Royal College of Ophthalmologists Guidelines

Visual Standards for Driving

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 120^o 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 20^o 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 120^o 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 120^o 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 Telephone: 0171-935 0702 Facsimile: 0171-935 9838