Driving with a Visual Impairment Chris Dickinson Department of Optometry and Neuroscience UMIST Faculty of Ophthalmologists May 21 2002

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


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


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


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


European standards

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


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


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


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


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)


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


Usually above line of sight


and need to be angled slightly upwards


but can be below line of sight

and behind the lens


or autofocus


or binocular


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


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


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


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


How does the driver use their bioptic?

NOT VIEWING THROUGH THEM ALL THE TIME


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


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


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)


So how do they learn to do all this?


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


AND THEN NEED ADDITIONAL SPECIFIC HELP in using for driving

combination of use of telescope and improving (speeding up) information gathering


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


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


Should bioptics be allowed in the UK?


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


And against….

Ring scotoma created by housing of telescope but these are fitted binocularly


...a much more realistic field plot

Fit monocularly reasonably equal acuities in each eye so unaided

eye can compensate


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


Monocular viewing

causes loss of depth perception this is lost anyway due to the magnification and

has to be learned as part of training


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


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


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


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


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


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


Do the highly-structured training programmes really happen?

73% of telescopic drivers received 1 hour or less of training


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


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


“InWave” lens for tunnel vision


“Peli prism” for hemianopia


Whichever side of the argument you believe about bioptics….

….is irrelevant!


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!


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


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


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


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


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


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


But they did report difficulty with

reading any signs, even the largest identifying correct lanes and exits seeing words on signs (identified by shape)


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


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


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


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


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?


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


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


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”!!)


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


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!!)


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


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

Documents

Driving with a Visual Impairment Chris Dickinson Department of Optometry and Neuroscience UMIST Faculty of Ophthalmologists May 21 2002