Abstract
Keywords
Driving is an important instrumental activity of daily living (IADL) because it is the primary mode of personal transportation in many parts of the world, including the United States (Hu & Young, 1999). Access to driving facilitates the performance of routine tasks of daily life, including those related to employment, and provides opportunities for social interaction. Safe driving depends heavily on vision, yet much is unknown about the degree of vision that is required for safe driving performance (Owsley & McGwin, 1999). One group of visually impaired people who are categorically denied licensure in many jurisdictions are those with homonymous hemianopia or quadrantanopia. In addition, ophthalmologists and neurologists commonly recommend driving cessation for their patients diagnosed with these conditions. Homonymous visual field defects occur when field loss is in the same relative position in visual space in each eye. The term hemianopia is used if one half of the field is involved; quadrantanopia is used if only one quadrant is affected. These conditions result from damage to the postchiasmal portion of the visual pathways, with the most common cause being stroke; other causes include traumatic brain injury and tumor (Cassidy, Bruce, & Gray, 2001; Townend et al., 2006; Zhang, Kedar, Lynn, Newman, & Biousse, 2006). Although homonymous hemianopia and quadrantanopia are not highly prevalent conditions, they are a relatively common consequence of brain injury. The prevalence of homonymous hemianopic visual field defects was recently estimated to be 0.8% in a community-dwelling population ≥49 yr old, with 52% of these reporting a history of stroke (Gilhotra, Mitchell, Healey, Cumming, & Currie, 2002).
Preventing a person from driving has potentially serious consequences for quality of life in that it has been linked to depression, social isolation, employment challenges, and increased risk for placement in long-term care (Fonda, Wallace, & Herzog, 2001; Freeman, Muñoz, Turano, & West, 2006; Marottoli et al., 2000). Therefore, policies that deny licensure to people with functional impairments must be evidence based. That is, if a driver’s license is going to be denied to applicants with certain types of functional impairments, clear evidence should exist that people driving with these problems are unsafe to drive.
Few previous studies have examined the impact of hemianopia and quadrantanopia on driver performance. One study (Tant, Brouwer, Cornelissen, & Kooijman, 2002) found problems with on-road steering stability in a group of 28 patients with homonymous hemianopia. This study specifically recruited people with hemianopia whose driving was suspected to be unsafe. A study using an interactive driving simulator (Szlyk, Brigell, & Seiple, 1993) reported similar findings, specifically that in their sample, the 6 people with hemianopia resulting from stroke had more lane boundary crossings than those without the condition. People with hemianopia were tested within 2 months of their stroke, so it is highly likely that the recovery process was still ongoing (Zhang et al., 2006). A retrospective chart review (Racette & Casson, 2005) examined occupational therapists’ assessments of the on-road driving of people with visual field impairment, including a subgroup of 20 drivers with hemianopia or quadrantanopia. This study found that localized visual field loss in the left hemifield and diffuse loss in the right hemifield were associated with impaired driving performance in this subgroup. As Racette and Casson (2005) acknowledged, this study had several methodological limitations such as a retrospective design, lack of a standardized driving route, and no reference group of drivers with normal visual fields to serve as a basis of comparison.
In the current study, Jennifer Elgin, an occupational therapist who is also a certified driving rehabilitation specialist with 8 yr of clinical experience in the assessment and rehabilitation of drivers, conducted on-road driving assessments for a group of people with hemianopia or quadrantanopia. The assessments were conducted on a standardized driving route in everyday traffic conditions, using a rating instrument typical of those used by driving specialists in that ratings are provided both for specific skills and for a global impression of driving (Fox, Bowden, & Smith, 1998; Hunt et al., 1997; Justiss, Mann, Stav, & Velozo, 2006; Kay, Bundy, Clemson, & Jolly, 2008). For comparison purposes, we also assessed an age-matched group of drivers with full visual fields (i.e., normal peripheral vision) on the road. We were interested in the extent to which drivers with hemianopia and quadrantanopia would display safe driving skills.
Method
Participants
Participants with hemianopia or quadrantanopia were recruited through the Neuro-Ophthalmology service at the University of Alabama at Birmingham. People with normal visual fields and in the same age range were recruited from a list of volunteers interested in research participation. Inclusion criteria for all participants were age ≥19, visual acuity of 20/60 or better in at least one eye (the vision requirement for licensure in Alabama), and a current Alabama driver’s license. If a potential participant had not driven in the past 2 yr but had an interest in returning to driving, that person was considered eligible as long as his or her driver’s license had not expired. Exclusion criteria were diagnoses of Parkinson’s disease, multiple sclerosis, Alzheimer’s disease, hemiparesis and other types of paralysis, ophthalmic or neurologic conditions characterized by visual field impairment (other than hemianopia or quadrantanopia for the visual field loss group), requiring adaptive equipment in a vehicle to drive, and lateral spatial neglect as determined by the Stars test (Halligan, Cockburn, & Wilson, 1991).
Additional inclusion criteria for participants with hemianopia or quadrantanopia were a homonymous hemianopic or quadrantanopic visual field defect as indicated by the most recent visual field assessment in the medical record and ≥6 mo from the brain injury date. Those people in the age-matched reference group were required to have normal visual fields (see Procedures section) and no history of brain injury (e.g., stroke, trauma, tumor, arteriovenous malformation).
The protocol was approved by the Institutional Review Board for Human Use at the University of Alabama at Birmingham. After the purpose of the study was explained, participants were asked to sign a document of informed consent before enrolling.
Procedures
We obtained the following information through interview: (1) demographics (age, gender, race or ethnicity); (2) number of comorbid medical conditions, estimated using a general health questionnaire that has been used extensively in previous studies (Owsley, McGwin, Phillips, McNeal, & Stalvey, 2004); and (3) driving status and licensure and an estimate of driving exposure (days/week, miles/week driven) in the recent past, confirmed via the Driving Habits Questionnaire (Owsley, Stalvey, Wells, & Sloane, 1999).
Visual acuity was assessed binocularly using the standard protocol of the Early Treatment of Diabetic Retinopathy Study chart (Ferris, Kassoff, Bresnick, & Bailey, 1982) and expressed as logMAR. Binocular letter contrast sensitivity was measured using the Pelli-Robson chart (Pelli, Robson, & Wilkins, 1988) under the recommended testing conditions and scored by the letter-by-letter method (Elliott, Bullimore, & Bailey, 1991). Visual acuity and contrast sensitivity were evaluated with the spectacle prescription typically worn for driving, if any. All participants had undergone a comprehensive eye examination within the past year.
Visual fields were assessed by automated static perimetry (Humphrey Field Analyzer Model 750i, Carl Zeiss Meditec, Dublin, CA). The monocular field for each eye was measured using the central threshold 24–2 test with the Swedish interactive threshold algorithm standard testing strategy. Results were used to confirm the presence of homonymous hemianopia, quadrantanopia, or normal visual fields. The Esterman (binocular) field test (Humphrey Field Analyzer Model 750i, Carl Zeiss Meditec) was also used to confirm these diagnoses. For people with hemianopia, field loss was classified as left side versus right side, as complete versus incomplete, and as whether macular sparing was present as per standard clinical definitions (Kline, 2008). For people with quadrantanopia, field loss was classified by left side versus right side, complete versus incomplete, and superior versus inferior. Classifications were made by a rater masked to all other clinical and driving performance characteristics of participants.
Several cognitive screening tests commonly used in driving evaluations by driving specialists were also administered (McKnight & McKnight, 1999; Odenheimer et al., 1994; Rizzo, Reinach, McGehee, & Dawson, 1997; Worringham, Wood, Kerr, & Silburn, 2006). General cognitive status was screened using the Mini-Mental State Examination (MMSE; Folstein, Folstein, & McHugh, 1975). Processing speed, short-term memory, and attention switching were measured using the Digit Symbol Substitution Test (Wechsler, 1981), which is part of the Wechsler Adult Intelligence Scale. Trail Making Tests A and B (Reitan, 1955) were used to examine visual search, processing speed, mental flexibility, and executive function. Medical record review also identified whether participants had undergone scanning training during previous occupational therapy. The Useful Field of View (UFOV®) test (Edwards et al., 2005) was not administered (even though it is commonly used in driving assessment clinics to evaluate divided attention) because when taking the UFOV test, the person fixates on the center of the screen and the peripheral target duration is so brief there is no opportunity to scan; thus, a person with hemianopia or quadrantanopia would by definition miss all targets in his or her affected field area, not because of an attention problem but because the targets would not be visible to the person.
On-road driving performance was evaluated under in-traffic conditions in a dual-brake vehicle (Chevrolet Impala 2007 with automatic transmission) using the same route for each participant. Jennifer Elgin, a certified driving rehabilitation specialist (CDRS), did all of the evaluations; she has 8 yr of clinical experience in the assessment and rehabilitation of drivers with a wide variety of medical conditions, including brain injury, neurological diseases, vision impairment, and cognitive impairment. She sat in the front passenger seat, had access to the dual brake, and was responsible for monitoring driving safety. The design of the route was based on our previous research with drivers with functional impairments (Bowers, Peli, Elgin, McGwin, & Owsley, 2005; Wadley et al., 2009; Wood, Anstey, Kerr, Lacherez, & Lord, 2008). The route covered 14.1 mi with 6.3 mi of noninterstate driving in residential and commercial areas of a city and 7.8 mi of interstate driving in a city. It included both simple and complex intersections and encompassed a broad range of traffic densities and operational maneuvers.
Before beginning the on-road assessment, the CDRS asked participants to carry out a series of basic driving maneuvers in a parking lot, devoid of other traffic, to ensure they had adequate vehicle control and to allow them to become familiar with the vehicle. Once she was satisfied that a participant exhibited adequate control, the on-road driving evaluation began. It started in low-traffic city streets in a residential neighborhood and proceeded to busier roads, then to interstate driving, and finally to city noninterstate driving in a commercial area. Driving evaluations were held between 9:00 a.m. and 3:00 p.m. to avoid rush hour traffic and were cancelled if there was precipitation or the road was wet. If a participant did not wish to drive on the interstate, that portion of the route was omitted.
The CDRS used a rating system for evaluating driving performance that had five skill components, each rated on a 5-point scale: interaction–communication with other road users and pedestrians, driving style (margin of anticipation), vehicle control skills (smoothness), adjustment to traffic speed conditions, reaction to unexpected events, and unusually bad driving maneuvers (e.g., stopping in a lane on the interstate, turning the wrong way on a one-way street). The points of the rating scale were 1 = driving was so unsafe that the drive was terminated (i.e., the driver was asked to pull over and the evaluation stopped); 2 = exhibited a couple of unsafe maneuvers but did not reach the level of drive termination; 3 = driving was unsatisfactory but not unsafe at that time given traffic circumstances; 4 = driver exhibited a few minor driving errors (e.g., some drift within the lane); and 5 = there were no obvious driving errors. The CDRS used the same scale to generate a rating of overall driving performance. In addition, she made a clinical judgment as to whether the driver had the potential for safe driving (response options: yes with no restrictions, yes with some restrictions, no). All these ratings were completed for noninterstate driving and interstate driving separately. Each time the CDRS made a verbal intervention (i.e., correction or recommendation) to the driver (e.g., “Slow down,” “Watch where you are in your lane”) or a physical intervention (applying the dual brake or taking the wheel), it was recorded on the score sheet.
As is standard in clinical practice, the CDRS was aware of the medical and functional characteristics of the clients she was evaluating on the road. However, because of the potential for bias and its impact on interpreting the results, we were interested in the extent to which her ratings of quality of driving would be in agreement with a person in the backseat masked with respect to the driver’s medical and functional characteristics. The backseat evaluator (Wood) also rated the quality of driving on a 5-point scale. This evaluator was not a driving rehabilitation specialist but had extensive training in using the rating scale. Comparison of the CDRS’s ratings and those of the backseat evaluator was designed to provide some information for research purposes about the reliability of the CDRS’s judgments with respect to safe driving (the study’s main dependent variable).
Statistical Analysis
Participants with hemianopia and quadrantanopia were compared with participants with normal visual fields with respect to demographic, medical and cognitive, functional, and driving characteristics using t and χ2 tests for continuous and categorical variables, respectively. When appropriate, we used the Wilcoxon rank-sum test and Fisher’s exact test. We considered ps ≤ .05 (two-tailed) statistically significant.
Results
The study included 22 participants with hemianopia, 8 with quadrantanopia, and 30 with normal visual fields, for a total of 60 participants. Their demographic, health, and functional characteristics are provided in Table 1. Both the group with hemianopia and the group with quadrantanopia were similar to the group with normal visual fields with respect to the distributions of age, race, and MMSE score (all had MMSE scores ≥24). The drivers with hemianopia or quadrantanopia were more likely to be men than were those with normal visual fields. The number of chronic medical conditions was significantly higher in the field loss groups than in the group with normal visual fields. Although the group with hemianopia had slightly worse visual acuity and contrast sensitivity than the group with normal visual fields, their visual acuity was still at a high level, averaging 20/25 or better, as was their contrast sensitivity (averaging 1.7–1.8). We found no difference between the group with quadrantanopia and the group with normal visual fields on either acuity or contrast sensitivity. Scores for visual processing speed and attentional skills as assessed by Trail Making Test A, Trail Making Test B, and the Digit Symbol Substitution Test were worse in those with hemianopia compared with those with normal visual fields. Participants with quadrantanopia had worse Trail Making Test A and Digit Symbol Substitution Test scores than did those with normal visual fields, but their Trail Making Test B scores were not different from those with normal visual fields.
Characteristics of Drivers With Normal Visual Fields, Hemianopia, or Quadrantanopia
Note. M = mean; SD = standard deviation; MMSE = Mini-Mental State Examination.
aOne participant chose not to respond to this item.
The most common cause of hemianopia or quadrantanopia was cerebrovascular accident, with the balance attributable to trauma, tumor, arteriovenous malformation, or presumed congenital abnormalities (Table 2). Of those with hemianopia, 77% had left hemianopia (17 of 22) and 23% had right hemianopia; for 9 of 22 participants with hemianopia, the field loss was complete. Eight of 22 had macular sparing. For those with quadrantanopia, for half the cases the quadrant with loss was on the right and for the other half it was on the left. Of 8 participants with quadrantanopia, 5 had field loss in quadrants in the superior field, and 3 had field loss in quadrants in the inferior field. Two had field loss in the affected quadrant that was complete. The time passed since brain injury was highly variable, but all participants except 1 were ≥1 yr from the date of injury, and almost half (14 of 30) were ≥4 yr from injury.
Brain Injury and Field Loss Characteristics of Participants With Hemianopia or Quadrantanopia
Ratings for overall driving performance on the noninterstate portion of the route are shown in Figure 1. For drivers with normal visual fields, most (>90%), although not all, drove with no obvious driving errors (rating of 5) or had only a few minor driving errors (rating of 4) in all skills evaluated, including overall driving performance scores. For drivers with hemianopia, about two-thirds to three-quarters drove with no obvious driving errors or had only a few minor errors on all skills evaluated (range = 59.1%–81.8%). When the distribution of ratings is compared for drivers with hemianopia versus those with normal visual fields, those with hemianopia were more likely to receive lower (poorer) ratings (p = .016). For drivers with quadrantanopia under noninterstate conditions, 7 of 8 (87.5%) drivers drove with no obvious driving errors or had only a few minor errors. One of 8 drivers (12.5%) had problems with all skills evaluated (score of ≤3). The distribution of ratings for drivers with quadrantanopia is displaced to lower ratings compared with the distribution for those with normal visual fields (p = .04).
Noninterstate driving: Percentage of each group as rated by the occupational therapist for overall driving performance. Group comparisons indicated by horizontal lines labeled with p values.
It is useful to consider which specific driving skills were problematic for drivers with hemianopia and quadrantanopia for noninterstate driving (Table 3). The distribution of ratings for drivers with hemianopia are lower for all skills evaluated compared with that for drivers with normal visual fields, except for interaction–communication with other road users, which was similar between the two groups. The percentage of drivers with hemianopia exhibiting problems (defined as scores of ≤3) for all skills evaluated was greater than the percentage of drivers with normal visual fields exhibiting these problems. For example, 40.9% of drivers with hemianopia exhibited difficulty with vehicle control skills; 36.3%, adjustment to traffic speed conditions; 27.2%, reaction to unexpected events; and 27.2%, unusually bad driving maneuvers. The corresponding percentages for drivers with normal visual fields were 6.7%, 6.7%, 0%, and 0%, respectively. With respect to drivers with quadrantanopia, their distribution of ratings for noninterstate driving, compared with that for drivers with normal fields, was displaced to lower ratings for driving style (margin of anticipation), adjustment to traffic speed conditions, and unusually bad driving maneuvers (p < .05). However, this difference was largely because of 1 driver with quadrantanopia who had serious problems on the road.
Noninterstate Driving: Number and Percentage in Each Group Rated by the Occupational Therapist as 1 for Specific Driving Skills
Note. Percentages may not total 100 because of rounding. 1 = terminate the drive; 2 = unsafe driving; 3 = unsatisfactory driving; 4 = a few minor errors; 5 = no obvious errors. See text for further explanation.
In evaluating the results for interstate driving, it is important to keep in mind that for a driver to be evaluated on the interstate, two criteria had to be met. First, the noninterstate driving had to be judged to be at a safe standard such that interstate driving was appropriate. Second, the participant had to choose to drive on the interstate because some of the field loss group reported that they usually avoided interstate driving. Meeting these criteria were 12 of 22 participants with hemianopia and 7 of 8 participants with quadrantanopia. Although all 30 participants with normal visual fields met these criteria, 1 person was not evaluated on the interstate because as soon as she entered the interstate, she encountered a severe traffic jam (so she left the interstate at the next exit). For interstate driving (Figure 2), results showed no differences in the distribution of the ratings for specific skills between participants with normal fields and those with hemianopia or quadrantanopia who met the criteria for going on the interstate portion of the route.
Interstate driving: Percentage of each group as rated by the occupational therapist for overall driving performance. Group comparisons indicated by horizontal lines labeled with p values. Some participants did not go on the interstate if they did not typically drive on the interstate or the therapist did not allow interstate driving on the basis of noninterstate driving performance.
Table 4 displays the clinical judgment with respect to each driver’s potential for safe driving. On the noninterstate, 100% of drivers with normal visual fields were judged to have the potential for safe driving with no restrictions. Compared with drivers with normal visual fields, a lower percentage of drivers with hemianopia (17 of 22, 77.3%)—16 with no restrictions and 1 with restrictions—were judged to have the potential for safe driving. Of drivers with quadrantanopia, 7 of 8 (87.5%) were judged to have the potential for safe driving on the noninterstate. With respect to interstate driving, it is important to keep in mind that some drivers were not evaluated on the interstate because they preferred not to drive on the interstate or they were not permitted to drive on the interstate. All drivers with normal visual fields except 1 (28 of 29, 96.6%) were judged to have the potential for safe driving with no restrictions on the interstate. Of those with hemianopia or quadrantanopia who drove on the interstate, most (91.7% and 85.7 respectively) were judged to have the potential for safe driving with no restrictions.
Judged Potential for Safe Driving
aOne driver with normal visual fields, 10 drivers with hemianopia, and 1 driver with quadrantanopia were not evaluated on the interstate.
Agreement (weighted κ) between the CDRS’s rating of overall driving performance on the 5-point scale and the rating of the backseat evaluator who was masked to the clinical characteristics of drivers was 0.79 on the noninterstate and 0.73 on the interstate. Agreement between the CDRS and the backseat evaluator was also evaluated for pass (scores of 3, 4, or 5 on overall driving performance) versus fail (scores of 1 or 2 on overall driving performance). For noninterstate driving, agreement was 1.0; for interstate driving, agreement was 0.79 (although disagreement occurred for only 1 driver of 48).
The CDRS was more likely to make verbal interventions for drivers with hemianopia and quadrantanopia than for drivers with normal visual fields (Table 5). Specifically, about half of the drivers with hemianopia (45.5%) or quadrantanopia (50%) received verbal feedback (e.g., “slow down,” “watch where you are in your lane”) compared with 16.7% (5 of 30) of drivers with normal visual fields. In terms of physical interventions, the therapist made corrections for 40.9% (9 of 22) of drivers with hemianopia but only 1 driver with normal visual fields. These physical interventions consisted of using the dual brake to slow the vehicle and briefly taking the wheel because the driver was drifting in the lane. We found no difference in the percentage of interventions between the drivers with quadrantanopia and those with normal visual fields.
Noninterstate Driving: Number and Percentage in Each Group Rated by the Occupational Therapist for Specific Driving Skills
We were interested in which of the in-clinic tests and other patient characteristics (i.e., as listed in Tables 1 and 2) were associated with the CDRS’s judgment of a potential for safe driving with no restrictions because these characteristics might provide information about prognostic indicators for a return to driving after a brain injury causing hemianopia or quadrantanopia. Better performance on the following in-clinic tests was associated with the judgment of a potential for safe driving: contrast sensitivity (p = .003), average visual field sensitivity in the intact field (p = .016), and Trail Making Test A (p = .0036). Other characteristics of the hemianopia or quadrantanopia (visual field side or quadrant affected, whether field loss in the affected area was complete, whether there was macular sparing) were not associated with the judgment of potential for safe driving (all ps > .15). Six of 22 participants with hemianopia or quadrantanopia had undergone in-clinic scanning training by an occupational therapist as part of their post–brain injury rehabilitation but having had the training was not associated with the rating of whether there was potential for safe driving (p = .3021).
Discussion
We embarked on this study to address the stereotypic notion held by licensing jurisdictions, and many health care providers, that drivers with hemianopic or quadrantanopic field defects are unfit to drive. Our results indicate that although drivers with hemianopia and quadrantanopia were more likely to receive lower skill ratings than drivers with normal visual fields, some drivers with hemianopia and quadrantanopia received good driving performance ratings similar to those of people with normal visual fields. Up to two-thirds of the drivers in our study with hemianopia and quadrantanopia drove with no obvious driving errors or had only a few minor errors on noninterstate roads as assessed by the CDRS and were judged to have the potential for safe driving. These results are consistent with an earlier report (Racette & Casson, 2005). It is important to emphasize that we did not enroll patients with lateral spatial neglect. Little or no controversy exists regarding whether hemianopic or quadrantanopic clients with lateral spatial neglect should drive because they behave as though objects in the affected field area do not exist. In addition, all drivers in our sample had MMSE scores ≥24.
Our findings provide strong evidence that some people with hemianopia and quadrantanopia can demonstrate that they are fit to drive if given the opportunity to undergo a standardized on-road evaluation by an occupational therapist who specializes in driving. These specialists are specifically trained to evaluate drivers who have functional impairments that could potentially interfere with safe driving skills. The CDRS’s ratings were in good agreement with those of the backseat evaluator who was masked to drivers’ medical and functional characteristics, implying that the results are not attributable to the CDRS’s bias on the basis of knowledge of each driver’s medical history. In addition to on-road driving evaluations, driving specialists administer in-clinic screening tests and assessments of visual, cognitive, and motor skills used in driving. Our data suggest that drivers with better contrast sensitivity and average light sensitivity in the remaining areas of visual field and those with faster processing speeds were more likely to be judged as safe drivers. These findings are preliminary and await confirmation through larger sample studies, however. Ultimately, it is critical to have an in-clinic battery that is evidence based so that its tests and assessments efficiently focus on those skills that are established prognostic indicators of driving fitness.
One might ask, If about 40% of the drivers with hemianopia had verbal or physical interventions from the occupational therapist, how could the CDRS judge about 75% of drivers with hemianopia as having the potential for safe driving? First, interventions are carried out not only for egregious behaviors but also for the mere suspicion that a dangerous maneuver may occur and provide the opportunity for the therapist to provide immediate feedback to clients regarding their driving. Thus, they are basically preventive actions but in many cases may not have been needed. Second, the therapist’s judgment about the potential for safe driving is based on all aspects of the driving performance, not just single snapshots in time. Previous research has confirmed that judgments of driving fitness, although related to evaluations of specific driving behaviors, are not synonymous with them (Di Stefano & Macdonald, 2003; Kay et al., 2008).
These results raise important questions regarding the fairness of government policies that categorically deny licensure to people with hemianopia or quadrantanopia. This study and that of Racette and Casson (2005) suggest that a more rational and fair policy would be to allow for an individualized assessment of driving fitness for people with these conditions, conducted by an occupational therapist who specializes in driving assessment and rehabilitation.
For drivers with hemianopia who received ratings of unsatisfactory or worse (≤3), the most noteworthy problem area was vehicle control skills (e.g., staying in one’s lane): About 40% of drivers exhibited this problem to various degrees. The finding of vehicle control skill problems is consistent with previous research involving on-road assessment or performance on a driving simulator, which has noted that drivers with hemianopia often have difficulty with steering steadiness (Szlyk et al., 1993; Tant et al., 2002). What remains to be determined is whether a driving rehabilitation program (e.g., scanning or visual search training while driving, practice in keeping within the lane) could improve driving skills in problem drivers with hemianopia or quadrantanopia. This issue is important because many people with field impairment secondary to brain injury want to eventually return to driving. People with hemianopia are sometimes prescribed spectacles that provide a prismatic correction to relocate or expand the field (Bowers, Keeney, & Peli, 2008; Perez & Jose, 2003; Smith, Weiner, & Lucero, 1982). At present, no evidence suggests that such optical devices improve on-road driving performance or driver safety in people with hemianopia (Szlyk, Seiple, Stelmack, & McMahon, 2005). Note that none of our drivers with hemianopia or quadrantanopia, including those who were judged to have good overall driving performance, wore prismatic devices for the driving assessments, suggesting that drivers with hemianopia have strategies that they use to compensate for their field loss during driving and that a prismatic correction is not a necessary condition for safe driving in this population. It is important to understand what these strategies are so that they can be incorporated into evidence-based driving rehabilitation programs.
We designed our study so that it could focus on a specific subpopulation of drivers with hemianopia or quadrantanopia, as a starting point for an exploration of the issue. Excluded from the sample were people with lateral spatial neglect, as mentioned earlier, because little disagreement exists regarding whether clinicians appropriately recommend no driving to such people. We also excluded people who had no interest in returning to driving because motivation to be a driver is required to carry out the skill effectively, and we excluded people with hemiparesis, many of whom may have the potential for safe driving if adaptive vehicular controls are made available. Future research should address driving fitness in people with the combined impairments of hemianopia and hemiparesis. In addition, in our study design, we are unable to dissociate the impact of the brain injury per se from the impact of the visual field impairment on driving performance because the two co-occur in all drivers with hemianopia and quadrantanopia.
In summary, this study has highlighted the need to provide the opportunity for individual driving evaluations for people with hemianopia and quadrantanopia who want to return to driving after brain injury. Denying these people the opportunity to demonstrate driving fitness as part of the rehabilitation process is inappropriate because some people with hemianopia and quadrantanopia display acceptable driving skills that are indistinguishable from those of drivers with no field loss. Our results also suggest that policies categorically prohibiting people with these functional impairments from holding a driver’s license without the opportunity to demonstrate driving fitness need to be reevaluated. These results underscore the importance of driving assessment and rehabilitation services as part of a comprehensive rehabilitation program after a brain injury that impairs vision.
Footnotes
Acknowledgments
This research was funded by National Institutes of Health grants P30–AG22838 and R21–EY14071, EyeSight Foundation of Alabama, Research to Prevent Blindness Inc., and a Queensland University Professional Development Leave grant.