View
1.145
Download
3
Category
Preview:
DESCRIPTION
Automated perimetry
Citation preview
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
Recommended