Driving with a Visual Impairment

1
Driving with a Visual Impairment

• Chris Dickinson
• Department of Optometry and Neuroscience
• UMIST
• Faculty of Ophthalmologists
• May 21 2002

2
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

3
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

4
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

5
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

6
European standards

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

7
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

8
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
• Dont want to withhold the privilege needlessly

9
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 cant
  pass the number plate test

10
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)

11
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

12
Usually above line of sight
13
and need to be angled slightly upwards
14
but can be below line of sight

• and behind the lens

15
or autofocus
16
or binocular
17
Such devices are not acceptable for driving in
UK(?)

• if you ask DVLA they will say it hasnt 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

18
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

19
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)
• lt45 mph
• no motorway driving
• limited radius from home
• no inter-state driving

20
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 cant by itself make them a safe and competent
  driver
• good visual skills might
• often users impose more severe restrictions
  themselves

21
How does the driver use their bioptic?

• NOT VIEWING THROUGH THEM ALL THE TIME

22
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

23
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

24
Cant 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)

25
So how do they learn to do all this?
26
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

27
AND THEN NEED ADDITIONAL SPECIFIC HELP in using
for driving

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

28
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

29
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

30
Should bioptics be allowed in the UK?
31
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

32
And against.

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

33
...a much more realistic field plot

• Fit monocularly
• reasonably equal acuities in each eye so unaided
  eye can compensate

34
Also when you make the whole situation dynamic...

• the movement of the car moves different objects
  into view
• this is why your windscreen posts dont 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

35
Monocular viewing

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

36
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
  lt6/12 VA, and then use fovea to home in on
  interesting items
• exactly same for telescope wearer whose bioptic
  is his fovea

37
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

38
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

39
The telescope can only improve the acuity, and
nothing else

• if an individual has lt6/12 acuity it is common
  for there to be other deficits
• eg glare disability, poor contrast sensitivity,
  poor colour discrimination, delayed adaptation

40
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

41
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

42
Do the highly-structured training programmes
really happen?

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

43
Very artificial situation which patient has only
adopted for this one task

• dont 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

44
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

45
InWave lens for tunnel vision
46
Peli prism for hemianopia
47
Whichever side of the argument you believe about
bioptics.

• .is irrelevant!

48
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 dont allow them
  to be used to pass the vision test!

49
Consider the US states which DONT allow bioptics

• eg Connecticut
• these states are much more radical because allow
  driving to some with VA 6/60

50
So an alternative strategy

• divide visually impaired into 3 groups on basis
  of VA and field
• gt6/12 and 120o field
• pass criteria, no problems
• lt6/60, lt100o 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

51
So what are the arguments for and against
relaxing the acuity standards?
52
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

53
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

54
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

55
But they did report difficulty with

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

56
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

57
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

58
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

59
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

60
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?

61
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

62
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

63
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!!)

64
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

65
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!!)

66
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
  doesnt compensate
• only 35 had the daytime restriction on their
  licences which was contrary to official guidelines

67
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