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Driving with a Visual Impairment Chris Dickinson Department of Optometry and Neuroscience UMIST Faculty of Ophthalmologists May 21 2002 Acknowledgements BiOptic Driving Network UK Simon Phillips Stefnee Lindberg Vision Researchers and Clinicians

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driving with a visual impairment

Driving with a Visual Impairment

Chris Dickinson

Department of Optometry and Neuroscience

UMIST

Faculty of Ophthalmologists

May 21 2002

acknowledgements
Acknowledgements
  • BiOptic Driving Network UK
    • Simon Phillips
    • Stefnee Lindberg
  • Vision Researchers and Clinicians
  • but the following is my personal opinion and a basis for discussion

Chris Dickinson UMIST Department of Optometry and Neuroscience

driving and vision often create very emotive stories
Driving and Vision often create very emotive stories
  • and if you asked a member of the public they would not expect blind people to be allowed to drive

Chris Dickinson UMIST Department of Optometry and Neuroscience

the reason seems self evident
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 (underestimate?)
      • 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 are traffic accidents
  • and anything which might make that worse must be eliminated

Chris Dickinson UMIST Department of Optometry and Neuroscience

uk regulations
UK regulations
  • tested routinely
    • standard number plate with figures 79.4mm high read from 20.5m (67 feet)
  • if known pathology
    • binocular visual field 120o horizontally with no significant defect within 20o above or below fixation

Chris Dickinson UMIST Department of Optometry and Neuroscience

european standards
European standards
  • VA 6/12 (or slightly better if monocular) and field 120o binocularly

Chris Dickinson UMIST Department of Optometry and Neuroscience

defining impairment disability and handicap
Defining impairment, disability and handicap
  • impairment
    • visual acuity, visual field, dark adaptation, contrast sensitivity, disability glare
  • disability
    • reading, watching TV, driving
  • handicap
    • fulfilling expected role in society

Chris Dickinson UMIST Department of Optometry and Neuroscience

to not drive is a major handicap
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

Chris Dickinson UMIST Department of Optometry and Neuroscience

permission to drive determined on the basis of impairment rather than disability
Permission to drive determined on the basis of IMPAIRMENT, rather than disability
  • licence is not denied because they have proven unsafe
  • but on the basis of an arbitrary visual standard
  • when patients seek aid, its not for the driving task
    • they claim would feel safe driving, but can’t pass the number plate test

Chris Dickinson UMIST Department of Optometry and Neuroscience

is this va test appropriate
Is this VA test appropriate?
  • generally conclude that VA is only weakly correlated with accident record (Burg 1967)
    • questionable interpretation
      • do you really believe it (face validity?)
  • correlation artificially low
    • population already screened for poor vision
    • accidents are rare, multi-factorial and discreet events
      • in US a driver would drive 102 years before suffering a disabling injury accident and 3738 years before a fatality (Owens et al 1993)

Chris Dickinson UMIST Department of Optometry and Neuroscience

and a visually impaired patient could pass it anyway
And a visually impaired patient could pass it anyway
  • telescopic magnification could be used to increase acuity
  • but telescope restricts field of view
  • so mount as “bioptic”
  • invented by William Feinbloom

Chris Dickinson UMIST Department of Optometry and Neuroscience

usually above line of sight
Usually above line of sight

Chris Dickinson UMIST Department of Optometry and Neuroscience

and need to be angled slightly upwards
and need to be angled slightly upwards

Chris Dickinson UMIST Department of Optometry and Neuroscience

but can be below line of sight
but can be below line of sight
  • and behind the lens

Chris Dickinson UMIST Department of Optometry and Neuroscience

or autofocus
or autofocus

Chris Dickinson UMIST Department of Optometry and Neuroscience

or binocular
or binocular

Chris Dickinson UMIST Department of Optometry and Neuroscience

such devices are not acceptable for driving in uk
Such devices are not acceptable for driving in UK(?)
  • if you ask DVLA they will say it hasn’t been done
  • but you can find practitioners who have patients who have driven with these devices
    • must have been assessed on an individual basis but no precedent/guidelines

Chris Dickinson UMIST Department of Optometry and Neuroscience

bioptics are allowed by 34 states in usa
Bioptics are allowed by 34(?) states in USA
  • gradual increase since around 1970
  • a typical example (Kentucky)
    • 6/18 with telescope
      • which is usual visual standard in this state
    • 6/60 through carrier lens

Chris Dickinson UMIST Department of Optometry and Neuroscience

limited licences may be given for example
LIMITED licences MAY be given, for example
  • daytime only
    • only 11 states allow night-time
    • may be assessed after having daytime licence for 1 year (eg Virginia)
  • weather restrictions! (“when headlights necessary”)
  • <45 mph
  • no motorway driving
  • limited radius from home
  • no inter-state driving

Chris Dickinson UMIST Department of Optometry and Neuroscience

very much an ethos of collective responsibility
VERY much an ethos of collective responsibility
  • judging all by the standards of one
  • a privilege not a right
  • getting a bioptic is only the start….
    • it can’t by itself make them a safe and competent driver
    • good visual skills might
  • often users impose more severe restrictions themselves

Chris Dickinson UMIST Department of Optometry and Neuroscience

how does the driver use their bioptic
How does the driver use their bioptic?
  • NOT VIEWING THROUGH THEM ALL THE TIME

Chris Dickinson UMIST Department of Optometry and Neuroscience

90 95 of the time the driver uses unaided vision
90-95% of the time the driver uses unaided vision
  • steering the correct distance from parked cars
  • keeping appropriate distance from car in front
  • being alert for pedestrian stepping off pavement
  • watching for another car approaching the crossroads

Chris Dickinson UMIST Department of Optometry and Neuroscience

5 10 of viewing through bioptic
5-10% of viewing through bioptic
  • occasionally used for scanning
    • “U” movement across the road ahead
  • mostly used with brief (0.5-1.0 second) “in and out” to check on detail
    • at greater distance than possible unaided
    • earlier opportunity to react
      • obtaining details from a sign
      • checking for freeway exits
      • seeing traffic lights from greater distance
      • following signals from person directing traffic

Chris Dickinson UMIST Department of Optometry and Neuroscience

can t be used for dashboard displays
Can’t be used for dashboard displays
  • vergence amplification
    • need to view through carrier
    • possible solutions
      • learn position of needle (perhaps paint light colour)
      • colour important section of speedometer gauge
      • fix sheet magnifier against glass
  • but mirrors are not a problem (optical infinity)

Chris Dickinson UMIST Department of Optometry and Neuroscience

so how do they learn to do all this
So how do they learn to do all this?

Chris Dickinson UMIST Department of Optometry and Neuroscience

training
Training
  • NOT common practice in the UK
    • ALL low vision patients with complex unfamiliar aids
      • would benefit from a structured rehabilitation programme
      • learning how to do the task by incorporating the aid
  • any telescope user should be taught how to use the device by
    • localising
    • focussing
    • tracking
    • scanning
      • but this is (usually) only stationary

Chris Dickinson UMIST Department of Optometry and Neuroscience

and then need additional specific help in using for driving
AND THEN NEED ADDITIONAL SPECIFIC HELP in using for driving
  • combination of use of telescope and improving (speeding up) information gathering

Chris Dickinson UMIST Department of Optometry and Neuroscience

indoor home activities
indoor/home activities
  • tracking moving objects (rolling ball)
  • tracking moving instructor who holds up flash cards to be read
  • wall-display with numbers which can be detected through carrier lens, but not identified
    • instructor picks a location (“third letter on fourth row”)
    • user finds through carrier lens
    • user drops head to look through telescope and reads letter as quickly as possible
  • face away from test chart
    • turn around and try to remember as much as possible in just 1 second

Chris Dickinson UMIST Department of Optometry and Neuroscience

outdoor in car
outdoor/in car
  • travelling as passenger
    • give a commentary on what is happening on road ahead
    • scanning for traffic lights, and identifying signal
    • seeing road signs and identifying through telescope
    • hold a hand mirror on dashboard and practice looking into it
  • standing by road
    • seeing an approaching car, spot with telescope
    • reading number plate, counting number of passengers

Chris Dickinson UMIST Department of Optometry and Neuroscience

should bioptics be allowed in the uk
Should bioptics be allowed in the UK?

Chris Dickinson UMIST Department of Optometry and Neuroscience

the argument for
The argument for….
  • There is a duty of public welfare, but cannot discriminate because of disability
  • driving should be permitted if impairment can be compensated through
    • special training
    • the use of assistive technology (personal eg prosthetic limb, or modified vehicle)
    • extra care and attention
  • such that the person does not jeopardise their own or others safety

Chris Dickinson UMIST Department of Optometry and Neuroscience

and against
And against….
  • Ring scotoma created by housing of telescope
    • but these are fitted binocularly

Chris Dickinson UMIST Department of Optometry and Neuroscience

a much more realistic field plot
...a much more realistic field plot
  • Fit monocularly
  • reasonably equal acuities in each eye so unaided eye can compensate

Chris Dickinson UMIST Department of Optometry and Neuroscience

also when you make the whole situation dynamic
Also when you make the whole situation dynamic...
  • the movement of the car moves different objects into view
    • this is why your windscreen posts don’t affect performance
  • and the user is encouraged/taught to scan constantly with their eyes
    • this can also compensate for their own field loss (eg central scotoma)
    • just like the monocular person not noticing their blind spot

Chris Dickinson UMIST Department of Optometry and Neuroscience

monocular viewing
Monocular viewing
  • causes loss of depth perception
  • this is lost anyway due to the magnification and has to be learned as part of training

Chris Dickinson UMIST Department of Optometry and Neuroscience

very small field of view
Very small field of view
  • so only small (10-15o) area has optimal (magnified) acuity
  • but fovea only 3-5o in normals
  • so normals appreciate much of their field at <6/12 VA, and then use fovea to home in on interesting items
  • exactly same for telescope wearer whose bioptic is his fovea

Chris Dickinson UMIST Department of Optometry and Neuroscience

attention distracted from road
Attention distracted from road
  • In time taken to view through bioptic
    • the car has travelled a long distance
      • at 50 mph about 25 yards in 1 second
    • something could have been missed
  • just like normal driver looking in rear-view mirror
    • would not do it whilst negotiating a tricky manoeuvre
    • and still aware of straight-ahead if device monocular

Chris Dickinson UMIST Department of Optometry and Neuroscience

well co ordinated head and neck movements required
Well co-ordinated head and neck movements required
  • and good scanning eye movements to compensate scotomas
  • physical limitations may occur especially in elderly
    • most acquired visual loss is age-related

Chris Dickinson UMIST Department of Optometry and Neuroscience

the telescope can only improve the acuity and nothing else
The telescope can only improve the acuity, and nothing else
  • if an individual has <6/12 acuity it is common for there to be other deficits
  • eg: glare disability, poor contrast sensitivity, poor colour discrimination, delayed adaptation

Chris Dickinson UMIST Department of Optometry and Neuroscience

acuity improvement not as great as expected
Acuity improvement not as great as expected
  • 3x telescope predicts 3x improvement in acuity but less than this because of
    • image smear
    • vibration-induced oscillopsia
    • incomplete image stabilisation by VOR
      • image motion opposite to head movement

Chris Dickinson UMIST Department of Optometry and Neuroscience

why not just use approach magnification
Why not just use “approach magnification”?
  • wait until nearer to object and then will be able to resolve it
  • need to drive slower to give adequate reaction time
    • this is what normally-sighted driver does in poor visibility/night driving
  • Fonda suggested that (so long as restricted speed licence) time was still adequate to make safe decisions
  • he argued that because of the
    • time taken to “find” object through telescope
    • and reduced improvement compared to predicted acuity
  • then there was little “early warning” gained from telescope

Chris Dickinson UMIST Department of Optometry and Neuroscience

do the highly structured training programmes really happen
Do the highly-structured training programmes really happen?
  • 73% of telescopic drivers received 1 hour or less of training

Chris Dickinson UMIST Department of Optometry and Neuroscience

very artificial situation which patient has only adopted for this one task
Very artificial situation which patient has only adopted for this one task
  • don’t use them for anything else
    • ?why not?
  • the best bioptic for driving may not be best for general purpose
    • binocular, autofocus
  • therefore may get careless about wearing once road test done
    • especially if uncomfortable
  • 13/57 reported NOT wearing the device when being involved in an accident/violation
    • just like normally-sighted drivers not wearing spectacles

Chris Dickinson UMIST Department of Optometry and Neuroscience

why single out bioptic telescopes for special mention
Why single out bioptic telescopes for special mention?
  • what about prisms or reverse telescopes for field loss
    • no US state specifically mentions these in their driving regulations

Chris Dickinson UMIST Department of Optometry and Neuroscience

inwave lens for tunnel vision
“InWave” lens for tunnel vision

Chris Dickinson UMIST Department of Optometry and Neuroscience

peli prism for hemianopia
“Peli prism” for hemianopia

Chris Dickinson UMIST Department of Optometry and Neuroscience

whichever side of the argument you believe about bioptics
Whichever side of the argument you believe about bioptics….
  • ….is irrelevant!

Chris Dickinson UMIST Department of Optometry and Neuroscience

the real argument
The real argument
  • is the user “safe to drive” WITHOUT bioptics
  • because this is how they will be 90-95% of the time
    • recognised in the driving regulations of US states like South Carolina and Michigan which allow the use of bioptics, but don’t allow them to be used to pass the vision test!

Chris Dickinson UMIST Department of Optometry and Neuroscience

consider the us states which don t allow bioptics
Consider the US states which DON’T allow bioptics
  • eg: Connecticut
  • these states are much more radical because allow driving to some with VA 6/60

Chris Dickinson UMIST Department of Optometry and Neuroscience

so an alternative strategy
So an alternative strategy
  • divide visually impaired into 3 groups on basis of VA and field
    • >6/12 and 120o field
      • pass criteria, no problems
    • <6/60, <100o degree field (or any arbitrary figure you choose)
      • vision too poor to drive
    • 6/12-6/60 and field 100-120o, stable, equal acuities
      • assess for the possibility of a restricted licence

Chris Dickinson UMIST Department of Optometry and Neuroscience

so what are the arguments for and against relaxing the acuity standards
So what are the arguments for and against relaxing the acuity standards?

Chris Dickinson UMIST Department of Optometry and Neuroscience

a lot of current drivers manage very well with impaired vision
A lot of current drivers manage very well with impaired vision
  • spatial and temporal vision and visual field
  • all impaired by low-light and poor visibility
  • but normally-sighted individuals can drive safely (if slightly more slowly) at night or in misty or foggy conditions
  • this would be equivalent to licencing visually impaired individuals for daytime only

Chris Dickinson UMIST Department of Optometry and Neuroscience

anecdotal evidence
Anecdotal evidence
  • Feinbloom 1977
    • was concerned about fitting his low vision patients with bioptics
    • took 12 experienced drivers with normal vision and gave them +3.00 blur
    • each drove their own cars for sessions of 1-4 hours
      • day and night conditions
      • varying weather and traffic conditions

Chris Dickinson UMIST Department of Optometry and Neuroscience

drivers reported no problems with
Drivers reported no problems with
  • monitoring traffic in front or sides
  • using mirrors
  • judging distances, speed and position of other cars
  • passing through crossroads
  • changing lanes
  • parking

Chris Dickinson UMIST Department of Optometry and Neuroscience

but they did report difficulty with
But they did report difficulty with
  • reading any signs, even the largest
  • identifying correct lanes and exits
  • seeing words on signs (identified by shape)

Chris Dickinson UMIST Department of Optometry and Neuroscience

this was borne out in a study by wood and higgins
This was borne out in a study by Wood and Higgins
  • 24 young, normally-sighted adults
  • tested at four VA levels from 6/6 to 6/60
  • significant reduction in ability to recognise signs and avoid speedbumps
  • no change in manoeuvring ability or gap perception

Chris Dickinson UMIST Department of Optometry and Neuroscience

should we be using other visual measures
Should we be using other visual measures?
  • specificity and sensitivity in relation to test outcome and driving safety
    • absolutely the key requirement
  • moderate prevalence of failures
  • reproducible
  • face validity
  • practicality
  • ?involves vision rather than other abilities
    • although those other factors (eg attention) may also be important
  • ?resistant to training
    • although the skill it is testing may be trained

Chris Dickinson UMIST Department of Optometry and Neuroscience

what are the measures which might be used
What are the measures which might be used?
    • (Peripheral) visual field
    • Contrast sensitivity
    • Dynamic acuity
    • Useful Field of View
  • But in each case, the sensitivity and specificity would not be 100%
  • because driving is a multi-factorial task

Chris Dickinson UMIST Department of Optometry and Neuroscience

it depends on non visual perceptual and cognitive skills
It depends on (non-visual) perceptual and cognitive skills
  • making quick decisions
  • predicting road layouts
  • judging situations early
  • being alert for the unexpected
  • concentration on the task
  • correctly interpreting shadows, reflections
  • good time-planning
  • accurate judgement of risk
  • extra care under more demanding circumstances

Chris Dickinson UMIST Department of Optometry and Neuroscience

if these skills are highly developed
If these skills are highly-developed
  • can compensate for considerable visual loss
  • and could potentially be taught
  • is it the visual skills training with the bioptics that provides safe driving, rather than the device?

Chris Dickinson UMIST Department of Optometry and Neuroscience

so for the group of visually impaired drivers who might be given a licence
So for the group of visually impaired drivers who might be given a licence
  • give a driving simulator test to see if safe to begin driving
  • followed by a period of visual skills training
  • and then a rigorous on-road test under different lighting conditions (eg, glare)
  • to be reviewed annually with possibility of withdrawal or extension

Chris Dickinson UMIST Department of Optometry and Neuroscience

what accident record should we expect and accept
What accident record should we expect - and accept?
  • disabled drivers in general have a worse record
  • visually impaired compare favourably
  • drivers in Texas USA before bioptics (Lippmann 1979)
    • accident rate per 100 drivers in a year
      • 8.5 neurological impairments
      • 5.63 cardio-vascular
      • 4.86 visual
  • currently study underway by Peli to find out if bioptic driving is safer

Chris Dickinson UMIST Department of Optometry and Neuroscience

earliest study of bioptic drivers by korb 1970
Earliest study of bioptic drivers by Korb 1970
  • 26 licenced individuals with 32 years of unblemished driving record
  • very carefully selected from 67 original applicants (one rejected because of “poor moral character”!!)

Chris Dickinson UMIST Department of Optometry and Neuroscience

bioptic drivers in texas compared to random control group lippmann et al 1988
Bioptic drivers in Texas compared to random control group (Lippmann et al 1988)
  • all 64 in the state who had driven more than 1 year
  • 1.34 x greater accident rate in bioptic wearers
    • but number of individuals involved in accidents is same suggesting some accident-prone
  • much greater rate of at fault incidents in bioptic wearers 82% compared to 40%
  • much lower violation rate suggesting more careful

Chris Dickinson UMIST Department of Optometry and Neuroscience

bioptic drivers in illinois compared to state averages taylor 1990
Bioptic drivers in Illinois compared to state averages (Taylor 1990)
  • their accident involvement rate is 120 per 1000
  • normally sighted of equivalent age group 97.6 per 1000
  • overall all ages 123 (for 16 year olds its 2200!!)

Chris Dickinson UMIST Department of Optometry and Neuroscience

californian bioptic drivers in 1996 clarke
Californian bioptic drivers in 1996 (Clarke)
  • age and gender adjusted total accident rates was 2.2x that of control group
  • but citation rate only 0.7x
  • these are careful and slower drivers, but still doesn’t compensate
  • only 35% had the daytime restriction on their licences which was contrary to official guidelines

Chris Dickinson UMIST Department of Optometry and Neuroscience

in summary
In summary
  • present acuity requirements for driving are more restrictive than necessary
  • restricted (daytime) licences could be issued to some visually impaired individuals
    • stable long-standing loss of vision
    • approximately equal in each eye
  • review annually for relaxation of conditions, or withdrawal
    • although acknowledge accident rate likely to be higher
  • such licences should not be dependent on the use of assistive devices

Chris Dickinson UMIST Department of Optometry and Neuroscience