1. Junu Shrestha
B. Optom 3rd year
MMC, IOM
Moderator
Sanjeev Bhattarai
5/3/2014 1

2. Contents
• Introduction
• Kinetic vs. static perimetry
• Basis of perimetry
• Goldmann Perimetry
• Automated perimetry
5/3/2014 2

3. Introduction
• The term "visual field" refers to the sum total of
visual perception for an eye fixed on a stationary
object of regard with the head and body held
fixed in position.
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4. 5/3/2014 4

5. • Traquair defined visual field as island of vision in
the sea of darkness.
• Hill of vision is a 3D representation of the retinal
light sensitivity
• Sea represents the areas of no light perception
• Under photopic condition,
the shape of hill of vision is
closely related to the
packing density of the cones
and receptive field size.
5/3/2014 5

6. • At 31.5 asb background luminance, fovea -
highest sensitivity and is able to detect both the
dimmest smallest targets.
• Sensitivity drops rapidly between the fovea and
3º decreases gradually out to 30º, and then drops
off more rapidly again beyond 50º
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7. 5/3/2014 7

8. • Reduction in light sensitivity evenly across the
visual field, causes generalised reduction in the
height of the hill of vision – DEPRESSION
• Reduction in circumference of the island of vision
or the peripheral margin of visual field –
CONTRACTION
• Non uniform reduction in light sensitivity in the
visual field – FOCAL LOSS
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9. • An area of reduced light sensitivity surrounded by
an area of normal sensitivity – RELATIVE
SCOTOMA
• An area of no light perception surrounded by
normal sensitivity – ABSOLUTE SCOTOMA
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10. Perimetry
• Is a subjective examination method for estimating
the extent of visual fields
• A decisive diagnostic technique for recognizing
disturbance of visual function/ functional loss of
vision
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11. • Standard unit of measurement differential light
sensitivity (DLS).
• the threshold of perception of a test object,
relative to its background (aka surround).
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12. 5/3/2014 12

13. Perimetry are based on:
Weber’s law/ Weber-Fencher Fraction
I = K
I
The luminance difference necessary for threshold
stimulation increases linearly with the luminance
of the surroundings or the adaption.
Applied to the area of photopic adaptation in
which standard clinical perimetry is based.
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14. Bloch’s law: Temporal summation
Within sufficiently short intervals (<100msec)the
visual system summates brightness information in
such a way that stimulus duration and stimulus
intensity are reciprocally proportional to each other.
T X I = K
A target has to be presented for at least
msec in order for the measured threshold or
sensitivity values to be independent of the duration
of target presentation.
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15. Ricco’s and Piper’s law: Spatial
summation
√(A X I) = K
The square root of the product of area of target
and stimulus intensity is constant.
Important when conversion of stimuli of definite
area and luminosity into equivalent stimuli of
different area or luminosity.
An increase of 0.5 log unit intensity produce the
same increase in field size as an increase of 0.6
log unit area.
5/3/2014 15

16. Measuring d.l. sensitivity
• Decibel is a negative logarithmic unit of
attenuation which is used in perimetry for scaling
differential light sensitivity.
• E(dB)= 10 log Lmax
• Apostilb is the unit of light intensity, whereas
the dB is the unit of retinal sensitivity.
• Apostilb and the dB are inversely proportional to
each other. Higher the apostilb value, lower will
be the dB value.
L
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17. • Threshold : the minimum light energy necessary
to evoke a visual response with a probability of
0.5, i.e. the observer can detect the stimulus
50% of the time it is presented.
• Infrathreshold: a light stimulus presented below
the threshold, not detected by the observer.
• Suprathreshold: stimulus intensity above
threshold which will be detected by the observer.
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18. • Threshold is recorded in terms of sensitivity
which is reciprocal of threshold. Sensitivity is
presented in decibel(dB)
• Higher the decibel value, higher the retinal
sensitivity.
5/3/2014 18

19. Shows a plot of stimulus intensity against the percentage of
“point seen”. Threshold is the intensity with probability of 50%
detection5/3/2014 19

20. Visual field testing
Visual field
screening
Confrontation
visual field
testing
Qualitative or
diagnostic visual
field testing
Quantitative
field testing
Fully quantifies a
known or
suspected VF
defect so that
future changes in
the defect can be
detected.
More sensitive to
visual field loss
Determine the
characteristics of a VF
defect s/a the location,
border, shape, size or
whether the field is
homonymous
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21. When to do perimetry?
• To find out the extent of VF
• To diagnose and detect diseases as well as
extent of damage caused in VF by the
disease
• To find out the progression of diseases
• To locate the possible lesion in
neurological disorder5/3/2014 21

22. Kinetic vs. static perimetry
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23. Kinetic perimetry
• A stimulus of known luminance is placed in an
unseen area(outside the border of hill of vision)
and moved towards seen area to find the local
threshold
• Generally performed centripetally
• The hill of vision is found by approaching it
horizontally
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24. • All the locations where the stimulus is first seen
have equal sensitivity, these locations can be
connected to form a ring shaped locus of points-
ISOPTER
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25. Static perimetry
• A stimulus is presented at a known location for a
known duration with varying luminance to find
local threshold
• The stimulus is not moved as in kinetic perimetry
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26. • The threshold is determined exactly by increasing
the luminance of an infrathreshold target as well
as by decreasing the luminance of a
suprathreshold targets, until the threshold has
been defined.
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27. Static suprathreshold
perimetry
Static threshold perimetry
Suprathreshold stimuli are
presented rapidly in a random
order at various preselected
locations in the visual field.
The stimulus are presented
twice if missed on the 1st
presentation Relative defect
and if again missed , the
brightest stimulus is
presented (if missed)
Absolute defect
For glaucoma screening,
neurological and retinal visual
field loss
The sensitivity at each test
point is determined by a
bracketting technique
3 to 5 stimulus presentation
for each normal point tested.
Indicated when a known or
suspected visual field defect
must follow with time to
detect progression or
regression.
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28. Comparing kinetic and static
perimetry
• Principle differences (in the ability to detect VF
changes)
• The kinetic examination with moving test objects
allows us to detect steep gradients or
circumscribed scotomas especially well.
• The static perimetry where the test target is
stationary is a method especially suited to detect
field defects with a flat gradient. Eg .
Circumscribed flat scotomas or a generalised
depression of d. l. sensitivity
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29. Eccentricity
E
d.Lsensitivity
d.Lsensitivity
Eccentricity
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30. • If we find a steep slope in the visual field the
kinetic principle with horizontal motion toward
the hill of vision or toward the margins of the
scotoma will provide a much sharper and well
delineated threshold than the vertical approach.
• If the slope is flat and if there is only a slightly
inclined nearly horizontal gradient, the static
method with vertical approach will be superior to
the kinetic method.
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31. • The physiologic distribution of differential light
sensitivity with a relatively flat slope in the
paracentral area and in the mid periphery make
the static principle for central VF the method of
choice.
• Similarly, the steep gradients of the peripheral VF
make the kinetic principle superior to the static
one.
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32. Kinetic
perimetry
Static perimetry
Measures the extent of
visual field by plotting the
isopters
Measures the sensitivity of
each retinal points
Stimulus moves from non
seeing to seeing area
Stimulus is stationary but
increases in luminance
until seen
Stimulus size can be
varied
Constant
2D measurement of hill of
vision
3D assessment of height
of predetermined areas of
hill of vision
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33. Kinetic perimetry Static perimetry
Results depend upon the
experience of the operators
Though it depends but has
very little role of the operator
Can rapidly evaluate the
peripheral VF, plot deep
defects.
Can accurately plot steep
bordered defects and useful
for localization,
characterization of
neurological defects
It has ability to detect
scotomas, particularly small,
shallow, or fluctuating
scotomas but cannot
correctly outline the border
of the defect
Eg. Confrontation perimeter,
tangent perimeter, Arc
perimeter, Goldmann
perimeter
Eg. Automated perimeter,
Goldmann perimeter
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34. • A moving stimulus will be detected more readily
in the periphery than a static stimulus because
of successive lateral spatial summation.
• As the stimulus moves across the visual field,
spatial summation of receptive fields adjacent to
the receptive field over which the stimulus is
placed occurs.
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35. • Thus, the detection of the stimulus will be
influenced by normal areas of visual field, in
addition to any damaged areas, which could lead
to shallow focal loss in the visual field being
missed.
• Also the position of the isopter is dependent upon
the patient’s reaction time to the detection of the
stimulus and addditionally the reaction time of
the examiner in responding to the patient’s
response.
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36. Indications of perimetry
• presence of RAPD
• reductions in visual acuity that cannot be
improved with a pinhole aperture, stenopaic slit,
or refractive correction
• visual disturbances of unknown cause including
desaturation of color perception,
• subjectively reduced brightness perception,
disturbances of orientation
• selfperception of visual field defects on the part
of the patient.
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37. Choices of perimetry
Manual perimetry
1. Inattentive patients who do not maintain fixation
well
2. Defects extending outside the central 30°
3. Residual islands of vision
4. Functional visual loss
Automated perimetry
1. Subtle relative defects in central or paracentral
vision
2. Sequential monitoring
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38. Goldmann perimetry
• Is the most common device
providing standardised
manual exploration of the
peripheral field.
• Presents targets on a bowl set
33cm away from the cornea of
the patient, with a
background illumination of
31.5 apostilbs or 10 cd/sq.m.
• Both kinetic and static method
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39. 5/3/2014 39

40. 5/3/2014 40

41. Automated perimetry
• Is merely a computer assisted examination (and
not a fully automatic test) since the results
depend on the patient’s collaboration and the
accuracy of the answers.
• Field testing strategy mainly static field testing
• Test target is placed at a preselected field
position, and is gradually raised until the patient
detects it.
• The output is in the form of grayscale with the
darkness of shading corresponding to decreased
sensitivity in the field.
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42. OCTOPUS 300 HUMPHREY 700
BOWL TYPE Direct projection A spherical bowl
(1/3m)
Background
luminance
31.4 asb 31.5 asb
Stimulus size Goldmann III and V Goldmann I-V
Duration 100ms 200ms
Luminance for 0
dB
4800asb 10000asb
Measuring range 0 – 40 dB 0-40dB
Test strategies 4-2-1dB bracketting
Dynamic strategy
TOP
4-2dB bracketting
SITA Normal
SITA Fast
Normal values Age correction per yr
of age
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43. Measurement strategies
• The method to determine the differential light
sensitivity is called test strategy.
Normal testing strategy/4-2 dB
bracketting
• Dynamic strategy
Tendency oriented perimetry
• SITA (Swedish Interactive
Threshold Algorithm)
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44. Normal test strategy/4-2 dB
bracketting in HFA
• The stimulus luminance is varied up and down in
steps.
• Testing starts in 4 primary anchor points at NV-
4dB, followed by increase in luminance.
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45. • Is capable of detecting shallow pathological
depressions in eyes that are supersensitive
• Takes 12 to 18 minutes.
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46. Dynamic Strategy
• The step sizes adapt to the slope of the FOSC
(frequency of seeing curve)
• With increasing depth of a defect, the stimulus
luminance step size increases from 2dB(near
normal values) to 10 dB (towards the most
depressed levels).
• The final measured value is calculated as the
mean between the two last stimuli.
• About 40-50% reduction in testing time.
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47. • Smaller steps near normal sensitivity where FOSC
is steep
• Larger steps when the FOSC is wider (defective)
dBdB
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48. Tendency Oriented
Perimetry
• The threshold values of neighbouring locations
are correlated. The anatomical and topographical
interdependence of visual field defects
establishes a tendency between the thresholds of
neighbouring zones. TOP utilises it by bracketting
method of d. l. sensitivity detection
• Assess the thresholds of neighbouring points by
interpolation
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49. • The field test location is divided into a network of
four evenly intermingled grids.
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50. SITA (Swedish Interactive
Threshold Algorithm)
• Adapts the stimulus presentation speed to the
reaction times of the patient, which in most cases
reduces test times further.
• Uses Bayesian probability which can make
predictions about the nature of the threshold.
• Estimated threshold + statistical analyses from
probability =Maximum Posterior Estimate
• SITA Standard
• SITA Fast
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51. Examination programs
OCTOPUS
300
G1/G2
PROGRAM
32
M1/M2
HUMPHREY 700
CENTRAL ZONE
PERIPHERAL ZONE
FULL FIELD
SPECIAL DESIGNS
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52. Examination program in OCTOPUS
G1/G2
• Central 30 degree, 59 test locations
• Glaucoma screening special attention to para-
central and nasalstep with resolution of 2.8 deg
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53. Program 32
• General threshold examination
• Maximum test location is 76 (spaced in an
equidistant grid pattern with 6 deg resolution)
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54. Macula M1/M2
• Covers central 10 deg VF
• M1- 56 test locations in an equidistant grid
pattern with a spacing of 2 deg
• M2- 45 test locations in central 4 deg area 0.7
deg spacing
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55. HUMPHREY
ZONE SCREENING THRESHOLD
TEST
AREA OF
FIELD
COVERED
CENTRAL
FIELD ONLY
Central 40 pt or
Central 80pt
Central 76pt or
Central 166pt
Macula
Central 10-2
Central 24-1
Central 24-2
Central 30-1
Central 30-2
0-4°
0-10°
0-24°
0-24°
0-30°
0-30°
PERIPHERAL
FIELD ONLY
Peripheral 68 pt Peripheral 30/60-1
Peripheral 30/60-2
30-60°
30-60°
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56. ZONE SCREENING TEST AREA OF FIELD
COVERED
FULL FIELD Full field 120 pt
Full field 246 pt
0-60°
0-60°
5/3/2014 56

57. Special designs
ZONE SCREENING
TEST
THRESHOLD
TEST
AREA OF FIELD
COVERED
GLAUCOMA/
OPTIC
NEUROPATHY
Armaly central
Armaly full field
Nasal step Nasal step
0-15° plus nasal
wedge to 25°
0-15° plus nasal
wedge to 60°
Nasal field only 30-
50°
NEUROLOGIC Temporal
crescent
Neurologic
20
Neurologic
50
Temporal field only
60-80°
Vertical meridian only,
0-20°
Vertical meridian only,
0-50°
5/3/2014 57

58. PROGRAM CHOICE:
ZONE OF TARGET PRESENTATION
Central zone:
• common region to test is the central 30° or the
central 24°(glaucoma)
• Threshold menu offers two versions marked by
the suffixes -1 and -2.
• Both space their locations 6° apart
• -1 versions start their points on the horizontal
and vertical meridians
• -2 versions place test locations flanking the
meridians (better suited for determining nasal
and hemianopic steps)
5/3/2014 58

59. Peripheral zone:
• Mapping of the field only between 30 and 60°
• To supplement central field examination when a
more extensive defect is suspected.
• It is seldom used, because such defects are
better diverted to Goldmann perimetry.
5/3/2014 59

60. Full field:
• The full-field 120-point screen is the most
commonly used.
• Take longer time
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61. 5/3/2014 61

62. 5/3/2014 62

63. Reliability parameters
• Fixation losses
• False positive error
• False negative error
5/3/2014 63

64. Fixation losses
• There is a video system to project an
image of the eye on monitor.
• Perimetrist should detect fixation
shifts and faulty head positioning
Observation by
perimetrist
(manual)
• Either signals the perimetrist when
fixation wanders or repeat the stimulus
presentation
• Inherent adv. Of excluding unreliable
data. However with poor fixation the
testing time is increased
Automatic
fixation
monitoring
5/3/2014 64

65. • Humphrey 700
• 5%of total stimuli, on the location of the blind spot.
• Fixation losses > 20% are indicative of unreliable
field tests
5/3/2014 65

66. 5/3/2014 66

67. False positive error
• This is a positive response by the patient even in
absence of stimulus or to an audible click by the
machine in full threshold tests
• Aka positive catch trials
• In short programs s/a SITA, anticipatory
responses faster than the expected reaction time
to stimulus are labeled as false positive
• False positive ≤ 15% are acceptable
5/3/2014 67

68. False negative error
• Some of the previously threshold “seen” points
are again presented with brighter stimuli and
absence of response is considered as a false
negative
• Aka negative catch trials
• Acceptable upto 20%
5/3/2014 68

69. Maps
• Three maps printed in any single-field analysis,
each represented by a number plot and an
accompanying pictorial representation.
– visual sensitivity
– total deviation
– pattern deviation.
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70. Visual sensitivity
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71. Total deviation
• The numerical value of
threshold is compared with the
age matched normative data
and the difference in value at
each point is printed in
numbers.
• Lower than normal value is
printed with — sign and points
with higher than normal value
is printed without any sign.
5/3/2014 71

72. • Probability plot of total deviation plot: gives the
probability of each deviation being normal or
abnormal.
• All dot signs are considered as normal, whereas
all other symbols denotes the different P-value,
• darker the symbol, more chances of it being
abnormal.
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73. Pattern deviation
gives the total deviation plot
after correcting it for the
generalized field defect.
The localized defect will be more
prominent in this plot.
5/3/2014 73

74. • Probability plot of pattern deviation plot: depicts
the probability of pattern deviation plot being
abnormal.
• Important for the detection of early
glaucomatous field defect.
5/3/2014 74

75. Global indices
• Are calculated after the completion of the
threshold testing.
• Mean sensitivity (MS)
• The average sensitivity of all the thresholded
points.
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76. Mean deviation (MD)/mean defect
• is the average deviation from the normative data
at all the tested points.
• Mean defect in Octopus
• negative (-) sign.
• A small localized defect will show a small MD,
whereas a generalized or an advanced defect will
show a high MD.
• The value does not differentiate a generalized
and a localized field loss. It also does not give the
location of the defect.
5/3/2014 76

77. Pattern standard
deviation(PSD)/Loss variance(LV)
• gives an idea about the resemblance of the
patients’ field to the shape of hill of vision.
• positive sign
• Low PSD indicates a normal shape of the hill,
whereas a high value indicates a disturbed shape
of the hill.
• Localized defect will give a high PSD, whereas a
generalized defect will give a low PSD.
• Improves with the generalization of the defect in
advanced field loss.
5/3/2014 77

78. Short term fluctuation(SF)
• Intra-test variability
• only with the full threshold
printouts.
• Ten preselected points are
thresholded twice and the
variation in the thresholds is
represented as a number
• SF > 3 indicates unreliable
result
5/3/2014 78

79. Long-term fluctuation
• inter-test variability
• while interpreting the multiple tests over time
• however, no machine provides any measure for
long-term fluctuation.
5/3/2014 79

80. Corrected pattern standard
deviation (CPSD) or corrected
loss variance (CLV):
• It is the PSD or LV corrected for the SF
• Provides a measure of the irregularity of the
contour of the hill of vision that is not accounted
for by patient variability (SF).
• increased when localized defects are present .
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81. P-value(probability value)
• (P < x%) indicates that less than x% of the
normal population has figure like this
• in other words there is an x% chance that the
index would be seen in normal.
• Lower the P value beside the global index the
higher chance of it being abnormal.
• If no P value is given beside a global index, it can
be considered normal.
5/3/2014 81

82. Glaucoma hemifield test
• It is based on the fact that the glaucomatous
defect occurs on either side of the horizontal
midline never crossing it and is unlikely to be
symmetrical across the horizontal meridian.
• Thresholds derived at the five sets of points,
which are mirror image along the horizontal
meridian
5/3/2014 82

83. 5/3/2014 83

84. Visual Field Index(VFI)
• is a single number that summarizes each patient’s
visual field status as a percentage of the normal age-
corrected sensitivity.
• originally designed to approximately reflect the rate
of ganglion cell loss.
• It is derived from PD and is centre weighted,
considering the high density of the retinal ganglion
cells in the central retina.
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85. • This index is less affected than the MD by factors
that cause a general reduction in sensitivity like
cataract, miosis,and refractive error.
• Minimum value is 0 for a blind field and 100% for
a normal individual.
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86. BEBIE CURVE/CUMULATIVE
DEFECT CURVE
• The Bebié curve is a cumulative distribution of
the defect depth at each location and is designed
to separate normal visual fields from those with
early diffuse loss
• X axis- rank of defect from smallest (left) to
largest(right)
• Y axis- magnitude of defect corresponds to the
5th and 95th percentiles.
5/3/2014 86

87. • A normal visual field yields a curve above or
closely following the 95th percentile line.
• A curve falling below (i.e. outside) the 95th
percentile line indicates visual field loss.
5/3/2014 87

88. BEBIE CURVE
5/3/2014 88

89. PRINTING RESULTS
The statistical package that is available with the
Humphrey device is called as STATPAC. The
analysis of the data acquired is presented in five
formats
1. Single field analysis
2. Change analysis
3. Overview printout
4. Glaucoma change probability (GCP, with the full
threshold tests)
5. GPA (with the SITA tests)
5/3/2014 89

90. How to read out a printout?
G = General information
R = reliability
A = abnormal or normal field
D = defects, after analysis of the field defect should be
named/classified
E = evaluate. Once the defect has been identified, one
should try and correlate clinically and evaluate about
the patient’s disease status.
S = subsequent evaluation. This is applicable in case
repeat fields are done after some time to evaluate
the progression (stable, deterioration, or
improvement) of the field defect.
@ GRADES5/3/2014 90

91. Single field
analysis
General information
Reliability indices →
Grayscale→ total
deviation → pattern
deviation → global indices
→ hemifield test
result → RAW DATA → VFI.
5/3/2014 91

92. ANDERSEN’S CRITERIA for
glaucomatous field defect
1. Abnormal GHT
2. Three or more nonedge points of the 30-2
printout, contiguous and with a P < 5%, out of
which at least 1 has a P < 1%
3. CPSD should be abnormal and should have a P <
5%
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93. 5/3/2014 93

94. R P MILL’S CRITERIA for subtle
hemianopic defect(suggestive of
neurological disorder)
1. First compare the dB value of adjacent rows on the
either side of the vertical meridian. At least three
adjacent pairs should show unidirectional difference
in sensitivity.
2. The corresponding points pairs on the next column
adjacent to the first column should also show
difference in sensitivity in the same direction.
3. At least a difference of 2dB is significant and is
suggestive of early hemianopic defect.
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95. 5/3/2014 95

96. Change Analysis Printout
• Includes a maximum of 16 tests and is presented
in the form of a box plot analysis of tests, a
summary of the global indices and linear
regression analysis of MD, all on one page.
5/3/2014 96

97. Box plot
• modified histogram that gives a
summary of TOTAL DEVIATION
test values for each test with
reference to the age-related
STATPAC database, but without
reference to the location on the
field
• A distribution of all the point
thresholds around their mean
and how much they deviate from
it.
5/3/2014 97

98. Diagnostic outcomes of box plot
5/3/2014 98

99. 5/3/2014 99

100. Overview
printout
5/3/2014 100

101. Glaucoma
Change
Probability
(GCP)
5/3/2014 101

102. Glaucoma
Progression
Analysis
5/3/2014 102

103. Factors influencing
perimetry
• Background luminance 31.5 asb
• Stimulus size
• Stimulus duration
• Interstimulus Time
• Refractive Errors
• Pupil Diameter
• Age
• Facial Structure
• Fatigue effect(Troxler fading or Ganzfield blankout)
• Psychological Factors
5/3/2014 103

104. 5/3/2014 104

105. Alternatives of standard
automated perimetry
Short-wavelength automated perimetry (SWAP)
• SWAP utilizes the koniocellular pathway and
selectively measures the short blue wavelength
function by projecting a blue stimulus on a yellow
background.
• SWAP has been found to identify early
glaucomatous damage in ocular hypertensives,
glaucoma suspects, and patients with glaucoma.
5/3/2014 105

106. Frequency doubling technology (FDT)
• a combination of low spatial frequency and high
temporal frequency preferentially targets
ganglion cells of the magnocellular pathway.
• Due to selective uncovering of functional deficits
in the My ganglion cells, FDT has been shown to
have high sensitivity and specificity for early
detection of glaucoma
5/3/2014 106

107. • Flicker perimetry
• Micro perimetry
5/3/2014 107

108. References
• OPHTHALMOLOGY PRACTICE Year :
2001;Interpreting automated perimetry
Ravi Thomas, Ronnie George
• Interpretation of autoperimetry,Barun K. Nayak,
Sachin Dharwadkar
• Conventional Perimetry, Ophthalmologe 2005
• A field of vision: Manual and atlas of perimetry
Jason J. S. Barton, Michael Benatar
• Automated perimetry visual field digest 5th
edition 2004
• Elsevier Eye essentials visual field, Robert
Cubbidge
• Borish clinical refraction 5th edition5/3/2014 108

109. 5/3/2014 109