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

.

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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.

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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.

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THANK YOU!