04/12/2023 1

Kinetic vs Static Perimetry

& Automated Perimetry

Junu ShresthaB. Optom 3rd year

MMC, IOM

Moderator Sanjeev Bhattarai

04/12/2023 2

Contents • Introduction• Kinetic vs. static perimetry• Basis of perimetry• Goldmann Perimetry• Automated perimetry

04/12/2023 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.

04/12/2023 4

04/12/2023 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.

04/12/2023 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

04/12/2023 7

04/12/2023 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

04/12/2023 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

04/12/2023 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

04/12/2023 11

• Standard unit of measurement differential light sensitivity (DLS).

• the threshold of perception of a test object, relative to its background (aka surround).

04/12/2023 12

04/12/2023 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.

04/12/2023 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.

100

04/12/2023 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.

04/12/2023 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

04/12/2023 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.

04/12/2023 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.

04/12/2023 19

Shows a plot of stimulus intensity against the percentage of“point seen”. Threshold is the intensity with probability of 50% detection

04/12/2023 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

04/12/2023 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 disorder

04/12/2023 22

Kinetic vs. static perimetry

04/12/2023 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

04/12/2023 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

04/12/2023 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

04/12/2023 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.

04/12/2023 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 technique3 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.

04/12/2023 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

04/12/2023 29

EccentricityE

d.L

sen

siti

vit

y

d.L

sen

siti

vit

y

Eccentricity

04/12/2023 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.

04/12/2023 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.

04/12/2023 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

04/12/2023 33

Kinetic perimetry Static perimetryResults 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

04/12/2023 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.

04/12/2023 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.

04/12/2023 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.

04/12/2023 37

Choices of perimetryManual perimetry1. Inattentive patients who do not maintain fixation

well2. Defects extending outside the central 30°3. Residual islands of vision4. Functional visual loss

Automated perimetry 2. Subtle relative defects in central or paracentral

vision2. Sequential monitoring

04/12/2023 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

04/12/2023 39

04/12/2023 40

04/12/2023 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.

04/12/2023 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 brackettingDynamic strategyTOP

4-2dB brackettingSITA NormalSITA Fast

Normal values Age correction per yr of age

04/12/2023 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)

04/12/2023 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.

04/12/2023 45

• Is capable of detecting shallow pathological depressions in eyes that are supersensitive

• Takes 12 to 18 minutes.

04/12/2023 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.

04/12/2023 47

• Smaller steps near normal sensitivity where FOSC is steep

• Larger steps when the FOSC is wider (defective)

dBdB

04/12/2023 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

04/12/2023 49

• The field test location is divided into a network of four evenly intermingled grids.

04/12/2023 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

04/12/2023 51

Examination programs

OCTOPUS 300

G1/G2

PROGRAM 32

M1/M2

04/12/2023 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

04/12/2023 53

Program 32 • General threshold examination• Maximum test location is 76 (spaced in an

equidistant grid pattern with 6 deg resolution)

04/12/2023 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

04/12/2023 55

HUMPHREYZONE SCREENING THRESHOLD

TESTAREA OF FIELD COVERED

CENTRAL FIELD ONLY

Central 40 pt orCentral 80ptCentral 76pt orCentral 166pt

MaculaCentral 10-2Central 24-1Central 24-2Central 30-1Central 30-2

0-4°0-10°0-24°0-24°0-30°0-30°

PERIPHERAL FIELD ONLY

Peripheral 68 pt Peripheral 30/60-1Peripheral 30/60-2

30-60°30-60°

04/12/2023 56

ZONE SCREENING TEST AREA OF FIELD COVERED

FULL FIELD Full field 120 ptFull field 246 pt

0-60°0-60°

04/12/2023 57

Special designsZONE SCREENING

TESTTHRESHOLD 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 crescentNeurologic 20Neurologic 50

Temporal field only 60-80°Vertical meridian only, 0-20°Vertical meridian only, 0-50°

04/12/2023 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)

04/12/2023 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.

04/12/2023 60

Full field: • The full-field 120-point screen is the most

commonly used.• Take longer time

04/12/2023 61

04/12/2023 62

04/12/2023 63

Reliability parameters• Fixation losses• False positive error• False negative error

04/12/2023 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

04/12/2023 65

• Humphrey 700• 5%of total stimuli, on the location of the blind spot. • Fixation losses > 20% are indicative of unreliable

field tests

04/12/2023 66

04/12/2023 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

04/12/2023 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%

04/12/2023 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.

04/12/2023 70

Visual sensitivity

04/12/2023 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.

04/12/2023 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.

04/12/2023 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.

04/12/2023 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.

04/12/2023 75

Global indices• Are calculated after the completion of the

threshold testing.• Mean sensitivity (MS)• The average sensitivity of all the thresholded

points.

04/12/2023 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.

04/12/2023 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.

04/12/2023 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

04/12/2023 79

Long-term fluctuation• inter-test variability• while interpreting the multiple tests over time• however, no machine provides any measure for

long-term fluctuation.

04/12/2023 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 .

04/12/2023 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.

04/12/2023 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

04/12/2023 83

04/12/2023 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.

04/12/2023 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.

04/12/2023 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.

04/12/2023 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.

04/12/2023 88

BEBIE CURVE

04/12/2023 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 analysis2. Change analysis3. Overview printout4. Glaucoma change probability (GCP, with the full

threshold tests)5. GPA (with the SITA tests)

04/12/2023 90

How to read out a printout?

G = General informationR = reliabilityA = abnormal or normal fieldD = defects, after analysis of the field defect should be

named/classifiedE = 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.

@ GRADES

04/12/2023 91

Single field analysis

General information Reliability indices → Grayscale→ totaldeviation → pattern deviation → global indices → hemifield testresult → RAW DATA → VFI.

04/12/2023 92

ANDERSEN’S CRITERIA for glaucomatous field defect

1. Abnormal GHT2. 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%

04/12/2023 93

04/12/2023 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.

04/12/2023 95

04/12/2023 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.

04/12/2023 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.

04/12/2023 98

Diagnostic outcomes of box plot

04/12/2023 99

04/12/2023 100

Overview printout

04/12/2023 101

Glaucoma Change

Probability (GCP)

04/12/2023 102

Glaucoma Progression

Analysis

04/12/2023 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

04/12/2023 104

04/12/2023 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.

04/12/2023 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

04/12/2023 107

• Flicker perimetry• Micro perimetry

04/12/2023 108

References

• OPHTHALMOLOGY PRACTICE Year : 2001;Interpreting automated perimetryRavi 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 edition

04/12/2023 109