Click for next page ( 6


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 5
5 CHAPTER two LITERATURE REVIEW Introduction describing a prevention strategy used by a fleet operator that employs a high percentage of older drivers, plus a study of Given the perennial shortage of qualified operators for how in-vehicle compensatory aids and training may be used heavy commercial vehicles and the enhanced risk manage- to enhance driver performance. ment skills of more mature, experienced drivers, there are clear advantages to the industry of retaining individuals who remain healthy into their 50s, 60s, and beyond. The over- Medical Conditions and Older Driver Safety all aging of the U.S. population means that a larger propor- tion of these workers will be older as well, and this trend Individuals may experience impairments in their ability will only be accentuated as economic challenges compel to drive safely owing to a host of medical conditions and people to remain in their jobs past the traditional retirement diseases that are more prevalent in later years. While it is age. The consequences of this societal shift for commercial functional capacity that directly mediates driving perfor- motor vehicle operations specifically, and for the safety of mance, and functional losses that predict crash problems, the nation's highways more generally, hinges on our emerg- it is important to consider the manner and extent to which ing understanding of how our ability to perform critical driv- underlying medical conditions can compromise critical safe ing skills changes as we get older and how this knowledge is driving abilities. Accordingly, the focus of this section is applied to ensure that commercial drivers are medically fit on diseases and medical conditions prevalent among older regardless of their age. adults: diseases that scientific evidence has linked to driving impairment and that are likely to define priorities for detec- An essential starting point in this review is that research tion by physicians because of their effects on specific visual, has shown that the status of an (older) individual's visual, perceptual-cognitive, and psychomotor functions. mental, and physical functions determines the safety risk that he or she poses, regardless of age. And while it is true Conditions That Impair Visual Function that normal aging is broadly associated with many declines in functional status, there are tremendous individual differ- The most prevalent medical conditions affecting vision among ences. Some 70-year-olds are every bit as capable to safely older drivers are cataracts, glaucoma, and macular degenera- operate a commercial vehicle as their 50-year-old coworkers. tion. Each of these conditions can be screened or detected by In this review, numerous references will attest to a signifi- primary care physicians, using brief in-office methods. cant decline in critical functional abilities with advancing age, but neither a person's age nor his or her medical diag- A cataract is a clouding or opacity in the lens of the eye nosis determines fitness to drive; rather, it is that person's that can impair function with respect to visual acuity, con- functional status. trast sensitivity, and disability glare. The most common symptoms of cataracts include blurry vision, double vision, The following discussion first addresses medical con- faded colors, poor night vision, and halos around lights. It is ditions that can lead to diminished capability and driver estimated that 20.5 million people in the United States older impairment, and which become increasingly prevalent with than age 40 have a cataract in one eye, a number that will advancing age. Next, the extent to which older persons increase to 30.1 million by 2020 (Eye Diseases Prevalence use medications--and in particular, classes of drugs that Research Group 2004). have been identified as "potentially driver impairing"--to treat these conditions, will be considered. It then reviews In the physician's office, impaired vision attributable to research that has revealed which visual, perceptual/cogni- cataracts may be detected through static acuity and contrast tive, and physical/psychomotor deficits most strongly pre- sensitivity tests, using eye charts; and impairments in visual dict a significant loss in driver competence (performance) function related to cataracts may be revealed through patients' or an increase in crash involvement. A concluding section questionnaire (VF-14) responses (Steinberg et al. 1997). In focuses on potential countermeasures to mitigate age-related an eye clinic, cataracts are typically detected and graded changes that compromise safe driving, including a case study through direct inspection in a slit lamp examination.

OCR for page 5
6 Cataracts have been associated with crash risk by Owsley found. MD exists in a "wet" (exudative) and a "dry" form of et al. (1999). Research by Higgins and Wood (2005) indicates the disease, and is graded by clinicians as mild, intermedi- that the most significant impairment for driving safety result- ate, or severe in its presentation. The wet form, though less ing from cataracts is the loss of contrast sensitivity. Fortunately, common, has a poorer prognosis and accounts for the high- cataract surgery can restore function and lead to measurable est proportion of those suffering a loss of functional vision. gains in safety for older drivers, as discussed here. Because of its increasing prevalence with advancing age, this disease is often labeled "age-related macular degeneration" Next, glaucoma is a relatively common medical condition (ARMD). The Eye Diseases Prevalence Research Group resulting in vision loss for older persons. Characterized by (2004) estimates that 1.5%, 1.75 million of Americans over elevated intraocular pressure, glaucoma destroys the optic age 40 has MD in one eye. By 2020, the total number of nerve. It is one of the leading causes of blindness accord- people with MD is expected to approach 3 million. ing to the American Academy of Ophthalmology; yet almost half of those afflicted are unaware of their condition. This Macular degeneration is detected and graded through is because many do not experience any symptoms (Horton a slit lamp examination. Screening for the disease may be 2001). With more advanced disease, patients may complain accomplished in an office using a procedure involving an about the loss of peripheral vision (Grierson 2000) and may Amsler grid of evenly spaced vertical and horizontal lines require frequent changes in eyeglass prescriptions while with a central fixation point. Other questionnaires, such as experiencing blurred vision, difficulty adjusting to darkened the National Eye Institute Vision Function Questionnaire-25, rooms, rainbows around objects, or mild chronic headaches. include items that screen for ARMD (DeCarlo et al. 2003). By 2020, the number of persons with the disease is expected to rise to more than 3 million (Eye Diseases Prevalence Logically, ARMD will impair drivers in reading traffic Research Group 2004). signs, and in detecting hazards in the forward line of sight. Increased crash risk has been demonstrated for MD patients Screening for glaucoma can be performed in a family phy- when driving at night (Szlyk et al. 1993, 1995), although both sician's office, using an ophthalmoscope to examine the optic of these studies were qualified by small samples. However, disk. Also, there are portable, noninvasive procedures (tonom- in a larger study, Owsley et al. (1998) also found a significant etry) to measure intraocular pressure, but such measures are association between MD and at-fault crash risk. not sensitive as some patients with the disease have normal pressure. Ophthalmologists who diagnose the disease rely on Conditions That Impair Cognitive Function techniques to map visual field loss in addition to changes or asymmetries in the optic disk. There are also questionnaires The medical conditions that most commonly affect cognitive with items designed specifically to detect visual impairment abilities needed to drive safely are dementia, stroke, and sleep associated with glaucoma, including the National Eye Insti- apnea. In this context, dementia must be distinguished from tute Visual Function Eye Questionnaire (Mangione et al. the normal decline in cognitive functioning that occurs with 1998) and the Glaucoma Symptom Scale (Lee et al. 1998). aging. The diagnosis of dementia is warranted only if there is demonstrable evidence of greater memory loss and other Multiple studies have addressed the safety of older per- cognitive impairment--for example, a loss of "executive sons with glaucoma. A 5-year retrospective study in Can- functioning," or the ability to think abstractly and to plan, ada compared patients in a glaucoma clinic with controls. initiate, sequence, monitor, and stop complex behavior-- The glaucoma patients were at higher risk for motor vehicle than would be expected owing to normal aging processes. crashes, including at-fault crashes (Haymes et al. 2007). Other studies have also shown an increase in crash risk in Common effects of dementia include spatial disori- patients with glaucoma (Hu et al. 1998; Owsley et al. 1998; entation and difficulty with spatial tasks, poor judgment, Szlyk et al. 2005); but some have not (McCloskey et al. 1994; and poor insight. Impaired judgment refers to the inability McGwin et al. 2004). Two studies that found an elevated to make correct decisions, such as when it is safe to turn crash risk for glaucoma patients included individuals with across the intersection. Although this function is difficult to moderate to severe disease, who had significant visual field measure in a clinical setting, it may be one of the most rel- loss (<100 degrees total horizontal field); or impairment in evant of disturbances for the demented driver. Individuals the central 24-degree radius field in the worse functioning may exhibit little or no awareness of memory loss or other eye (McGwin et al. 2004; Szlyk et al. 2005). cognitive abnormalities. They may underestimate the risks involved in activities, such as driving. Impulsivity can lead Another disease affecting visual function among large to problematic behaviors, such as prematurely pulling out numbers of older persons is macular degeneration (MD). This into traffic or running a red light. condition affects the central region (macula) of the retina, where the highest density of photoreceptors--as required The most troubling of the dementias is Alzheimer's dis- for good acuity; that is, the ability to resolve fine detail--is ease (AD). Alzheimer's disease is the most common cause of

OCR for page 5
7 dementia, with prevalence estimated at 13% for Americans attack; stroke is the leading cause of serious disability in the age 65 and older (Alzheimer's Association 2007). In 2007, United States (American Heart Association 2006). 2% of Americans ages 65 to 74 had AD, compared with 19% of those ages 75 to 84, and 42% of those ages 85 and older. Although stroke symptoms can include vision and motor With the increase in the number of baby boomers turning impairments, stroke-related sensory loss (numbness or loss age 60 (a rate of approximately 330 every hour), the number of sensation) and cognitive impairments are most likely to of Americans age 65 and older with AD could increase from cause problems with driving. These include memory loss, 11 million to 16 million by the year 2050 (Alzheimer's Asso- hemianopia (inattention or neglect to one hemisphere of ciation 2007). These estimates reflect the prevalence of AD, vision) or visual field cuts, impairment of "executive" func- regardless of whether a diagnosis of AD has been made or is tions (e.g., decision making), and aphasia (inability to under- noted in their medical record. The Alzheimer's Association stand or express speech). Muscle weakness or paralysis is notes that in one study, less than one-fifth of those diagnosed also a possible consequence of stroke. with AD or another dementia had this condition noted in their medical record. The evidence of crash involvement with stroke survivors remains inconclusive. Sims et al. (2000) reported that a his- Impairments in critical driving skills may be among the tory of stroke or TIA (a transient ischemic attack, or "mini- first signs of AD (Silverstein 2008). In a review of the lit- stroke," that produces stroke-like symptoms) was the only erature on crash rates for control drivers and drivers with medical condition significantly associated with crashing in a AD, Carr (1997) found that there is a twofold increased crash prospective cohort study of 174 older adults in Alabama. An rate for drivers with dementia when compared with controls. increase in crash risk with stroke patients when compared Crash rates for control subjects in studies on dementia and with controls was found by Koepsell et al. (1994), but not driving ranged from 0.02 to 0.08 per driver per year. The by Salzberg and Moffat (1998). An additional perspective crash rate for drivers with AD or other dementias in these on these findings is provided by the reality that a significant studies ranged from 0.04 to 0.14. number (approximately 42%) of community-dwelling stroke patients continue to drive (Legh-Smith et al. 1986). Most In a retrospective study in British Columbia, the driving notable is the finding by Fisk et al. (1997) that 87% of stroke records of 165 older drivers classified as having dementia patients resumed the operation of a motor vehicle without any were examined to determine whether cognitively impaired type of formal screening or evaluation for fitness to drive. individuals experience a higher crash rate than their age- and sex-equivalent counterparts in the general population (Coo- Sleep apnea, a periodic cessation of breathing during per et al. 1993). Crash records showed that the dementia sleep--clinically, a cessation for intervals of 10 seconds or group drivers were involved in 86 crashes during the driving longer--is a common though often undiagnosed (and under- period. This result is 2.5 times more than that found for the treated) condition with potentially serious consequences for general driving population. driving safety. A prevalence rate of 4% for men and 2% for women has been reported (Young et al. 1993). Some patients Drivers with dementia are at the highest risk for crashes in experience a related condition, "hypopnea," or repeated epi- the advanced stages of their disease. Drachman and Swearer sodes in which airflow is reduced during sleep. (1993) found that for all years of driving following the onset of dementia, AD patients had a mean of 0.091 reported The (daytime) functional impairments of apneahy- crashes per year compared with 0.040 reported crashes per popnea include drowsiness and sleepiness, memory loss, year for controls in the same time period. The average num- impaired concentration and coordination, anxiety, and ber of crashes per year changed with each year of driving depression. Questionnaires have been used in the diagnosis following the onset of AD, with considerably lower reported of sleep apnea, including the Berlin Questionnaire (Netzer crash rates during the initial years of dementia. In year one, et al. 1999) and the Epworth sleepiness scale (Johns 1991). the crash rate was 0.068; in year two, 0.097; in year three, Polysomnography, an overnight sleep study that allows clini- 0.093; in year four, 0.159; and in year five and beyond, 0.129. cians to grade the presence and severity (mild, moderate, or When the data for the first 3 years post-AD are combined, severe) of the disease, is the "gold standard" for diagnosis. the crash rate is 0.072. The AD patients incurred their first crash an average of 2.20 years post-AD. Studies have linked crash risk to the amount of sleep that was previously obtained (Garharino et al. 2001); and Next, a stroke or cerebrovascular accident (CVA) occurs anecdotal reports of drowsy driving as a crash-contributing when the blood supply to the brain is reduced or interrupted. factor easily exceed 100,000 per year. Maycock (1996) has The CVA may be ischemic, producing an infarct (a small, correlated scores on the Epworth sleepiness scale with crash localized area of dead tissue), or it may be hemorrhagic risk. Sleep apnea patients, specifically, have been associated (bleeding). Each year, about half a million people in the U.S. with a twofold to a sevenfold increase in crash risk, depend- experience a first stroke, and 200,000 experience a recurrent ing on the study (Teran-Santos et al. 1999). These drivers are