As the lens stiffens with age, it takes more time for the eyes to accommodate from a more distant focal length (eg, the road) to a nearer focal length (eg, the speedometer). By driving more slowly, a person travels a shorter distance during the time it takes to check the speed of the vehicle and also reduces the perceived risk of getting a speeding ticket. The steady pace reduces the frequency with which the speed needs to be checked. Cataracts, although present in increased incidence in elderly patients, are the result of pathologic processes and not physiologic changes associated with aging. Dilated pupils also are not a result of a physiologic change associated with aging; instead, the pupils tend to constrict with increased age. Macular degeneration can lead to decreased vision (especially in low ambient light), which may cause a person to drive at a slow, but not necessarily steady, speed. In fact, as unexpected hazards suddenly come into the reach of the headlights, a person with macular degeneration would be expected to exhibit erratic changes of speed and direction. Memory loss severe enough to impair a persons ability to drive is a pathologicnot physiologicchange, because it is severe enough to interfere with occupational functioning.1
- Stiffening of the lens.
1. Diagnostic and statistical manual of mental disorders: DSM-IV-TR. 4th ed, text revision. Washington (DC): American Psychiatric Association; 2000:148-9.
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