Visual Impairment, Age and Driving

Chris Dickinson and Marliana Mahmud Department of Optometry and Neuroscience,

UMIST

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Driving and Vision often create very emotive stories

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Specsavers Opticians in March 2003

Call for Govt action on drivers who do not wear spectacles and fail minimum standard

738 out of 2000 people failed a vision test Tested at International Motor

Show in October 2002 If behind the wheel, they

would be driving illegally

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A survey by Specsavers suggested

Members of the public would support more rigorous regulations over 40’s to have compulsory regular eye-tests random police checks of drivers’ vision at the roadside

Shipp (1998) Vision-related re-licensing procedures in 10 states were

significantly associated with a reduction in the number of fatal accidents to older drivers

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The reason seems self-evident

90% of information received whilst driving is visual Driving is a dangerous activity

In 2000 • 29 million vehicles and 232000 injury accidents • only fallen by 0.5% compared to 1985 despite Govt target to

cut by one-third• 20% of all deaths of 5-19 year olds were traffic accidents

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However, to not drive is a major handicap

Driving is an important skill in society 1998/2000 32.3 million full driving licences held in UK 71% of all UK adults (risen from 48% in 1975/76)

Consequences for self-esteem, financial security, quality-of-life dependence on others to travel to work or socialise need to live near public transport no identification for opening bank account

Don’t want to withhold the privilege needlessly Disability Discrimination legislation

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Study to determine

Does poor vision cause increased likelihood of accident? Are changes in eyesight requirements justifiable?

Is the effect of poor vision equal for all individuals? Is there an argument that drivers should be assessed

individually (as in hemianopia “failures”) rather than have a blanket regulation?

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Dickinson and Rabbitt (1991) results

Young normal subjects Test of reading comprehension and memory One text viewed “normally” and one text viewed “blurred” One text “easy” and one text “difficult”

Subjects remembered less of “blurred” text ESPECIALLY the “difficult” one BUT severity of effect depended on IQ

Argument is that better IQ = faster information processing of degraded images = more processing capacity devoted to actually managing the task

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What might be expected to happen?

Driving performance is made worse by blur Especially more difficult aspects of the task But drivers with “faster information processing” suffer

significantly less effect What drivers should we check?

• Young/Old

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Useful Field of View (UFOV)

“functional” “effective” “working”

The area from which information can be simultaneously acquired without moving the head or eyes

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Concept of UFOV

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Comparison with clinical visual field testing

“standard” visual fieldMonocularThresholdDetectionSingle targetsNo background

UFOVBinocularSuprathresholdIdentification and localisationMultiple targetsDistracting background

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UFOV predicts accident history/risk

89% sensitivity and 81% specificity for predicting which older drivers have a crash history (Ball et al, 1993)

Older drivers with 40% loss of UFOV are 2.2x more likely to crash in following 3 years (Owsley et al, 1998)

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UFOV area not measured directly

test measures rate of information processing targets presented at various durations to find time for 75%

correct task performance NOT reaction time

What does the test consist of? Subtest 1 – processing speed Subtest 2 – divided attention Subtest 3 – selective attention

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Subtest 1 Processing Speed

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……continued

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Subtest 2 Divided Attention

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……continued

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Subtest 3 Selective Attention

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“Risk” can be graded in 5 categories – examples

Category Level

Risk Statement

Subtest 1

(msec)

Subtest 2

(msec)

Subtest 3

(msec)

1 Very Low 0-30 0-99 0-349

3 Low to Moderate

30-59 100-349 0-349

5 High 61-349 350-500 350-500

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Study

20 young adults aged 20-29 years (24.3 ± 2.36) 17 older adults aged 56-90 years (67.6 ± 9.26)

Baseline Normal vision and contrast sensitivity, fully corrected,

binocular Simulations

Using plus lenses • logMAR 0.3 (6/12: 20/40: 0.5)• logMAR 0.7 (6/30: 20/100: 0.2)• logMAR 1.0 (6/60: 20/200: 0.1)

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Why these levels?

European standards VA 6/12 (or slightly better if monocular)

Lowest US standard for bioptic wearer VA 6/60

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Adaptation to loss

Present in order of increasing difficulty for plus lenses

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Effect of blur in young and older adults

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Comparing older and younger on different subtests

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What does this mean?

Blur has a significant effect (compared to baseline) Young, 6/12 for subtest 3; 6/60 for subtests 1 and 2 Old, 6/30 for subtest 1

Age has a significant effect On subtests 2 and 3

No apparent interaction between them – older subjects are not more severely affected (parallel curves?) But is this due to the artificial “ceiling” effect?

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6/12 effect is not practically significant, as seen when converted to risk

6/30 increases risk significantly for both age groups

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Accident risk will increase more for older subjects with the same visual loss

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Reduced Contrast Sensitivity

Ryser Occlusion Foils 0.1 grading

Young (mean CS 1.46, logMAR 0.345 (6/13: 20/43: 0.47))

Old (mean CS 1.3, logMAR 0.55 (6/21: 20/70: 0.29))

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Effect of reduced contrast on younger and older subjects

Young: only subtest 3 significantly increased Old: all subtests show significant increase

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Risk assessment with reduced contrast

Only old group show significantly increased risk

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Individual differences

Table 6.1

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Conclusions

Acuity loss has increased effects on more complex tasks There are large inter-individual differences in ability to cope

with processing demands such as those found in driving Age is one contributory factor

Should each driver be tested individually? Would some of our subjects have “adapted” better than

others? Can the ability be taught?

Bioptic driving training programs

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Please contact me for discussion or information

chris.dickinson@umist.ac.uk