3. Objectives:
Identification and quantification of abnormal visual
fields
Longitudinal assessment to detect glaucomatous
progression and measure rates of change.
4. The Visual Field:
The visual field can be represented as a three-
dimensional structure akin to a hill of increasing
sensitivity.
7. Common terms used in V.F & Perimetry
An isopter is a line connecting points of the same
sensitivity, and on a two-dimensional isopter plot
encloses an area within which a stimulus of a given
strength is visible.
When the field is represented as a hill, isopters
resemble the contour lines on a map.
8. Cont….
A scotoma is an area of reduced (‘relative’) or total
(‘absolute’) loss of vision surrounded by a seeing
area.
Luminance is the intensity or ‘brightness’ of a light
stimulus, measured in apostilbs (asb).
10. Cont…
Stimulus brightness:
Apostilbe (Asb): Unit of intensity of light projected as
stimulus.
Decibel (dB): Unit of neutral density filters used to make
stimulus dimmer.
0dB(withoutfilter)=10,000Asb
(Humphrey)
10dB = 1/10th = 1000Asb
20dB = 1/100th = 100Asb etc.
(10dB = 1Lu)
11. Cont…
Threshold at a given location in the visual field is the
brightness of a stimulus at which it can be detected by
the subject.
After the age of 20 years the sensitivity decreases by
about 1 dB per 10 years.
13. Cont…
Background luminance: The retinal sensitivity at
any location varies depending on background
luminance.
Rod photoreceptors are more sensitive in dim light.
Cone photoreceptors are more sensitive in Bright light
Peripheral retina more sensitive in proportion to the
central retina.
14. Types of perimetry
Kinetic
Goldmann
Lister
Bjerrum s Screen
Static
Humphrey
Octopus
Henson
15. Automated Static Perimetry
To find visual field sensitivity at pre-selected
locations
Presenting stimulus of known size and brightness
known background for known amount of time.
We measure differential light sensitivity or contrast
sensitivity.
16. Testing algorithms
Threshold
Used for detailed assessment of the hill of vision
By plotting the threshold luminance value at various
locations
17.
18. Cont…
Suprathreshold
Testing with stimuli of luminance above the expected
normal threshold levels
It enables testing to be carried out rapidly
Reserved for screening.
19. Fast algorithms
Introduced with shorter testing times,
Providing efficiency benefits with little or no
detriment to testing accuracy.
SITA-Standard and SITA-Fast versions are available
24. SITA (Swedish interactive threshold algorithm)
Dramatic reduction of test time
without sacrificing accuracy.
More accurate choice of stimulus
brightness.
Complete use of patient information.
Test pace completely determined by
patient.
27. Zone 1 Patient data & test data
Zone 2 Foveal Therashold & Reliable
indices
Zone 3 Gray Scale
Zone 4 Total Deviation Plot
Zone 5 Pattern Deviation Plot
Zone 6 Global Indices
Zone 7 Glaucoma Hemifield test
Zone 8 Raw data
28. Zone 1 Patient data & test data
Zone 2 Foveal Therashold &
Reliable indices
Zone 3 Gray Scale
Zone 4 Total Deviation Plot
Zone 5 Pattern Deviation Plot
Zone 6 Global Indices
Zone 7 Glaucoma Hemifield
test
Zone 8 Raw Data
31. Reliability indices
B) False positive error rates :
Should be < 33%
Increased fixation loss value.
C) False negative error rates :
Should be < 33% ( No ‘xx’ for FN %
in newer SITA strategy).
32. Reliability indices –
a) Gaze stability –
Heijl-Krakau blind spot
method - Fixation loss
should be <1/5th
Gaze monitor
Video monitoring
34. Total Deviation plots-zone-4
I . Numeric value in upper plot - diff. in dB between the
patients test results and the age corrected normal values at each
tested point in the visual Field. Value is abnormal -> if 5 dB
less than normal .
2. Gray -scale symbols in lower plot -> translates values in
upper plot, Darker the symbols, more the depth of defect.
35. Total deviation (from
normal values for age) -
Normal sensitivity
range – larger peripherally
than centrally and
superiorly than inferiorly.
36. Pattern Deviation
Is similar to total deviation
Except that any generalised depression in the field caused by
other factors such as lens opacities or miosis.
37. Pattern deviation :zone-5
Single most useful analysis
For exposing localized
defect masked by
generalized depression or
elevation
Early field defect appear
first in probability map
Doesn’t come in very
advanced field defects
38.
39. P- Value
Probability (Chance) - Chances of occurrence by chance
expressed by 'P'. Ranges -> from '0' to I . P = 0, means no
chance of an event happening or its occurrence is impossible
e.g. Chances of survival after rabies are zero or nil .
P = 1, means chances of an event happening are 100% e.g.
death of any living being.
P value -> Significant in 5% level, (95% confidence limit)
41. Uniform total dev. plot
depression but normal pattern
dev. plot – Media opacity
Normal total dev. but
abnormal pattern dev.–
trigger happy pt.
42. Statistical Analysis: zone; 6
Global indices :
Mean deviation (M.D.) –
Denote average severity of field
loss.
Pattern standard dev. (PSD) –
It is the S.D. around M.D.
↑ PSD - ↑ focal defect.
43. Global indices:
Short term fluctuation (SF) -
Index of intra test measurement variability.
Between 1-2.5 dB.
Significance limited by small no. of points tested.
High in inconsistency and in diseased area (not done in
SITA).
Corrected PSD (CPSD) -
When SF removed from PSD.
44. 5 Zones in upper
field compared with
5 mirror-image zones
in lower field
In 30-2 and 24-2
tests only
Glaucoma hemifield test
(GHT):zone-7
45. Glaucoma Hemifield Test (GHT)
Five possible messages :
Outside normal limits (one or more zone difference by
P < 0.01)
Borderline
General reduction of sensitivity
Abnormally high sensitivity
Within normal limits
46. Visual Field Index(VFI)
The VFI represents the entire visual
field as a single percentage of
normal
Based largely on the pattern
deviation; weighs central points
more than peripheral ones.
A full visual field has a VFI of
100%; perimetrically blind visual
field has a VFI of 0%.
47.
48. Overview -
Minimum 4 field
tests -- for evidence of
progression. 6 or
more -- for certainty.
49. Glaucoma Progression
Analysis(GPA)
Like GCP, but smarter
Adjusts for cataract
Deterioration from baseline at
P<5% - ∆
Deterioration at same location, 2
consec. tests –
Deterioration at same location, 3
consec. tests –▲
53. 53
Stimulus – Blue (440 nm),
Size V
Background – Intense
yellow
Can detect presence and
progression of glaucomatous
V. F. change several years
earlier than standard white
on white auto perimetry
(SAP).
56. Microperimetry
Microperimetry is a visual field test that measures
retinal sensitivity and fixation behaviour in patients
with macular disease and focal glaucoma involving
the central visual field.
56
57.
58. Cont...
Goldmann size 3 stimuli are projected onto the central
9° of the fundus.
A 4-2 staircase thresholding technique is used,
Using this instrument normal retinal sensitivity is 18
dB.
59. Cont...
Results are printed, together with reliability indices
(fixation loss), probabilities, and retinal sensitivity
values,
Which are colour-coded.
It can also be helpful in patients with early glaucoma,
particularly when there is subtle change close to
fixation.
60.
61. Sources of error in perimetry
Inexperienced or unskilled technician
Incorrect patient details
Miosis
Lens opacities
Uncorrected refractive error
Spectacles rim artefact
Ptosis
Poor patient performance
Inadequate retinal adaptation
