in sensitivity
4.
Abnormally high sensitivity
5.
Within normal
59
60
Glaucomatous visual field defects can be :
1.
Generalized depression
2.
Paracentral scotoma :island of relative or absolute visual loss within 10°
of fixation
3. Arcuate or Bjerrum scotoma :occurs in the area 10°–20° from fixation
4.
Nasal step :relative depression of one horizontal hemifield compared to
the other
5. Altitudinal defect :with near complete loss of the one hemisphere visual
field
6.
Temporal wedge
61
62
63
64