TESTING OF FIELD OF VISION
By
SRIDEVI RAJEEVE2008 BATCH
VISUAL FIELDVisual field 3 dimensional area of a subjects surrounding that can be
seen at any one time around an object of fixation
Extent of normal fieldSuperiorly 50* Nasally 60*Inferiorly 70* temporally 90*
VISUAL FIELD 1.Central field includes an area from
fixation point to a circle 30* away.Contains the Physiological Blind Spot on its temporal side.
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 isopters.
Various methods of kinetic perimetry are; Confrontation method
Lister’s perimetery Tangent screen scotometry Goldmann’s perimetry
.
.
b. Static perimetry.
This involves presenting astimulus at a predetermined position for preset duration with varying luminance.
Various methods of static perimetry adopted are; Goldmann perimetry Friedmann perimetryAutomated perimetry.
Extent of normal visual field
Peripheral versus central field charting
Peripheral field charting Central field charting Confrontation method Perimetry: Lister’s, Goldmann’s
& Automated Campimetry or scotometry Goldmann’s perimetry 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 fields
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 and left.
Lister’s perimeter
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 noted. Perimeter extent of Peripheral field is noted
3. Campimetry (Scotometry)
.To evaluate the central and paracentral area (30*) of the visual field.
The Bjerrum’s screen is used and can be of size 1 metre or 2 metres square.
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*
Vertically 10-11*
Central & paracentral scotoma -
Found in - Optic neuritis
Open angle glaucoma
BJERRUM’S SCREEN.
4. Goldmann’s perimeter
Goldmann’s perimeter
Hemispherical dome
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 field defect.
Commonly used automated perimeters are;
Octopus
Field Master
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.
Other advantages;
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.
Humphrey field analyser
INTERPRETATION OF AUTOMATED PERIMETRY PRINT
OUT FIELD CHARTS
Automated perimeter variables Testing strategies and
programme
Following discussion is based on the HFA.
A. AUTOMATED PERIMETER VARIABLES
1. Background illumination
2. Stimulus intensity
3. Stimulus size
4. Stimulus duration
. 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
3.STIMULUS SIZE HFA offers 5 sizes of stimuli corresponding to
Goldmann’s perimeter stimuli 1 through v Standard target size equivalent to Goldmann
size III (4 sq.mm)
4. STIMULUS DURATIONShorter than latency time for voluntary eye movements (about 0.25 sec)HFA - 0.2sec
OCTOPUS - 0.1sec
Stimulus intensity scales comparison
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
TESTING STRATEGIES &PROGRAMMES
Basic strategies
Supra threshold testing
Threshold testing
1. Full threshold testing
2. Fast Pac
3. SITA (Swedish Interactive Threshold
Algorithm)
.
SUPRA THRESHOLD TESTINGTarget obove brightness a patient should be able to see
Screening procedure for gross defects
THRESHOLD TESTING
Precise
Clinician preferred
More time consuming
Expensive
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 steps Once threshold crosses stimulus intensity is
decreased 2db steps till stimulus not seen
2. FAST PAC
More rapid Threshold once cross strategy not applicable
3. SITA Swedish interactive threshold algorithm Reduces test time Fast SITA Standard SITA
TEST PROGRAMMESA. Central field tests central 30-2 test central 24-2 test central 10-2 test macular grid testB. Peripheral field tests peripheral 30/60-1 peripheral 30/60-2 nasal step temporal cresent C. Speciality tests Neurological-20
Neurological-50Central 10-12 Macular test
D. Custom tests
Central 30-2 test
Most comprehensive form of visual field assessment of central 30
degrees
Consists of 76 points, 6 degrees apart on either sides of vertical &
horizontal axis
Inner most points are 3* from fixation point.
Central 24-2test
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 24*)
Central 10-2 test
Most pt.s in arcuate region b/w 10* & 30* -marked depression
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 PRINT OUT
Software used - Statpac printout. Divided into 8 zones viz;
I. Patient data & test parameters 1. Patient data: Name Date of birth Eye (right/left) Pupil size Visual acuity 2. Test parameters: Test name Strategy Stimulus used Background
.
II. Reliability Indices (RI)
Shows Reliability indices & Test durationVisual field examination = Unreliable - if three or more of the
following reliability indices have below mentioned values; 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 plot2.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.
.
Probability plot 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 value.
.
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 fibres
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.
2. Borderline 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.
.
THANK YOU!
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