automated perimetry

Automated Perimetry

Dr.Vikram.S.NakhateDr.Vijay.Shetty

Automated way of mapping the visual fieldImportant diagnostic test in glaucomaDiagnosing and monitoring progression of

other disease

Traquair described it as a field of vision in a sea of darkness

It has a shape of a hillPeak representing fovea2 slopes representing nasal and temporal

field of vision

Kinetic perimetryStimuli is moved from a non seeeing area to a

seeing area along a set meridianAim is to find points in the visual field of

equal retinal sensitivityLister perimetryCampimetryGoldman perimetry

Static perimetryIntensity of the stimuli at the same pre

determined spot is varied Find out threshold at those locationsMore accurate than kinetic perimetryGives a 3D picture of the hill of visionPicks up field defects more accurately

Apostlib is an absolute measure of luminance and is equal to 0.3183 candela m2 or 0.1 mililambert

Decibel is a measure of sensitivity of retina Inversely proportionalIt is a relative measure varies from machine

to machine

Testing strategyFull threshold Threshold Suprathreshold

Full threshold strategyStaircase method (4-2 bracketing strategy) Used to detect threshold

4-2 bracketing Intensity of stimulus is decreased in 4-db step

till stimulus is no longer seenIncreasing the stimulus in 2-db step till

stimulus is seen again

Threshold perimetryThreshold found at predetermined pointsTime consuming process

Suprathreshold perimetryIntensity of stimulus shown at a spot much

higher than threshold at that spotMainly for screeningPicks up gross visual defects

Newer threshold strategyFastpac:Decreases the test time by 40%3-db increment instead of 4-dbThreshold crossed only once

Sita standard: Takes half time than full threshold method

Sita fast:Takes half time than fast pac threshold

method

30-2Number of test points:76Density :6 degreeOnly 3 degree bare area is left surrounding

the fixation spot

24-2 Number of test points:54Density: 6 degreeOnly 3 degree bare area is left surrounding

the fixation spot

10-2 central threshold testNumber of test points: 68Density: 2 degreeOnly 1 degree bare area is left surrounding

the fixation spot

Macular programmeNumber of test points: 16Density: 2 degreeOnly 1 degree bare area is left surrounding

the fixation spot

Reliabilty indicesFixation losses:Indicates steadiness of gazePresenting stimuli at blind spotloss.>20% is unreliable

False positivesTrigger happy patientsResponds to an audible stimuli when no

target is presented>33% is unrelible

False negative:Fails to respond to a suprathreshold stimuli Indicates fatigue,inattentiveness>33% is unreliable

Zone 1Colour of the stimulusBackground illumination: 31.5 asbStimulus size: IIITesting strategy

Zone 3

Zone 4 total deviationDepicts difference between patients

threshold fom that of age matched normalsReveals generalised depression Cannot confirm scotoma

Zone 5 pattern deviationReveals focal defects after adjusting for

overall depressionConfirms scotoma

Global indicesMean deviation:Indicates overall deviation of the visual field

from normalPositive number indicates an elevated fieldNegative number indicates a depressed fieldCannot confirm scotoma

Psd Derived from total deviationIndicates the degree to which the numbers

differ from each otherHighlights pot-holes in hill of visionCalls attention for scotoma

Short term fluctuationMeasure of intra-test variabilityThreshold at 10 pre selected points is testedDifference between 1 & 2 measurement

noted

Cpsd is psd corrected for sfIf sf is due to unreliabilityThen cpsd is betterIf sf is due to pathologyThen psd is better

GHT 5 set of points above horizontal meridianCompared to mirror image below horizontal

meridian

Zone 8 Numerical display:Gives the threshold for all points checkedValue in () indicates that the point has been

tested twice

Never rely on first reportAlways correlate clinicallyCorrect any significant refractive error

before proceeding

Sources of errorMiosis: decreases the threshold sensitivity in

peripheral field Increases the variability in central fieldUncorrected refractive errors: Threshold sensitivity appears lessHyperopic patient with contact lens: Defect gets magnified & vice versa

Spectacles can cause rim scotomasPtosis : Suppression of superior visual field

Principle Is there a field defect ?Is it due to glaucoma ?Is the defect progressing ?

Compare to selected baselineDiscard learning fields from baselineRecognise false progression

False progressionLearning curveLong term fluctuationPupil size

Pupil: 1 mm

Pupil: 2.5 mm

Andersons criteria1. pattern deviation plot:3 non-edge points with p<5%One point with p<1% Cluster in arcuate area

2.cpsdAbnormal with p<5% on 2 consecutive

occasion

3.abnormal GHT

CATARACT

GLAUCOMA

CATARACT & GLAUCOMA

Detecting progressionOverview printoutGlaucoma change probability analysis

Overview print outSequential series of field of same patient over

a period of timeDisplays gray scales,total &pattern deviationStatistical analysis is however not provided

This patient developed cataract,which was extracted later

Pattern deviation plot remained clear

Glaucoma progression

Glaucoma change probability analysis

Compares rate of change in patients visual field,with that of stable glaucoma patient

Clear triangle represents improvementsSolid ones shows points of deteriorationProgression represented by a cluster of black

triangles in same area increasing in size with time

2 or more points deteriorate on 2 consecutive test

3 or more points deteriorate on 3 consecutive test

Advanced field defectsWhy pattern deviation plot not showing

defect

Not enough points with sensitivity to produce pattern deviation plot

Follow up with 10-2Enough sensitive points to produce pattern

deviation

Advanced defect f/u with a size V target(64mm2)

Macular programme in advanced defects

Size V target:macular splitMacular split (0 db) next to fovea may

indicate wipe out

Thank you