TESTING OF FIELD OF
3 dimensional area of a subjects surrounding that can be seen at any
one time around an object of fixation
Extent of normal field
1.Central field includes an area from fixation point
to a circle 30* away.
Contains the Physiological Blind Spot on its
2. Peripheral field refers to rest of the area beyond
30* to outer extent of field of vision
Methods of estimating Visual fields
(1) Perimetry .
It is the procedure for estimating extent of the visual fields.
It can be classified as below:
a. Kinetic perimetry: In this the stimulus of known luminance is
moved from periphery towards the centre to establish
Various methods of kinetic perimetry are; Confrontation
Tangent screen scotometry
b. Static perimetry.
This involves presenting a
stimulus at a predetermined position for preset
duration with varying luminance.
Various methods of static perimetry
Peripheral versus central field charting
Peripheral field charting
Central field charting
Perimetry: Lister’s, Goldmann’s &
Campimetry or scotometry
Automated field analysis
Manual perimetry & Automated perimetry
A. Manual perimetry
1. Confrontation method (central field): Assuming the examiner’s field
to be within the normal range, they are compared with patient’s visual
Rough, rapid & extremely simple method
MoE: The patient is seated facing the examiner at a distance of 1 metre. While
testing the left eye, thepatient covers his right eye and looks into the examiner’s
right eye. The examiner occludes his left eye and moves his hands in from the
periphery keeping it midway between the patient and himself. The patient and the
examiner ought to see the hand simultaneously, for the patient’s field to be
considered normal. The hand is moved similarly from above, below and from right
2. Lister’s Perimeter
Extent of peripheral field
Metallic semicircular arc, graded with degrees
& white dot in centre for fixation.
Arc can be rotated in different meridians
MoE: Patient seated facing arc. One eye
occluded, fixates on the central white dot.
Test object (white, 3-5mm) moved along the
arc from periphery towards centre.
Point which is 1st seen is registered on chart
Arc moved 30* each time & 12 readings
Perimeter extent of Peripheral field is noted
3. Campimetry (Scotometry)
To evaluate the central and paracentral area (30*) of the
The Bjerrum’s screen is used and can be of size 1 metre or 2
MoE: Pt seated at 1m or 2m. Screen has white object for
fixation in centre around which concentric circles from 5* to
30* are marked. Pt fixates on the central dot with one eye
occluded. A White target (1-10mm) moved from periphery
towards centre in various meridians
Initially physiological blind spot (15* temporal
to fixation pt) is charted which corresponds
to optic nerve head.
Blind spot dimensions: Horizontally 7-8*
Central & paracentral scotoma -
Found in - Optic neuritis
Open angle glaucoma
Test condition & intensity of target are always same
Permits greater reproducibility
.B. AUTOMATED PERIMETRY
Automated perimeters are computer assisted and test
visual fields by a static method.
The automated perimeters automatically test supra-threshold
and threshold stimuli and quantify depth of
Commonly used automated perimeters are;
Humphrey field analyser
Advantages over manual perimetry
Automated computerized perimetry offers an unprecedented flexibility, a
level of precision and consistency of test method that are not generally
possible with manual perimetry.
Data storage capability
Ease of operation
Well controlled fixation
Menu driven software
Online assistance making them easy to learn and use.
Facility to compare results statistically with normal individuals of
the same age group and with previous tests of the same individual.
1. BACKGROUND ILLUMINATION
HFA Uses 31.5 apostilb[asb] background illumination.
Apostilb [asb] = Unit of brightness per unit area (1/35 candela/sq.m)
2. STIMULUS INTENSITY
HFA uses projected stimuli
Intensity varied more than 5%log units (51 decibel) b/w 0.08 &
10,000 asb. In db notation, value refers to retinal sensitivity.
Higher no. Indicate logarithmic reduction in test object
brightness & greater sensitivity of vision
HFA offers 5 sizes of stimuli corresponding to Goldmann’s
perimeter stimuli 1 through v
Standard target size equivalent to Goldmann size III (4
4. STIMULUS DURATION
Shorter than latency time for voluntary eye movements
(about 0.25 sec)
HFA - 0.2sec
OCTOPUS - 0.1sec
Testing strategies and programmes
Visual threshold - physiological ability to detect a stimulus under
defined testing conditions.
Normal threshold = Mean threshold in normal peoplein a given age
goup at a given location in the visual field.
Machine compares patient sensitivity against these values.
Threshold: 0-50 db
50 db – dimmest target
0 db - brightest illumination perimeter can project
50 db - high sensitivity
0 db low sensitivity
Supra threshold testing
1. Full threshold testing
2. Fast Pac
3. SITA (Swedish Interactive Threshold
SUPRA THRESHOLD TESTING
Target obove brightness a patient should be able to see
Screening procedure for gross defects
More time consuming
1. FULL THRESHOLD TESTING
Determines threshold value at each pt. By bracketing tech
4-2 on HFA
4-2-1 on OCTOPUS
Stimulus test pt. 0.2 sec
Machine wait y/n
If stimulus not seen-intensity of stimulus increased 4db
Once threshold crosses stimulus intensity is decreased
2db steps till stimulus not seen
2. FAST PAC
Threshold once cross strategy not applicable
Swedish interactive threshold algorithm
Reduces test time
A. Central field tests
central 30-2 test
central 24-2 test
central 10-2 test
macular grid test
B. Peripheral field tests
C. Speciality tests
D. Custom tests
Central 30-2 test
Most comprehensive form of visual field assessment of central 30
Consists of 76 points, 6 degrees apart on either sides of vertical &
Inner most points are 3* from fixation point.
54 points examined
Near similar to 30-2 test except -
2 peripheral nasal points at 30* on either side of
horizontal axis are not included (while testing
Central 10-2 test
Most pt.s in arcuate region b/w 10* & 30* -
Assess and follow 68 pt.s 2 degrees apart
in central 10 degrees
Macular grid test
Used when field is limited to central 5 degrees
Test examines 10 points spaced on 29 degree
square grid centered on point of fixation
Arbitraty division of Humphry Single Field printout(Statpac
printout) with central 30-2 test in sparts (zones)
EVALUATION OF HFA SINGLE FIELD
Software used - Statpac printout. Divided into 8 zones viz;
I. Patient data & test parameters
1. Patient data: Name
Date of birth
2. Test parameters: Test name
II. Reliability Indices (RI)
Shows Reliability indices & Test duration
Visual field examination = Unreliable - if three or more of
the following reliability indices have below mentioned
Fixation losses >= 20%
False positive error >= 33%
False negative error >= 33%
Short term fluctuations >= 4.0dB
Total questions >= 400
III. Gray scale stimulation
Depicted in Zone 3.
The darker the print out the worse is the field.
Provides field defects at a glance.
We do not make a diagnosis based on this.
Nb: Main emphasis on statistical help shows in
zone IV to VIII of the printout.
IV. Total deviation plots
Provides deviation of patients threshold values from that of
age corrected normal data.
1.Numerical value plot
2.Probablity plot (grey scale symbol plot)
Numerical value plot
Represents the differences in decibels .
Zero value-expected threshold for that age.
Positive numbers –points that are more sensitive than
average for that age.
Negative numbers-reflect points that are depressed
compared with the average.
In the lower part of zone IV of the printout, the total
deviation plot is represented graphically.
Darker the representation,the more significant it is.
V.Pattern deviation plots
1. Numeric PDP
2. Probability PDP
Shown in zone V
Similar to the total deviation plots except that here Statpac
software has corrected the results for the changes caused by
cataract, small pupil etc.
VI. Global indices
Depicted in zone VI of printout.
Are calculations made by Statpac to provide overall
guidelines to help the practitioner assess the field
results as a whole.
Used to monitor progression of glaucomatous
damage than initial diagnosis.
1. Mean deviation - Mean difference between
the normative data for that age compared with that
of collected data.
Indicator of general depression of field.
Worse than normal value is indicated by a negative
2. Pattern std deviation (PSD) -Measure
of variability within the field. It measures the diff
between a given point & adjacent points.
Points out localized field loss & is most useful in
identifying early defects.
3. Short term fluctuation (SF) - Measure
of the variability between two different
evaluations of the same 10 points in the field.
Not available with SITA strategy.
High SF means either decreased reliability or an
early finding indicative of Glaucoma.
4.Corrected pattern std deviation (CPSD)- PSD
corrected for SF.
Indicates the variability between adjacent points that may be due to
disease than intra-test variability.
VII. Glaucoma hemifield test (GHT)
Compares the 5 clusters of points in the upper field with the
5 mirror images in the lower field.
Clusters developed based on anatomical distribution of nerve
Specific for detection of Glaucoma.
Depending on differences between upper and lower clusters
of points, five inferences can be made;
1. Outside normal limits
Denotes that either the values in upper & lower clusters differ to
an extent found in less than 1% of population or any one air of
clusters is depressed to the extent that would be expected in less
than 0.5% of population.
Difference between any one of the upper & lower mirror clusters is
what might be expected in less than 3% of population.
3. General reduction in sensitivity
Best part of visual field is depressed to an extent expected in less
than 0.5% of the population.
4. Abnormally high sensitivity
Best part of visual field is such as would be found in less than 0.5%
of population .
5. Within normal limits
When none of above criteria is met.
VIII. Actual threshold values
Inspected for any pattern or Scotoma when
clinical features are suspeciant and even if all the
seven other parts of printout are normal.
A Scotoma is the depressed part of field as
compared to surroundings (not w.r.t normal).
When actual test threshold values are below
15dB – sensitivity of the test is lost.