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Visual Impairment, Age and Driving
Chris Dickinson and Marliana Mahmud Department of Optometry and Neuroscience,
UMIST
Bioptic Driving Conference June 2004 Slide 2
Driving and Vision often create very emotive stories
Bioptic Driving Conference June 2004 Slide 3
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
Bioptic Driving Conference June 2004 Slide 4
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
Bioptic Driving Conference June 2004 Slide 5
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
Bioptic Driving Conference June 2004 Slide 6
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
Bioptic Driving Conference June 2004 Slide 7
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?
Bioptic Driving Conference June 2004 Slide 8
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
Bioptic Driving Conference June 2004 Slide 9
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
Bioptic Driving Conference June 2004 Slide 10
Useful Field of View (UFOV)
“functional” “effective” “working”
The area from which information can be simultaneously acquired without moving the head or eyes
Bioptic Driving Conference June 2004 Slide 11
Concept of UFOV
Bioptic Driving Conference June 2004 Slide 12
Comparison with clinical visual field testing
“standard” visual fieldMonocularThresholdDetectionSingle targetsNo background
UFOVBinocularSuprathresholdIdentification and localisationMultiple targetsDistracting background
Bioptic Driving Conference June 2004 Slide 13
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)
Bioptic Driving Conference June 2004 Slide 14
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
Bioptic Driving Conference June 2004 Slide 15
Subtest 1 Processing Speed
Bioptic Driving Conference June 2004 Slide 16
……continued
Bioptic Driving Conference June 2004 Slide 17
Subtest 2 Divided Attention
Bioptic Driving Conference June 2004 Slide 18
……continued
Bioptic Driving Conference June 2004 Slide 19
Subtest 3 Selective Attention
Bioptic Driving Conference June 2004 Slide 20
“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
Bioptic Driving Conference June 2004 Slide 21
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)
Bioptic Driving Conference June 2004 Slide 22
Why these levels?
European standards VA 6/12 (or slightly better if monocular)
Lowest US standard for bioptic wearer VA 6/60
Bioptic Driving Conference June 2004 Slide 23
Adaptation to loss
Present in order of increasing difficulty for plus lenses
Bioptic Driving Conference June 2004 Slide 24
Effect of blur in young and older adults
Bioptic Driving Conference June 2004 Slide 25
Comparing older and younger on different subtests
Bioptic Driving Conference June 2004 Slide 26
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?
Bioptic Driving Conference June 2004 Slide 27
6/12 effect is not practically significant, as seen when converted to risk
6/30 increases risk significantly for both age groups
Bioptic Driving Conference June 2004 Slide 28
Accident risk will increase more for older subjects with the same visual loss
Bioptic Driving Conference June 2004 Slide 29
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))
Bioptic Driving Conference June 2004 Slide 30
Effect of reduced contrast on younger and older subjects
Young: only subtest 3 significantly increased Old: all subtests show significant increase
Bioptic Driving Conference June 2004 Slide 31
Risk assessment with reduced contrast
Only old group show significantly increased risk
Bioptic Driving Conference June 2004 Slide 32
Individual differences
Table 6.1
Bioptic Driving Conference June 2004 Slide 33
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
Bioptic Driving Conference June 2004 Slide 34
Please contact me for discussion or information