Visual Impairment, Age and Driving Chris Dickinson and Marliana Mahmud Department of Optometry and Neuroscience, UMIST

Bioptic Driving Conference June 2004Slide 2 Driving and Vision often create very emotive stories

Bioptic Driving Conference June 2004Slide 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 2004Slide 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 2004Slide 5 The reason seems self-evident  90% of information received whilst driving is visual  Driving is a dangerous activity  In million vehicles and 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 2004Slide 6 However, to not drive is a major handicap  Driving is an important skill in society  1998/ 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 2004Slide 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 2004Slide 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 2004Slide 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 2004Slide 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 2004Slide 11 Concept of UFOV

Bioptic Driving Conference June 2004Slide 12 Comparison with clinical visual field testing  “standard” visual field  Monocular  Threshold  Detection  Single targets  No background  UFOV  Binocular  Suprathreshold  Identification and localisation  Multiple targets  Distracting background

Bioptic Driving Conference June 2004Slide 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 2004Slide 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 2004Slide 15 Subtest 1 Processing Speed

Bioptic Driving Conference June 2004Slide 16 ……continued

Bioptic Driving Conference June 2004Slide 17 Subtest 2 Divided Attention

Bioptic Driving Conference June 2004Slide 18 ……continued

Bioptic Driving Conference June 2004Slide 19 Subtest 3 Selective Attention

Bioptic Driving Conference June 2004Slide 20 “Risk” can be graded in 5 categories – examples Category Level Risk Statement Subtest 1 (msec) Subtest 2 (msec) Subtest 3 (msec) 1Very Low Low to Moderate High

Bioptic Driving Conference June 2004Slide 21 Study  20 young adults aged years (24.3 ± 2.36)  17 older adults aged 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 2004Slide 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 2004Slide 23 Adaptation to loss  Present in order of increasing difficulty for plus lenses

Bioptic Driving Conference June 2004Slide 24 Effect of blur in young and older adults

Bioptic Driving Conference June 2004Slide 25 Comparing older and younger on different subtests

Bioptic Driving Conference June 2004Slide 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 2004Slide 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 2004Slide 28 Accident risk will increase more for older subjects with the same visual loss

Bioptic Driving Conference June 2004Slide 29 Reduced Contrast Sensitivity  Ryser Occlusion Foils 0.1 grading  Young (mean CS 1.46, logMAR (6/13: 20/43: 0.47))  Old (mean CS 1.3, logMAR 0.55 (6/21: 20/70: 0.29))

Bioptic Driving Conference June 2004Slide 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 2004Slide 31 Risk assessment with reduced contrast  Only old group show significantly increased risk

Bioptic Driving Conference June 2004Slide 32 Individual differences  Table 6.1

Bioptic Driving Conference June 2004Slide 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 2004Slide 34 Please contact me for discussion or information 