Perimetry by surendra

06-10-2016SAH SURENDRA
INTERPRETATION OF
PERIMETRY

What is perimetry?
 The science of measuring the visual
field is called perimetry.
 It is the measurement of “Hill of
Vision” in terms of establishing the
patient’s differential light sensitivity
across the visual-field.

VISUAL FIELD!!!! What is
it?????
Normal visual field:-The normal visual
field is described by Traquair as “Island of
vision surrounded by a sea of blindness”.
The dimensions of the field of
vision are defined relative to fixation.

Boundary:- The peripheral limits of the
visual-field, which normally measures from
the fixation points are approximately -60°
above & nasally,70°-75°below, & 100°-110°
temporally.
Point of Fixation:- The area of maximum
visual acuity in the normal field, & it
corresponds to the foveola of the retina.

Blind Spot:- This is an area of absolute
scotomas (non-seeing area) within the
boundaries of normal visual-field, & it
corresponds to the region of optic nerve
head. It is located approximately 15°
temporal to the fixation point.
SCOTOMA:-A Scotoma is an absolute or
relative area of depressed visual sensitivity
surrounded by normal vision. In an absolute
scotoma all vision is lost, whereas in a
relative scotoma a variable amount of vision
remains.

TYPES OF PERIMETRY:-
 Kinetic perimetry.
 Static perimetry.
 Static Suprathreshold perimetry.
 Static Threshold perimetry.

KINETIC PERIMETRY
 Two dimensional assessment of the boundary of
hill of vision.
 Involves presentation of the moving stimulus of
known luminance or intensity from a non seeing
area to a seeing area until they are perceived.
 The stimulus is moved at a steady speed along
the various meridian ,i.e. clock hours & the point
of perception is recorded on a chart.

CONT…….
 Those points are joined with each other in
different meridian to create an isopter for that
stimulus size & for that specific luminance level
keeping other factors constant.
 By using different stimulus of several intensities,
several different other isopters can be plotted on
a chart.
 Can be done by simple Confrontation method,
Tangent’s Screen, Lister’s perimeter & Goldman
automated perimeter.

ADVNTAGES:-
 Can rapidly evaluate the peripheral visual field.
 Can rapidly plot deep defects.
 Quick & accurate for steep-bordered defects.
 Useful for localization, characterization of
neurological defects.

DISADVANTAGES:-
 Compromised ability to detect scotomas,
particularly small, shallow, or fluctuating
scotomas, as in glaucoma.
 No effective system of quantifying the results of
kinetic perimetry; difficult to recognize early
visual-field deficits.
 Not effectively automated, therefore examiner has
much influence on visual-field outcome.
 The examiner must be well trained; he or she
controls the test.

STATIC PERIMETRY
 In static perimetry, the size &location of the target
remain constant.
 The retinal sensitivity at a specific location is
determined by varying the brightness of the test
target.
 The shape of the island is defined by repeating
the threshold measurement at various locations in
the field of vision.

STATIC SUPRAHRESHOLD
PERIMETRY
 It is mainly used for screening purposes.
 It involves the presentation of visual stimuli above
expected normal threshold (Suprathreshold) in
various locations inside the visual-field.
 Detected targets indicate grossly normal visual
function, whereas missed targets (stimulus) are
definitely abnormal or in other words , areas of
decreased visual sensitivity.

CONT….…
 Determination of threshold values are extremely
important.
 Because Suprathreshold is more than that of the
threshold value & the difference being much more
in terms of luminous intensity of the stimulus.
 Then early defects in different pathological
situations will be missed.
 whereas if it is too low then many of the normal
subjects may feel difficulty in identification of the
stimuli.

ADVANTAGES:-
 Excellent balance of sensitivity & specificity .
 Rapid.
 Excellent choice for screening.
 No need for highly trained perimetrist.
 Reproducible conditions.

DISADVANTAGES:-
 Expensive instrument (automated perimeters).

STATIC THRESHOLD
PERIMETRY
 This is used for detailed assessment of the hill of
vision by plotting the threshold luminance in
various locations in the visual-field & comparing
the results with age matched normal values.
 In Humphrey perimetry, the luminous intensity of
the stimuli is increased by 4dB & until the
threshold value is reached.

CONT…….
 Then the intensity is reduced by 2dB to
redetermine the previously assessed threshold
value.
 Because the threshold perimetry represents the
quantitative assessment of the visual-field, it is
the most accurate method of assessment of
visual-field; specially applicable for glaucomatous
subjects.

ADVANTAGES:-
 Very sensitive to shallow field loss & the early
fluctuations in glaucomatous field loss.
 Excellent quantitative data (i.e., defect depth).
 Good statistical analysis programs to assist in
recognition of defects & in identifying change.
 Very reproducible visual-field test & testing
conditions-minimizes induced variability of results.
 Highly skilled perimetrist not necessary.

DISADVANTAGES:-
 Slow, fatiguing for patients —>reliability of results
may be compromised.
 Only a few test points can be assessed.
 Relatively expensive—hardware & software costs.

TESTING PROCESS:-DUTIES OF
THE PERIMETRIST
 Patient education.
 Proper room illumination.
 Occlude the appropriate eyes: position the patient.
 Enter appropriate patient information (i.e., age or
birthday) if needed.

CONT…….
 Select appropriate trial lens or lenses for the
refractive error and test distance position lens holder.
 Monitor & evaluate patient responses.
 Maintain patient alertness.

Humphrey Automated Visual Field
Tests
Threshold Tests Screening Tests
Central 30-2
Central 24-2
Central 10-2
Macular program.
Peripheral 60-4
Nasal step
Temporal crescent
Neurological
20
Neurological
30
Central Tests Peripheral Tests Specialty
Tests

Humphrey Automated Visual Field
Tests
Threshold TestsScreening Tests
Glaucoma [Armaly central, Armaly full field, Nasal
step]
[Central-40/76/80/166]Central 30 deg
test
Full field tests [Full field-81/120/246 ]
Peripheral [Peripheral-68]

30-2 Central threshold test
pattern
No. of test points: 76
Dist. between each two points: 6
deg

24-2 Central threshold test
pattern
Dist. between each two points: 6 deg

10-2 Central Threshold test Pattern
Point density: 2 deg

Macular program
Point density: 2 deg

SYSTEMATIC APPROACH TO
INTERPRETATION OF PERIMETRIC
SCREENING
 Consideration of patient information.
 Consideration of the field-testing strategy & test point
pattern.
 Analysis of reliability indicators.
 Decision-normal or anomalous visual-field.
 Diagnostic decision (if possible)-cause of field
defect; site of lesion, type of lesion, or both.

Apostilbs & Decibel
 Apostilbs are absolute units of light intensity
 In contrast, Decibels are relative units
 Decibel value depends on the maximum intensity
projected by each perimeter.
 As the brightest light projected by a perimeter varies the
db value also varies.
 E.g. the Humphrey perimeter projects the maximum
intensity of light of 10,000 asb units.

CONT…….
 The brightest of the stimulus is attenuated by the
use of filters.
 If there is no attenuation of light intensity it is
labelled as 0 dB.
 So by convention the perimeter’s maximum
intensity of stimulus is assigned a value of 0 dB.
 So in HVFA 0 dB value = 10,000 asb units.
 So it is very important to note that 0 dB light
intensity means the brightest light that is
projected by the perimeter.

We can take the following values representing intensity in
apostilbs and convert them to logarithms.
Please note that higher the dB value, lower the light intensity in asb
units and higher the retinal sensitivity.

Threshold, Supra threshold & Infra
threshold
 The threshold is the physiological capacity to detect a
stimulus at a given location under specified
conditions.
 If a particular intensity of light is shown 100 times and
if it is appreciated 50 times and that particular intensity
of light is termed as Threshold.
 If the stimulus intensity is seen 90% of times, it is
termed as Supra threshold, &
 If it is seen 15% of times, it is termed as Infra
threshold.

PERIMETER USED IN LEI
 HUMPHREY®FIELD ANALYZER 2-i SERIES
(World leader in automated perimetry)
 Attached with Brother Model HL-52 printer.

HUMPHREY PERIMETRY
 One of the most reliable & time saving method,
thus accepted throughout the world.
 The background luminance is generally set at
31.5 asb.
 The target luminance is variable from 0.08 asb to
10,000 asb brighter than the background
luminance.
 Variation of stimulus intensity can be achieved by
altering the target size & luminance.

CONT…….
 The stimulus size is set prior to the test.
 The luminance level is varied to determine the
threshold level for each point tested in the visual-
field.

PROGRAMS AVAILABLE IN OUR
PERIMETER
 Central 30-2 Fovea on.
 Central 24-2.
 Central 10-2.
 Peripheral 60-4.
 Macula.

CONT…….
 C-40 screening.
 C-76 screening.
 P-60 screening.
 Central 10-2 SIZE5, Fovea on.
 Full Field (FF)-120 screening.

SITA
 SITA stands for Swedish Interactive Threshold
Algorithm.
 It is designed to decrease the amount of test time
by incorporating patient’s response in an
intelligent way in real time.
 Threshold values are constantly calculated
throughout the test at the same points.
 If results are too different, those points are tested
again.

CONT…….
 In SITA-FAST, more variability is allowed between
the repeated measurements.
 In this way, the test is faster.
 In SITA-STANDARD, only small differences are
acceptable.
 Therefore, the machine continues to measure
those points again & may take longer than SITA-
FAST.

CONT…….
 Overall SITA tests are much faster than older
testing strategies.
 Generally, SITA-STANDARD is the more
commonly used program for patients with known
glaucoma.
 SITA-FAST is saved for patients who are
glaucoma suspects or those who can sit at the
machine only very briefly.

INTERPRETATION OF
PERIMETRY

RELIABILITY INDICES
 Reflects the extent to which the patient’s results
are reliable & should be analyzed first.
 If grossly unreliable, further evaluation of visual-
field is useless.

MAJOR INDICES OF
RELIABILITY
 Fixation Losses.
 False Positive.
 False Negative.

FIXATION LOSSES
 This indicates the steadiness of the gaze during
the test.
 They are detected by presenting stimuli within the
physiological blind spot (Heijl-Krakau Technique).
 If the patient responds to it-the fixation loss is
recorded.
 The less the no. of fixation loss the more reliable
the test is.
 A high fixation loss is recorded if the patient does
not co-operate with the examiner by constantly
looking at the fixation target.

CONT…….
OR
 It may be due to the instrument itself which has
plotted the blind spot wrongly.
 When the number of fixation losses is greater
than 20%, a symbol (XX) will appear next to the
fixation losses to alert the doctor , there is reason
for concern.

Heijl-Krakau method of Blind spot fixation

POSSIBLE CAUSES OF “FIXATION LOSSES ON AN
AUTOMATED PERIMETER USING HEIJL-KRAKAU
FIXATION MONITOR
 True fixation shifts.
 Head misalignment after the blind spot has been localized.
 False positive responses.
 False-negative responses during blind spot localization.
 Poor blind spot localization.
 High refractive error.

FALSE POSITIVE
 These are detected when patient responds to the sound
stimulus not the light stimulus.
 Every stimulus is accompanied with the sound.
 When a patient response to the sound stimulus which
does not accompanied by light stimulus is known as
false positive.
 A false positive result suggest “Trigger Happy Patient”
who immediately response by listening to the sound
without seeing the stimulus light.
 False positive is the most important indicator for an
unreliable test.

FALSE NEGATIVE
 False negative is detected by presenting stimulus much
brighter than the threshold at a place or location when
the sensitivity has been already recorded.
 If the patient fails to respond then false negative is
recorded.
 A high false negative score represents inattention by the
patient.
 It may also be due to short-term fluctuation as seen in
some cases of glaucoma.
 Therefore, it may be an important indicator of disease
severity rather than patient’s unreliability.

DISPLAY SYSTEM
 Grey scale display.
 Numerical display.
 Total Deviation.
 Pattern Deviation.

GREY SCALE DISPLAY
 In which the decreasing sensitivity is represented
by the darker tones of the black & that is most
easy way of representation of a visual-field.
 The scale at the bottom of the chart shows
corresponding values of grey scale in asb & also
in dBs.
 Each change in grey scale is equivalent to 5dBs
change in threshold.

NUMERICAL DISPLAY
 It gives the threshold in dBs for all points
checked.
 The figures in brackets indicate the threshold at
the same point checked for the 2nd time & on
initial testing it was at least 5dB less sensitive
than expected.

TOTAL DEVIATION
 It corresponds to the deviation of patient’s result
from the age matched control.
 The upper numerical display illustrates the
differences in dBs, whereas the lower display
exhibits the differences in grey scale symbols.

PATTERN DEVIATION
 It is similar to the total deviation except it is
adjusted for a generalized depression in the
overall field which might be caused by other
factors like lens opacities & miosis.

Probability of Abnormality
 The P value represents the probability whereto a
patients findings have deviated from the expected
normal values.
 The probability statements is based on the Hill Of
Vision distribution seen in the normal population.
 This P value is computed from the total deviation
and the pattern deviation plots.
 It indicate the significance of the defect & shown as
<5%, <2%, <1%, <0.5%.

CONT…….
 P<1% means that this deviation happens in less
than 1% of the normal population and must be
consider highly suspicious.
 The lower the “P”value, greater is the significance
& lesser is the chance of the defect occurred by
chance.

GLOBAL INDICES
It summarize the result in a single view & principally
used to monitor progression of glaucomatous
damage rather than initial diagnosis.
 Mean Deviation(MD).
 Pattern Standard Deviation(PSD).
 Short-Term Fluctuation(SF).
 Corrected Pattern Standard Deviation(CPSD).

MEAN DEVIATION OR
DEFECT(MD)
 The (MD) is the mean difference in decibels between the
"normal" expected hill of vision and the patient's hill of
vision.
 If the deviation is significantly outside the normal’s, a P
value will be given.
 Example: P< 0.5% means that less than 0.5% of the
normal population showed a (MD) larger than the value
found for this test.
 This index is a measure of overall depression, elevation
of the field or significantly deep losses in one part of the
field and not in others.

Pattern Standard Deviation
(PSD)
 This is a measure of variability within the field
taking in account any generalized depression in
the “Hill of Vision”.
 Therefore, it is more specific indicator of
glaucomatous field damage rather than MD.
 The value is expressed in decibels and any value
of 2dB or greater will have a (P) value next to it
indicating the significance of the deviation.

SHORT-TERM
FLUCTUATION(SF)
 This is what the Field Analyzer has been testing
all along.
 It is simply an index of the consistency of the
patients responses during the field testing.
 This value is obtained when ten (10) pre-selected
points are tested twice and the difference, in
decibels, of the patient's responses are
compared.

CONT…….
 There are two reasons for an abnormal Short-
Term Fluctuation (SF), inattentive patient or a
patient with a diseased visual system.
 LOW FLUCTUATION: < 1.5 dB
 NORMAL FLUCTUATION 1.5dB TO 2 dB
 MEDIUM FLUCTUATION >2 dB BUT < 3 dB
 HIGH FLUCTUATION >3 dB

CORRECTED PATTERN
STANDARD DEVIATION(CPSD)
 It is a measure of variability within the field after
correcting for short-term fluctuation.

GAZE TRACKER
 Gaze tracking is printed at the bottom of the print-
out.
 It measures how often & how far from fixation the
patient looked away during this test.
 Higher spikes indicate larger eye movements.

Glaucoma Hemi field Test

CONT…….
 In glaucoma, the upper and lower hemispheres
of the field are often significantly different.
 Points within the visual field are grouped
together into 5 smaller zones with mirror images
of one another above and below the horizontal
meridian.
 Probability values are used rather than threshold
values.
 The mirror images are compared to one another.
 There are 5 possible interpretations of the
results that are printed.

GHT INDICATORS
 1. GHT outside normal limits: If the difference between the mirror
image zones would be expected in less than 1% of the normal age-
matched population, this message will appear.
 2. GHT borderline: The same as above except that for the
comparison between zones, the probability only has to be at the
3% level and the pair at the 1% level.
 3. General reduction of sensitivity: Here the criteria for a
localized depression are absent and the general height adjustment
yields a result in which the best part of the field is depressed to a
degree that would be expected in less than 0.5% of the age-
matched population.
 4. Abnormally high sensitivity: If the patient's threshold values
are higher than those occurring in less than 0.5% of age-matched
normal’s, this message will appear. The best part of the field is
more sensitive than that of 99.5% of the normal age-matched
population. This will supersede all other messages and indicates
that the patient's responses are unreliable.
 5. Within normal limits: None of the above criteria are met.

Diagnosing Glaucoma with Visual
Fields: (Anderson Criteria)
 GHT outside normal limits on 2 consecutive fields
 Cluster of 3 or more non-edge points on the
pattern defect at p < 5% with 1 point at p < 1%
over 2 consecutive fields
 CPSD < 5% over 2 consecutive fields
 Moderate loss defined as MD between 6 and 12
dB
 Severe loss defined as > 12 dB defect on MD
 A value of “0” within the central 5% of fixation is
considered severe.

SURENDRA SAH
M.OPTOM
INTERPRETATION OF
PERIMETRY

STATIC Vs KINETICSTATIC KINETIC
Quantitative Qualitative -YES/NO
Visual Field Defect detected earlier than
kinetic, with 20% nerve damage
Visual Field Defect when 40% nerve
damage
Area is fixed but Stimulus varies in
intensity
Fixed stimulus seen from non-seeing to
seeing area, area is not fixed.
Three dimensional Two dimensional
Computerized Not Computerized
Threshold type Non Threshold
Good quality & less error so widely used Not used so much

PERIMETER USED IN LEI
 HUMPHREY®FIELD
ANALYZER 2-i SERIES
(World leader in automated
perimetry)
 Attached with Brother Model
HL-52 printer.

NORMAL THRESHOLD VALUES
 First four paracentral points are 3° from vertical &
horizontal lines,12.7° from the fixation point & next
all stimulus points are 6° apart.
 Maximum threshold is at the fovea say, 35dB
dimmest light, with each degree to periphery
threshold decreases by .03 dB.

ZONE I
ZONE II
ZONE III
ZONE VII
ZONE VI
ZONE IV ZONE V
ZONE VIII

ZONE 1 - PATIENT DATA & TEST DATA
PATIENT’S DATA THE TEST DATA
Name of the patient: Fixation monitor:- Blind
spot
DOB & age: Fixation target:- Central
Pupil diameter: Colour of the stimulus:-
White
Visual acuity: Background illumination:-
31.5 asb
Refractive error
correction for NV:
Stimulus size:-
Goldmann size III point
pattern Testing strategy.

ZONE 2-RELIABILITY INDICES
 Information about reliability indices
and foveal threshold.
 Foveal threshold is compared
with the visual acuity.
 Reliability indices - include:
 Fixation losses
 False positive response rate
 False negative response rate

CONT….
Fixation losses –
 Stimuli presented on the blind spot.
 The patient responds to this stimulus
indicates shift of fixation.
 >20% is unreliable.
False positive response –
 If the patient pushes the button to the non
projected stimulus it will be recorded as
false positive.
 A sound is presented without stimulus.
 “Trigger Happy” patient.

CONT….
False negative response –
 In this stimuli are presented
much brighter than threshold at a
location where sensitivity has
already been tested.
 Fields should not be considered
unreliable solely upon a false
negative response rate.

CAUSES OF UNRELIABILITY OF
THE TEST
TECHNICIANS FAULTS PATIENT’S LACK OF
PERFORMANCE SKILL
Age of the patient not properly
entered
High fixation losses >33%
Refractive error not properly
corrected for NV
High false (+)ve errors>33%
Pupil size <3 mm High false (-)ve errors >33%
Improper positioning of the patient’s
head
SF>2.5 dB

GAZE TRACKER
 Gaze tracking is printed at the bottom of the print-
out.
 It measures how often & how far from fixation the
patient looked away during this test.
 Higher spikes indicate larger eye movements.

ZONE 3 - GRAY SCALE
 The darker the printout, the
worse is the field.
 Darker area represents lower
sensitive zone.
 Gives information about gross
false positive, false negative
errors.
 The diagnosis is not made on the
basis of gray scale.

PLOT
 It is the difference in decibels between
the patient's results and age-matched
normal results.
 Draws our attention to any overall
sinking of field of vision - cataract,
miosis, refractive error, corneal
opacity, advanced glaucoma.
 It is depicted as total deviation numeric
value plot and total deviation
probability plot (Gray scale symbol
plot).

NUMERIC VALUE PLOT
 Represents the difference in dB.
 0= patient has expected threshold for that age.
 +ve= more sensitive than average for that age.
 -ve= depressed compared with the average.

(GRAY SCALE SYMBOL PLOT)
 In the lower part of zone 4 of the printout, the total
deviation plot is represented graphically.
 The darker the graphic representation, the more
significant it is.
NOTE: The total deviation plot is an indicator of
the general depression & is not capable of
revealing the hidden scotomas that may be
present in the overall depressed field.

APOSTILBS & DECIBEL
 Apostilbs are absolute units of light sensitivity .
 100 asb intensity on one instrument is same as
100 asb intensity on another instrument.
 Decibels are relative units.
 That means dB value depends on the maximum
intensity projected by each perimeter.
 As the brightest light projected by each perimeter
varies, the dB value also varies.

We can take the following values representing intensity in apostilbs and
convert them to logarithms.
Please note that higher the dB value, lower the light intensity in asb units
and higher the retinal sensitivity.

High dB value
High Retinal sensitivity
It means more attenuation
of light intensity stimulus
which results in projecting
If retinal points respond to
this less intensity of light
stimulus, it indicates
Low intensity of light
stimulus

Low dB value
Low Retinal sensitivity
It means less attenuation
of light intensity stimulus
which results in projecting
If retinal points respond to
this high intensity of light
stimulus, it indicates
High intensity of light
stimulus

ZONE 5 - PATTERN DEVIATION
PLOT
 In similar to total deviation plot
except that it is adjusted for any
generalized depression in the
overall field .
 which might be caused by factors
such as lens opacities or miosis,
etc.
 Below the pattern deviation
numerical plot there is a pattern
deviation probability plot.

ZONE 6 - GLOBAL INDICES
 In TDNP and PDNP statistical
manipulation are provided by
point to point calculation.
 In global indices all the points
are reduced to one.
 It includes:
 Mean deviations (MD)
 Pattern standard deviation (PSD)
 Short-term fluctuations (SF)
 Corrected pattern standard
deviation (CPSD)

MEAN DEVIATION (MD)
 It is elevation or depression of the patient's
overall field from normal reference.
 It is more an indicator of the general depression
of the field.
 Worse than normal value is indicated by a –ve
value.

PATTERN STANDARD DEVIATION
(PSD)
 It is the standard deviation of the difference
between the threshold value at each test location
and expected value.
 It actually points out towards localized field loss &
is most useful in identifying early defects.
 It loses its advantage in marked depression.

SHORT-TERM FLUCTUATION
(SF)
 In this, threshold is measured twice at 10 pre-
selected points and the standard deviation of
these values is SF.
 Usually between 1 - 2.5 dB in a reliable field.
 Low fluctuation: < 1.5 dB
 Normal fluctuation: 1.5 dB-2 dB
 Medium fluctuation: >2 dB but < 3 dB
 High fluctuation: >3 dB

CORRECTED PATTERN STANDARD
DEVIATION (CPSD)
 The SF is removed from PSD to produce CPSD.
 It indicates the variability between adjacent points
that may be due to disease rather than due to intra-
test variability.

NOTE:
 The single field analysis printout with SITA strategies
do not calculate short-term fluctuations and hence
CPSD cannot be calculated. Only full threshold
strategy and FAST PAC calculate SF and hence
CPSD.
 If the global indices are outside the normal range the
P value appears next to it. Any global indices having
P value less than 5% - abnormal.

INTERPRETATION OF GLOBAL
INDICES...
MD CPSD Interpretation
1. Normal 1. Normal 1. Normal
2. Abnormal 2. Normal 2. Generalized loss of sensitivity
3. Normal 3. Abnormal 3. Small localized field defect
4. Abnormal 4. Abnormal 4. Large defects + localized
component

TEST (GHT)
 In GHT, five sectors shown in
the upper half of the field are
compared to five mirror images
in the lower half of the field.
 Depending upon the difference
between the upper & lower field
the following 5 messages may
be displayed.

CONT…. GHT outside normal limits: If the values between any
sector in the upper and lower zone differ to an extent
found in the 1% of the general population.
 GHT borderline - The difference between any one of
the upper and lower zones is what might be expected
in less than 3% of the population.
 GHT General reduction in sensitivity - If the best part
of the visual field is seen less than 0.5% of the
population.
 GHT Abnormally high sensitivity - Appears when the
overall sensitivity is higher than expected in 99.5% of
the normal population.
 Within Normal Limits – Non of the above criteria met.

ZONE 8-ACTUAL THRESHOLD
VALUES
 Inspected for any pattern or
scotoma when clinical features are
suspeciant & even if all the 7 other
parts of the printout are normal.
 A scotoma by definition is the
depressed part of the field as
compared to the surrounding & not
as compared to normals.
 When the actual test threshold
values are below 15 dB, the
sensitivity of the test is lost.

ISOPTER CONTRACTION:-
 Peripheral isopter contraction may significantly
affect a person before any typical glaucomatous
field loss.

EXCLUSION OR BARING
OF THE BLIND SPOT:-
 This is also considered as an early sign of glaucoma.

ANGIO-SCOTOMA:-
 This is a type of scotoma having long branching
processes above & below the blind spot.
 which are presumed to be the result of large
retinal vessels &
 Also considered to be one of the early sign of
glaucoma.

PARACENTRAL SCOTOMA
(FIELD DEFECT):-
 One may encounter one or more isolated
paracentral scotoma that may develop in the
Bjerrum’s area or arcuate area.

SEIDEL’S SCOTOMA:-
 It is a sickle shaped scotoma that may arise from
the blind spot &
 Tackers to a point in a curved course with a
concavity towards the point of fixation.

BJERRUM’S SCOTOMA /
ARCUATE SCOTOMA:-
 Bjerrum’s scotoma or arcuate scotoma affects a
larger area in the form of arching scotoma.
 Which eventually fills up the whole Bjerrum’s area
from the blind spot up to the median raphe.
 When Bjerrum’s scotoma occurs both above & below
the point of fixation (i.e. both superiorly & inferiorly)
then double arcuate scotoma said to occur.

CONT….
 This is to be mentioned in this context that
generally double arcuate scotoma is not uniform
& similar considering the superior & inferior field
defect.
 Which is because of the inequality in affection of
arcuate fiber due to glaucoma which may result in
a notch or a nasal step.

RONNE’S NASAL STEP:- Arcuate field defects may not progress in the same
rate along the upper & lower portion of an eye.
 So step or a notch like defect is produced when we
study the perimetric result of a moderately advanced
case of glaucoma.
 This nasal step occurs on the nasal part of the visual
field suggesting the significance of these step when
arcuate field defect meet the median raphe.
 Therefore, the inequality of Bjerrum’s scotoma on
superior & inferior aspect of the visual field is
responsible for creation of any form of nasal step
including ronne’s nasal step.

CONSTRICTION OF THE
VISUAL FIELD (PERIPHERAL
VISUAL FIELD
CONSTRICTION):-
 This occurs upon progression of double arcuate
scotoma which gradually restricts the vision to a
limited central area around the point of fixation.
 This is also called “TUBE VISION” in advanced
cases as if the person is looking through small
tube.

AREA OF PARACENTARAL VISION
OR ISLAND OF PARACENTRAL
VISION:-
 In some extreme cases of glaucoma, we find
preservation of isolated island of paracentral vision
with loss of central vision.

NO PERCEPTION OF LIGHT:-
 When all the retinal fibres get affected by
glaucoma, then the person lands up in perfect
blindness or “NO PL”.

SUMMARY OF THE THRESHOLD
FIELD TEST PATTERNS
Test Pattern Point density
(degrees)
No. of test
points
Notes
10-2 2° 68 Test points straddles the
horizontal & vertical
meridians. The region
tested is the same as the
Amsler grid.
24-2 6° 54 Test points straddles the
meridians & used for
routine glaucoma
monitoring.
30-2 6° 76 Test points straddle
meridians. Used for first
glaucoma field.

CONT….
Macular program 2° 16 For testing extent
of macular
lesions or central
scotomas.
Nasal step 14 50 degrees
extension of the
field. Screen for
nasal step.
24-1 6° 56 Test points fall on
horizontal &
vertical meridians.
Not used much.
30-1 6° 71 Test points fall on
horizontal &
vertical meridians.
Not used much.

Fig.1-1o-2
Fig.2-24-2
Fig.3-Macular program
Fig.4-Full Threshold
Fig.5-30-2

P-VALUE <5% indicates that this degrees of loss
sensitivity of that point is seen in <5% of
normal population.
 <2% indicates that this degrees of loss
normal population.
 <1% indicates that this degrees of loss
normal population.
 <0.5% indicates that this degrees of loss
sensitivity of that point is seen in <0.5% of
normal population.

THE FEATURES OF SINGLE FIELD ANALYSIS &
CHANGE ANALYSIS PRINTOUTS WITH FOUR
MAJOR THRESHOLD STRATEGIES ARE
PRESENTED IN THE FOLLOWING TABLE:-Threshold
strategy
Reliability
indices
SF CPSD GHT Change
analysis
printout
Test time
Full
Threshold
FP errors
FN errors
Fixation
losses are
indicated in
fractions.Eg
3/26
Calculates
SF
Calculates
CPSD
Present Normal
box plot
printed on
the left
side of
the dB
scale
The most
standard
way of
determini
ng
threshold
sensitivity
FASTPAC
strategy
FP errors
FN errors
Fixation
losses are
indicated in
fractions.Eg
3/26
Calculates
SF
Calculates
CPSD
Absent Normal
box plot
printed on
the left
side of
the dB
scale
40% of
Full
Threshold
time

CONT….
SITA
Standard
FP errors FN
errors are
indicated in
percentage.Eg
2%,3%
(Fixation
losses are
indicated in
fractions.Eg
3/26)
Does not
Calculates
SF
Does not
Calculates
CPSD
Present Normal
box plot
not
printed
on the
left side
of the
dB
scale
50%
of
Full
Thres
hold
time
SITA Fast FP errors FN
errors are
indicated in
percentage.Eg
2%,3% (Fixation
losses are
indicated in
fractions.Eg
3/26)
Does not
Calculates
SF
Does not
Calculates
CPSD
Present Normal
box plot
not
printed
on the
left side
of the
dB scale
50%
of
FAST
PAC
time

VISUAL FIELDS: (ANDERSON
CRITERIA)
 Three criteria (Anderson’s criteria) to pick up
minimal abnormality:-
 Three non-edge adjacent scotomas in total or
pattern deviation probability plot with P values as
follow:-
-Two points P<5%
-One point P<1%
 PSD P<5%
 GHT- Abnormal.

CONT….
 Criteria to pick early generalized depression
comparing MD index with the other eye.
 2 dB difference of the mean deviation index.
 1.5 dB difference in the MD index in the two
consecutive tests.
 An average difference as small as 1 dB in four
consecutive tests.

CHALLENGES TO
INTERPRETATION:
 Artifacts.
 Trial lens rim artifacts.
 Eyelids and brows.
 Refraction scotoma.
 Wrong fixation target.
 Dim light bulb.
 Inexperienced perimetrist.
 Inexperienced patient and learning curve.
 Cataract progression.
 Long-term fluctuation.

Perimetry by surendra

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