auto perimetry

INTERPRETATION OFAUTOMATED PERIMETRY

Automated perimetry

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

Bracketing strategy

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

Computers and ease ofinterpretation

Sensitivity

+Simple set of rules

Computer

Diagnosis

Perimeter logic (1)

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

– Includes the values of 95% of thenormal population

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

Perimeter logic (3)

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

• 1 glaucoma patient• 5 normal individuals

Perimeter logic (4)

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

• 30 glaucoma patients• 3 normal individuals

Interpretation is not child’s play

Automated perimeters still need interpretation

Before interpretation …

… a few principles

Rely on threshold tests

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

Screening tests

• Screening

• Fishing

• Fatigue

Interpreting decibel values isjust half the challenge …

• False positives• False negatives• Fixation• Fluctuation

• Strategy• Experience• Technicians• Artefacts

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.

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

‘Clover leaf’ pattern associatedwith false negatives

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

Questions

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

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

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

• 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

180° 0°

90 60 30 0 30 60 90

Normal ‘hill’ of vision

180° 0°

90 60 30 0 30 60 90

Generalised depression

180° 0°

90 60 30 0 30 60 90

Generalised depression with‘hidden’ localised scotoma

180° 0°

90 60 30 0 30 60 90

Pattern deviation plot: scotoma revealedafter adjusting for generalised depression

• 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

Normal ‘hill’ of vision

‘Normal’ hill of vision withlocalised scotoma

SEAGIG. Asia Pacific Glaucoma Guidelines. 2003–2004.

180° 0°

90 60 30 0 30 60 90

‘Normal’ hill of vision with localised scotoma

Generalised depression with‘hidden’ localised scotoma

Generalised depression

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

• 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)

• Provides similarinformation to totaldeviation

• Cannot confirm thepresence of a scotoma

Global indices: mean deviation (2)

• 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)

Global indices:pattern standard deviation (2)

• Provides similarinformation to thepattern deviation

• Calls attention toscotomas

28 29 33 32 32

2728293332

28 29 32 32 32

272803434

(32) (30)

(30) (31)

• Intra-test error inthreshold determination

• Standard deviation of10 predeterminedpoints that are eachtested twice

Global indices:short-term fluctuation

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

MDTotal deviation plot

PSDPatterndeviation plot

Generalised depressionCan suspect a scotoma

Review of key points

Local irregularityConfirms scotoma

Glaucoma Hemifield Test

Zone 7: Glaucoma Hemifield Test

• Never rely on thegrey scale alone tomake a diagnosis

• Never rely on thevisual field alone tomake a diagnosis

• Always correlatewith the clinicalfindings

Questions

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

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.

Criteria for glaucomatousdefects (1)

Pattern deviation plot• ≥ 3 non-edge points

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

CPSD or PSDdepressedwith p < 5%

Abnormal GHT

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

Visual acuity should correlatewith the foveal threshold

• Continueinterpretingthis visual field:zones 3–8

• Remember:no more than aglance at thegrey scale

Revision: typical cataract

Revision: typical glaucoma

Revision: glaucoma and cataract

Does this patient haveglaucoma? (1)

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

Does this patient haveglaucoma? (2)

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

Questions

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

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

False progression

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

Pupil: 1 mm

Pupil: 2.5 mm

Detecting change

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

(GPA™)

1. Select appropriate baseline2. Discard learning fields from baseline

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

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

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

Overviewprogramme showsprogression

Full threshold

SITA standard

SITA, Swedish InteractiveThreshold Algorithm.

Overviewprogramme showsprogression

• SITA is differentfrom full threshold

• Can't compareapples to oranges

• Fields may fluctuate

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.

GPA™Right eye:baseline

GPATM, Glaucoma ProgressionAnalysisTM.

GPA™Right eye:follow-up

3 or more points deteriorate in at least 2 consecutive tests

3 or more points deteriorate in at least 3 consecutive tests

GPA™Left eye:baseline

GPA™Left eye:follow-up

GPATM, GlaucomaProgressionAnalysisTM.

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

Don’t forget to discard‘learning’ fields frombaseline

Follow-up of advancedfield defects

Advanced field defect

Why is the patterndeviation plot notshowing a defect?

Not enough points withsensitivity to produce thepattern deviation plot

Follow-up with a 10–2 programme –now there are enough sensitive pointsto produce a pattern deviation plot

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

Disadvantage: we losestatistical help forinterpreting the total andpattern deviation plots

More advanced defects: followwith macular programme

Macular programme inadvanced glaucoma

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

Recent developments: SITA

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

deviation• Shallower defects• Significant because of less variability

SITA is interpreted inthe same 8 zones aspreviously described

SITA uses the samecriteria to identify aglaucomatous fielddefect

Applying the skills

Does this field fulfilthe criteria for aglaucomatous defect?

Does this patienthave glaucoma?

Not unless the fielddefect correlates withclinical findings

Never diagnosebased on the visualfield ALONE

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

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.

[[Credit line to be added]]

Probabilityplots

Comparisontables

Grey scale

Patient dataand refraction

Strategy andtest parameters

Actual values

Bebie (defect)curve

Deviation

Global indices

RP: permissionrequested

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

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.

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.

Comparison of Octopus andHFA fields from a single patient

Patient data, strategy and testparameters

Grey scale

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

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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