AUTOMATED PERIMETRY SIVATEJA CHALLA

INTRODUCTION

• Automated way of mapping the visual field• Important diagnostic test in glaucoma• Diagnosing and monitoring progression of other disease

TRAQUIARS HILL OF VISION

NORMAL VISUAL FIELD

BASICS

• Current standard unit of luminous intensity is candela/m² (cd/m²)

• Apostilbs [asb units] – HVF• asb to cd/m², multiply by 1/pi (0.31831)• 1 asb is the least intense stimulus that can be seen foveally.

LIGHT INTENSITY

• describes retinal sensitivity

• Lower intensity (asb) required at particular point, higher is the sensitivity (db value) at that point.

DECIBELS

• HIGH db VALUE------- low asb intensity of light stimulus ------ HIGH RETINAL SENSITIVITY

• LOW db VALUE------ high asb intensity of light stimulus ------ LOW RETINAL SENSITIVITY

• Background illumination in HFA is 31.6 asb

STIMULUS SIZE

THRESHOLD

• The intensity of stimulus which is appreciated 50% times and missed 50% times is called threshold intensity

starting with a stimulus which the patient is very likely to observe

reducing it by 2-4 dB to non seeing intensity

again increasing the intensity to cross the threshold

TYPES

• KINETIC

Eg. Goldmans projection perimeter• STATIC and KINETIC

Eg. Humphreys visual analyser, octopus

STATIC KINETICComputerised Manual

Stimulus size constant Stimulus is moved from a non seeing area to a seeing area along a set meridian

contrast sensitivity is tested thru out speed,size,colour and brightness of target are the different variables

ADVANTAGES

quantifiable,reproducablestatistical manipulation easy

inexpensive and durable machinesStatistical manipulation difficult

Threshold detection is more sensitive Patients are comfortable

reduces the need for highly trained technicians

can define scotomas rapidly

DISADVANTAGES

Large amounts of unfamiliar data interpretation difficult

skill,training important

tedious and time consuming and expensive

early or subtle changes can be overlooked

ANATOMICAL BASIS OF FIELD OF VISION

FORMATION OF OPTIC NERVE

STAGES OF ARCUATE FIELD DEFECTS

OTHER FIELD DEFECTS

• Centro caecal defect (optic nerve disease)• Altitudinal defects (advanced glaucoma/AION)• central scotoma (optic neuruitis or mac disease)• Hemianopic defects

Heteronymous defectsHomonymous defects

INTERPRETATION OF FIELDS

APPROACH

11 Check patient and test data

Obtain general impression

22

Observe defectsand defect curve

33

Review statistics44

PATIENT DATA

CORRECTED COMPARISONSPDNP

COMPARISONSTDNP

PROBABILITYTDPP

CORRECTEDD PROBABILITYPDPP

GLOBAL INDICES

GREY SCALEVALUES

RAW DATA

BABIE’S CURVE

TEST DATA

WANDER

• What was done?

• Accuracy (Reliability)

• Normal or abnormal

• Defect pattern

• Evaluate compatible disease

• Review

ZONE 1 Patient data and test parameters

PATIENT DATA

• Name• Age/sex• Eye• Pupil size• V/A with refractive status

EXAMINATION DATA

• Programme• Strategy• Stage/ Phase

• Test target/ duration

( Goldmann size III )• Background illumination

( 31.5 apostilb )

ZONE 2reliability indices

RELIABILITY

• Fixation loss >20% is unreliable• False positive >33% is unreliable• False negative >33% is unreliable

ZONE 3Grey scale

GRAY SCALE

• Most Colourful- Least reliable

ZONE 4total deviation

NORMAL RETINAL SENSITIVITY

PATIENT’S RETINAL SENSITIVITY

DIFFERENCE

HUMPHREYTOTAL DEVIATION NUMERICAL PLOT

- media opacities.- cataracts .- corneal opacities.- refractive errors.- rarely miosis.

Normal ‘Hill’ Of Vision

Generalised Depression of Hill

ZONE 5pattern deviation

Total deviation

Generalized depression in

field

Pattern deviation

• Probability values (P) :Indicates the significance of the defects .

• Shown as P< 5%, P< 2% , P<1% and P< 0.5%.

• The lower the P value, the greater is its clinical significance

clinical significance : if there are abnormal points in total deviation plot that persist in the pattern deviation plot, we are looking at scotomas .

ZONE 6global indices

GLOBAL INDICES - MD

A

B

<-6dB MILD GENERALISED DEPRESSION

-6 TO -12dB MODERATE GENERALISED DEPRESSION

->-12dB SEVERE GENERALISED DEPRESSION

GLOBAL INDICES - MD

MEAN DEVIATION

NO OF POINTS <5%

NO OF POINTS <1%

CENTRAL FIELD

EARLY <6DB <18 <10 O POINTS <15 DB

MODERATE 6-12 DB 18-37 11-20 No points ‘0’ db and 1point <15 db in one hemifield

SEVERE >12 DB >37 >20 No points ‘0’ db and 1point <15 db in both hemifields

GLOBAL INDICES – PSD OR LV

150

160150

150

150

140

170 110

MEAN STANDARDDEVIATION

0

10

40

GLOBAL INDICES

MD: NORMALPSD: NORMAL

MD:ABNORMALPSD: NORMAL

MD: ABNORMALPSD:ABNORMAL

MD: ABNORMALPSD: ABNORMAL

SHAPE(PATTERN STD DEVIATION)

HEIGHT(MEAN DEVIATION)

Short term fluctuation ( STF)

Corrected pattern standard deviation (CPSD):

• Measure of variability within the field after correcting for short term fluctuation ( intra-test variability )

• Newer programs like SITA do not determine CPSD and STF.

PSD STF CPSD

Interpretation of the field defect using the MD and CPSD :

ZONE 7Glaucoma hemifield test

ZONE 8Numerical display

• Gives the threshold for all points checked• Value in () indicates that the point has been tested twice

IS THE DEFECT DUE TO GLAUCOMA??

CPSD 4 dB P <5%

GHT – outside normal limits

ANDERSON’S CRITERIA

1

2

3

CPSD 4 dB p< 5%

Step wise interpretation

Basic data

ReliabilityTotal & Pattern deviation

Statistical indices

Glaucoma hemi field test

Actual threshold values/fovea

Is it abnormal –Anderson’s criteria

Is it glaucoma –correlate clinicallyEstablish a baseline

TEST 30-2 24-2 10-2 MAC PROGRAMME

TEST POINTS 76 54 68 16

DENSITY(DEGREES)

6 6 2 2

BARE AREA AROUND FIXATION PT

3 DEGREES 3 1 1

PIT FALLS

ARTEFACTS

• OBSTRUCTION

RIM ARTEFACTS

PTOSIS

MEDIA OPACITIES

ANGIOSCOTOMA

• MIOSIS

• REFRACTION ARTEFACTS• HIGH POWER PLUS AND MINUS LENSES

PRACTICAL PEARLS(DURING RECORDING)

• pause the test in between if he/she is tired• >50% stimulus will not be seen so that he is reassured

and does not press the trigger due to impatience• Should have taken enough rest,may be given coffee,

ensure he is attentive• Give practice sessions esp to glaucoma patients• Close other eye well• If test is abnormal repeat• Always record same program which was done earlier

T h a n k Y o u !!