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Vision and Driving: Canada

Yazdan-Ashoori, Payam BMSc; ten Hove, Martin MD

Journal of Neuro-Ophthalmology: June 2010 - Volume 30 - Issue 2 - p 177-185
doi: 10.1097/WNO.0b013e3181dfa982
State-of-the-Art Reviews

Supported by the findings of a major review of vision standards for driving in Canada, the Canadian Ophthalmological Society's Committee on Vision Standards for Driving issued a series of recommendations in 2000 to the Canadian Medical Association. Many of these recommendations, including changes in visual acuity and visual field standards and consideration for exceptional cases, have been implemented across Canada. Canadian courts have stated that it is important to provide on-road assessments for visually impaired individuals who wish to continue driving. Most Canadian provinces and territories will allow visually impaired drivers a license if they pass the test. However, these on-road assessments use scarce resources and may be expensive for the driver. Limited licensure is a widespread practice, but whether it effectively protects drivers is not established. Except for Alberta, Quebec, and Nova Scotia, all Canadian provinces and territories have legislated mandatory reporting of visually impaired drivers by vision care providers.

Department of Ophthalmology, Queen's University, Kingston, Ontario, Canada.

The recently published Canadian Vehicle Survey shows that in 2008, Canadian drivers logged more than 294 billion vehicle-kilometers in vehicles up to 4.5 tons (1). Considering that 74% of Canadians aged 16 and older own a motor vehicle, this translates to an average of 16,000 kilometers driven per driver (2).

Such a high level of vehicular travel creates the potential for motor vehicle accidents. The Canadian Council of Motor Transport Administrator's (CCMTA) Mid-Term Review of its Road Safety Vision 2010 (3) initiative showed that serious injuries due to motor vehicle accidents in Canada decreased more slowly than desired. Between 2002 and 2005, driving fatalities decreased but have now increased back to 2002 levels. In terms of fatalities per vehicle-kilometers traveled, Canada performs poorly when compared to other Organization for Economic Development and Cooperation (OECD) member countries, ranking only 11th of 30 nations.

The CCMTA is focused on 7 major traffic safety issues: speed, unbelted occupants, drinking drivers, commercial vehicles, vulnerable road users, intersections, and rural roads (2). Although the causes of most motor vehicle crashes are multifactorial and complex, medical fitness and adequate vision are recognized as essential prerequisites for drivers to operate motor vehicles safely. Specific data linking driving accidents to vision are lacking. However, it can be argued that impaired vision may be a contributory cause of accidents involving at least 4 of the 7 aforementioned traffic safety issues, including commercial vehicles, vulnerable road users, intersections, and rural roads. Moreover, the prevalence of impaired vision among Canadians in their driving years is significant. More than 4 million Canadians suffer from age-related ocular conditions, including macular degeneration, glaucoma, diabetic retinopathy, and cataract (4). In 2006, 278,000 Canadians had a visual acuity between 20/40 and 20/200; 108,000 were legally blind. These figures are projected to double over the next 25 years (4). Setting an appropriate minimum vision standard for driver licensure is therefore critical to the safety of our society.

In 2000, Casson and Racette (5) reviewed vision standards for driving in Canada, which helped the Canadian Ophthalmological Society's Committee on Vision Standards for Driving to form its recommendations to the Canadian Medical Association (CMA) and CCMTA (6). Many of these recommendations, including changes in visual acuity and visual field standards and consideration for exceptional cases, have been implemented across Canada and published in the CMA's Determining Medical Fitness, seventh edition (7).

This review will outline the current visual standards in each of the Canadian provinces and territories for private drivers and include the newly implemented functional assessments being used to evaluate exceptional cases. The current literature on vision and driving is discussed and graded.

In preparing this report, we reviewed all official ministry Web sites as well as links to acts and regulations of the respective provinces and territories for relevant information on vision standard policies to obtain a class 5 driving license. (Private drivers are called class G in Ontario and class 5 in all other provinces and territories.)

Because some information is not available online or in print, we contacted appropriate representatives from each jurisdiction directly by telephone and interviewed them. Questions focused on vision standards for driving, functional assessments, restricted licensing, and mandatory reporting. We interviewed medical professionals in each jurisdiction, including physicians and occupational therapists, to determine which specific tests were used in clinical evaluations. Finally, the current literature on vision and driving was reviewed and graded. We searched relevant databases, including Ovid MEDLINE, AARP AgeLine, and CINAHL with an emphasis on literature published after 2000. Appropriate limits were applied, and Medical Subject Heading terms were used. Following the Canadian Task Force system of grading evidence (8), we assigned numbers from highest to lowest levels of evidence by study design (Table 1).

Table 1

Table 1

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The CCMTA publishes medical standards for drivers (9) that are largely derived from the CMA's Guidelines for Physicians: Determining Medical Fitness to Operate Motor Vehicles (7). Although each province and territory determines its own visual standards, most adopt the standards published by the CCMTA and all participate in the development of the standards through their active membership in the CCMTA.

Most of the existing literature on vision and driving fails to provide high-grade evidence on which to base visual performance standards for safe driving. Because most studies employ outcome measures of vehicular crash or serious injury, it would be unethical to conduct a randomized control trial involving drivers with naturally occurring visual impairments. Therefore, the majority of studies are descriptive or observational in nature, ranging from evidence level 2 to 5. A 2009 Cochrane review (10) failed to find any level 1 studies on vision screening in older drivers and motor vehicle crashes. Studies on vision and driving are frequently contradictory. For instance, the implementation of minimal vision requirements in the United States for older drivers attempting to renew their licenses was found in one study to reduce crash fatalities (11) but not in another (12).

Given that our present standards and guidelines are based on the current literature and expert opinion, it is not surprising that there are varying views on whether they are well founded. After searching through more than 1,500 publications, Molnar et al (13) concluded that published guidelines for determining medical fitness to drive were not evidence based. Beran (14) concluded that Australia's guidelines were not supported by published studies. The following is an overview of visual standards used or under consideration for use in Canada.

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Visual Acuity

The corrected visual acuity requirement for obtaining a class 5 driving license in most Canadian jurisdictions is a Snellen equivalent 20/50 with both eyes open. New Brunswick and Nova Scotia require a minimum of 20/40 in the better eye.

Studies examining the relationship between visual acuity and driving performance reach conflicting conclusions. Some older studies suggest that poor visual acuity is linked to a greater number of accidents. Hofstetter (15) found that drivers with binocular visual acuity in the lowest quartile experienced an increased number of crashes in a study that involved 13,786 drivers over a 12-month period. A similar analysis of 1,000 British drivers aged 55 years or older found that a binocular visual acuity of 20/30 or better distinguished accident-free drivers from accident-involved drivers (16). In contrast, Fonda (17) found that a visual acuity of 20/200 was sufficient to recognize 6 specified traffic signals at a safe enough distance to allow for early stopping at 40 miles per hour. A 5-year retrospective cohort study of all Florida drivers aged at least 80 years, published in 2008 (18), found lower rates of motor vehicle collisions after a visual acuity standard was implemented for license renewals and extensions.

In the United Kingdom, visual acuity screening for drivers is measured by reading a number plate like that fixed to a motor vehicle with letters and numbers geometrically equivalent to a Snellen visual acuity of 20/50 (19). Individuals must be able to read this number plate from a distance of 20.5 m (letters and numbers, 79 mm high and 57 mm wide). A 2003 study (20) showed that only 92.3% of 210 individuals with a corrected visual acuity between 20/30 and 20/40 could read all number plates correctly, suggesting that this visual acuity standard is more difficult to meet than that of Canada. A similar study (21) showed that 26% of 50 patients with a visual acuity of 20/30 failed and 35% of 50 patients with a visual acuity of 20/40 passed the plate test, further demonstrating the poor correlation between Snellen visual acuity and success on the number plate reading test. This discrepancy may occur because of the crowding effect (22), the reduced probability of correctly identifying optotypes when letters and numbers are combined, or the variation in letter acuity of different fonts (23). Another study (24) found that letter acuity is a function of the complexity of the font, stroke width, and letter height. This finding becomes especially pertinent because as of September 1, 2001, drivers in the United Kingdom must be able to pass the test when viewing from a distance of 20 m, a newer font of letters and numbers 79 mm high but only 50 mm wide.

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Visual Fields

Visual field requirements are consistent throughout Canada in that most jurisdictions adhere to the CCMTA recommendation of unimpaired vision within an area of 120 continuous degrees along the horizontal meridian and 15 continuous degrees above and below fixation, as measured in the binocular viewing state. Quebec is exceptional in requiring an area of 100 continuous degrees along the horizontal meridian, 10 continuous degrees above fixation, and 20 continuous degrees below fixation.

Most jurisdictions no longer specify how visual fields are to be performed, relying on the individual practitioner to ascertain the quality of the test. Only Ontario stipulates acceptable levels for reliability parameters-false-positives and false-negatives less than 20% and fixation losses less than 20%.

In studying the impact of field defects on driving in 10,000 California drivers, Johnson and Keltner (25) found that those with binocular field loss had accident and traffic conviction rates twice that of individuals with no losses. In studying motor vehicle accident rates among patients with glaucoma, McGwin et al (26) found a greater risk among those with moderate (odds ratio [OR] = 3.6 with 95% confidence interval [CI], 1.4-9.4) or severe (OR = 4.4 with 95% CI, 1.6-12.4) visual field deficits in the central 24° than in those with no defects. A study of the use of driving simulators in 40 patients with glaucoma (27) found that a visual field less than 100° along the horizontal meridian was associated with an almost 3 times greater level of simulated accidents compared to age-matched control subjects without field loss. However, a small prospective cohort study involving 9 patients with cerebral field defects including homonymous hemianopia (28) found no differences as compared to a control group of 10 individuals without a history of cerebral injury in driving simulator performance as measured by speed, reaction time, or driving error rate.

Cause and effect relationships are difficult to establish with respect to visual field loss and driving. In an Australian study of 100 senior drivers (29), investigators determined that an expanse of 120° along the horizontal meridian and 10° above and below the horizontal meridian is a poor predictor of on-road driving performance. The European Commission recommends a visual field standard of 120° along the horizontal meridian as well as a binocular visual acuity of 20/40 for its member states (30). These standards were implemented in a study involving 100 individuals with central and/or peripheral visual field defects who underwent a standard driving test conducted by the Dutch driving license authority. The standards had a sensitivity of only 0.79 and specificity of only 0.48 for predicting practical fitness to drive based on a standard checklist administered by a driving examiner (31).

Based on this evidence, the characteristics of visual field loss that make motor vehicular operation unsafe remain unknown, and therefore, a valid standard for visual field testing remains elusive.

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Monocular Vision

There are no restrictions on class 5 licensure for monocularly sighted individuals in Canada. The CMA Driving Fitness document states that monocular vision limits depth perception. However, it recognizes that monocular cues, such as relative size, texture, interposition, and parallax, may help individuals with no binocular stereopsis. Currently, every jurisdiction allows monocular driving. The CMA and the CCMTA recommend that drivers who suddenly become monocular refrain from driving for an adjustment period of several months, with implementation of the adjustment period and its duration left to the physician.

Published evidence supports the current policies of permitting unrestricted driving for individuals with adequate vision in one eye only. In the study by Johnson and Keltner (25), drivers with monocular visual field loss had accident and traffic conviction rates comparable to those of age-matched control subjects. McKnight et al (32) reported similar driving abilities among 40 monocular and 40 binocular truck drivers. In a 1994 study (33), 1,400 male drivers from Quebec who were involved in accidents during their 70th year were compared to subjects who were not involved in accidents during their 70th year. The binocular status and visual acuity of each driver were known. The risk of accidents was equal in drivers who were monocular (as defined by a stereoacuity of greater than 200 seconds) and those who were binocular at acuities of 6/12 to 6/15. Edwards and Schachat (34) reported that self-reported driving ability was unaffected in 71 patients who had had one eye enucleated. Racette and Casson (35) found on-road performance to be unaffected in monocular drivers regardless of the side of the affected eye.

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Diplopia within the central 40° of the visual field is not tolerated for any driver class unless it is corrected by obscuring one eye or using prisms while maintaining the requirements for visual acuity and fields.

In 2001, White et al (36) compared 10 Saskatchewan drivers with stable diplopia of various causes to 10 age-matched control subjects on driving simulator cue recognition involving braking, accelerating, and steering, as well as threat-recognition performance. The outcome variables were reaction times and missed responses. The diplopic drivers performed as well as the control subjects. The degree of misalignment, duration of diplopia, presence or absence of diplopia in primary position, and presence or absence of compensatory head position did not alter performance. Age was the only significant predictor of driving performance in both groups.

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Color Vision

No driving standards are in place regarding color vision in Canada. The CMA and CCMTA agree that drivers must be able to distinguish traffic light colors. The CMA and CCMTA recommend that drivers be made aware of color deficiencies by their physicians.

Studies investigating the role of color vision in driving have shown a possible effect on driving ability. Atchison et al (37) found that error rates and response times were worse in 49 color-deficient men than in 20 men with normal vision asked to identify a red or yellow stimulus. Another laboratory study (38) found that as compared to color-normal subjects, deuteranopes were less able to detect red, orange, and green (but not yellow or blue) road traffic signs projected for 300 milliseconds. Therefore, the color coding of signs and signals has a potential effect on driving performance. Another study (39) discovered that when a sunglass tint was similar to the stimulus color, response times and errors were poorer in color-deficient individuals than that in normal control subjects. A questionnaire study (40) comparing color-normal subjects to 151 individuals with color deficiencies found that the color-deficient individuals had relatively greater difficulty in detecting road reflectors and rear signal lights of preceding cars ahead at night than during the day. The importance of adequately recognizing brake and traffic lights prompted Australia to preclude protanopes from obtaining a commercial driving license in 1994 (41). Owing to a paucity of evidence and improvements in hue and intensity of red signal lights, current Australian medical standards for drivers allow licensure for any color vision defect (42).

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Contrast Sensitivity

There are several methods by which contrast can be measured, and there is no consensus on a gold standard. Moreover, the measurement of contrast sensitivity is rarely performed by ophthalmologists except in research studies. Experts acknowledge that impaired contrast sensitivity may affect driving, but no rules govern this issue as it is still unclear what level of reduction poses a risk (7). The CMA and CCMTA recommend that physicians inform their patients of a deficit in contrast sensitivity.

Although there is no driving standard involving contrast sensitivity, studies have shown that poor contrast sensitivity may affect driving performance. Owsley et al (43) found that older drivers with cataract were 2.5 times more likely to have had at-fault motor vehicle accidents in the past 5 years than those without cataract. A subsequent study by Owsley et al (44) found this difference to be attributable to impaired contrast sensitivity even when the lens opacity was in one eye only. In another study (45), driving performance was measured in 29 patients who had undergone bilateral cataract surgery after a period of at least 1 month (mean of 80 days). In a closed-road circuit, driving scores were found to be significantly improved from preoperative levels and similar to scores of 18 normally sighted control subjects. Logistical regression analysis determined that contrast sensitivity was the main determinant of the difference.

Improvement in contrast sensitivity after cataract surgery was explored further in a double-masked study using a driving simulator under night vision conditions (46). Patients who had undergone cataract surgery with an aspherical intraocular lens had braking response times 0.5 seconds faster than those with a spherical lens. Driving at 55 miles per hour, drivers with an implanted aspheric lens would detect highway signs and pedestrians 45 feet earlier. Driving simulators were also used to determine a relationship between contrast sensitivity and driving. Patients with glaucoma with lower contrast sensitivity, as determined by Pelli-Robson letter contrast sensitivity charts (47), drove in a simulator at slower speeds, had more lane boundary crossings, and had longer braking response times despite normal visual acuity with mild to moderate visual field loss (48). On-road driving performance was also poorer. Those with impaired Pelli-Robson contrast sensitivity made inappropriately fast approaches at intersections and tended to initiate braking too late (49).

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In 2004, the CMA guidelines added a section on functional (on-road driving) assessment to the present visual standards in order to allow those with reduced visual function to demonstrate that they could drive safely. This modification resulted from a 1999 Supreme Court decision in British Columbia (50) in which a man with stroke-induced homonymous hemianopia was repeatedly denied a class 5 driving license based on his failing to meet the 120° visual field standard. The Supreme Court determined that the blanket refusal to issue a driving license was unjustified and that individuals have the right to a valid assessment of their driving abilities. Another pertinent judicial precedent was set in a case involving a commercial driving license (51). A man with binocular acuity of 20/70 owing to congenital optic atrophy had earned a living as a truck driver for 13 years until his visual impairment became known, at which time his driving license was revoked despite a good driving record and favorable opinions from several ophthalmologists. The court reinstated his driving privileges after he successfully passed a functional assessment at the province's expense and awarded him lost wages.

As a result of these judicial rulings, Canadian provinces and territories allow functional assessments in some cases. For example, Ontario permits them only for those who fail to meet the 120° horizontal visual field standard. However, all other jurisdictions permit them even for those who fail the visual acuity standard. For example, Saskatchewan will allow a functional assessment for individuals with binocular visual acuity between 20/50 and 20/60. In other smaller jurisdictions, the decision of whether or not to perform a functional assessment is physician driven. The level of driving license eligible for a functional assessment varies as well. In Ontario, only private class 5 (or G) drivers may be eligible, whereas in Manitoba, all classes are eligible.

A vision waiver pilot program was implemented in Ontario in May 2005 whereby drivers have the ability to obtain a license despite failing to meet the visual field requirement. Such drivers must successfully complete a clinical assessment by an occupational therapist and an on-road driving test. The clinical assessment involves measurements of physical strength, range of motion, visual perception through the Motor-Free Visual Perception Test, visual attention as measured by the Useful Field of View test (UFOV), visual scanning through the Brain Injury Visual Assessment Battery for Adults (biVABA scan course), and an interview to determine the individual's level of insight and awareness of visual limitations. The on-road assessment consists of 2 road tests designed to assess target maneuvers and the use of strategies to compensate for the visual field impairment.

Other Canadian provinces and territories have not formalized their vision waiver process but do use similar assessments. In most instances, the functional assessment is conducted by an occupational therapist. Referrals for a functional assessment may come from a physician, the relevant provincial licensing authority, an insurance company, a family member, or even the patient. An occupational therapist chooses a battery of tests and schedules a road test conducted by a driving evaluator and an occupational therapist. The functional assessment report is sent to the provincial licensing authority where the final decision is made based on the functional assessment and reports from eye care providers.

Since 1978, Quebec has had a statute to allow drivers with a medical disability to prove their ability to drive safely. But functional assessments began only in 2004, consisting of a predefined circuit road test conducted at any of the 41 service centers. Implementation has increased at a rate of 15% per year. Among 750 license suspensions each year based on medical reasons, approximately 70% involve visual problems, mostly visual field defects. Many of these suspensions result from an eye examination required at the age of 75 years. Nearly 50% of individuals whose driving license has been suspended for these reasons request a functional assessment. About 97% of these patients pass the functional assessment and are granted a driving license. This pass rate is appreciably higher than the approximately 50% pass rate of functional road assessments from all medical causes in Quebec and the 65% pass rate of Ontario's Vision Waiver Program (Dr. Jamie Dow, MD, oral communication, August 14, 2009).

A recent unpublished study by Dr. Jamie Dow of the Société de l'Assurance Automobile du Québec prospectively conducted road assessments from January 1, 2009 to April 30, 2009, on 109 visually impaired individuals with visual field defects. Of these, 91 successfully passed the test. He found that the only significant predictor of driving performance was age; everyone younger than 60 years passed. Neither the type nor the degree of visual field defect was predictive of driving performance.

These results are in agreement with data from Ontario's Vision Waiver Program. As of September 2010, 755 individuals have successfully obtained a driving license. Among the 403 individuals who did not pass, more failures resulted from poor performance on the clinical testing than on the road test. Licenses were not granted to 55 individuals; only 17 failed the road assessment. The other 38 failures were due to the elements in the vision waiver program that Quebec omits, namely, clinical occupational therapy assessments (Angela Litrenta, Driver Improvement Office, Ministry of Transportation, Ontario, oral communication, September 10, 2009). Data have not been widely available on the number of functional assessments that have been conducted, pass rates, and subsequent accidents, violations, or withdrawals.

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An emerging tool in vision and driving research is the UFOV. This test is incorporated into many functional assessment protocols because it is easy to administer and is a valid and repeatable measure of visual attention. The rationale behind measuring visual attention is that visual fields do not capture the complexity of visual information that the driver must process concurrently from both central and peripheral fields.

The UFOV test has 3 components, each scored from 0 to 30, a higher score indicating poorer performance. The processing speed is assessed by measuring the average time required to correctly identify a series of centrally presented stimuli. Divided attention is tested by identifying a simultaneously presented central and peripheral stimulus. Selective attention is measured in the same way. To perform well, the subject must ignore distracting stimuli added to the viewed panorama. Scores are summated to obtain an overall UFOV score.

Ball et al (52) discovered that a deficient UFOV predicted motor vehicle crashes with 89% sensitivity and 81% specificity. Owsley et al (53) later found a reduced UFOV in older drivers with increased accident risk (54) and traffic accidents that produced injuries. In drivers older than 60 years, poor UFOV was associated with environmental scanning difficulties and positioning difficulties (cognitive tunnel vision) (49). Ackerman et al (55) found that an impaired UFOV was a contributory risk factor for driving cessation in the elderly. Fisk et al (56) discovered a poor UFOV in 50 stroke (57) and 23 traumatic brain injury survivors. A cumulative meta-analysis by Clay et al (58) showed that a poor UFOV was associated with unsafe driving in the elderly.

Such studies suggest that UFOV may be a good predictor of driving performance. In a recent study of 1,801 older drivers (59), glare sensitivity, visual field loss, and UFOV were all predictive of motor vehicle crashes, whereas visual acuity, contrast sensitivity, and stereoacuity were not.

Because it is difficult to find a single visual measure that can independently predict performance on the road, the road test has a valid role. Drivers who suffer from age-related macular degeneration, glaucoma, and retinitis pigmentosa learn to employ compensatory strategies. For instance, one study found that reducing speed for central field defects and increasing scanning for peripheral field defects were deemed effective strategies in a driving simulator and on the road (60). Therefore, an individualized road assessment (35) and a battery of clinical tests including UFOV may combine to form a powerful predictor of traffic safety and the motivation behind functional assessments for exceptional cases.

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Functional assessments may lead to unrestricted or restricted driving licensure. Restricted licenses may permit driving only in daylight, within a given area, on 2-lane highways, with automatic transmissions, or with speed restrictions. With the exception of Ontario, every Canadian province and territory offers restricted licenses. Interprovincial interchangeability may be an issue.

Marshall et al (61) found that restricted licensure significantly decreased the number of crashes and traffic violations in Saskatchewan. In Manitoba, speed and daytime restrictions are placed automatically if visual acuity falls to 20/60 binocularly. For the restrictions to be removed, the individual must successfully undergo functional assessment.

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Mandatory reporting of drivers deemed unfit by physicians is not universal in Canada. With the exception of Alberta, Quebec, and Nova Scotia, all provinces and territories have legislated mandatory reporting by physicians with protection against legal liability. In Nova Scotia, optometrists must mandatorily report. In Alberta, the patient must self-report. Where physician reporting is discretionary, as in Alberta, Quebec, and Nova Scotia, physicians are protected against legal liability. In British Coumbia, where the physician must report a driver who continues to drive after being warned, protection from legal liability is limited to those circumstances. All reports must be mailed or faxed in writing, usually on a letterhead or predefined form to the appropriate provincial or territorial office.

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The vision standards for driving in Canada continue to follow the recommendations of the CCMTA and CMA. Although it has been shown that problems with sight can be a major reason why individuals restrict themselves from driving (61), courts have stated that it is important to provide assessments for individuals who wish to continue driving. Ontario limits these assessments to the private class driving license and only for visual field deficits, whereas other provinces and territories will consider a waiver for any visual deficit in more than 1 class of driving license.

Functional assessment is an evolving concept that currently involves clinical assessment performed by an occupational therapist followed by a road test. In Quebec, only the road test is necessary. Two obvious concerns with functional assessments include the lack of standardization, especially with regard to the clinical tests, and the growing demand on scarce resources. For example, in the province of Newfoundland and Labrador, drivers are assessed by a single occupational therapist. Many jurisdictions have only 1 or 2 institutions where functional assessments can take place, making it difficult for individuals who are not near major centers. Although the costs of functional assessment may be offset by government subsidy, most assessment centers charge substantial fees for their services. Finally, the data collection process necessary to analyze the driving records of those currently driving as a result of a functional assessment is not well defined, making it difficult to determine whether these practices are effective in ensuring public safety.

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