auto perimetry

INTERPRETATION OFAUTOMATED PERIMETRY

© Thomas R

Automated perimetry

© Thomas R

Automated perimetry

I. Perimetry logicII. Identifying field defectsIII. Criteria for glaucomatous defectsIV. Detecting glaucomatous progressionV. Advanced field defects

© Thomas R

Bracketing strategy

B

A

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Normal thresholds

• Mean threshold in disease-free fields• In a given age group• At a given location in the visual field• Mean normal values are stored in the

automated perimeter and comparedagainst patient data

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Computers and ease ofinterpretation

Sensitivity

+Simple set of rules

Computer

Diagnosis

© Thomas R

Perimeter logic (1)

• Sensitivity determined at each location• Normal range developed• Normal range is arbitrary

– Includes the values of 95% of thenormal population

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Perimeter logic (2)

• ‘Abnormal’ values include the lowest5% of those in normal individuals

• Therefore, 5% of normal individualswill be labelled abnormal

‘Abnormal’ is not the sameas diseased

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Perimeter logic (3)

• General population – 100 tested• 1% glaucoma; 99% normal• Six will have abnormal tests:

• 1 glaucoma patient• 5 normal individuals

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Perimeter logic (4)

• Clinic population – 100 tested• 30% glaucoma; 70% normal• 33 will have abnormal tests

• 30 glaucoma patients• 3 normal individuals

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Interpretation is not child’s play

Automated perimeters still need interpretation

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Before interpretation …

… a few principles

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Rely on threshold tests

• First real evidence of glaucoma• Detect scotoma• Detect depression of the ‘hill’ of vision• May predict visual loss

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Screening tests

• Screening

• Fishing

• Fatigue

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Interpreting decibel values isjust half the challenge …

• False positives• False negatives• Fixation• Fluctuation

• Strategy• Experience• Technicians• Artefacts

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Optimising patient performance

• Choose the most appropriate investigation– Test pattern and strategy

• Ensure the patient is comfortably positioned– Support feet, back and arms– Adjust chin rest– Cover the other eye fully

• Provide careful instructions prior to the test• Support the patient during the test• Give feedback on test performance

SEAGIG. Asia Pacific Glaucoma Guidelines. 2003–2004.

© Thomas R

A word about the grey scale

• Never use the grey scale alone forinterpretation

• It is useful to educate the patientand to identify false-positiveand false-negative errors

‘White’ scotomas associatedwith false positives

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‘Clover leaf’ pattern associatedwith false negatives

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© Thomas R

Using the grey scale

• To educate the patient• White scotomas with false positives• Clover leaf pattern with false negatives• Never interpret using the grey scale alone

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Questions

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

© Thomas R

Is the field abnormal?

• Without obvious defects, it is difficultto make a decision based on thefirst field

• Repeat examinations providedefinitive information

• Never make a diagnosis based onthe visual field alone

Interpret the fieldsystematically usingzones 1–8

© Thomas R

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© Thomas R

AGE 57 2

FIXATION LOSSES 0/24

FALSE POS ERRORS 0/14

FALSE NEG ERRORS 1/13

QUESTIONS ASKED 449

FOVEA: 33 DB

TEST TIME 13:59

• Just glance at thegrey scale and moveon to zones 4 & 5

• Never interpret usingthe grey scale alone

3

© Thomas R

© Thomas R

• Point-by-point difference from theexpected value for age-relatednormal individuals

• Reveals generalised depression

• Cannot confirm a scotoma

• Look at the number and patternof symbols

Zone 4: total deviation

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180° 0°

40 dB

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90 60 30 0 30 60 90

Normal ‘hill’ of vision

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180° 0°

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90 60 30 0 30 60 90

Generalised depression

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180° 0°

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Generalised depression with‘hidden’ localised scotoma

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180° 0°

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Pattern deviation plot: scotoma revealedafter adjusting for generalised depression

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• Reveals focal defectsafter adjusting foroverall depression(or elevation) of thehill of vision

• Confirms a scotoma::

::

Zone 5: pattern deviation

Examples of total and patterndeviation plots in different situations

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Normal ‘hill’ of vision

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‘Normal’ hill of vision withlocalised scotoma

SEAGIG. Asia Pacific Glaucoma Guidelines. 2003–2004.

180° 0°

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‘Normal’ hill of vision with localised scotoma

© Thomas R

Generalised depression with‘hidden’ localised scotoma

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Generalised depression

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MD –2.18 dBPSD 4.63 dB; p < 1%SF 1.24 dBCPSD 4.44 dB; p < 0.5%

• All the informationfrom all the pointstested is reduced tosingle numbers

Global indices

MD, mean deviation; PSD, pattern standard deviation; SF, short-term fluctuation;CPSD, corrected PSD.

• Both MD and PSDare derived from thetotal deviation plot

• However, theyprovide differenttypes of information

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© Thomas R

• Average of all the numbersin the total deviation plot

• Indicates overall deviationof the visual field fromnormal

• Positive numbers indicatean ‘elevated’ field

• Negative numbers indicatea ‘depressed’ field

Global indices: mean deviation (1)


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• Provides similarinformation to totaldeviation

• Cannot confirm thepresence of a scotoma

Global indices: mean deviation (2)


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• Also derived from thetotal deviation plot

• Indicates the degreeto which the numbersdiffer from each other

• Highlights ‘roughness’or ‘pot-holes’ in the hillof vision

Global indices:pattern standard deviation (1)


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Global indices:pattern standard deviation (2)


• Provides similarinformation to thepattern deviation

• Calls attention toscotomas

© Thomas R

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• Intra-test error inthreshold determination

• Standard deviation of10 predeterminedpoints that are eachtested twice

Global indices:short-term fluctuation

© Thomas R

Global indices: correctedpattern standard deviation

• CPSD is PSD corrected for the SF– If SF is due to unreliability,

then CPSD is better– If SF is due to pathology,

then PSD is better

© Thomas R

MDTotal deviation plot

PSDPatterndeviation plot

Generalised depressionCan suspect a scotoma

Review of key points

Local irregularityConfirms scotoma

Glaucoma Hemifield Test

© Thomas R

© Thomas R

Zone 7: Glaucoma Hemifield Test

44 5

32

1

8

© Thomas R

• Never rely on thegrey scale alone tomake a diagnosis

• Never rely on thevisual field alone tomake a diagnosis

• Always correlatewith the clinicalfindings

© Thomas R

© Thomas R

Questions

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

© Thomas R

Glaucomatous defects

• Characteristics of glaucomatous defects:– Asymmetrical across the horizontal midline*– Located in the mid-periphery*

(5–25 degrees from fixation)– Reproducible– Not attributable to other pathology– Localised– Correlating with the appearance of the optic disc

and neighbouring areas

* Applicable to early/moderate cases.SEAGIG. Asia Pacific Glaucoma Guidelines. 2003–2004.

© Thomas R

Criteria for glaucomatousdefects (1)

Pattern deviation plot• ≥ 3 non-edge points

with p < 5%• One point with p < 1%• Cluster in arcuate area

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CPSD or PSDdepressedwith p < 5%

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Abnormal GHT

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Three criteria for glaucomatousdefects*

1. Pattern deviation plot– ≥ 3 non-edge points

with p < 5%– One point with p < 1%– Cluster in arcuate area

2. CPSD or PSDdepressed with p < 5%

3. Abnormal GHT

*Anderson DR, Patella VM. Automated Static Perimetry. 2nd Edn. St Louis: Mosby, 1999.

• Try interpretingthis visual field,going fromzones 1–8

© Thomas R

2

2

Visual acuity should correlatewith the foveal threshold

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• Continueinterpretingthis visual field:zones 3–8

• Remember:no more than aglance at thegrey scale

© Thomas R

© Thomas R

Revision: typical cataract

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Revision: typical glaucoma

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Revision: glaucoma and cataract

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Does this patient haveglaucoma? (1)

Only if the defects are repeatable and correlate with disc and clinical findings

© Thomas R

Does this patient haveglaucoma? (2)

Only if the defects are repeatable and correlate with disc and clinical findings

© Thomas R

Questions

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

© Thomas R

Principle

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

– Compare to selected baseline– Discard learning fields from baseline– Recognise ‘false’ progression

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False progression

• Learning curve• Long-term fluctuation• Artefacts• Patient factors• Pupil size

Pupil: 1 mm

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Pupil: 2.5 mm

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© Thomas R

Detecting change

• Change analysis – box plot• Overview programme• Glaucoma progression analysis™

(GPA™)

1. Select appropriate baseline2. Discard learning fields from baseline

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Overview programme

• Sequential series of fields for the samepatient over a period of time

• Has all the single field information,including total and pattern deviation plots

• Tells us at a glance what is happeningand allows us to deduce WHY it ishappening

Fluctuation over time

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Overview: the patient developed a cataract, which wasextracted. Note that the pattern deviation plot remains clear.

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Overview: glaucoma is progressing. Both the total and patterndeviation plots show worsening.

© Thomas R

© Thomas R

Overviewprogramme showsprogression

Full threshold

SITA standard

SITA, Swedish InteractiveThreshold Algorithm.

© Thomas R

Overviewprogramme showsprogression

• SITA is differentfrom full threshold

• Can't compareapples to oranges

• Fields may fluctuate

© Thomas R

Glaucoma Progression Analysis™*

• GPA™ is now in clinical use

• Change is based on the pattern deviation plot

• Compatible with both SITA and full threshold(baseline only)

*Carl Zeiss Meditec.

© Thomas R

Diagnosis of visual fieldprogression

• Different for research purposes– Set criteria in isolation

• Clinical follow-up scenario– Other criteria (IOP, disc changes) to consider– A corresponding repeatable change is sufficient– If in doubt, REPEAT

• Baseline fields are not constant– Select accordingly

Advanced defectand/or low sensitivities –follow-up with a size Vtarget

Disadvantage: we losestatistical help forinterpreting the total andpattern deviation plots

© Thomas R

Size V target: macular splitMacular split (0 dB) next to the foveawith a size V target may predict ‘wipe out’

© Thomas R

© Thomas R

Recent developments: SITA

• Asks smart questions• Gold standard• More abnormal points on pattern

deviation• Shallower defects• Significant because of less variability

Applying the skills

Does this field fulfilthe criteria for aglaucomatous defect?

Does this patienthave glaucoma?

© Thomas R

© Thomas R

Automated perimetry: warning

Sophisticated techniques and elaboratedata printouts should not seduce us intoa false sense of security or a misplacedbelief in the validity or reliability ofautomated perimetry*

*Zalta AH. Ophthalmology 1989; 96: 1302–11.

INTERPRETATION OFOCTOPUS FIELDS

© Thomas R

Test parameters – Octopus vs.HFA

4–2 dB bracketingstrategy

SITA standardSITA fast

4–2–1 dB bracketingstrategy

DynamicTendency oriented

perimetry (TOP)

Test strategies

0–40 dB0–40 dBMeasuring range

Goldmann I–V200 ms10,000 asb

Goldmann III and V100 ms4800 asb

Stimulus sizeStimulus durationLuminance for 0 dB

10 cd/m2 (31.5 asb)10 cd/m2 (31.4 asb)Background luminance

Aspherical bowlDirect projectionBowl type

HFA 700 seriesOctopus 300Parameter

Fankhauser F et al. Automated Perimetry: Visual Field Digest. 5th Edn. Köniz: Haag-Streit AG, 2004.

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Probabilityplots

Comparisontables

Grey scale

Patient dataand refraction

Strategy andtest parameters

Actual values

Bebie (defect)curve

Deviation

Global indices

RP: permissionrequested

© Thomas R

Octopus global indices

• MS Mean sensitivity– Average of all measured values

• MD Mean defect – Average of all values corrected for age

• LV Loss variance – Equivalent to PSD

• SF Short-term fluctuation• CLV ‘Corrected’ loss variance

– Equivalent to corrected PSD• RF Reliability factor

© Thomas R

Is the visual field abnormal?

• Octopus criteria for a visual field defect1– MD greater than 2 dB– LV greater than 6 dB– At least 7 points with sensitivity decreased

by ≥ 5 dB, three of them being contiguous• How do these compare to HFA criteria?

1. Morales J et al. Ophthalmology 2000; 107: 134–42.

© Thomas R

HFA criteria for glaucomatousdefects*

1. Pattern deviation plot– ≥ 3 non-edge points

with p < 5%– One point with p < 1%– Cluster in arcuate area

2. CPSD or PSDdepressed with p < 5%

3. Abnormal GHT

*Anderson DR, Patella VM. Automated Static Perimetry. 2nd Edn. St Louis: Mosby, 1999.

© Thomas R© Sihota R

Octopus: comparison tables

Phase I Phase 2 Mean# 59 59 59MS 21.8 18.6 20.2MD 6.8 10.1 8.5LV 46.6 73.2 51.0CLV 42.2SF 4.9RF 3.1

© Thomas R© Sihota R

GHT Outside normal limitsMD –7.58 dB; p < 0.5%PSD 6.30 dB; p < 2%SF 2.27 dB; p < 10%CPSD 5.75 dB; p < 1%

HFA: total and pattern deviation

auto perimetry

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