Slide 1: Low Vision and Driving: Mobility Or Liability?

Slide 1: Low Vision and Driving: Mobility or Liability?

Chris Dickinson

Department of Optometry and Neuroscience

UMIST

Second National Low Vision Services Implementation Conference

October 28th 2002

Slide 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

Slide 3: Driving and Vision often create very emotive stories

Shows cuttings extracted from a variety if sources.

·  and if you asked a member of the public they would not expect blind people to be allowed to drive

Slide 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 traffic accidents

·  and anything which might make that worse must be eliminated

Slide 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

Slide 6: 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

- Disability Discrimination legislation

Slide 7: 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

Slide 8: 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)

Slide 9: 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

Slides 10 – 14:

Shows telescopic magnification and include the following observations.

·  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

Slide 15: 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

Slide 16: 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

Slide17: 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

·  with passenger

Slide 18: 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

Slide 19: Bioptic only used infrequently

·  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

Slide 20: Brief episodes (0.5-1.0 second) of bioptic viewing

·  Approximately 5-10% of total time

- Occasionally used for scanning

- “U” movement across the road ahead

- Mostly used 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

Slide 21: 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)

Slide 22: Driver needs training in the required skills

·  Training is 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

Slide 23: AND THEN NEED ADDITIONAL SPECIFIC HELP in using for

driving

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

Slide 24: 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

Slcie 25: 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

Slide 26: Should bioptics be allowed in the UK?

Slide 27: 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

Slide 28: And against….

·  Ring scotoma created by housing of telescope

- but these are fitted binocularly.

See graph on slide

Slide 29: ...a much more realistic field plot

·  Fit monocularly

·  reasonably equal acuities in each eye so unaided eye can compensate

Slide 30: 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)

j- ust like the monocular person not noticing their blind spot

Slide 31: Monocular viewing

·  causes loss of depth perception

·  this is lost anyway due to the magnification and has to be learned as part of training

Slide 32: 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

Slide 33: 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

Slide 34: 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

Slide 35: 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

Slide 36: 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

i- ncomplete image stabilisation by VOR

- image motion opposite to head movement

Slide 37: 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

Slide 38: Do the highly-structured training programmes really happen?

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

Slide 39: 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

Slide 40: 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

Slide 41: “InWave” lens for tunnel vision

Slide 42: “Peli prism” for hemianopia

Slide 43: Whichever side of the argument you believe about

bioptics….

·  ….is irrelevant!

Slide 44: 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!

Slide 45: 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

Slide 46: 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, <90o degree field (or any arbitrary figure you choose)

- vision too poor to drive

- 6/12-6/60 and field 90-120o, stable, equal acuities

- assess for the possibility of a restricted licence

Slide 47: So what are the arguments for and against relaxing the

acuity standards?

Slide 48: 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

Slide 49: 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

Slide 50: 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

Slide 51: 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 on young adults

with simulated impairment

Slide 52: 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

Slide 53: 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