| With
the ever increasing number of vehicles using our roads it is inevitable
that drivers need to call upon increasing use of sensory and motor skills
in order to negotiate safely through the traffic. Whist approximately 95%
of the sensory input to the brain required for driving comes from vision
there is surprisingly little evidence that defects of vision alone cause
road accidents. 1,2 Despite this, it is obviously essential for adequate
standards of vision to be set for the driver of any vehicle and these are
set down as either statutory requirements or guidance from the professional
body i.e. the Royal College of Ophthalmologists. 3
The
Secretary of State for Transport has the responsibility for granting driving
licences in this country, and these duties are discharged by the Driver
and Vehicle Licensing Agency (DVLA) in Swansea. A team of DVLA doctors
provides the medical advice on which the Secretary of State decides whether
or not an applicant is fit to drive. This team, currently led by Dr Jane
Durston, consults the Secretary of State for Transport's Honorary Medical
Panels in six specialities not only for general advice regarding driving
ability but also to discuss individual cases who pose specific problems.
The Visual Standards Subcommittee of the Royal College of Ophthalmologists
has been the body to which the DVLA looked for advice regarding vision
and riving but the relevant activities of this subcommittee have been recently
separated to form the Secretary of State for Transport's Honorary Advisory
Panel on Driving and Visual Disorders. This meets twice a year and retains
the same membership as the Visual Standards Subcommittee and co-opts the
chief medical advisers of the DVLA and the Department of Transport.
In
recent months the DVLA have noted a large increase in the number of queries
related to visual standards and are anxious that the statutory requirements
and the guidelines issued by this College are firstly appropriate and secondly
widely known to ophthalmologists. It is therefore the purpose of this booklet
to outline and clarify the visual requirements for driving in the U.K.
to allow ophthalmologists to accurately complete the appropriate forms
sent out by the DVLA for their patients.
Since
January 1983, the European Commission has laid down definite minimum visual
standards for driving licence holders in the member states and this has
now been incorporated into U.K. law. With effect from 1 January 1997, the
driver licensing legislation in the U.K. has been amended to implement
the requirements of the Second EC Directive on the driving licence. This
has not altered the requirements for a Group 1 licence (private car) to
any great extent but does have some effect on Group 2 drivers (Large Goods
Vehicles and Passenger Carrying Vehicles).
Group
1 Drivers
Visual
Acuity
Poor visual
acuity is prescribed as a relevant disability for the purposes of Section
922 of the 1988 Road Traffic Act thus;
the
inability to read in good light (with the aid of corrective lenses if necessary)
a registration mark fixed to a motor vehicle and containing letters and
figure 79.4mm high at a distance of 20.5 metres.
This
corresponds to a binocular visual acuity of approximately 6/10 on the Snellen
chart.4
The
number plate standard is absolute in law and is not open to interpretation.
Visual
Fields
As well
as the statutory number plate test, the DVLA recognise that an adequate
field of vision is necessary for driving. As with visual acuity, published
data shows equivocal and sometimes conflicting evidence of the correlation
between visual field defects and road traffic accidents. 1 There
is, however, some evidence that drivers with binocular field defects do
have a higher incidence of accidents especially of a sideswipe nature 2.
The Royal College of Ophthalmologists in its advice to the DVLA has defined;
the
minimum visual field for safe driving is a field of vision of at least
120o on the horizontal meridian measured by the Goldmann perimeter
on the III4e settings (or equivalent perimetry). n addition there should
be no significant field defect in the binocular field which encroaches
within 20o of fixation either above or below the horizontal meridian. By
this means, homonymous or bitemporal defects which come within 20o of fixation,
whether hemianopic or quadrantanopic, are not accepted as safe for driving.
Isolated scotomata represented in the binocular field near to the central
fixation area are also inconsistent with safe driving.
The
test must therefore monitor the central area of field as well as its outer
perimeter and the intervening meridians. It is obviously essential
that the application of the standard should not be equipment specific and
the phrase "equivalent perimetry" allows the development of equivalent
programs using other perimeters including autoperimeters. The use of older
manual perimeters such as the Lister, Aimark or Priestley Smith where fixation
is more difficult to monitor accurately are more likely to produce inaccuracies
in measurement especially in the central field and are not now considered
suitable for assessment of the standard. Suprathreshold screening tests
which cover the central and peripheral field in each eye are commonly available
on most autoperimeters and will satisfy the standard. Central threshold
tests, commonly used for routine monitoring of glaucoma, are helpful in
assessing the significance of a scotoma in the central field but in isolation
are not useful.
This
definition is not statutory, but reflects the requirements of the Second
E.C. Directive and is issued by the College as advice to both the Department
of Transport and the DVLA. The inability to satisfy the standard is considered
to be a relevant disability within the meaning of the 1988 Road Traffic
Act and the driving licence will therefore be revoked or the application
refused.
Where
the driver has obvious field defects such as a homonymous hemianopia or
quadrantanopia then no confusion arises and the licence is refused. This
applies even when the patient has, for whatever reason, been driving with
this condition for many years. The problem arises, however, when there
are equivocal field losses that only just encroach into the permitted field
for driving. These may not necessarily be repeatable especially in the
elderly who can have problems mastering the perimeter, or in patients with
early glaucoma or lightly photocoagulated diabetics. To be fair to these
patients, it is important to test them on more than one occasion to enable
an appropriate decision to be made regarding their driving ability. The
Esterman binocular field test 5, 6 allows some enhancement of
the binocular field as occurs naturally and also allows fixation by the
dominant eye. Hence it can be seen to be the least stringent test fulfilling
the required standard. It may therefore be used to the benefit of the patient.
However, it must be stated that if the Esterman test is failed, even by
one spot within the 20o limit, it is likely that this represents
a significant scotoma which will lead to the loss of the driving licence.
The score given by the program is weighted to the areas of field important
to driving but is of little help in the assessment of the standard. Severe
bitemporal hemianopia which extends to the midline on either side can still
give a horizontal binocular field of 120o on an Esterman or other binocular
field by way of binasal vision. It is felt that despite this "full" field,
driving is unsafe due to the instability of the two hemifields and the
inability of the driver to "lock" the fields from the two eyes together.
Monocular
vision is not a cause for disqualification, providing the visual field
in the remaining eye is within the above definition. This physiological
blind spot may be picked up on an Esterman test in a monocular patient
and if this is the case, other central visual field tests such as the Humphrey
24-2 threshold tests should be supplied to demonstrate the otherwise normality
of the central field.
Some
patients produce very different field test results at different times and
it is important to maximise reliability and reproducibility of the visual
field test in all cases. False negative and positive errors as well as
fixation losses must be minimised to produce accurate results. A field
should be rejected if there are more than 20% of false positive errors.
A perimetrist should be present with the patient at all times during
the test and should carefully explain the test to the patient prior to
beginning. Spectacles, especially for a high ametrope, may produce aberrations
and a more accurate test may be produced without them. With binocular testing
the supplied trial frame in the autoperimeter is redundant.
A field
of binocular single vision of 120o is acceptable for driving
and diplopia in a very limited direction of gaze may be tolerated. Diplopia
in the primary position presents an extreme hazard to safe driving, but
if it can be remedied by prisms or a patch it is acceptable provided a
time has been allowed for adaptation.
Group
2 Drivers
Terminology
Group
2 vehicles originally called HGVs (Heavy Goods Vehicles) and PSVs (Public
Service Vehicles) are now classified as Large Goods Vehicles (LGV) and
Passenger Carrying Vehicles (PCV). These are vehicles in excess of 7.5
metric tonnes laden weight or minibuses with more than 8 seats if driven
for hire or reward. In addition, new applicants who wish to drive 3.5 to
7.5 tonne lorries need to meet the Group 2 standard. Existing licence holders
in this latter group need only satisfy the numberplate requirement as above.
The Medical Commission on Accident Prevention in their publication "Medical
Aspects of Fitness to Drive" advises that these standards should generally
apply to emergency police, fireman and ambulance drivers as well as taxi
drivers, although some local authorities/constabularies vary from the standard.
The
Motor Vehicles (Driving Licences) Regulations 1996 which came into force
on 1 January 1997 prescribe standards of visual acuity for Group 2 drivers.
New
applicants and those same applicants on renewal require:
a.
A visual acuity, with corrective lenses if necessary, of at least 6/9 in
the better eye and at least 6/12 in the worst eye.
b.
If corrective lenses are used, the uncorrected acuity in both eyes must
be at least 3/60.
The
appropriate correction needs to be tolerated by the driver.
Visual
field is not prescribed but failure to achieve a normal binocular horizontal
field of at least 120o is considered to be a relevant disability
as is uncontrolled diplopia.
Current
Group 2 Licence holders
There
are individuals who may not be able to satisfy the above standard but who
may be permitted to continue to drive providing that they supply a certificate
of recent driving experience and have not during the period of 10 y ears
immediately before the date of application been involved in any road accident
in which defective eyesight was a contributing factor. These so-called
"grandfather rights" are set out in Motor Vehicles (Driving Licences) Regulations
1996 Section 68 and the standard which applies depends on the time when
the individual was first licensed and is related to previous misdrafting
of the Regulations. These licence holders need to consult the DVLA about
their continuing entitlement to hold a Group 2 licence.
Medico-legal
considerations
Some ophthalmic
treatments such as laser photocoagulation may produce visual field defects
that can affect safe driving. This includes pan-retinal photocoagulation
which can produce restriction of the peripheral field and focal paramacular
photocoagulation which can produce isolated central field defects. It should
therefore be part of the informed consent to point out to the patient that
the treatment is essential to prevent or slow down the progression of their
disease but it may in itself jeopardise the right to drive because of limitation
of the field of vision.
The
DVLA has the responsibility for deciding whether any individual patient
is fit to hold a driving licence. The onus is on the licence holder to
declare to the DVLA if they develop a medical problem which affects their
fitness to drive. Doctors may be asked to provide appropriate reports for
the DVLA but they will not be required to express an opinion as to the
patient's fitness to drive.
All
doctors owe their patients a duty of confidentiality and this may be enforced
by the General Medical Council. When an ophthalmologist feels that their
patient does not fulfil the visual standards for driving it is important
that this feeling is made known to the patient at the time. In addition
it is advisable for an entry to this effect to be made in the hospital
notes and the general practitioner informed by letter. The patient should
then be advised to notify the DVLA him or herself. If the patient then
continues to drive or does not notify the DVLA he or she should be challenged
by the ophthalmologist, and where appropriate, advised that the ophthalmologist
will inform the DVLA directly. In these rare cases, the DVLA will treat
this as strictly confidential and the source of the notification will not
be released.
Ophthalmologists
should only breach confidentiality in good faith and where the patient's
vision is likely to make them a danger to themselves or others if they
drive. Members of a defence organisation are recommended to discuss such
cases with a medico-legal adviser in advance. The patient's general practitioner
should also be informed.
February
1999
References
1. Johnson
CA, Keltner JL (1983). Incidence of visual field losses in 10,000 eyes
and its relationship to driving performance. Arch Ophthal. 101 371-375.
2.
Hills RL, Burg A (1977). A re-analysis of Californian driver vision data:
general findings. research Report LR 768, Transport and Road Research Laboratory,
Crowthorne.
3.
Munton CGF (1995). Vision. A chapter in Medical Aspects of Fitness to Drive.
Ed. Taylor J. pub. Medical Commission on Accident Prevention.
4.
Drasdo M, Haggarty CM (1977). A comparison of British number plates and
Snellen vision test for car driving. Research Report RF 676, Transport
and Road Research Laboratory, Crowthorne.
5.
Esterman B. (1968). Grid for scoring visual fields by perimeter. Arch Ophthal.
79 400-406.
6.
Esterman B. (1982). Functional scoring of the binocular field. Ophthalmology
89 1226-1234.
The
Royal College of Ophthalmologists 17 Cornwall Terrace, London. NW1 4QW
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