Changing visual standards in driving: but a high proportion of eye patients still drive illegally

Many people drive either deliberately or unwittingly with inadequate vision to legally hold a licence.

A survey in Australia showed that 8% of drivers failed the state visual acuity requirements.¹ It is the duty of doctors to let their patients know if they do not fulfil the legal requirements.

In England group I drivers should be able to read a standard number plate at 20.5 metres in a good light using both eyes with correction worn if necessary. They should also have a binocular field of 120 degrees along the horizontal with no significant defect within 20 degrees of fixation in any direction. This should be tested with an Esterman binocular field test. Recent guidelines from the Driver and Vehicle Licensing Agency (DVLA) have changed with regard to visual field interpretation, allowing small areas of field loss within these areas to qualify for a pass for group I licence holders. In particular, patients with static long term field defects, particularly those who have a safe driving history who would previously have failed to meet the field requirements, may still be considered for a licence.²

This prospective clinic based audit is the first to use the licence plate test at 20.5 metres rather than a Snellen chart to quantify the size of the problem in a typical ophthalmology clinic in a district general hospital. The use of a number plate is important since Snellen acuity is known to be a poor predictor of an individual’s ability to meet the required visual standard for driving³; this is probably because of the differing symbol format, lighting levels, and other conditions involved.

Participants and methods

In all, 156 consecutive patients were reviewed prospectively in general ophthalmology clinics with subspecialty interests in glaucoma and diabetes. All patients were asked if they held a group I (private car) or group II (large goods vehicles or passenger carrying vehicle) licence. Patients were tested in good light with a standard number plate (letters 79.4 mm high) at 20.5 metres using both eyes with their glasses when appropriate. They were given two attempts to read the number plate. Patients who were felt to be at risk of failing the field regulations (typically on the basis of monocular field tests for glaucoma or patients who had had bilateral panretinal photocoagulation) were asked to have an Esterman binocular field test. The notes of all patients who failed to achieve the visual standard for driving were reviewed and the patients were asked if they had ever been told not to drive before.

Results

A total of 156 patients were asked if they held a driving licence. Of these, 66 (average age 63.6, range 30–83, 52/66 male) held a group I driving licence, only two patients held a group II licence. Eleven patients (average age 72, range 62–81) who held a licence failed to meet the driving standard (Table 1).

Table 1.

		Best corrected visual acuity
Sex	Age	RE	LE
M	70	6/9+4	6/9+4	Failed on field
M	72	6/9	6/9+2	Failed on field
M	77	6/12-1	6/12-2
M	67	6/12	6/12
M	72	6/36	6/9+4
M	81	6/18	6/18
M	62	6/9-2	6/9-3	Group II licence holder
M	72	6/6-2	6/9
M	74	6/9	6/36
M	72	6/18	6/18
F	74	6/18+3	6/9

One of the group II patients failed the test on acuity but was due to surrender his licence in the next few months as he was retiring and had already ceased driving.

None of these patients had been told not to drive previously although the notes indicated vision (less than or equal to 6/18 in each eye) or field loss at the previous visit which should have made it clear that it was unlikely that these patients would be legally fit to drive in four of the cases. There was no documentation on whether these patients drove or had been advised not to in any of their notes. Three of the 11 patients had already ceased driving because they no longer felt confident enough but had retained their licences.

Nine of 11 patients failed to meet the driving standard because of poor visual acuity with two patients failing because of glaucomatous field loss. The new fields requirements would not have allowed either of these two patients to pass.

Conclusion

A total of 42% of patients seen in a busy eye clinic still held a driving licence and of these 17% did not fulfil the legal criteria to drive (7% of all patients seen). None of them had been informed previously that they should give up their licences despite evidence that at least 4/11 would have been unfit to drive from measurements made at a previous visit. Men were much more likely than women to be driving with inadequate vision (91% of those failing the driving standard in this study) and most of them were over the age of 70 (90%).

All patients should be asked if they drive or not and this should be recorded in the notes. If vision is inadequate for driving the notes should contain a statement that the patient has been informed of this and a letter sent to the general practitioner. This is particularly important from a medicolegal point of view since in one study half of the patients informed that they should surrender their licences continued to drive.⁴ Doctors should remain aware that they have a responsibility to alert patients that they should stop driving and that the patient should inform the DVLA. If the doctor does not do this then they may be liable to litigation should an accident occur.⁵ It may be worth pointing out to those patients who do not inform the DVLA of their poor eyesight that driving with inadequate vision may jeopardise insurance cover, as this may persuade many of them to stop driving.⁶

As previously reported the Snellen acuities did not correspond well with the ability to read a number plate.³ Ideally all eye clinics should have a number plate which can be viewed in good light from 20.5 metres for use when advice about driving is given. Unfortunately some number plates are easier to read than others and a “good light” is not defined in law so the test is not standardised. Although it is easy for a policeman to perform the test at the side of the road it is not a very reliable means of visual assessment particularly in equivocal cases and better standards would be helpful.

Most people in this study failed the test due to poor acuity rather than an inadequate field. It is possible that a few more people would have failed field tests if every driver had an Esterman binocular field test done. It is unlikely that the new more lenient field requirements will have a significant impact on the number of people seen in each clinic who drive illegally.

Whether these patients actually pose a significant risk to themselves or other road users is debatable; drivers with poor acuity appear to drive more carefully to compensate. However drivers with binocular field defects have been estimated to have twice the normal rate of driving accidents in some studies.^7–10 What is worrying is that patients who attend an eye clinic seem unlikely to have been spontaneously warned to stop driving and doctors should be more aware of their role in protecting both their patients and society from road traffic accidents.