Drivers’ eyesight

Professor Steve TaylorEye Health Alliance

Vision and Driving

Prof Steve TaylorProfessional Adviser to FODO

Purpose

To demonstrate that drivers’ vision is important and raise issues for discussion

Aspects to be covered: Visual acuity Visual fields How assessments are made Should there be any changes

Why consider vision?

Intuitively driving performance must be affected by ability to see – we would not expect someone with no useful vision to be driving

Vision is an important aspect of driving and potentially improving standards could reduce accidents

Accident rate and potential costs In the UK in 1992 300,000 injuries and 5000

fatalities resulting from road accidents 1992 Economic costs to UK estimated £5.5 billion 10% reduction saves £0.55 billion

Is there evidence to link road accidents to poor vision?

No really credible evidence because: Vision data relating to drivers involved in

accidents is not recorded routinely Statistically motor accidents are rare events.

It was estimated that in the US a driver could be expected to travel for 102 years before experiencing a disabling-injury accident, and one is not likely to fall victim to a fatal accident for 3738 years when driving.

What information is available?

There is a substantial body of research linking driving performance to visual deficiencies

There is considerable data showing a proportion of the drivers on the roads in the UK do not achieve the statutory requirement

Where does this leave us?

Accepting that registered blind drivers should not be allowed onto the road the question is not should vision be assessed? but what level of vision is acceptable?

The EC has already outlined a standard The following questions are important

How accurately should vision be measured? How frequently should vision be assessed?

Accuracy Directive 2009/113/EC – visual requirements for Group 1 Drivers

Distance Vision – visual acuity of 0.5 (6/12) with both eyes together, with corrective lenses if necessary

Peripheral Vision – 120 degrees horizontal, 20 degrees up and down. No visual field loss in central 20 degrees

If using only one eye, assessment by competent medical authority

Standards should be met every time a driver gets behind the wheel!

Snellen Chart

Visual Acuity Evidence - Effect of vision on processing time

Travelling at 50Kph if a road sign is read at 50 metres with normal vision (6/6)

Processing/reaction time: 6/6 vision has 3 secs 6/12 has 1.5 secs (New EC standard) 6/18 has 1 second

17-2021-30

31-4041-50

51-6061-70

70+

S1

0

0.2

0.4

0.6

0.8

1

1.2

acuity

Age in yrs

Fig 1 Visual acuity for different age groups

What is the legal requirement?

It is an offence to drive at any time with vision below the required standard

Where a driver has been assessed as requiring a visual correction to meet the driving standards it is an offence to drive without wearing the correction

Wearing habits in sample

0

10

20

30

40

50

60

70

80

90

%

17 -29 30-39 40-49 50-59 60-69 70+

Age

Vision without specs <6/12

% M drivers

% F drivers

17-2930-39

40-4950-59

60-6970+

male

female

0

2

4

6

8

10

12

% not w earing specs

age in yrs

Fig 2 Spectacle wearing habits of drivers by age

male

female

In brief

Visual acuity decreases naturally with age from about 60

The number of drivers who fail to reach an acuity of 6/12 without spectacles increases with age from 50

Drivers are more inclined to not wear their spectacles for driving when needed to meet the standard after the age of 40

Retinitis pigmentosa

Macula Degeneration

Glaucoma

Field of Vision This assesses the boundaries of vision to

the side and above and below Visual fields do decline slightly with age There are many eye conditions that can

affect the visual field There is a correlation between field of

vision and accident rate Incidence 3-3.5% in 16-60 Incidence 13% in over 60 Binoc field loss drivers accident rate twice as

high as monoc loss

What does this mean?

We now have 2 visual parameters that are relevant to driving performance visual acuity affects processing time to react and loss of peripheral visual field makes it easier to miss objects at the edge of vision

Where next? We have an acuity standard and a field

standard set by the EC so how is this implemented in the UK?

There is no routine assessment of visual fields Visual acuity is measured at the driving test by

the use of a number plate Drivers are required to self-assess their vision

standard by routinely checking that they can satisfy the number plate test requirement (and self certify after 70 yrs of age)

Self Certification

0

10

20

30

40

50

60

%

17-29 30-39 40-49 50-59 60+

Age

% of drivers underestimating legal test distance

What does this show?

Most drivers in the UK have no concept of what the required test distance is for the number plate test

Almost 50% underestimate the required test distance and this would mean that they think their vision is better than it is!

Summary

There is no statutory re-assessment of vision in the UK for domestic Group 1 drivers

There is a statutory declaration at age 70 that the number plate test can be met

There is no statutory assessment of visual field at any time in the UK

The only official measure of vision relies on a number plate that will provide a different task depending on the background contrast, the light level, the test distance, the letter combination etc which is carried out at the time of the driving test

I hope this brief talk convinces you that

Vision is not treated with the respect it deserves in drivers

A clinical assessment of an individuals vision should be undertaken before they are allowed on the road

Re-evaluation should be undertaken at regular intervals

self assessment currently is inadequate but could provide a gross mechanism for monitoring between re-evaluation

Public awareness of the vision requirements for drivers should be substantially raised

Thank You for your attention