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Driving with a Visual Impairment
Chris Dickinson
Department of Optometry and Neuroscience
UMIST
Faculty of Ophthalmologists
May 21 2002
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
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
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-third20% 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
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
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
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
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
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?
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
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
Chris Dickinson UMIST Department of Optometry and Neuroscience
and need to be angled slightly upwards
Chris Dickinson UMIST Department of Optometry and Neuroscience
but can be below line of sight
and behind the lens
Chris Dickinson UMIST Department of Optometry and Neuroscience
or autofocus
Chris Dickinson UMIST Department of Optometry and Neuroscience
or binocular
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
gradual increase since around 1970 a typical example (Kentucky)
6/18 with telescopewhich 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
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
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?
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
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
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 signchecking for freeway exitsseeing 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
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?
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
combination of use of telescope and improving (speeding up) information gathering
Chris Dickinson UMIST Department of Optometry and Neuroscience
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 lensuser 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
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?
Chris Dickinson UMIST Department of Optometry and Neuroscience
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….
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
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...
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
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
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
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
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
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
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”?
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 telescopeand 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?
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
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?
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
Chris Dickinson UMIST Department of Optometry and Neuroscience
“Peli prism” for hemianopia
Chris Dickinson UMIST Department of Optometry and Neuroscience
Whichever side of the argument you believe about bioptics….
….is irrelevant!
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
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
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 acuitiesassess 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?
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
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 conditionsvarying weather and traffic conditions
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
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
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?
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 trainingalthough the skill it is testing may be trained
Chris Dickinson UMIST Department of Optometry and Neuroscience
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
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
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
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?
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 impairments5.63 cardio-vascular4.86 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
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)
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)
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)
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
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
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