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 • 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-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 • 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 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 • 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 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 • 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 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 • 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 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? • 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 acuities • assess for the possibility of a restricted licence Chris Dickinson UMIST Department of Optometry and Neuroscience

Driving with a Visual Impairment