Introduction

The Canadian Ophthalmological Society (COS) Working Group on Driving Standards has developed a set of recommendations for new vision standards for driving in Canada and a new standardized approach to the application of these standards. These recommendations have been presented to the Canadian Medical Association for inclusion in the ongoing revision of the Physician’s Guide to Driver Examination. The recommendations represent the consensus opinion of the working group and are based on a literature review, the experience and expert opinion of the members of the working group and comments from other individuals and organizations. The recommendations contain substantial changes from the existing document, including changes in the minimum requirements for licensing, assessment and review procedures, and the classification of vehicles. It is the working group’s opinion that these changes reflect a more sensitive, evidence-based approach to both vehicle classification and the minimum vision requirements for licensing.

Recommendations

Good visual function is essential for safe driving. Any significant loss of visual function, such as visual acuity or visual field, will diminish a person’s ability to operate a motor vehicle safely on today’s congested, high-speed roadways. A driver with a marked visual defect may fail to perceive a potentially dangerous situation altogether or may see it too late to react appropriately.

When a patient is visually impaired, the COS recommends that the physician inform him or her of the nature and extent of the visual defect and report the problem to the appropriate authorities if required. Reporting by ophthalmologists, other physicians and optometrists is one of the most effective ways to screen for visual defects that may be incompatible with safe driving.

This report presents information about recommendations for mandatory standards, other important visual functions that should be taken into consideration in determining fitness to drive, and recommendations for exceptional cases that require individual assessment. It also provides modifications of the classification of vehicle types for the purposes of vision standards (Appendix 1), further details on recommended testing procedures (Appendix 2), and a list of medical conditions with increased risk for vision problems and a statement on the use of vision aids in driving (Appendix 3).

Recommended vision standards for driving

Visual acuity
The corrected visual acuity standards are shown in Table 1. A driver’s visual acuity must at least be such that s/he has time to detect and to react to obstacles, pedestrians, other vehicles and signs while moving at the maximum posted speed in daylight and in darkness. Greater levels of visual acuity are required for some classes to ensure public safety. Road signage should be designed to be easily legible at a safe distance for all drivers who meet the minimum visual acuity standard.

Table 1. Corrected visual acuity* standards for the various classes of driving licences
Class of licence†	Recommended standard
5 (Personal Use)	Not less than 20/50 (6/15) with both eyes open and examined together
4 (Taxi) and 5 (Commercial)	Not less than 20/40 (6/12) with both eyes open and examined together. Worse eye not less than 20/200 (6/60).
1, 2, 3,4 (Emergency) and 6	Not less than 20/30 (6/9) with both eyes open and examined together. Worse eye not less than 20/100 (6/30).
*The recommended testing procedure is outlined in Appendix 2. †See Appendix 1.

Visual field
The visual field standards are shown in Table 2. An adequate continuous field of vision is important to safe driving. Any significant scotoma or restriction in the binocular visual field can make driving dangerous. Conditions often associated with visual field loss are listed in Appendix 3. If a visual field defect is suspected (based on a medical condition, subjective report or confrontation field assessment), the patient should be referred to an ophthalmologist or optometrist for further testing.

Table 2. Visual field* standards
Class of licence	Recommended standard
5 (Personal Use)	120 continuous degrees along the horizontal meridian and 15 continuous degrees above and below fixation with both eyes open and examined together
4 (Taxi) and 5 (Commercial)	120 continuous degrees along the horizontal meridian and 15 continuous degrees above and below fixation with both eyes open and examined together
1, 2, 3,4 (Emergency) and 6	150 continuous degrees along the horizontal meridian and 20 continuous degrees above and below fixation with both eyes open and examined together
*The recommended testing procedure is outlined in Appendix 2.

Diplopia
Diplopia (double vision) within the central 40° (i.e., 20° to the left, right, above and below fixation) of primary gaze is incompatible with safe driving for all classes of licence. Patients with uncorrected diplopia within the central 40° of primary gaze should be referred to an ophthalmologist or optometrist for further assessment. If the diplopia can be corrected completely with a patch or prisms to meet the appropriate standards for visual acuity and visual field, the patient may be eligible to drive. Before s/he resumes driving, there should be an adjustment period of 3 months or sufficient to satisfy the treating ophthalmologist or optometrist that adequate adjustment has occurred.

Colour vision
The colour vision standards are shown in Table 3. Adequate colour vision is important for safe driving for certain classes of licence. All affected patients should be made aware of any abnormality of colour vision in order to allow them to compensate for this difference in their vision.

Table 3. Colour vision* standards
Class of licence	Recommended standard
5 (Personal Use)	No required standard
4 (Taxi) and 5 (Commercial)	No required standard
1, 2, 3,4 (Emergency) and 6	Discrimination of red, green and yellow
*The recommended testing procedure is outlined in Appendix 2.

Other important visual functions for driving

Contrast sensitivity
People with reduced contrast sensitivity may experience difficulty with driving, in spite of having adequate visual acuity to drive. However, it is unclear at this time what level of reduction in contrast sensitivity represents an unacceptable risk for driving. Loss of contrast sensitivity can be associated with increased age, cataract and refractive surgery as well as other ocular disorders. Patients should be made aware of any significant reduction in contrast sensitivity.

Depth perception
Automobile accidents sometimes occur because of the driver’s inability to judge distances accurately. However, judging distance is a skill that can be learned, even by people with monocular vision. Judgements of depth can be made based on monocular clues, such as the relative size or interposition of objects, and clearness of details. A more refined form of distance judgement, called stereopsis, is based on information coming from both eyes.

A driver who has recently lost the sight of an eye or stereopsis may require a few months to recover the ability to judge distance accurately.

Dark adaptation and glare recovery
The ability to adapt to decreased illumination and to recover rapidly from exposure to glaring headlights is of great importance for night driving. The partial loss of these functions in older drivers, particularly those with cataracts or macular disease, may at times justify limiting their driving to daylight hours.

Exceptional cases
The loss of certain visual functions can be compensated for adequately, particularly in the case of long-standing or congenital impairments. When a person becomes visually impaired, the capacity to drive safely varies with his or her compensatory abilities. As a result, there may be people with visual deficits who do not meet the vision standards for driving but who are able to drive safely. On the other hand, there may be people with milder deficits who do meet the vision standards but who cannot drive safely.
 
In these exceptional situations, it is recommended that the person undergo a special assessment for fitness to drive. The decision regarding fitness to drive can be made only by the appropriate licensing authorities. However, the COS recommends that the following information be taken into consideration: favourable reports from the ophthalmologist or optometrist; good driving record; stability of the condition; no other significant medical contraindications; other references (e.g., professional, employment); and assessment by a specialist at a recognized rehabilitation or occupational therapy centre for driver training.
 
In some cases it may be reasonable to grant a restricted or conditional licence to a driver to ensure safe driving. It may also be appropriate to make such permits exclusive to a single class of vehicles.


Reference
1. Canadian Medical Association. Physician’s guide to driver examination. 5th ed. Ottawa: The Association; 1991.

Appendix 1. Vehicle classification for the purposes of vision standards
Class 1	As outlined on p. 3 and 4 of Physician’s Guide to Driver Examination1
Class 2	As outlined on p. 3 and 4 of Physician’s Guide to Driver Examination
Class 3	As outlined on p. 3 and 4 of Physician’s Guide to Driver Examination
Class 4	Divided into 4 (Emergency) (i.e. operators of emergency response vehicles such as ambulances, fire trucks and police cars) and 4 (Taxi) (i.e., operators of taxis with fewer than 5 passengers)
Class 5	Divided into 5 (Commercial) (i.e., vehicles that are driven for commercial purposes) and 5 (Personal)
Class 6	As outlined on p. 3 and 4 of Physician’s Guide to Driver Examination