KNAW Amsterdam

Strooilicht in het Oog

Tom van den Berg fysicus; NIN/KNAW Amsterdam [email protected] www.ioi.knaw.nl/ost, www.glare.eu

Functie-effecten van verblinding • Immediate blinding • Differences between individuals of more than 10x found, depending on ocular condition • Recovery time follows the primary effect • Fatigue effects • Shock/disorientation effects Oog en Werk, 6 Oktober 2006

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The problem Everybody experiences a spreading of light around bright light sources. It deteriorates vision, because contrast is lost. To what extent? The seeming luminosity of the light spreading.

Oog en Werk, 6 Oktober 2006

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Verblinding ≡ Strooilicht (according to international standards as set by the CIE)


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Commission Internationale d’Eclairage (CIE): Disability Glare ≡ Straylight retinal straylight is caused by scattering of light in the optically imperfect optical components of the eye Primary straylight contributors: • normal eye • cornea • lens 4 straylight sources in the healthy eye • sclera / iris • fundus Point Spread Function (PSF) • increased in no stray light • cataract • corneal problems stray light • refractive surgery • vitreous turbidity θ (deg)


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Strooilicht kan worden gemeten met behulp van psychofysische technieken It is characterized by the straylight parameter s usually log(s) is given typical values e.g. young normal eye log(s) = 0.87 (s = 7) first signs of cataract log(s) = 1.5 (s = 30) (difference by a factor of 4 in straylight)

Point Spread Function (PSF) no stray light stray light Level = s θ (deg)


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Hoe beinvloedt strooilicht het zien? gesimuleerde beelden voor vroege lens-troebeling


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Straylight effects Blinding at night Intraocular light scatter increases retinal adaptation, which desensitizes the retina => GLARE

4 x increased straylight Older healthy eye, log(s)=1.0


Eye with (early) cataract, log(s)=1.6

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Glare/Straylight effects Glare is not restricted to twilight conditions


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Glare/Straylight effects Contrast loss by retinal straylight The signs in the NORI elevator straylight difference of a factor of 2

Normal 67y, log(s)=1.3


Early cataract, log(s)=1.6

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Glare/Straylight effects Non-traffic related effects Against-the-light face recognition Young normal


First signs of cataract, log(s)=1.4

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Kwantitatieve effecten N.B. in geval van retinale aandoeningen vormt strooilicht een dubbele handicap, dit in tegenstelling tot de situatie bij gezichtsscherpteverlies door (lens)troebeling


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Kwantitatief Strooilicht Effect The amount of contrast loss in typical traffic glare situations

Oncoming lights

Illuminance on the eye In lux

Eye condition (cataract stadium/cornea problem/vitreous opacity)

0.34

Young healthy

0.8

0.17

1.2

preclinical

1.4

0.7

2

mild/medium

1.8

1.7

3.4

Young healthy

0.8

1.4

3

preclinical

1.4

5.8

9

mild/medium

1.8

14

21

Young healthy

0.8

40

58

preclinical

1.4

165

237

mild/medium

1.8

400

572

low beams

DRL (daytime running light)

high beams


2.8

79

Straylight parameter 10log(s)

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Straylight luminance In cd/m2

Contrast loss (factor)

13

Populatie-waardes voor strooilicht


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Glare/Straylight and healthy aging Straylight increases on average with age in healthy eyes (Visual Acuity ≥ 1.0), but is highly individual dependent Log straylight parameter Log(s)

.


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Straylight among European drivers 2.5

Data from the 2003-2004 GLARE study among 2422 European drivers

2

straylight increase >4x compared to young eye

1.5 log(s)

Frequently > 4x increased straylight levels are found.

danger zone for driving (at night) ?

1

0.5

0 20

30

40

50

60

70

80

90

age Oog en Werk, 6 Oktober 2006

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Straylight compared to visual acuity. Often (early OS cataract) problems are missed by visual acuity


danger zone for driving (at night) 2 S ta ry lig h t V a lu e (lo g (s ))


2.5

1.5


Visual acuity < 0.5 (<10/20) logMar>0.3

1

0.5

0 -0.4

good -0.3

Decimal visual acuity 1.6 1.0 -0.2

-0.1

0

0.1

0.5 0.2

0.3

bad 0.4

0.5

Visual Acuity (logMar) Oog en Werk, 6 Oktober 2006

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O

Hoe meten we het (functionele) strooilicht?


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behoefte aan een praktisch meetinstrument voor strooilicht / verblindingsgevoeligheid - Occupational testing. Pilots, driver licensing - FDA: standard as defined by driving simulation - First complaints in early cataract development. Early cataract surgery - Refractive surgery effects on clarity of the cornea (functional effect of haze) - Evaluation of corneal transplant procedures - Corneal dystrophies ect. - Contact lens induced changes Oog en Werk, 6 Oktober 2006

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Assessment method for Glare/Straylight

Direct compensation method Stimulus ring (straylight source) Test field


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Direct compensation method for retinal straylight assessment Ring on: straylight on fovea (fixed)

On

L t

Stimulus ring (straylight source) Test field with counterphase modulation


Retinal modulation

Off

Ring off: compensation light on fovea (variable)

No compensation

0

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Direct Compensation s

modulation in test field

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Compensation Comparison approach for clinical use Two half fields, one with compensation flicker of different strengths 40 retinal modulation

35 30

Compensation comparison

25

modulation right

20

modulation lef t

15 10 5 0 0

5

10

15

20

Direct compensation

a

25

30

35

40

45

50

com pensation light

1

Subject’s task: Which test field flickers most?

average score

0.8 0.6

50%

0.4 0.2 0 0

5

10

15

b

20

25

30

35

40

45

50

com pensation light

Subject’s answer: Field with compensation: 1 Field without compensation: 0

- Subject’s responses allow for estimation of psychometric curve for the comparison - Position of 50% point of psychometric curve gives straylight value Oog en Werk, 6 Oktober 2006

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Oculus C-Quant Based on the Compensation Comparison method Van den Berg et al. ARVO 2005 Patent owned by Royal Academy characteristics

• Functional assessment • Fixed set of stimulus presentations, 1.5 min. test duration • Data suitable for analysis with robust statistical techniques, such as Maximum Likelihood estimators • Data allow estimation of measurement reliability Oog en Werk, 6 Oktober 2006

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0.07 log units = typical measurement s.d. 0.3 log units


normal population values ± 2 s.d.

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. .

Standard error for an individual measurement (0.07 log units = population average s.d.)

0.3 log units = factor of 2



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. .

Standard error for an individual measurement (0.07 log units = population average s.d.)

0.3 log units = factor of 2

log(s)=1.47 safe criterion value (0.6 log units increase = factor of 4)



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Klinische voorbeelden Relatieve onafhankelijkheid gezichtsscherpte en strooilicht


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. .

glasvochttroebeling preop visus 0.4++ strooilicht meer dan 10-voudig verhoogd


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. .

vitrectomie postop visus 0.8 strooilicht binnen normale grenzen


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. .

Fuchs dystrofie visus 0.7 strooilicht 6x verhoogd


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. .

na PKP vanwege Fuchs strooilicht bijna normaal


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. .

Cataract preop visus 0.7 Straylight 8x increased


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. .

Cataract postop visus 0.9 Straylight low age-normal


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. .

pseudofaak beperkte YAG opening OD visus 0.4++ strooilicht >10x verhoogd


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. .

litteken na ulcus OD visus 0.8+ strooilicht sterk verhoogd


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. .

onbegrepen klachten OD visus 1.25 strooilicht hoog normaal


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. .

onbegrepen klachten OS visus 1.25 strooilicht net verhoogd


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. .

ontevreden LASIK patient visus 1.0 Strooilicht 2.5x verhoogd


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Resumé •verblinding = (retinaal) strooilicht •wordt veroorzaakt door optische imperfecties •kan betrouwbaar worden gemeten •ook voor de praktische routine •is van belang voor functie uitoefening •is onafhankelijk van de gezichtsscherpte Dank U


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In pseudophakia straylight values often below that of the non-cataract age-peers

Straylight lens exchange?

2.50

log straylight parameter

OD phakic

OD pseudo

ref. norm

+ 2sd

-2 sd

2.00

1.50

1.00

0.50 10

30

50

70

90

Age (years)


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Straylight values in pseudophakics compared to age-control values 2.5

Data from Dr R. Nuijts mono OD mono OS diffractive OD diffractive OS age normal age normal +2SD age normal -2SD

2.2

1.9

log(s)

1.6

1.3

1

0.7

0.4 10

20

30

40

50

60

70

80

90

age


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Oculus C-Quant results on 17 subjects • Repeatable (measurements #1 and #3 compared to #2; y = x line)

log(s) measurement #1/#3/#4

• Accurate (dashed line expected value with the BPM2 light scattering filter) 1.6 1.4

measurement #1 measurement #3 #4 with BPM2

1.2

x=y #4 expected

1 0.8 0.6 0.6

0.8

1

1.2

1.4

1.6

log(s) measurement #2 Oog en Werk, 6 Oktober 2006

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Straylight compared to visual acuity. Often (early OS cataract) problems are missed by visual acuity


danger zone for driving (at night) 2 S ta ry lig h t V a lu e (lo g (s ))


2.5

1.5


Visual acuity < 0.5 (<10/20) logMar>0.3

1

0.5

0 -0.4

good -0.3

Decimal visual acuity 1.6 1.0 -0.2

-0.1

0

0.1

0.5 0.2

0.3

bad 0.4

0.5

Visual Acuity (logMar) Oog en Werk, 6 Oktober 2006

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Rough indications of straylight values in different patient groups Key: ***** = as a rule; ****= often; ***=regularly; **=occasionally; *=rare Log(s) Straylight increase

0.9 1x

1.2 2x

Young normal

*****

*

Healthy 65 year VA>0.8

**

****

**

***

****

*

***

***

*

***

****

**

Healthy 80 year VA>0.8 Pseudophakic 80 year

*** (!)

Early cataract (VA > 0.4)

1.5 4x

LASIK (high myopia….)

****

**

*

keratoconus (CL problem)

****

**

*

Cornea dystrophy or edema (VA > 0.4)

1.8 8x

****

2.1 16x

****

Fish eye VA = 0.4

One case

Vitreous turbidity (VA>0.7) Oog en Werk, 6 Oktober 2006

2.4 32x

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KNAW Amsterdam

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