Visualfields (toric09, Handout)

Topography of Vision

Visual Fields Paul H Artes, Dalhousie University, Halifax TORIC, 2009

Topography of Vision

detect disease differential diagnosis assess severity monitor disease & therapy estimate impact on the individual

Topography of Vision

% of maximum, log

Visual Acuity Contrast Sensitivity Flicker Motion Colour

100 10 1 0.1 0

10

20

30

eccentricity, degrees

Topography of Vision Static

Topography of Vision

Kinetic

Impact on patient’s real-world function Crossing a street, taking a walk, climbing stairs Awareness: negative vs positive scotomata.

1

Dimensions

Brief History 1850s – von Graefe, arc perimeters 1890s – Bjerrum, central field

70 degs 60 degs

100 degs

80 degs

1945

1979

I4e

1995 Blind spot, 5° temporal 2.5° inferior diameter 5°

Dimensions, stimuli area-logarithmic scale (Goldmann, 1945) I II Standard: III

Fields without Instruments finger-counting

peripheral fields

red dot

0.43°

IV 1.73°

V

Manual kinetic (Goldmann) perimetry

Static automated perimetry dB (decibel) scale logarithmic scale of “attenuation” relative to the instrument’s maximum stimulus.

Size

Area (mm2)

subtense (°)

I

0.25

0.11

II

1

0.22

III

4

0.43

IV

16

0.87

V

64

1.73

10 dB = 1 log unit = 10 times 3 dB = 2 times

2

Static automated perimetry

Static automated perimetry

threshold

threshold

suprathreshold

suprathreshold

bright 2 dB

22

dB dim

4 dB

24 26

4 dB 30

“bracketing” of sensitivity ~5 presentations per location “spot-check” with stimuli a little brighter than normal sensitivity. 1 presentation / location (if healthy)

New adaptive strategies

Reading the printout

maximum-likelihood / Bayesian combine “prior information” with patient’s responses – more efficient adaptive stimulus timing – faster pacing ~3.5 presentations / location take half the time of “classic” strategies (5-7 min)

Reading the printout

Reading the printout

DOB: if entered incorrectly, age-related interpretation wrong Rx: often provides a clue Strategy: Standard more accurate than Fast Test settings: watch strategy & stimulus size

Fixation losses: ”catch trial” in blind spot False Positives: response earlier than expected (<180 ms) False Negatives: no response, but stimulus previously seen. Long test: less reliable – fatigue?

3

Reading the printout Greyscale Useful for overview, but can be misleading. Look for nasal / vertical steps, then examine the numbers.

Greyscale

Reading the printout Interpolated – suggests higher resolution that in really obtained.

Total Deviation Reduction & elevation cf. experienced healthy controls.

Emphasizes peripheral and deemphasizes central reductions.

Reading the printout Pattern Deviation Reduction & elevation cf. experienced healthy controls, corrected for diffuse change!

Pattern vs Total Deviation 4 dB ‘overall’ reduction PD = TD + 4 dB

emphasizes pattern of localised loss

4

Pattern vs Total Deviation

Localised & Diffuse

Pattern Deviation useful to highlight localised, focal changes (eg. nasal step). However, diffuse change is part of glaucoma – therefore examine both TD and PD maps.

Mainly localised

Significance Maps

Mainly diffuse

Compare the values with distribution in practiced healthy controls (±5.00 DS). This does not mean that “this point has only a 5% chance of being normal”. Correct interpretation: “A TD value like that is only found in fewer than 5% of practiced healthy controls.”

Variability Map High variability in the periphery, particularly superiorly, and at the blind spot.

Low variability in the central field

Signficance maps “weigh” the deviations by variability.

5

Reading the printout Summary indices

Large deviation may not mean much in superior periphery

Smaller deviation may be highly significant in the centre.

Glaucoma Hemifield Test: rough guidance on asymmetry MD: overall damage PSD: smoothness of hill of vision

Glaucoma Hemifield Test

Always compare MD between R/L

Topography of Nerve Fibre Layer

modified from RS Harwerth et al.

Progress In Retinal & Eye Research, vol 21 (2002) 91-125

6

Common Artefacts (1)

Common Artefacts (2)

Common Artefacts (3)

Things to remember Develop a systematic approach to evaluate the print-out. First examinations often poor – learning effect. To be certain about visual field loss, it must be repeatable. Always compare right and left results, for pattern of loss as well as MD differences.

Courtesy Algis Vingrys

Detecting progression

Subjective inspection: error-prone

Glaucoma Change Probability (event analysis) follow-up value (dB)

Detecting progression

better ?

no

ifi gn i s

c nt ca

h

5th & 95th percentiles of retest-values

ge an

worse?

baseline value (dB)

7

Detecting progression

Detecting progression

Glaucoma Change Probability (event analysis)

Glaucoma Change Probability (event analysis)

change from baseline (dB)

interpretation

can’t tell better worse

2 baseline fields: mean

Glaucoma Progression Analysis (for SITA)

Baseline

follow-up fields: compared to baseline

Follow-up

Similar to GCP, but based on pattern deviation Different meaning for the triangles Analysis used in EMGT

MD regression

Peridata (www.peridata.org)

0

MD, dB

0

-5

MD, dB

-5

-0.60 dB/y

-10

-15

-20

-20

-25

age, y

-30 40

50

60

70

80

-0.22 dB/y

-10

-15

-25

age, y

-30 40

50

60

70

80

8

Rates of Progression 5

-15 -20

-20

-25

-25

0 -5

10-15% with rapid change.

-15 -20 -25 -30

-30

-30

-5

-10

-10

-10

10-15% with rapid change.

-15

0

-15

-5

-5

-10

60% slow change, or no change at all.

-20

0

0

Mean Deviation (dB)

60% slow change, or no change at all.

-30

Mean Deviation (dB)

5

-25

Rates of Progression

30 40 50 60 70 80 90 100 30

40

50

60

70

80

90

100

age, yrs

30

40

50

60

70

80

90

100

age, yrs

PPP guidelines (AAO) – revised in 2003

Non-standard SAP Loss close to fixation

24-2

A burnt-out case

10-2

24-2, size III: Most locations not measurable.

30 40 50 60 70 80 90 100

24-2, size V: “room for change”

Alternative types of perimetry Frequency-Doubling Perimetry (FDT, Matrix) Short Wavelength Automated Perimetry, SWAP (“Blue-On-Yellow”) Flicker-Defined Form (Flanagan et al.) Motion Detection Perimetry (Moorfields MDT)

9

Frequency-Doubling Perimetry

Frequency-Doubling Perimetry

Stimulus with low spatial & high temporal frequency: specific to magnocellular pathway 5° 0.43° FDT1 Only 19 test locations (good and bad!) Less sensitive to blur, but sensitive to cataract Many patients perceived it as easier

Right

Humphrey-Matrix (2nd generation FDT) 69 test locations (FDT1 tests compatible) ZEST: 4 min, independent of loss.

Left

18 months later

36 months later

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